November 2003
Ref : 2003-030-0769
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Power Quality
in European Electricity Supply Networks
- 2nd edition
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Network of Experts for
Standardisation
...................................................................................................
Power Quality
in European Electricity Supply Networks
............................................................................................
NE Standardisation specialist group
N-E EMC & Harmonics
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Reviewed by: NE Standardisation
NE EMC & Harmonics
Paper prepared by:
Co-ordinator: J. Gutierrez Iglesias (ES) and G. Bartak (AT)
Members: N. Baumier (FR), B. Defait (FR), M. Dussart (BE), F.
Farrell (IE), C. Graser (DE), J. Sinclair (GB)
Copyright © Union of the Electricity Industry –
EURELECTRIC 2003
All rights reserved
Printed in Brussels (Belgium)
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LIST OF CONTENTS
Executive Summary
Introduction
1. General Outline
1.1 Electricity as a Product
1.2 The Phenomena Considered
1.3 Managing the Characteristics of Electricity
1.3.1 Connection of Disturbing Loads
1.3.2 Non-load-generated Disturbances
1.3.3 Utilisation Equipment Requirements
1.4 The Contribution of Electromagnetic Compatibility (EMC)
1.5 Co-ordination of Responsibilities of the Parties Involved
1.5.1 Network-operator – Electricity consumer
1.5.2 Electricity consumer – Equipment supplier
1.5.3 Network operator – Equipment supplier
2. The PQ Phenomena
2.1 Harmonics
2.1.1 Description of Phenomenon
2.1.2 Effects of Harmonics
2.1.3 Measurement Results
2.1.4 Conclusions
2.2 Flicker
2.2.1 Description of Phenomenon
2.2.2 Effects of Flicker
2.2.3 Measurement Results
2.2.4 Conclusions
2.3 Voltage Dips
2.3.1 Description of Phenomenon
2.3.2 Effects of Voltage Dips
2.3.3 Measurement Results
2.3.4 Conclusions
2.4. Further Phenomena
2.4.1 Voltage Variations
2.4.2 Transient Overvoltages
2.4.3 Temporary Power Frequency Overvoltages
2.4.4 Interharmonics
2.4.5 Unbalance
3. Summary
3
4
5
5
6
7
7
8
8
8
9
9
10
10
10
10
10
11
12
14
14
14
15
16
16
17
17
17
18
19
19
19
20
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22
Annexes
A. Quality: Terms and Definitions
B. Additional Detailed Measurements Results
C. Considerations on the Role of the Network Impedance
D. Measurement Methods
E. Mitigation Methods
F. Standards in the Context with the PQ Report
G. Bibliography
H. Abbreviations
I. List of Figures
27
27
29
46
48
49
52
56
60
61
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EXECUTIVE SUMMARY
Electricity supply represents one of the most essential basic services for the support of an
industrial society. From the point of view of electricity consumers this basic service is
required
-
to be available all the time (i.e. a high level of continuity) and also
-
to enable all the consumers’ electrical equipment to work safely and satisfactorily (i.e.
a high level of power quality).
Based on measurement results of several main PQ phenomena, obtained in measurement
campaigns in several European countries, this report gives an overview of the power quality
(PQ) situation in European public electricity supply networks.
The measurement results are found largely to conform to the limiting or indicative values
specified in EN 50160 “Voltage characteristics of electricity supplied by public distribution
systems” [1, 2], but in some cases there are grounds for concern, with levels having risen to
near or beyond these values:
−
Harmonic levels show a steady increase over the last ten years, particularly in relation to
the 5th harmonic. In some places the levels specified in EN 50160 [1] are at increasing
risk of being exceeded. Due to this tendency, networks are being forced to deliver an
assortment of voltages at a series of unwanted frequencies. One consequence is an
extra cost which is estimated at some hundreds of billion Euro world-wide.
−
While voltage fluctuations leading to flicker are generally at a low level, there are local
examples of the specified levels being exceeded.
−
Voltage dips are an increasing disturbance to the functionality of electrical equipment,
which is increasingly sensitive to that phenomenon. Appropriate measures on the
equipment side allow cost-effective mitigation.
−
Concerning overvoltages, which are a consequence of the natural behaviour of large
electricity systems, with a considerable additional contribution from atmospheric
phenomena, there is anecdotal evidence that electrical equipment does not always have
the capability of performing adequately and safely in the presence of this disturbance.
One clear conclusion from the measurement results is that there is no room for complacency
in regard to the EMC emission standards. The adequacy of the limits they specify and the
diligence with which they are applied need to be considered carefully, with particular
attention to the cumulative result of the aggregation of emissions from innumerable small
devices.
Equally, the immunity of electrical equipment should be sufficient for the given EMC environment, ensuring adequate freedom from performance degradation and safe operation of
electrical equipment.
As a general conclusion, it is clear that the control of disturbances through the implementation of effective EMC standards for both emission and immunity is increasing in importance. Any change that may be contemplated in the approach to EMC needs to be assessed
very carefully, with due consideration of all possible consequences. Over-emphasis on the
cost of meeting EMC limits should be avoided, since due account needs to be taken of the
purpose for which these costs are incurred, without overlooking hidden or less transparent
costs imposed on the generality of electricity users.
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INTRODUCTION
Of all the basic services on which modern society relies for support, electricity supply
is one of the most essential. In order to provide that support, several qualitative
aspects are significant:
1. Constant availability, involving
• for continuity of supply in day-to-day terms, an operating regime whereby the inevitable supply interruptions are prevented from being either unduly prolonged
or unduly frequent
• for more long-term security of supply, a stable balance between user demand
and the availability of generation, transmission and distribution assets as well as
energy sources.
2. The utilisation of electricity for many beneficial purposes requires both voltage and
frequency to be standardised in order that the supply as delivered to the user is coordinated with the equipment by which it is utilised. It is very important to maintain
the supply within reasonable range of the standard values that are adopted for
voltage and frequency.
3. Notwithstanding acceptably stable levels of voltage and frequency, there are
several quite short-term, low-amplitude or occasional irregularities superimposed
on the voltage that can hinder the proper functioning of electrical equipment within
electricity users’ installations or on the electricity network itself.
It is with the third of those aspects of quality that this report is mainly concerned. Its
purpose is to provide information on the more important of the phenomena concerned.
However, numbers 1 and 2 are the primary aspects of quality in relation to network
investment and the day-to-day concerns of network operators. The importance of
item 3 lies in the avoidance of problems such as malfunctioning of customer appliances (and hence customer complaints) or other components of the supply system.
Note: There have been many different approaches to classifying the qualitative aspects of
electricity supply, complicated further by the current practice of separating the functions of generation, supply, network operation, etc. For example, a recent report by
CEER [3] uses the following terms:
–
Commercial quality — concerning the business relationships between suppliers
and users with respect to how well the various services are delivered (The services
concerned are not confined to network operation)
–
Continuity of supply — concerning the extent to which customers find that their
electricity supply is interrupted for various reasons (see 1.above).
–
Voltage quality — concerning the technical characteristics of the supply with
respect to the voltage delivered to customers, i.e. its magnitude and frequency, as
in 2. above, together with the potentially disturbing aspects, referred to in 3. above.
Note: The term “voltage quality” is to be considered identical to the internationally
used term “power quality” [27].
This report gives an overview of the results of different measurement campaigns in
Europe and follows several previous reports [ e.g. 4, 5, 6, 7, 8, 9, 10, 11]. As the
measurements were conducted under different network and load conditions they allow
some general conclusions to be derived. Of course strict statistical accuracy cannot
be ascribed to these measurements or indeed to any similar measurements.
Nevertheless the comparison of the results with the levels that are normally regarded
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as acceptable and with results from previous measurements in the same areas enables certain trends to be discerned.
EURELECTRIC intends to update this report from time to time as newer information
becomes available.
An overview of the definitions used for quality issues, in particular concerning power
quality, in English, French and German, is given in Annex A.
1. GENERAL OUTLINE
The purpose of this report is to present an overview of the present PQ situation in
European electricity networks. The particular phenomena concerned are described in
some detail in Chapter 2, which discusses the levels at which they are found and the
implications of those levels. Before presenting that detail, however, it is worthwhile to
discuss some general issues that are important in relation to the technical aspects of
the quality of the electricity supply.This present chapter provides a general outline of
those issues: considering electricity as a product, the principal phenomena involved,
managing the characteristics of electricity, the contribution of electromagnetic
compatibility (EMC) and the interrelated responsibilities of the various parties
involved.
1.1.
Electricity as a Product
In 1985 a European Directive (85/374/EEC) [12] declared that electricity is a product.
It is, however, rather a unique product because of its intangible and transient nature.
Strictly, it is a product that exists only for an instant at a given point of delivery,
comes into existence at the same instant at which it is being used and is replaced
immediately by a new product with rather different characteristics. Its characteristics
are different at each separate point of delivery. Moreover, it is a product whose quality
depends not only on the elements that go into its production, but also on the way in
which it is being used at any instant by the equipment of multiple users.
Therefore, the quality control that is possible for more tangible and concrete products
is not applicable in the case of electricity. All that can be attempted is some control of
the conditions under which it is produced, transmitted and distributed and those under
which it is used. In particular, the capacity of utilisation equipment to impinge on the
quality of electricity, including that delivered to other equipment, must be recognised.
Electrical equipment has become increasingly complex in terms of the functions it fulfils and the way in which it interacts with other electrical equipment. Frequently, that
interaction takes place through the medium of the electricity network, which is the
common energy source for all the equipment. It arises because the network, intended
to be a common energy source, also provides a conducting path interlinking all
equipment.
In effect, the electromagnetic phenomena arising from the behaviour of utilisation
equipment are superimposed on the other characteristics of the electricity supply, and
become part of the product that is delivered to the user. They are joined also by
phenomena arising from atmospheric and other external events and from the intrinsic
response of a large electricity system to such events.
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1.2.
The Phenomena Considered
The degree of economic development has a great influence on the importance
attached to the different elements of supply quality. At a more primitive stage of
development the primary concerns are likely to be that electricity is actually available
and, when available, that the voltage and frequency are within reasonable range of
their nominal values for most of the time. When these are the primary concerns, such
matters as voltage dips, transients, etc. are seen as having minor relevance. With
more advanced economic development, however, continuity, voltage and frequency,
while remaining important, begin to be taken for granted, and the emphasis shifts to
the set of phenomena encompassed by the modern term, “power quality”. These are
the phenomena covered in some detail in the next chapter of this report, listed more
briefly below:
Harmonics and other departures from the intended power frequency: These
arise mainly from users’ equipment that draws a current not linearly related to the
voltage, thereby injecting currents at unwanted frequencies into the supply
network.
Flicker, as a main effect of voltage fluctuations, which are caused by users’
equipment drawing current of fluctuating magnitude, resulting in corresponding
fluctuation of the voltage on the network.
Voltage dips and short interruptions: These are caused by the sudden
occurrence and termination of short circuits or other extreme current increase on
the supply system or installations connected to it – typically arising from network
faults.
Further phenomena like
Voltage variations: They arise from the independent switching on and off of
literally hundreds or thousands (in the case of networks) of items of utilisation
equipment in each network. As mentioned in the Introduction, this is a
fundamental aspect of quality.
Transient overvoltages: Several phenomena, including the operation of
switches and fuses and the occurrence of lightning strokes in proximity to the
supply networks, give rise to transient overvoltages in distribution networks and
in the installations connected to them.
Temporary power frequency overvoltages: High temporary overvoltages in distribution networks occur almost exclusively as a consequence of a neutral conductor
interruption, which may occur in customers’ installations as well as in public supply
systems, with higher probability in private installations. The proliferation of embedded
generation might present a further risk of overvoltages.
Interharmonics: These are voltages at frequencies other than multiples of the
fundamental frequency. They arise from the operation of frequency converters
and similar control equipment.
Unbalance: Unbalanced voltages on three-phase systems arise from a failure
or inability to keep the currents drawn by users’ equipment evenly balanced
between the phases.
The levels at which the above phenomena can be found at the supply terminals
forming the interface between the public network and the users’ installations were set
down in the European standard EN 50160 [1]. Therefore the values of that standard
are used as references for the measurement results of this report.
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1.3
Managing the Characteristics of Electricity
All of the above phenomena are unwanted and constitute defects in the product,
electricity. Yet they are absolutely intrinsic in the supply and utilisation of electricity as
a public utility. Since they cannot be eliminated, the practical requirement is to
manage them in a proper way. This management task is one to be undertaken jointly
by electricity generators, network operators and electricity users.
These phenomena have the potential of hindering the operation of electrical
equipment, either on the public network itself or, more often, within the installations of
electricity users. They are therefore referred to as disturbances. When they are
caused by users’ equipment, as in the case of the first two of the phenomena listed,
that equipment is referred to as a disturbing load.
1.3.1 Connection of Disturbing Loads
Throughout the century-old history of public electricity supply, network operators have
always sought to control the connection of disturbing loads to the network. It is usually
a condition of supply to all users that they avoid disturbing the operation of the
network or the supply to other users. When the disturbing load is part of a large
installation, the relevant details are declared to the network operator before the
connection is provided. This gives the network operator the opportunity to design a
suitable method of supply and agree an acceptable operating regime with the user, in
conjunction with his equipment provider and other expert advisors. In that way the
level of the disturbance can be maintained at an acceptable level.
By these means, in the case of harmonics, for example, unwanted frequencies were
kept to quite low voltage levels on almost all networks – quite lower than the values
specified in EN 50160 [1].
In more recent decades, disturbances are being generated to an increasing extent by
small-load devices that users purchase on the retail market and install without
reference to the network operator. They include IT and other electronic devices, such
as television receivers, personal computers, etc. These devices are small users of
electricity and the level of the disturbance is correspondingly small in absolute terms.
They are installed in very great numbers, however, and there is frequently a high level
of simultaneity in their operation. Consequently, the cumulative level of the
disturbance generated by them is quite high.
Since they are installed without reference to the network operator, they bypass the
control system that had existed since the start of public electricity supply, as
described above. Indeed, the disturbing devices are far too numerous to be
considered individually. It was in recognition of the greater difficulty of control,
coupled with the realisation that voltage levels at unwanted frequencies were already
rising due to television receivers and other electronic devices, in particular PCs, that
the comparatively high levels of EN 50160 [1] were specified.
Yet it remains the obligation of the electricity user to avoid generating excessive
disturbance. The only means by which the user can fulfil this obligation is by having
equipment available which, by its design and construction, moderates the generation
of disturbance to an adequate degree. That means that the manufacturers of the
devices concerned have a vital contribution to make, by providing suitable equipment
for electricity users.
The last one of the listed phenomena, relating to phase unbalance, is mainly a
concern for three-phase induction motors. The limit adopted many years ago, and
specified again in EN 50160 [1], was based on the characteristics of induction motors.
Electricity networks are very largely three-phase while many utilisation devices are
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single-phase. Careful management is necessary, both on the networks and in users’
installations, to balance the loads between the three phases.
1.3.2 Non-Load-Generated Disturbances
The remaining phenomena, in regard to the potential magnitude of the disturbance
they present, are not subject to real control by the network operator, since they are
intrinsic to the very existence and nature of the electricity network. It has been found,
however, that some modern equipment, especially electronic devices or the electronic
control modules of equipment, has become susceptible to these phenomena at levels
that previously presented no problem. Since there is no practical way of reducing the
disturbance level of either voltage dips or transient overvoltages, the only solution,
apart from accepting the risk of damage or malfunction that might be involved, is to
provide the equipment with the necessary resilience or to install specific protection.
In the case of transient overvoltages, network operators protect the more critical
components of the network by installing bypass devices that shunt the excess energy
to earth. This effectively limits the magnitude of the overvoltage that the network can
transmit to the user to the levels indicated in EN 50160 [1], except when the source is
within or very close to the user’s own installation. It is open to the user to install
specific protection for especially critical devices that would be susceptible at these
residual levels of overvoltage.
1.3.3 Utilisation Equipment Requirements
In summary, in addition to ensuring that the electricity network is adequate for the
energy demands made upon it, a very important part of the task of managing the
characteristics of electricity is the provision of suitable equipment for its utilisation. In
this regard, it is necessary to distinguish between conditions at the supply terminals,
to which EN 50160 [1] and the results presented in this report relate, and the
conditions at the actual terminals of the equipment concerned. There are two
requirements for that equipment: It
should not generate disturbance excessively and it
should not be excessively sensitive to disturbance.
1.4
The Contribution of Electromagnetic Compatibility (EMC)
The design and construction of equipment that fulfils both those needs is the goal of
the EMC project in IEC and CENELEC. Electromagnetic compatibility is defined as the
ability of equipment to function satisfactorily in its electromagnetic environment
without introducing intolerable electromagnetic disturbances to anything in that
environment. Therefore, EMC seeks what is sought also for the utilisation of electricity
by users’ appliances, namely, that the generation of disturbance must be limited and
equipment must be capable of tolerating a reasonable level of disturbance.
(Of course, EMC extends also to equipment that is not connected to the electricity
network and to electromagnetic phenomena that are not relevant to those networks).
The EMC family of documents in the 61000 series (see Annex F) includes standards
establishing limits for both the emission of and immunity from disturbance, as well as
numerous other supporting standards, reports, etc. describing the electromagnetic
environment and phenomena found in it, methods of measurement and test,
mitigation, etc. Among them are standards for compatibility levels, which are
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reference values established to enable emission and immunity limits to be coordinated with each other and with the actual disturbance levels to be expected or
regarded as acceptable in the various environments.
Given that relation between compatibility levels and the levels of disturbance in the
actual environment, it is natural, in the case of the phenomena that are the subject of
this report, that there is a close correspondence between the compatibility levels and
the levels specified in EN 50160 [1]. Equally, if the measured disturbance levels are
found to exceed or be very close to the EN 50160 [1] levels, that is a cause of
concern about whether the emission limits are sufficiently low or are being applied
sufficiently strictly. Moreover, if electricity users’ equipment is actually being disturbed
by one or other of the phenomena, that raises the question of whether the immunity
limits are adequate or are being applied properly.
Therefore, the quality of the electricity supply is very dependent on the EMC project,
and requires suitable limits and requirements properly applied.
1.5
Co-ordination of Responsibilities of the Parties Involved
In relation to supply quality, three different relations are to be considered:
network operator – electricity consumer,
electricity consumer – equipment supplier
network operator – equipment supplier.
1.5.1 Network Operator – Electricity Consumer
The quality of the supply involves two parties directly, the network operator and the electricity
consumer.
a. For the electricity delivered at the supply terminals, the responsibility of the
network operator is to take all practical steps to ensure that its characteristics
remain within such limits as are specified and to inform the consumer of the levels
that can occur in normal conditions (The consumer needs also to be aware that
abnormal conditions occur occasionally).
To fulfil the above responsibility, the network operator is also obliged to maintain
reasonable control of the way in which all consumers use the electricity, and to
provide each consumer with such network information as may be necessary to
enable him to use the supply without disturbance to others.
b. The responsibility of the consumer is to use the electricity in a way that avoids
disturbing the operation of the network or the supply to other users and, insofar as
such disturbance arises, to take all necessary steps to reduce it to an acceptable
level.
That responsibility of the consumer includes providing the network operator with all
information reasonably requested regarding the equipment that is or will be
installed and the way in which it will be operated, and to comply with such
conditions for its operation as may be specified by the network operator to prevent
the emission of disturbance at an excessive level.
Note: For practical reasons this responsibility is fulfilled in this way only for
relatively large loads and installations. In relation to other equipment, the
quality of the supply, avoidance of disturbance and proper functioning of the
networks and users’ equipment are dependent on the proper implementation
of the EMC project.
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1.5.2 Electricity Consumer – Equipment Supplier
Since the consumer uses electricity by means of electrical equipment, the supplier of
that equipment is indirectly involved in the relationship between consumer and
network operator:
a. The equipment supplier is responsible to the consumer to ensure that the
equipment can perform the intended function, including avoidance of disturbance,
and is suitable for the electromagnetic environment in which it is intended to
operate, including the conditions that can arise in public electricity supplies.
b. The equipment supplier is further responsible to provide the consumer with such
information about the characteristics of the equipment as may be required for
transmission to the network operator or the instruction of the user.
1.5.3 Network Operator – Equipment Supplier
Finally, at representative level, both network operators and equipment manufacturers
are jointly involved in the EMC project, in order to ensure
a. that emission limits are such as to prevent disturbance levels on electricity
networks rising to values that would hinder the proper functioning of electricity
users’ equipment or the proper operation of the electricity networks
b. that electricity users’ equipment is provided with adequate immunity from the disturbances
that can be transmitted via the supply terminals at the levels that can be found in practice.
Note 1: Although the fundamental purpose of EMC is that the consumer should obtain
the intended performance from his equipment, it is unfortunate that
consumers are not involved, in practice, in EMC standardisation.
Note 2: While the concern of EMC is to secure the intended operation of equipment, it
is clear that the consumer also requires that his equipment should not be
damaged. If operation as intended is secured, that normally would be
presumed to prevent damage also.
2.
2.1
THE PQ PHENOMENA
Harmonics
2.1.1 Description of Phenomenon
Harmonics are sinusoidal voltages or currents having frequencies that are multiples of the
fundamental frequency at which the supply system is designed to operate (e.g. 50 Hz in
Europe).
When such harmonic waves are superimposed on the sinusoidal voltages or currents
present on the electricity supply system, the result is a distorted wave as illustrated in Fig. 21. It should be noted, that individual currents and voltages are actually present at the
harmonic frequencies and many harmful effects arise from the presence of one or more of
these frequencies, rather than from the shape of the wave.
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Fundamental Wave
Amplitud
Distorted shape
t
5th harmonic
Fig. 2-1 – Distorted wave: fundamental, 5th harmonic
An electric power supply system is inherently passive in terms of the production of harmonics. Harmonic currents are mainly generated by loads having non-linear voltage-current
characteristics, such as TV receivers, IT equipment or other appliances using switched-mode
power supplies in the residential and commercial environment. Examples of industrial loads
being a source of significant harmonic distortion are power converters (rectifiers), variable
speed drives, induction furnaces, arc furnaces, etc.. The ratio of non-linear loads to linear
loads has rapidly increased in recent years.
Cumulative effects of harmonics can be of great significance in relation to conducted low
frequency disturbances when considering mass-produced equipment.
2.1.2 Effects of Harmonics
The effects of harmonic distortion on the electricity supply network are not instantly visible
but can have serious consequences in the medium and long term, the most important ones
being
- causing equipment in both electricity users’ installations and the network to be subjected
to voltages and currents at frequencies for which it was not designed.
- derating of network equipment, such as cables and overhead lines, due to the
additional harmonic load.
- derating and overheating of transformers, particularly due to saturation effects in the
iron core.
- premature ageing of network equipment and consumer appliances, due to the
exposure of e.g. insulation materials or electronic components to excessive harmonic
currents.
- additional Joule losses in the conductors. Due to harmonic currents the losses in the
conductors are increased above the level due to the 50-Hz-current.
- neutral conductor overload. Due to the cumulative action of currents at harmonic
orders of odd multiples of three, an excess amount of such harmonics might cause
overload.
- destruction of power factor correction capacitors in customers’ installations due to
the amplification of the normal operating current, by resonance.
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2.1.3 Measurement Results
2.1.3.1
Long Term Development of Harmonic Distortion
Over the past twenty years utilities all over Europe have carried out measurement
campaigns in LV, MV and HV networks for various purposes. These measurement
campaigns were focussed on MV and LV networks. Although the results cannot be
directly compared with each other there is clear evidence that an increase in harmonic
distortion has taken place over the past 15 years. Typical examples for MV and LV
networks are given in Figs. 2-2, 2-3 for residential areas: the measurements in
residential areas are deemed to be more representative of the overall development of
harmonics in electricity supply networks, since they exhibit continuous long-term
development much more than in industrial areas.
Residential Estate LV(year on year)
ResidentialEstateMV(yearonyear)
5
5
4,5
4,5
4
4
3,5
3,5
3
3
Un%2,5
Un%2,5
3rd
2
2
1,5
3rd
1
5th
0,5
1,5
7th
0
1979
1980
1981
1982
1983
1984
1985
1988
1999
5th
1
0,5
7th
0
THD
1980
1981
1982
Year
1983
1984
1988
1995
THD
Year
Typical example for the development of 3rd, 5th and 7th harmonic and THD in a
substation in a residential estate
Fig. 2-2 –LV
Fig. 2-3 - MV
It is clear that there is an increasing trend in the level of harmonics, especially evident in the
case of the 5th harmonic.
In some cases, in particular locations, a decrease of the harmonic distortion has
been measured. This is due either to the diminution of the distorting loads or, more
% Un
6
5
4
3
3rd
2
5th
1
0
3rd
1996 1997 1998 1999 2000 2001 Year
Fig. 2-4 –Maximum 95 % level of 3rd and 5th harmonic voltages (The Netherlands)
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often, to the improvement made on the network (generally strengthening it and
increasing of the Short Circuit Power).
A more comprehensive overview of measurement results obtained in European electricity supply networks is given in Annex B.
2.1.3.2
Harmonic Load Distribution Over the Week
Other measurements highlight the fact that there is a coincidence between the use of
certain electrical appliances, e.g. TV sets, and the occurrence of harmonic distortion
on the network.
For this purpose, short and medium term measurements were carried out which
clearly show the cumulative effect produced by harmonic generating equipment (Fig.
2-5). In addition, this diagram shows that the 5 th harmonic is transformed over the
voltage levels up to 110 kV, where usually no distorting loads are present.
As an example, the graph shows the results of a survey concerning the 5th harmonic, carried
out at the 110-kV-busbar and the 30-kV-busbar of a substation, as well as at the 0,4-kV-busbar of a transformer station connected to this substation via a mixed 30-kV-network (overhead line/cable). The 5th harmonic is shown at the three levels, with the significant rise in the
early evening, coinciding with the main period of TV watching and the application of privately
owned PCs, and a rapid decrease at about 10 pm. The graph also demonstrates that the 5th
harmonic is transferred upstream from one voltage level to another, given the presence of
harmonic distortion at the 110-kV-level where usually no sources of harmonic emissions can
be found.
7
6
5th harmonic
5
4
3
2
1
0
2 1 .0 6 .2 0 0 0
0 0 :0 0
2 2 .0 6 .2 0 0 0
0 0 :0 0
2 3 .0 6 .2 0 0 0
0 0 :0 0
2 4 .0 6 .2 0 0 0
0 0 :0 0
2 5 .0 6 .2 0 0 0
0 0 :0 0
2 6 .0 6 .2 0 0 0
0 0 :0 0
2 7 .0 6 .2 0 0 0
0 0 :0 0
2 8 .0 6 .2 0 0 0
0 0 :0 0
0 ,4 -k V -b u s b a r tra n s fo r m e r 2 ,5 M V A (o n 3 0 -k V -b u s b a r 5 0 M V A )
3 0 -k V -fe e d e r b u s b a r, 2 5 0 M V A
1 1 0 -k V - fe e d e r b u s b a r, 7 0 0 M V A
Fig. 2-5 – Example for the 5 th harmonic distribution at 400-V-, 30-kV and 110-kVbusbar over one week (Austria [29])
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2.1.4 Conclusions
The overall conclusion of the measurement campaigns is that
-
harmonic levels show an increasing trend
-
in several cases harmonics are already exceeding EN 50160 values and, consequently, the compatibilty levels [13].
Together with the capability of the networks to absorb a certain amount of harmonic
distortion, the harmonic emission limits as currently set out in the relevant standards
[14, 15, 16] are helping to keep the harmonic distortion under some control, despite
the continuous proliferation of non-linear loads like switched-mode power supplies for
IT equipment. These limits must continue to be carefully applied.
The principal harmonics are now found at levels of several percent on distribution networks,
and of about 2 % on many transmission networks. In several places, compatibility levels
have already been reached or even exceeded. Some twenty years ago, the corresponding
levels were only a fraction of these present levels. This situation, in conjunction with the continuing tendency towards increasing harmonic distortion levels in the majority of cases,
imposes on the network operators the obligation to stay vigilant about harmonics and to
maintain the ability to manage the phenomenon. In this context, the fact that dispersed
generation will further contribute to harmonic distortion in public distribution networks must
be taken into account.
2.2
Flicker
2.2.1 Description of Phenomenon
The voltage level on electricity supply networks is subject to continuous variations
under the influence of switching operations of electric equipment connected to the
supply network. Loads being connected to the network have a tendency of decreasing
the voltage on the supply system, whereas the connection of generation units
potentially increases the voltage.
For the better understanding of this phenomenon, it is worthwile to clarify at least
three important terms:
Voltage change: a single variation of the r.m.s. value of a voltage between two
consecutive levels which are sustained for a certain duration (according to [1]).
Note: The term “voltage change” is meant to describe the transition in r.m.s
voltage between two steady state conditions, as opposed to transient
phenomena.
Voltage fluctuation: A series of voltage changes or a cyclic variation of the voltage
envelope [18, Def. 161-08-05]
Voltage fluctuation causes changes of the luminance of lamps which can create the
visual phenomenon called flicker. Above a certain threshold, flicker becomes annoying. The annoyance grows very rapidly with the amplitude of the fluctuation. At certain
repetition rates even very small amplitudes can be annoying.
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Flicker: Impression of unsteadiness of visual sensation induced by a light stimulus
whose luminance and spectral distribution fluctuates with time [18, Def. 161-0813]
Flicker is described by the following units of measurement [19, 20]:
P st : Short term value (observation time: 10 minutes)
The compatibility level for P st is 1; P st =0,7 represents the average
susceptibility threshold.
P lt : Long term value (observation time: 2 hours, according to [1]). P lt is
calculated from 12 successive values of P st .
The compatibility level for P lt is 0,8. As a P lt value is obtained over an
observation time of 2 hours, a flicker with P st = 1 over such a long
period of time may be annoying.
The indicators P st and P lt take into account :
-
the characteristic of the source of flicker by the form of the envelope of rms
values,
-
the characteristics of the human eyes by the frequency response of the
eye,
-
the fact, that during a short period of exposure, higher amplitudes can be
accepted than in case of longer exposure times.
If the current change caused by the switching operation is small relative to the total,
the voltage changes have the appearance of a slow and gradual variation. It is
characteristic of some equipment and some uses of electricity, however, that they
give rise to current changes that are large relative to local load, resulting in
pronounced step-changes in the voltage. In case of a repetitive pattern of such
changes, the result is the visible effect of flicker as described above.
Among the equipment that is a source of flicker are arc furnaces, electric welding
equipment, motors which are switched frequently, as in lifts and hoists, motors driving
loads whose mechanical torque and power vary rapidly over wide ranges, as in rolling
mills, saw mills, X-ray machines, lasers, large industrial motors with variable loads,
large capacity photocopying machines or copying machines in offices, motors in heatpumps in homes or air-conditioning equipment, wind generators, etc. and electronic
devices and resistance welding machines
2.2.2 Effects of Flicker
The irritating effect of flicker is a peculiarity of the human eye-brain system. It was
observed that widespread complaints from electricity users occurred in the vicinity of
industry involving activities such as repetitive electric welding operations. A
flickermeter was devised to simulate the human eye-brain response to lighting from a
60 W incandescent lamp subject to fluctuating voltage. Given a fluctuating voltage as
an input, this instrument provides an indication, designated P st , representing the
short-term effect on a typical human subject over an observation period of 10 minutes.
In cases of severe flicker, there is a risk of inducing epileptic seizures in persons
prone to that disease.
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2.2.3 Measurement Results
Measurement results show that flicker levels are generally well below the
susceptibility level P st = 0,7 as set out in 2.2.1, which, however is exceeded
occasionally.
Fig. 2-6 shows the results from a measurement campaign conducted in Denmark, in
the course of which approximately 200 points on the LV network were monitored from
November 1996 to May 1998 [21].
The results could be considered as being typical for the general P lt situation on LV
systems, given the absence of pronounced sources of flicker. The mean values of
0,45 in urban and 0,5 in rural areas are relatively low compared to the P lt value of 1
as set out in EN 50160 [1].
However, other measurements have shown a considerable number of places, in which
P lt values far in excess of P lt = 1 have been measured (see Annex B).
2,5
2
Maximum value
1,5
Maximum value
1
0,5
Minimum value
Minimum value
0
Rural areas
Urban areas
Source: CIRED 1999 [35]
Fig. 2-6: Typical mean Plt values in urban and rural distribution networks
2.2.4 Conclusions
Complaints due to flicker are usually a localised problem. As a consequence, routine
measurement campaigns are not carried out often. On the other hand, the available data
confirm that the long term and short term flicker levels are commonly below those levels that
might give rise to complaints. Values in excess of the EN 50160 value do occur, however.
Especially in remote areas, flicker levels might increase up to critical values, as demonstrated
by other measurement results [e. g. Annex B].
Given the localised nature of complaints arising from flicker, excessive flicker values tend to
be found in the framework of measurements that are targeted specifically at areas of
complaint.
Given the immediate visibility of the phenomenon and the severe human discomfort that can
be caused, each case of complaint must be taken very seriously. In order to prevent flicker
becoming a widespread problem, appropriate emission limitation is essential, with due
allowance for the cumulative effect across the network levels (different from the harmonic
cumulative effect) .
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2.3
Voltage Dips [1, 2, 22]
2.3.1 Description of the Phenomenon
A voltage dip is defined as a sudden reduction of the voltage at a particular point on an electricity supply system below a specified dip threshold followed by its recovery after a brief
interval. It is a two dimensional electromagnetic phenomenon, the disturbance level of which
is determined by both voltage level and time (duration).
Typically, a voltage dip is associated with the occurrence and termination of a short circuit or
other extreme current increase on the system or installations connected to it. Therefore, it is
caused by the same events that bring about network faults or other extreme increases in the
current. While a more robust or less exposed network can normally be expected to suffer less
frequent faults, the fact is that a significant incidence of voltage dips, of varying severity, is to
be expected by every user of the network. Overhead networks tend to be more exposed to
fault, and thereby lead to more frequent voltage dips.
The level to which the voltage falls at a particular observation point during the dip is a random
value, depending on its position on the network relative to a short circuit. Near a short circuit
the voltage falls virtually to zero; as the distance increases residual voltages are found over
the entire range from zero to the normal operating value of the network.
The duration of the voltage dip is determined by the operating time of the device which acts
to disconnect the short circuit from the system, mainly fuses, circuit breakers and protection
relays. These times are designed to be graduated according to the position of the short
circuit. Voltage dip duration is found mainly in the range from below one tenth of a second to
several tenths of a second. The faster times tend to apply to short circuits on transmission
systems.
Reclosing operations can result in multiple voltage dips from the same primary causative
event. To take account of this effect, the concept of aggregation can be applied for statistical
analyses. It consists of applying a set of rules which define how to group events occurring
within a limited interval of time and to characterise the resulting equivalent event in terms of
amplitude and duration. For example, all events within a 1 minute interval can be counted as
one single event whose amplitude and duration are those of the most severe dip observed
during this interval.
2.3.2 Effects of Voltage Dips
Voltage dips have been an intrinsic feature of public electricity supply since the earliest
times. Yet in recent decades they have become an increasingly troublesome phenomenon
giving rise to inconvenience and even considerable economic loss. The reason is that some
modern electricity utilisation equipment, either in its own design or because of control
features incorporated in it, has become more sensitive to voltage dips.
The effect of a voltage dip derives from the fact that the energy delivery capacity of the network at a given point of supply decreases as the voltage decreases. Voltage dips and short
interruptions, therefore, cause a temporary diminution or stoppage of the energy flow to the
equipment. Since the equipment cannot continue to function without its energy supply, it is
clear that such an event, although extremely brief, can be a problem. It leads to a degradation of performance in a manner that varies with the type of equipment involved, possibly
extending to a complete cessation of operation.
As with all disturbance phenomena, the gravity of the effects of voltage dips and short
interruptions depends not only on the direct effects on the equipment concerned, but
also on how important and critical is the function carried out by that equipment.
For a particular user it may be possible to take limited action on the electricity network
to reduce the incidence of voltage dips arising from local faults or to reduce the
frequency of dips that have very low residual voltages. However, a significant risk of
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voltage dips at all levels of severity will still remain. In the general case, the incidence
of voltage dips is more or less beyond control, while being quite variable with
differences of network type, atmospheric conditions, etc.
Therefore, the main requirement is to take appropriate action either in the design and
construction of the susceptible device or in the installation or process of which it
forms a part. Various options are available to increase the capacity of a device to
withstand voltage dips or to apply local mitigation of the effects of a voltage dip.
Economic considerations play an important part in balancing the cost of the remedial
measures with the gravity of the possible disturbance arising from voltage dips.
2.3.3 Measurement Results
IEC 61000-2-8 [22] shows results from several countries, with considerable variations
in the methods of measurement and the presentation of results. These results show
that the number of voltage dips experienced by an individual user can range from
some tens per year, where the networks are largely underground, to several hundreds
per year, where overhead lines are involved. For example, Table 2.1 shows the
results of one of the measurement campaigns, with details as follows:
o
Measurements using 45 dip recorders at 109 measurement sites on a MV overhead
line network
o
o
o
carried out for three years on from 1996
recording the results at each selected site for one full year
taken phase-ground in general, but phase-phase where necessitated by the available
voltage transformer connections
using voltage dip thresholds of 90% (start) and 91% (end) of the nominal voltage
o
Residual
voltage u
(% of ref.
Voltage)
20≤t<100
(ms)
100≤t<500
(ms)
0,5≤t<1
(s)
1≤t<3
(s)
3≤t<20
(s)
20≤t<60
(s)
60≤t<180
(s)
90 > u ≥ 85
150
37
9
6
3
2
1
85 > u ≥ 70
238
93
14
5
1
0
0
70 > u ≥ 40
141
128
15
5
1
0
0
40 > u ≥ 1
55
113
12
4
1
0
0
1>u≥0
0
4
1
6
7
2
3
Duration t
Table 2.1 - MV overhead networks: voltage dip incidence – 95th percentile
The IEC report [22] summarises the results as follows:
–
The surveys have much in common with respect to the relative density with which dips
are distributed in the depth-duration plane
–
There is confirmation that dips occur throughout the entire extent of the depth-duration
plane
–
There is confirmation that the type of network has an impact on dip incidence, and that
overhead networks have higher incidence rates
–
The high incidence rates near zero duration and near the normal voltage range are
suggestive of inflation by voltage transients and ordinary load fluctuation, respectively.
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–
Where surveys involve rather large numbers of measurement sites, a very wide range of
incidence rates is found, presumably reflecting differences due to network type and configuration, climatic conditions and other features of both the natural and constructed environments.
–
Further evidence of the dispersion of incidence rates is seen in the differences between
maximum, mean, percentiles and other measures of the number of voltage dips recorded.
2.3.4 Conclusions
The measurement results confirm that voltage dips are found with the values indicated in EN
50160.
In terms of power quality, voltage dips are a secondary effect of events whose primary result
is loss of supply to electricity users or damage to and removal from service of significant
components of the network. It is to be expected that all possible action is taken to prevent
events having such serious results, by making the networks as robust as possible and
installing such protective features as are effective and economic. Therefore the incidence of
voltage dips is determined by the residual events that occur despite all efforts at prevention.
(A small proportion of the voltage dips can arise from large surges of current that are
characteristic of certain loads – the connection of such loads is strictly controlled)
Accordingly, voltage dips and short interruptions must be accepted as an intrinsic feature of
public electricity supply systems. The voltage during the dip can be anywhere in the range
from zero to the normal operating value; the duration can be up to or even above one
second. The frequency of occurrence and the probability of occurrence at any level are
highly variable both from place to place and from one year to another.
There is therefore a need for an increased awareness of the phenomenon among electricity
users and the manufacturers of their electrical equipment. In particular, the maximum
possible immunity should be provided in electrical equipment, having regard to the economic
significance of mal-operation of each device. Remedial measures may need to be considered within the user’s installation, possibly targeted at particularly important devices or
processes.
2.4
Further Phenomena
2.4.1 Voltage Variations
For the purpose of this section, the term “voltage variations” is meant to describe slow variations of the supply voltage around the nominal voltage Un, under normal operating conditions
within a range of Un +6/-10 % in continental Europe and +10/-6 % in UK as being standardised in [23].
Note: Cenelec BT 109 has decided that until the year 2008 the acceptable range for low
voltage is to be as specified in HD 472 S1 [23].
Variations of supply voltage arise from the independent switching on and off of literally
hundreds or thousands (in the case of networks) of items of utilisation equipment in each
network, and are characterised by daily, weekly and seasonal cycles, which under normal
operating conditions are within the range as set out in [23]. In that case, voltage variations
are not supposed to adversely affect any equipment connected to the supply network, or to
create annoyances to human beings.
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In some situations, however, the magnitude of the supply voltage could be outside that
range, with possible unwanted consequences for equipment connected to the network.
Examples for such situations are
electricity supplies in remote areas with long lines, in which case the voltage might
drop below the lower tolerance value
connection of dispersed generation units to the LV network, which involves the risk of
raising the supply voltage above the upper tolerance value.
If certain types of equipment, e. g. electric motors, are exposed to excessive undervoltages,
this could result in a degradation of the performance or damage by overheating due to the
additional current input. On the other hand, exposure of any type of equipment to excessive
overvoltages has the possible consequence of reduced lifetime or damage.
In assessing supply voltage magnitude, measurement has to take place over a relatively long
period of time to avoid the instantaneous effects on the measurement caused by individual
load switching (e.g. motor starting, inrush currents) and faults.
For these reasons the 10 min. r.m.s. value is used to characterise these slow variations with
their associated long cycle times. Variations outside of these limits of shorter duration are
characterised as voltage dips or overvoltages.
2.4.2 Transient Overvoltages
The following description is taken from [13]:
Several phenomena, including the operation of switches and fuses and the occurrence of
lightning strokes in proximity to the supply networks, give rise to transient overvoltages in
LV power supply systems and in the installations connected to them.
The magnitude, duration, and energy-content of transient overvoltages vary with their origin.
Generally, those of atmospheric origin have the higher amplitude, and those due to switching
are longer in duration and usually contain the greater energy. Magnitudes up to 2 kV are
generally regarded as typical of transients of atmospheric origin, but values up to 6 kV and
even higher have been recorded.
The overvoltages may be either oscillatory or non-oscillatory, and have rise times ranging
from less than one microsecond to a few milliseconds. These transients propagate within the
network. Usually, they are highly damped, and their amplitude and energy content decrease
with the distance from the point of origin of the overvoltage. However, in some cases – especially when switching capacitive loads – wave reflections and voltage magnification can occur
as the transient is propagated along a line, amplifying the overvoltage incident on connected
equipment.
The possible impact of transients can be limited by the use of surge arrestors. They can be
applied throughout the electricity supply system as well as at the customers’ premises. Critical equipment needs to be protected by individual surge protective devices, and these should
generally be selected to cater for the greater energy content of the switching overvoltages.
Another possible mitigation technique is synchronized switching, with a view to minimize
capacitor, reactor and transformer switching transients.
2.4.3 Temporary Power Frequency Overvoltages
High temporary overvoltages in LV networks occur almost exclusively as a consequence of a
neutral conductor interruption, which may occur in customers’ installations as well as in public supply systems, with higher probability in private installations. It can also occur as a result
of an earth fault in the HV system or as a result of embedded generation.
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Temporary overvoltages also have the potential of stressing the insulation or components of
appliances and network equipment, thus leading to either premature ageing or damage.
A loss of the neutral conductor can either occur due to unqualified human intervention into
the supply system or by a system fault. However, the probabilities for such occurrences are
generally very low. In addition, in public LV systems the load is usually more balanced than
in customer installations, especially in proximity of the transformer. Hence, a loss of the
neutral in the public supply system usually causes less high overvoltages than in private
installations.
According to IEC 60664-1 [24] the magnitude and duration of a temporary overvoltage in LV
equipment due to an earth fault in the high voltage system are
Un + 1200 V for a duration up to 5 s, and
Un + 250 V for longer durations.
These values are above what can be expected in European LV networks as a result of a
break in the neutral conductor.
In MV networks, this type of overvoltage generally appears during an earth fault in the public
distribution system or in a customer’s installation and disappears when the fault is cleared.
The expected value of such an overvoltage depends on the type of earthing of the system. In
systems with a solidly or impedance-earthed neutral, the overvoltage generally does not
exceed 1,7 times the declared system voltage (Uc), whereas in isolated or resonant-earthed
systems this value is generally not above 2,0 times (Uc).
2.4.4 Interharmonics
Interharmonics are sinusoidal waveforms of the voltage or current at frequencies that are
non-multiples of the fundamental frequency.
Currently, interharmonics appear not to be a major problem, but there is some indication that
the level of interharmonics is increasing due to the emerging proliferation of frequency
converters and similar control equipment.
Given the lack of experience, no figures with respect to the level of interharmonics to be
expected on the supply networks are available. Consequently, beside some indicative values
given by [13], there are no standardised levels or limit values for interharmonics.
In certain cases, interharmonics may cause flicker or interference in ripple control systems.
2.4.5 Unbalance
Voltage unbalance is a condition in a polyphase system in which the r.m.s. values of the lineto-line voltages (fundamental component), or the phase angles between consecutive line-toline voltages, are not all equal. The degree of the inequality is usually expressed as the ratios
of the negative and zero sequence components to the positive sequence component.
To define unbalance, the symmetrical components V+, V- and Vo are used, where [10]
V+ is the positive sequence voltage,
V- the negative sequence voltage
Vo the zero-sequence voltage
Very often the unbalance is defined by τ = V-/V+
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Sources of unbalance are single or two-phased loads like
- arc furnaces on the HV and MV system, induction furnaces, trains …
- customer loads on the single-phase LV system.
In LV networks single-phase loads are almost exclusively connected phase-to-neutral but
they are distributed more or less equally over the three phases. In MV and HV networks
single-phase loads can be connected either phase-to-phase or phase-to-neutral. Apart from
very rare exceptional cases, unbalanced loads are generally not directly connected to MV
and HV public supply systems, but rather have a transformer of their own.
Rotating machines operating on an unbalanced supply will draw a highly unbalanced current.
As a result, the three-phase currents may differ considerably, thus resulting in an increased
temperature rise in the machine. The most extreme form of unbalanced supply is the
disconnection of one phase, a condition that can quickly lead to destruction of a machine.
Motors and generators, particularly larger and more expensive ones, may be fitted with
protection to detect this condition and disconnect the machine.
The unbalance is found generally at all network levels to be below 2 % and therefore satisfying the related compatibility levels [13]. Exceptions may occur in certain places where, for
example, arc furnaces with a 2-phase-connection to the supply network are installed or
where significant segments of the local load are on a single phase.
3.
SUMMARY
The strategic status of power quality is increasing for the competing electricity industry as well as for the manufacturers of utilisation equipment. The increasing economic
pressure arising from a liberalised electricity market could impinge on power quality in
the future. Any decrease in quality could cause high costs, such as production losses,
thereby having an impact on the choice of locations of industries in the future.
The measurement results presented in this Report generally appear as being within the
limiting or indicative values specified in EN 50160 [1], but in some cases there are grounds
for concern, showing levels rising near to or beyond these values. Therefore, the task of
ensuring that the values of EN 50160 [1] are observed needs to be managed carefully by the
electricity industry in cooperation with the manufacturing industry, with due regard to the
competitive environment in which both operate.
Some general conclusions can be derived from the measurements, conducted under
different network and load conditions. Of course strict statistical accuracy cannot be
ascribed to these measurements or indeed to any similar measurements. To produce
statistically accurate material would involve measurements at several thousands of
carefully selected points over two or more years. In relation to the limited amount of
additional information that could be achieved, the financial and other resources
needed for such measurement campaigns would be prohibitive.
Given the technological development of electricity utilisation equipment and the
proliferation of certain equipment types, the following main conclusions can be drawn:
As regards the margins between measured PQ levels and the EN 50160 values
or LV compatibility levels, the different phenomena show different behaviours.
In the case of PQ phenomena, such as harmonics and flicker, subject to a cumulative
effect within the supply network, - the means by which the cumulative disturbance level
can be controlled is by the application of emission limits at the design and construction
stage of the individual devices contributing to the disturbance. The observance of such
limits, including those specified in the EN 61000-3 series (see Annex F), is absolutely
essential to retain the voltage characteristics of public electricity supplies within standardized PQ levels. Such observance is a legal obligation under the EMC Directive,
89/336/EEC [17],
2003-030-0769
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PQ levels continue to be lower than the EN 50160 values and compatibility
levels in some areas, attributable to appropriately applied standards within the
EMC framework and the effective management by network operators with
respect to the connection of major disturbing loads.
The increasing connection of equipment generating harmonics makes this
management an increasingly critical task and therefore reliance on appropriate
limits applied in the design and manufacture of the equipment is of increasing
importance.
Thus the control of disturbances through the implementation of effective EMC
standards for emission is increasing in importance, with those for immunity also having
an important contribution to the management task.
There is no room for complacency in regard to the EMC emission standards. The
adequacy of the limits they specify and the diligence with which they are applied need
to be considered carefully, with particular attention to the cumulative result of the
aggregation of emissions from innumerable small devices.
Given the vital contribution of EMC standardisation and the very complex mutual
interdependence of different areas -- e.g.:
-
reference network impedance – emission limits;
emission limits – compatibility levels;
compatibility levels – immunity requirements;
definition of a phenomenon – specification of PQ levels;
PQ levels -- product (family) standards;
product design – PQ levels;
definition of a phenomenon – specification of EMC limits/requirements
any change that would be contemplated in the approach to EMC would need to
be assessed very carefully, with due consideration of all possible consequences.
The following is a summary of what has been found in relation to the different
phenomena dealt with in this report:
Harmonics:
In most cases, the harmonic levels show a steady increase over the last ten years,
particularly in relation to the 5th harmonic which is characteristic of the devices
referred to above.
In some places the EN 50160 values, and hence the compatibility levels, have
already been reached or are at increasing risk of being exceeded.
While, as yet, the problems tend to be localised, the potential for practical or
operational problems is much greater today than it was 10 years ago, and the
effects of non-linear loads are becoming a steadily increasing concern.
Particular harmonics that are characteristic of the power supplies used in television
receivers, personal computers and similar equipment have increased by a factor of 3
and have been shown to follow patterns of usage of such equipment.
Most surveys given in this report show a constant increase of the THD voltage,
as well as the predominance of the 5 th harmonic in LV, MV and HV networks. In
only a few countries a relatively static situation can be observed in recent
years.
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In general, in MV networks, the annual increase of the THD and 5th harmonic grows at
a similar scale to that in LV networks. Also in MV networks, the impact of the 5th
harmonic is significant, together with the 3rd harmonic. In several large MV systems
both harmonic orders exceed the compatibility levels [25] in around 5 % of the cases.
Taking into consideration that harmonics can circulate between the low, medium and
high voltage levels, there is a risk that harmonic pollution in MV, and even in HV networks could dangerously increase.
The principal harmonics are now found at levels of several percent on distribution networks, and at about 2 % on many transmission networks. Some
decades ago the levels were only a fraction of these levels now present. A
constant increase of 1 % of the THD voltage as well as of the 5 th order
harmonic can be observed over each 10-year period.
On LV networks, a significant percentage of the 5th harmonic values are already
around the compatibility levels established in IEC 61000-2-2 [13]. In some cases, 5 %
to 20 % of the values exceed these compatibility levels.
Thus, networks are being forced to deliver an assortment of voltages at a series of
unwanted frequencies.
Notwithstanding that there is often some margin between the measured values
and the compatibility levels, there is evidence of an increasing incidence of the
compatibility levels being exceeded.
Due to the cumulative effect and the transfer of harmonics from LV to MV and
HV networks, the harmonic levels in the HV networks are already found to
exceed the design (planning) levels.
Harmonic pollution, as evidenced by the growth of the harmonic voltages, can
cause considerable cost in power networks, which may be counted in hundreds
of B$ worldwide [e.g. 26].
For the continued realisation of the goals of electromagnetic compatibility and the maintenance of adequate levels of power quality, altering the compatibility levels is not an
option; indeed, that would require also the immunity requirements to be modified and
would endanger the functionality of equipment already in operation.
There is an urgent need for the effective application of EMC, taking due account of the
cumulative effect of multiple devices emitting harmonics simultaneously together with the
economic impact of those emissions.
Flicker:
The immediate visibility of the phenomenon and the severe human discomfort that it
causes result in voltage fluctuations leading to flicker being a PQ phenomenon that
provokes a quite immediate reaction by the customers.
Measurement results in different countries show that
flicker levels are generally relatively low, showing values well below the susceptibility
level Pst = 0,7, being characterized by a frequency distribution of Plt with maxima
within the range of from 0,2 and 0,6 in general.
in certain cases, particularly in remote areas, Plt flicker levels might increase up to
and even above the EN 50160 value and the compatibility level.
Flicker giving rise to complaints is usually localised, and can be influenced by
different human susceptibilities in more remote areas.
2003-030-0769
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November 2003
unlike harmonics, flicker does not propagate upstream throughout the network.
the flicker level is higher in urban areas than in rural areas, in general.
in order to prevent flicker becoming a widespread problem, appropriate emission
limitation is essential, taking due account of the cumulative effect across the network
levels.
Voltage Dips:
Voltage dips
have been an intrinsic feature of public electricity supply since the earliest
times, but some modern electrical equipment, either in its own design or
because of control features incorporated in it, has become more sensitive to
voltage dips, giving rise to inconvenience and even considerable economic
loss.
There is therefore a need for an increased awareness of the phenomenon by
the manufacturers of equipment using electricity and among the users and
suppliers of electricity.
are unpredictable in place and time of occurrence as well as in levels, involving
voltages down virtually to zero and durations up to and above one second.
The frequency of their occurrence and the probability of their occurrence at any
level are highly variable both from place to place and from one year to another.
cannot be eliminated, although their incidence can sometimes be reduced
somewhat by appropriate measures.
are dependant in their incidence on the type of network, showing higher incidence rates in overhead networks, reflecting the higher exposure of these networks to various fault causes, especially severe climatic conditions and other
features of both the natural and constructed environments.
may reach even several hundreds per year in rural areas supplied by overhead
MV lines, depending in particular on the number of lightning strokes and other
meteorological conditions in the area. On cable MV networks, an individual
user of electricity connected at low voltage may be subjected to voltage dips
occurring at a rate which extends from around ten per year to about a hundred
per year, depending on local conditions.
Further Phenomena:
Voltage Variations:
The maintenance of voltage within the levels specified in EN 50160 is part of
the ordinary management of distribution networks, with local reinforcement
being implemented from time to time to keep pace with changes in the level of
load. Particular problems can arise in special cases, such as
-
specific topographic network situations, involving remote areas with long
lines, in which case the voltage might drop below the lower tolerance
value
-
change of the operating conditions in a distribution network due to connection
of dispersed generation units, which involves the risk of raising the supply
voltage above the upper tolerance value.
2003-030-0769
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November 2003
Overvoltages:
For transient power frequency overvoltages, caused by the operation of
switches and fuses, or of atmospheric origin in the case of lightning strokes,
magnitudes up to 2 kV are generally regarded as typical, but values up to 6 kV
and even higher, with rise times from less than 1 µs to a few milliseconds, have
been recorded.
The most prominent cause of temporary overvoltages in LV networks is a break in the
neutral conductor; in this case the maximum value is the phase-to-phase voltage of
the system (i.e. 400 V in 230/400 V three-phase systems). These voltage levels cannot endanger the insulation of electrical equipment designed according to IEC 606641 [24], since that caters for the higher LV values that can result from an earth fault on
the HV system.
In MV networks, this type of overvoltage generally appears during an earth
fault in the public distribution system or in a customer’s installation. In systems
with a solidly or impedance-earthed neutral, the overvoltage generally does not
exceed 1,7 times the declared system voltage (U c ), whereas in isolated or
resonant-earthed systems this value is generally not above 2,0 times (U c ).
Interharmonics:
Interharmonics do not yet appear to be a major problem, but there is some indication
that the level of interharmonics is increasing due to the emerging proliferation of
frequency converters and similar control equipment.
Caution is required regarding the possible effects of interharmonics in causing flicker
or interfering with ripple control systems, not to mention the clear inadvisability of
exposing networks and utilisation equipment to non-standard frequencies for which
they are not designed.
Unbalance:
The levels of unbalance found at all network levels are generally below 2 % at all network levels and therefore comply with EN 50160 [1]. Exceptions may occur in certain
places where, for example, arc furnaces with a 2-phase-connection to the supply network are installed or where significant segments of the local load are on a single
phase.
2003-030-0769
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November 2003
ANNEX A
QUALITY: TERMS AND DEFINITIONS
Concerning the technical characteristics of electricity supply with respect to the voltage delivered to
customers, i.e. its magnitude and frequency together with the potentially disturbing effects [3], the
following terms and definitions are usual:
Voltage / Power quality [27]: The characteristics of the electricity at a given point on an electrical
system, evaluated against a set of reference technical parameters.
Note: These parameters might, in some cases, relate to the compatibility between
electricity supplied on a network and the loads connected to the network.
Qualité d’alimentation [27]: Les caractéristiques de l’électricité à un point donné du système électrique, évaluées par rapport à un ensemble de paramètres techniques de référence.
Note : Ces paramètres peuvent, dans certains cas, se rapporter à la compatibilité
entre l’électricité fournie par un réseau et les charges connectées au
réseau.
Spannungsqualität [Übersetzung laut 27]: Die Merkmale elektrischer Energie an einem bestimmten
Verknüpfungspunkt, bewertet an einem Set technischer Referenzparameter.
Anmerkung: Diese Parameter können sich auf die elektromagnetische Verträglichkeit zwischen der Stromversorgung und den angeschlossenen Geräten
auswirken.
Quality of supply: Quality of supply is a general term which, besides reliability of supply and power
quality, may also include commercial aspects such as service quality or pricing.
Qualité du service: Qualité du service est un terme générale comprenant des caractéristiques téchniques, notamment continuité du service et qualité d’alimentation, ainsi que des
aspects commerciaux comme qualité du service et définition des prix.
Versorgungsqualität: Versorgungsqualität ist ein Oberbegriff, der neben den technischen Merkmalen
Spannungsqualität und Versorgungszuverlässigkeit auch kommerzielle Aspekte
wie Servicequalität und Preisgestaltung enthalten kann.
2003-030-0769
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November 2003
Concerning the extent to which customers find that their electricity supply is interrupted for various
reasons:
Continuity/Reliability of supply [52]: Probability of satisfactory operation of a power system over the
long run. It denotes the ability to supply adequate electric service on a nearly continuous
basis, with few interruptions over an extended period of time
Note: Reliability is the overall objective in power system design and operation.
---------------------------------------Note: For the description, the following terms are commonly used at international level:
Number of supply interruptions per year (SAIFI, System Average Interruption
Frequency Index), in relation to the total number of customers (unit is numbers per
year)
Overall duration of supply interruptions in relation to the total number of customers
affected (CAIDI, Customer Average Interruption Duration Index; unit is minutes per
year)
Overall duration of supply interruptions in relation to the total number of customers
(SAIDI, System Average Interruption Duration Index; unit is minutes per year)
(SAIDI = SAIFI x CAIDI)
Continuité/Fiabilité du service [52]: Probabilité de fonctionnement satisfaisant d’un système électrique à long terme. Elle caractérise son aptitude à fournir, de façon quasi continue, une
alimentation électrique adéquate, avec peu d’interruptions sur une longue durée.
Note : La fiabilité est le principal objectif de la conception et de l’exploitation d’un système
électrique.
------------------------------------------Note : Pour la description, les termes suivants sont généralement employés au niveau international:
nombre d'interruptions du service par an (SAIFI, System Average Interruption
Frequency Index), par rapport au nombre total de clients (l'unité est nombres par an)
durée globale des interruptions du service par rapport au nombre de clients affectés
CAIDI, Customer Average Interruption Duration Index; l'unité est minutes par an)
durée globale des interruptions du service par rapport au nombre de clients (SAIDI,
System Average Interruption Duration Index; l'unité est minutes par an) (SAIDI =
SAIFI x CAIDI)
Versorgungszuverlässigkeit: (Übersetzung laut [52]): Versorgungszuverlässigkeit ist ein Maß für
zufriedenstellende Langzeit-Funktion eines Stromversorgungssystems. Sie beschreibt die
Fähigkeit zur quasi unterbrechungsfreien Elektrizitätsversorgung, mit wenigen Unterbrechungen über einen langen Zeitraum.
Anmerkung: Versorgungszuverlässigkeit ist das grundsätzliche Ziel von Planung und Betrieb
eines Versorgungssystems.
-----------------------------------------Anmerkung: Zur Beschreibung sind international unter anderem folgende Begriffe gängig:
Anzahl von Versorgungsunterbrechungen je Jahr (SAIFI, System Average Interruption Frequency Index), bezogen auf die Gesamtzahl aller Kunden (Anzahl je
Jahr)
Gesamtdauer der Nichtverfügbarkeit bezogen auf die Gesamtzahl der betroffenen
Kunden (CAIDI, Customer Average Interruption Duration Index) (Minuten je Jahr)
Gesamtdauer der Nichtverfügbarkeit bezogen auf die Gesamtzahl aller Kunden
(SAIDI, System Average Interruption Duration Index) in Minuten je Jahr (SAIDI =
SAIFI x CAIDI)
2003-030-0769
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November 2003
ANNEX B
ADDITIONAL DETAILED MEASUREMENT RESULTS
This Annex contains additional measurement results obtained in measurement campaigns in
a number of EURELECTRIC Member countries. It may be noted that the presented
measurement results are not to be taken as representative for the country where the related
surveys have been conducted; it is the aim of this Annex, together with Chapter 2 of this
Report, to give an overview of the measurement results being available for the main PQ
phenomena throughout Europe.
B.1 INDEX
B.2
Long Term Measurements
B.2.1 Harmonics
Switzerland
1979 -- 1997
Austria
2000 -- 2003
Belgium
1996 – 2002
B.2.2 Flicker
Belgium
B.3
1996 – 2002
Short Term Measurements
B.3.1 Harmonics
B.4
France
1987 – 1989
Slovakia
1995
UK
1999
Statistic Distribution Measurements
B.4.1 Harmonics
France
1991, 2000, 2001
Spain
1987 – 1989
Austria
2000 – 2001
Austria
2000 – 2001
Denmark
1996 – 1998
Czech Republic
1997 - 1998
B.4.2 Flicker
Belgium
1994
Austria
2000 – 2001
B.4.3 Voltage Dips
Austria
2000 - 2003
B.4.4 Voltage variations
Austria
2003-030-0769
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29
November 2003
B.2 LONG TERM MEASUREMENTS
B.2.1
Harmonics
Switzerland [28]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
3rd, 5th, 7th, 9th, 11th harmonic
Several LV networks
1979 - 1997
all year
1 week per measurement point
95 %
%Un
4,5
4
3,5
3rd
3
5th
2,5
7th
2
9th
1,5
11th
1
0,5
0
79-80
81-83
84-88
89-91
92-94
95-97
Jahr
Fig. B-1 Development of the odd harmonics 1979 – 1997 in Swiss LV networks
Comment: Over an observation period of 19 years, the levels of the odd harmonics in
Switzerland seem to have slightly increased, on average. After about ten years
of increase, by around 1 %, the level of the 5th harmonic -- still being the prevalent one -- appears as having stabilized at 3,5 %.
Austria [29]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2003-030-0769
30
5th harmonic
Several LV, HV networks
2000 - 2003
January, June
1 week each
95 %, 100 %
November 2003
7
Compatibility level
6
level [% Un]
5
peak of all 10min maximum values
95%-quantile of 100% values
4
100% mean values
3
95%-quantile of 95% values
95% mean values
2
confidence interval for
95%-mean values
1
0
06.2000
02.2001
06.2001
02.2002
06.2002
02.2003
date of measurement
Fig.B-2a: Evolution of the 95% 5 th , 100% 5 th harmonic, LV, 2000 – 2003 (Austria)
Notes: - On average, the mean values of the 5th harmonic appear as being stable,
around 2,5% for the 95% values, around 3% for the 100% values
(sample size is too small to obtain an accurate trend).
- 95% quantiles of 95% / 100% values: The meaning of these values is that 95% of the
individual measurement results can be expected to be lower than these values. The
calculation of these quantiles is based on the Gaussian normal distribution curve.
6
5
peak of all 10min maximum values
level [% Un]
4
95% mean values
3
95% quantile of 95%-values
100% mean values
2
95% quantile of 100%-values
1
confidence interval for
95% mean values
0
06.2000
02.2001
06.2001
02.2002
06.2002
02.2003
date of measurement
Fig. B-2b: Evolution of the 95% 5 th ,100% 5 th harmonic, HV, 2000 – 2003 (Austria)
Belgium [30]
2003-030-0769
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November 2003
5th, 7th, 11th harmonic, THD
MV busbar of HV/MV substation
1996 - 2002
February
1 week (same one each year)
95 %
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2
1,5
h5
h7
1
h 11
THD
0,5
0
1996
1997
1998
2000
2001
2002
Fig.B-3: Evolution of the 95% 5 th , 7 th , 11 th harmonic and THD 1996 – 2002
Belgium, TC: 70/10 kV Ssc HV = 1590 MVA; Ssc MV = 350 MVA;
residential 50% and industrial 50%
B.2.2
Flicker
Belgium [30]
Measured values
Location of measurement
Measurement campaign from:
Time of measurement (during the year)
Duration of measurement(s):
Level type
Plt
MV busbar of 3 HV/MV substations
1996 - 2002
February (A, B), September (C)
1 week (same one each year)
95%
0,25
0,2
0,15
Plt
0,1
0,05
0
1996
1997
1998
2000
2001
2002
Fig.B-4: Evolution of Plt 1996 – 2002
Belgium, Site A: 70/10kV; Ssc HV = 1590 MVA; Ssc MV = 350 MVA;
residential = 50%, industrial = 50%
2003-030-0769
32
November 2003
0,250
0,200
0,150
Plt
0,100
0,050
0,000
1996
1997
1998
2000
2001
2002
Fig.B.5: Evolution of Plt 1996 – 2002
Belgium, Site B: 70/15kV; Ssc HV = 1950 MVA; Ssc MV = 340 MVA;
residential = 95%, industrial = 5%
0,250
0,200
0,150
Plt
0,100
0,050
0,000
1996
1997
1998
2000
2001
2002
Fig.B-6: Evolution of Plt 1996 – 2002
Belgium, Site C: 36/12kV; Ssc HV = 800 MVA; Ssc MV =180 MVA;
residential + industrial
B.3 SHORT TERM MEASUREMENTS
B.3.1
Harmonics
France [31]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2003-030-0769
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5th harmonic
LV network, winter sports resort
2000
March
12 days
95 % value
November 2003
Fig.B-7: Distribution of the 5 th harmonic during 12 consecutive days in a substation (French winter sports resort)
Comment: Due to ski-lifts with variable speed drives, the 5th harmonic level is very high between 9 am and 5 pm.
When the first customers complained, a 95-%-value for the 5th harmonic of more
than 15 % was measured. After modifying the use of the compensation capacitor
banks installed in the HV/MV substation, a decrease of this 95-%-value to 11 %
could be achieved.
Slovakia [32]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
3rd, 5th, 7th harmonic, THD
Substation 220/110 kV, arc furnace
connected to the outgoing 110-kV-line
2001 - 2002
Periodically, 12 times / year
4 days, 9 hours, 20 minutes
actual voltages
THD voltage
Harmonic voltages spectrum
Fig.B-8 Harmonics on 110-kV-level close to an arc furnace (Slovakia)
2003-030-0769
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November 2003
Comment: Related to the maximum levels (red colour), the 3rd harmonic is the prevalent one
(0,59 % Un; 5th harmonic: 0,48 %, 7th harmonic: 0,33 %). The maximum THD
voltage level amounts to 1,27 %.
UK [33]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type
3rd, 5th, 7th harmonic, THD
Residential estate (252 houses),
IT Office
Plastic extrusion factory
1999
April
1 week
Residential Estate
5
4,5
4
3,5
3
Un%2,5
2
3rd
1,5
5th
1
7th
0,5
THD
0
0
0
0
0
23
:0
21
:0
19
:0
17
:0
Hour
15
:0
0
0
13
:0
11
:0
0
0
09
:0
0
rd
07
:0
0
05
:0
03
:0
01
:0
0
0
Comment: The 5th harmonic is the
dominant one and follows the typical
daily load pattern. It has its peak of 4.4
% at 7 pm (THD = 4.52 %). There is no
coincident rise in the 3rd and the 7th
harmonics, indicating that the source of
the rise in the 5th harmonic might be on
an adjacent section of the network. The
most likely cause for the rise in the 5th
harmonic would be TV load.
th
Fig.B-9 3 , 5 and 7th harmonic and THD in UK residential estate over 24 hours
1:
0
2: 0
1
3: 5
3
4: 0
4
6: 5
00
7:
1
8: 5
3
9: 0
11 45
:
12 00
:
13 15
:3
14 0
:
16 45
:
17 00
:
18 15
:
19 30
:
21 45
:
22 00
:
23 15
:3
0
Fig.B-10 3 rd , 5 th and 7 th harmonic and THD in UK industrial area over 24 hours
Comment: The level of the 5th
harmonic and hence THD is high
IT Office (Ind Estate)
8
throughout the day, and often exceeds
7
the 6 % compatibility limit for that
6
5
harmonic order. In this instance the
3rd
Un %4
consumer paid for neutral uprating,
5th
3
7th
load balancing and anti EMF hoods for
2
THD
mitigating effects on VDUs (Before,
1
0
the neutral current was approximately
150 % of the highest phase current;
this was due to third harmonic current
Time of day
and severe out of balance loading).
2003-030-0769
35
November 2003
Factory (Plastic Extrusion)
3,5
Comment: The rise in the
5th harmonic characterises the start of
production in the factory at 7 pm. The
5th harmonic continues to rise
throughout the day, reaching a peak
of 3.19 %, at about 9 pm, this is most
likely due to TV load within the
surrounding residential houses. The
planning limit used at 11 kV in the UK
is 3 % THD.
3
2,5
3rd
2
Un%
5th
1,5
7th
1
THD
0,5
1:
00
2:
15
3:
30
4:
45
6:
00
7:
15
8:
30
9:
4
11 5
:0
12 0
:1
13 5
:3
14 0
:4
16 5
:0
17 0
:1
18 5
:3
19 0
:4
21 5
:0
22 0
:1
23 5
:3
0
0
Time of day
Fig.B-11: 3 rd , 5 th and 7 th harmonic and THD in a UK plastic extrusion factory
over 24 hours
B.4 STATISTIC DISTRIBUTION MEASUREMENTS
B.4.1
Harmonics
France: survey on 20 public LV systems 1991, 2000, 2001 [34, 35]
5th harmonic
20 public LV systems, 16 out of them
supplying only one type of customer each
(residential, industrial or tertiary)
4 out of them chosen with a high THD value
Measurement campaign from:
1991, 2000, 2001
Time of measurement (during the year): all the year
Duration of measurement(s):
1 week (1991) per measurement point
Level type:
50 %, 95 %, maximum
Measured values:
Location of measurement:
% measurement locations (%)
45
40
1991
35
30
2000
25
2001
20
15
10
5
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
5,5
6
>6
V5 5th harmonic voltage (%Un)
Fig.B-12: 50-% level of the 5th harmonic in French LV networks
Status 1991, 2000, 2001
2003-030-0769
36
November 2003
% measurement locations (%)
45
40
1991
35
30
2000
25
2001
20
15
10
5
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
5,5
6
>6
V5 5th harmonic voltage (%Un)
Fig.B-13: 95-% level of the 5th harmonic in French LV networks
Status 1991, 2000, 2001
45
% measurement locations (%)
40
1991
35
30
2000
25
2001
20
15
10
5
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
5,5
6
>6
V5 5th harmonic voltage (%Un)
Fig.B.14: Maximum level of the 5th harmonic in French LV networks
Status 1991, 2000, 2001
Comments:
In 1991, the distribution of the maximum levels was quite similar to that one for the 95%-levels. Contrary to that, comparing the distribution of maximum levels and 95-%levels in 2000 and 2001, a clear move to higher occurrence of higher levels – for the
95-%- as well as for the maximum case – can be recognized (Fig. B-13 & B-14)
2003-030-0769
37
November 2003
In 2001, the 95-%-level of the 5th harmonic was between 4 % and 6 % for four out of
the monitored LV networks (Fig. B-13)
In 2001, 44% of the maximum levels were equal or even exceeding the compatibility
level of 6 %. 69 % of the maximum levels exceeded the compatibility level of 5 % as
having been specified in earlier times. In three networks the maximum levels exceeded
the recent compatibility level of 6 % (Fig. B-14).
Comparing the results over the years, a move of the 5th harmonic voltages to higher
occurrence of higher levels is to be recognised, i.e.
o
for the 95-%-value from 2,5 % to 3 % in 1991 to 3,5 % to 4 % in 2001. Taken this
example, over a period of 10 years a mean increase of the 5th harmonic voltage on
public LV supply systems of about 1 % can be recognized.
o
for the maximum levels from about 3 % in 1991 to 5 % in 2001, with an increase of
about 1 % from the year 2000 to 2001.
Spain [36]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year)
Duration of measurement(s):
Level type:
Harmonics up to the 13th order
79 MV MV/LV substations, at MV side
1987 - 1989
periodically, whole year
1 week per measurement point, each
hour
Mimimum, 95 %, maximum (average
values over 79 measurement points)
6
5
4
minimum
95%
maximum
3
2
1
0
2
3
4
5
6
7
8
9
10
11
12
13
Fig.B-15 Harmonics up to order 13 in 79 Spanish MV substations, 1987 - 1989
Comment: Whilst the (average values of the) 95-%-values show a comfortable margin to the
compatibility levels, some of the maximum values are close to (i.e. 3rd, 5th) or
exceeding (even harmonics) the compatibility levels.
2003-030-0769
38
November 2003
Austria [29]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
Harmonics
30 - 40 measurement points in LV networks (65 % residential, 10 % industrial,
25 % mixed environment)
2000 – 2003 (6 series)
June 2000, January 2001, June 2001,
January 2002, June 2002, January 2003
1 week each
95 % and 100% value of the 5th
harmonic
20,0%
relative frequency
17,5%
compatibility
level
15,0%
12,5%
10,0%
7,5%
5,0%
2,5%
6,
5
>
-6
,5
6
-6
5,
5
-5
,5
5
-5
4,
5
-4
,5
4
-4
3,
5
-3
,5
3
-3
2,
5
-2
,5
2
-2
1,
5
-1
,5
1
0,
5
-1
0,0%
level
% Un[%]
100%
95%
Fig.B-16: Frequency distribution of 95-%- and 100%-values of 5th harmonic
in Austrian LV networks, 2000 - 2003
Comments:
Measurements in all three voltage levels show a wide dispersion of the measurement results. In LV (and MV) networks the measurement results are within the
compatibility levels in general, but 7 out of 202 measurements are exceeding.
Austria [29]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2003-030-0769
39
5th harmonic
LV, MV and HV networks of 15 utilities
2000 – 2001
June 2000, January 2001
1 week each
95 % value
November 2003
95-%-Percentile of the 5th Harmonic
7
6
5
4
3
2
1
0
0
1
10
100
1 .0 0 0
1 0 .0 0 0
S s c in M V A
9 5 -% -W e rte d e r 5 . O b e rs c h w in g u n g
M itte ls p a n n u n g
H ochspannung
Fig.B-17 95-%-values of the 5 th harmonic vs. fault level
in Austrian
LV,
MV and
HV systems
Comments:
On all network levels, the 95-%-value - similar to the maximum 10-min-values, with
somehow lower values -- of the 5th harmonic shows a broad dispersion over the fault
level. On LV and MV level, the maximum values cover the whole admissible range
(5th harmonic: 6 %). At certain sites in LV networks, the maximum value of the 5th
harmonic exceeds or is just below the compatibility level.
On HV level, the maximum values are quite below the compatibility level being specified for MV networks.
A correlation between the highest values per network level and the fault level could
be recognized, but is not ensured. Within a certain network level, such a correlation is
not given.
Denmark [21]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2003-030-0769
40
THD, odd harmonics up to 15th order
200 delivery points in the LV network in
rural and urban areas
November 1996 – May 1998
5 weeks with a time difference of 3
months each per measuring point
(check for seasonal variations)
1 week
THD, 95 %, mean
November 2003
% Un
7
6
5
4
mean 50%
3
maximum
2
1
0
mean urban
95% urban
mean rural
95% rural
Fig.B-18: THD values in Danish rural and urban LV networks
Comments:
Generally, the harmonic level is higher in urban than in rural areas.
With respect to the 5th harmonic, in urban areas higher values exceeding the compatibility level of 6 % were found during some periods of the observation time of a
week.
12
Czech Republic [37]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
THD, 5th harmonic
Different locations MV in Prague
1997 - 1998
1 week
100 %, 95 % values
% Un
4,5
4
3,5
3
2,5
2
1,5
1
0,5
0
Underground
Administrative complex
Commercial center
Electric transport
THD 100%
THD 95%
5th 100%
5th 95%
Fig. B-19 -THD and 5th harmonic in different locations of Prague
with different specific types of loads
2003-030-0769
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November 2003
Comments:
For load type “Underground”, comparing the 100-%-values as well as the 95-%values of the 5th harmonic and the THD, that results in the recognition, that the 5th
harmonic is the predominant harmonic, by far.
Depending on the type of load, the 95-% values as well as the maximum levels for
the 5th harmonic and for the THD show some margin to the compatibility levels.
B.4.2
Flicker
Belgium [30]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
Pst, Plt
10 LV networks
1994
12/93 – Jan/95
2 weeks per measurement point
Pst, 99 %, Plt max, Plt, 95%
Pxt
3
2,5
2
Pst 99%
Plt max
Plt 95%
1,5
1
0,5
0
A
B
C
D
E
F
G
H
I
sites
J
Fig.B-20 Flicker values in Belgian LV networks, 1994
Comments:
At 50 % of the sites, the average susceptibility threshold Pst = 0,7 % has been
exceeded by the Pst, 99 % - value – in two cases with a factor > 3
At three sites, the compatibility level Plt = 0,8 has been reached or – in two cases –
exceeded, by a factor > 2
Austria [29]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2003-030-0769
42
Plt
LV networks
2000 - 2001
June 2000, January 2001, June 2001
1 week each
Maximum, 95-%-value
November 2003
50
Counts of measured values
45
EN 50160
limit for 95-%-Plt
40
35
30
25
20
15
10
5
Plt class
Pl
t
>
1,
6
0
Flicker level
Plt max
ohne DIPs, Plt-Max.
without Dips
withDIPs,
Dips Plt-Max.
mit
Plt 95%
without Dips
with Dips
ohne DIPs, Plt-95-%
mit DIPs, Plt-95-%
Fig.B-21 Counts of measurement results per Plt class in Austrian LV networks
Comments:
In most cases, Plt, 95 % is below the compatibility level Plt =0,8; but in several cases
this limit has been exceeded – as well as by the maximum values (Possibly due to
misinterpretation of automatic reclosing dips as flicker, by the measuring units)
Practice shows that it hardly comes to complaints because of disturbing fluctuations by lighting systems.
B.4.3
Voltage Dips
Austria [29]
Measured values:
Location of measurement:
Measurement campaign from:
Time of measurement (during the year):
Duration of measurement(s):
Level type:
2003-030-0769
43
Voltage dips
30 – 40 LV networks (85 % residential,
10 % industrial, 25 % mixed environments)
2000 – 2003
June 2000, January 2001, June 2001,
January 2002, June 2002, January 2003
1 week each
November 2003
count of measurements per
measurement series
90%
80%
70%
60%
50%
40%
30%
20%
January 2003
June 2002
January 2002
June 2001
January 2001
June 2000
10%
0%
0
1
2
3
4
5 to
10
10 to
50
50 to 100 to
> 1000
100
1000
count of voltage dips per measurement
Fig. B-22: Distribution of voltage dips in Austrian LV networks,
6 measurement series, 2000 - 2003
Comment:
- most measurements are without dips
- dip frequency increases in summer, caused by lightning discharge
Count of Dips, 202 measurements in LV with 1 week observation time
t<
20ms
20ms
≤t<
100ms
100ms
≤t<
0,5 s
0,5s
≤t<
1s
1s ≤ t
< 3s
3s ≤ t
< 20s
20s ≤ t
< 60s
sum
10% ≤ d < 15%
4643
1707
759
101
134
167
70
7581
15% ≤ d < 30%
45
55
53
15
5
6
9
188
30% ≤ d < 60%
4
12
37
5
0
0
0
58
60% ≤ d < 99%
1
9
19
3
0
2
0
34
4693
1783
868
124
139
175
79
7861
sum
Tab. B-1: Classification of dips according to UNIPEDE
Comment: - The count of dips decreases rapidly with rising depth and duration of the
voltage sag
- Dips in the range of 90% to 85% of the nominal voltage are mainly caused by
load switching in sites with low supply voltage (rural areas)
2003-030-0769
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November 2003
B.4.4
Voltage Variations
Austria [29]
Measured values
Location of measurement
Measurement campaign from
Time of measurement (during the year):
Duration of measurement(s):
Level type
Voltage level
~ 30 LV networks (85 % residential, 10
% industrial, 25 % mixed environments)
2000 - 2001
June 2000, January 2001, June 2001
1 week each
Minimum values, Maximum values
Count
12
Anz ahl
10
8
6
4
2
24
5
45
24
0
>
-2
5
-2
40
35
23
22
23
0
5
-2
-2
30
25
0
22
21
21
5
-2
-2
15
0
-2
0
21
<
20
0
U [V]
MMeasurement
in i m al w e r te d eseries
r 1 0 -M i1n u te n -M
i tte2000
l w e r te [V ]
June
2
1 . M e s sr e ih e
2. M e s3
sr e ih e
January 2001
June
3 . M e s2001
s re ih e
Fig.B-23: Distribution of (10-minutes average) minimum values of the voltage in
Austrian LV networks
Count
20
Anzahl
15
10
5
5
24
>
45
-2
0
24
23
5
-2
40
35
-2
0
23
-2
30
22
5
25
-2
0
22
21
5
-2
15
21
0
-2
0
21
<
20
0
U [V]
M ax i ma lwe rte d e r 1 0 -M in u te n -M itte l we rte [V]
Measurement series 1
June 2000
2
January 2001
1. M e s sr e ih e
2. M e s sr e ihe
3. M e s s re ihe
3
June
2001
Fig.B-24: Distribution of (10-minutes average) maximum values of the voltage
in Austrian LV networks
Comment: The measured values cover the range 207 V – 243,8 V being specified by EN
50160 [1], the majority of the values (83 %) lying in the range 230 ± 10 V.
2003-030-0769
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November 2003
ANNEX C
CONSIDERATIONS ON THE ROLE OF THE NETWORK IMPEDANCE
C.1 Description
Network impedance is a characteristic of the system that delivers electricity, not a component
of power quality which is determined purely by the characteristics of the voltage at the point
of delivery. The impedance, however, is an important value in relation to the disturbing effect
of some devices that electricity users connect to the network. In very general terms, a low
impedance tends to reduce the disturbing effect.
In practice, the value of the network impedance varies very considerably from point to point
on the system, and varies also with the type of network.
For example, in case of electricity supply in remote areas with long lines, the coupling points
between the public network and customers’ premises are characterized by high impedance
values. This does not affect the ability of the public network to deliver the required amount of
electricity.
In contrast, in areas with high load density and short distances from the feeding substation,
the impedance at the coupling points can be several orders of magnitude lower. This is
equally true for coupling points in MV and HV networks.
Therefore a wide range of values for the network impedance can be found on public supply
networks. It would be incorrect to generally associate high impedance with a low supply
quality, or low impedance with a high supply quality, since ultimately the actual quality related
properties of a certain network area are the cumulative result of many aspects.
C.2 Relation between Network Impedance and Emission Limits
The disturbing action of loads that are connected to the electricity networks is a
function of the current that they draw from or inject into the networks. The disturbing
effect on other users, however, is a function of the voltage delivered to them. Voltage
fluctuations and harmonics are two important examples. The conversion of the emitted disturbing current to the delivered disturbing voltage is a function of the impedances of the circuits through which the current flows – the network impedances.
As described in C.1, network impedances are quite variable, and measurement campaigns
carried out in various countries [39] have confirmed this situation. Table C.1 presents the
measurement or assessment results.
Country
Percentage of consumers with less than stated impedance
98%
95%
90%
85%
0,43 + j 0,33
_
0,63 + j 0,33
0,32 + j 0,17
0,28 + j 0,15
0,55 + j 0,34
0,45 +j 0,25
0,34 + j 0,21
0,45 + j 0,25
0,36 +j 0,21
0,31 + j 0,17
1.47 + j 0.64
1,26 + j 0,60
1,03 + j 0,55
0,94 + j 0,43
0,59 + j 0,32
0,48 + j 0,26
0,44 + j 0,24
0,70 + j 0,25
0,41 + j 0,21
0,32 + j 0,17
0,60 + j 0,36
0,42 + j 0,25
0,30 + j 0,18
0,46 + j 0,45
0,25 + j 0,23
-_
0,63 + j 0,30
0,50 + j 0,26
_
Australia
Belgium
France
Germany
Ireland*
Italy
Netherlands
Switzerland
United Kingdom
Union of Soviet
Socialist Republics
* System impedances for household consumers in Poland are similar to those in Ireland
Table C.1: System impedance in Ohms at 50 Hz
2003-030-0769
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November 2003
More recent studies, e. g. in Spain and France, have in principle confirmed this situation as
being still actual.
Given this variety of impedance values, it is quite logical that no standard values for the network impedance values can be given, based on which e.g. the maximum admissible
emission of disturbances for specific appliances of categories of appliances could be determined.
Based on the analysis of the already mentioned measurement campaigns, IEC 60725 [39]
points out very clearly, that the situation is fundamentally different among the countries
considered, not only in terms of existing impedances, but also in terms of options for an
eventual harmonisation. The only way to come to an appropriate statement was finally to
specify the percentage of customers deemed to meet an impedance less than a stated
impedance.
In order to be able to fix limits for the emissions for mass market products, whose final
conditions of use are unpredictable for the respective manufacturer, a so-called “reference
impedance” was recommended, based on a statistical evaluation of the measured
impedance values. For a three-phase 230/400 V supply system at 50 Hz the reference
impedance is as follows:
Phase conductor: (0,24 + j 0,15) Ω
Neutral conductor: (0,16 + j 0,10) Ω
Phase to Neutral: (0,40 + j 0,25) Ω
For harmonics up to the 40th order the value is approximately (0,40 + j n 0,25) Ω. In LV networks, the overall experience show that it is sufficient to only take into account the inductive
portion.
These values are in fact an attempt to summarize in the best possible way a variety of
existing experiences with the operation of electrical appliances in present supply systems.
Another point is that the vast majority of appliances placed on the market meets emission
limits which are based on the reference impedance.
The practical consequences are unique and transparent conditions for the definition of limits
in all countries, and simplified test procedures for appliances.
However, for high-power appliances, e.g. professional appliances, the reference impedance
is normally not used, since in such cases the conditions of connection are verified on a
single-case basis. This is equally true for the MV network, and therefore there is no recommendation at all for a reference impedance in MV networks.
As a conclusion, the contents of IEC 60725 [39] are still valid, they appear as appropriate for
the given impedance situation, and there is no reason to assume that the situation might
substantially change in the near future. In particular, the reference impedance has turbed out
to be quite useful for LV mass market equipment and is also referred to in other standards.
In case of any future consideration of modifications such one should be done only by
considering the comprehensive impact of the reference network impedance on the
construction of EMC standards and the limits and requirements contained.
2003-030-0769
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November 2003
ANNEX D
MEASUREMENT METHODS
It has been widely recognised for some time that there is a need for consistency when
making measurements of power quality parameters. Appropriate guidance should now be
given with the publication of EN 61000-4-30 [27] in February 2003. In addition to providing
normative guidance on the measurement of most of the voltage related PQ parameters, the
standard also contains a set of informative annexes which provide guidance on current
measurement and other PQ related topics. For the measurement of harmonics and flicker,
61000-4-30 [27] makes reference to the specific measurement standards 61000-4-7 [40] for
harmonics and 61000-4-15 [41] for flicker respectively.
IEC 61000-4-30 [27] proposes measurement methods and interpretation of results for power
quality parameters in 50/60 Hz a.c.
Since 61000-4-30 [27] is a new standard, it has a short maintenance cycle (five years). It is
intended that the first revision will include a practical guide on how to conduct power quality
measurements within installations and also a new section on how to determine the direction
of harmonic currents.
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November 2003
ANNEX E
MITIGATION METHODS
E.1 General
When it is necessary to take action to correct a breach or potential breach in the power
quality limits as applied to public electricity networks (in Europe specified by EN 50160 [1]),
three points are to be considered where mitigation measures can be put in place:
a. Network
b. Customer’s installation
c. Equipment
If we now consider the advantages and disadvantages of each location in turn:
E.2 Network Level Mitigation
Technical Issues
The most common method is to reduce the system impedance by some form of network
uprating e.g. installation of additional circuits or larger sized lines and cables. There are very
rare cases of filters being installed on the public network to compensate for the general
background level of harmonic distortion caused by equipment connected at low-voltage. The
main issue is that network mitigation is often a very blunt tool, in that the mitigation is applied
over a wide area, often much wider than the area affected by the power quality disturbance
for which the mitigation measure has been installed.
Commercial Issues
Where it is possible to trace the source of a breach in power quality limits to a single
customer the network operator is able to insist that the customer pays for the mitigation
measures. However under these circumstances the customer may, depending upon the
nature of the disturbance, chose to take mitigation measures within his installation.
E.3 Installation Level Mitigation
Technical Issues
There are cases where installations have installed ancillary equipment, often close to the
electrical intake position (supply terminals) to mitigate the risk of equipment within the installation causing a breach in the power quality seen on the public network that supplies the
installation. Examples of commonly used mitigation equipment include filters (either passive
or active) and UPS.
This option is particularly attractive if it can be considered at the design stage, when the
network operator and customer are in a position to agree upon the level and type of mitigation that will be necessary. However, it becomes incumbent upon the customer to keep the
network operator informed of any equipment changes within the installation that could see
power quality disturbances in excess of those for which the mitigation equipment was originally designed.
2003-030-0769
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November 2003
Commercial Issues
When large commercial and industrial installations are faced with the need to take measures
to mitigate the risk of their equipment causing a breach in power quality levels, it can often be
more economic to provide the mitigation within the installation rather than incur the cost of
network level mitigation. It would be prohibitively expensive and as such regulatorily unjustified for the network operator to monitor at the terminals of each large customer to check for
ongoing (i.e. after commissioning) compliance with power quality standards. Therefore it can
often happen that the network operator is unaware that a customer is causing a breach in
power quality limits until complaints are received from other customers or as a result of network monitoring in advance of a new connection. Under these circumstances it can be difficult for the network operator to positively identify the cause to the extent that the offending
customer(s) pays the full cost of mitigation, this can lead to the network operator picking up
the costs which then have to be aggregated across his customer base, that contradicting to
what has been explained in Chapter 1.5.
E.4 Equipment Level Mitigation
Technical Issues
For smaller items of equipment mitigation measures at equipment level it can often be most
effective to fit mitigation at the equipment level since it can be targeted precisely at achieving
the minimum level necessary to ensure that the equipment does not cause or contribute to a
breach in power quality levels, either individually or as part of the general load on a network.
This is particularly true for small equipment (rated up to 16 A per phase) which are subject to
emission limits in order to comply with EMC standards.
It is often far simpler for the customer and the network operator if the manufacturer provides
equipment with integral (“on board”) mitigation, since this can be incorporated at the design
stage and will not present the customer with the need to purchase any ancillary mitigation
equipment. For the network operator the assessment of new connections is much simpler
and there is less risk of background levels of power quality parameters breaching recognised
limits.
The mitigation method will depend upon the size of equipment and the particular power
quality parameter that needs to be protected.
Commercial Issues
Mitigation at equipment level is often seen as the most cost effective and cost reflective solution to ensure that power quality levels are not breached. It is cost effective because the mitigation measures can be designed to be an integral part of the equipment rather than ancillary to it. The costs are also seen as cost reflective since the equipment owner has also paid
for the mitigation measures; there is no risk of the mitigation costs being aggregated across
the network operator’s customer base.
E.5
Examples for Mitigation
E.5.1 Harmonics
Harmonic sources generally behave as current generators. Harmonic voltages appear as a
consequence of the flow of currents through the frequency dependent network impedance.
To reduce the harmonic distortion, usually to a specified limit, at a coupling point where
sensitive load is connected, several measures can be taken:
2003-030-0769
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November 2003
- separation of disturbing and sensitive loads, i.e., having separate coupling points
- reduction of the generation of harmonic currents by increasing the pulse number of
converters. If several sources are involved, connecting them through transformers with
different phase shifts such that the vectorial summation of harmonic currents will have
favourable diversity
- installation of a filter at the bus with the disturbing source. A similar method is to install
reactors in series with existing shunt capacitors so as to make the impedance inductive
for the characteristic harmonics. Care has to be taken with parallel (anti-) resonances
which may occur below the tuning frequency or between tuning frequencies if several
filters are installed.
Passive mitigation consists of a low impedance filter for one or several harmonic orders.
They are based on series resonant filters. Passive filters at the point where the loads are
connected to the public distribution systems are technically difficult to be applied due to
continuous change of system conditions. In fact, it is technically impossible to install a
passive filter at each point of connection for each residential installation because connection
of a large number of identical filters on the same network would create other serious
problems.
Active mitigation may be applied at equipment site or system level. It consists of filters that
-- by electronic techniques -- may continuously adapt to changing conditions in the network.
Active mitigation is more expensive but technical improvements made these filters more cost
effective now. Mitigation measures at equipment level are less costly to be implemented in
general.
It is generally less costly to apply mitigation measures at individual equipment level.
E.5.2 Flicker
Some mitigation or preventive measures are possible when it is known that a potential
source of flicker will be connected to the network. These include reducing the
impedance of the relevant part of the network, moving the point of common coupling
to a higher voltage level, and installing particular control or compensation equipment
with the load itself. It may also be possible to modify the operation of the load to
reduce either the frequency or magnitude of the voltage changes induced.
E.5.3 Unbalance
Concerning planning of a reduction of voltage unbalance, different technical solutions are
available. The most common options are:
o
rearrangement of phase connections
o
change of the load’s configuration or its operating conditions
o
increase of the fault level at the PCC
o
special transformers
o
static var compensators.
For more information see [10].
2003-030-0769
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November 2003
ANNEX F
STANDARDS IN THE CONTEXT WITH THE PQ REPORT
F.1
Harmonics
Compatibility levels are given in
-
IEC respectively EN 61000-2-2 for LV networks [13] and
-
IEC 61000-2-12 for MV networks [25]
-
IEC 61000-2-4 [42], which specifies compatibility levels for harmonic voltages at the
IPC (in-plant point of coupling) for industrial installations, establishing three classes
according to required immunity of equipment.
These are set by experience in order to give guidance for setting appropriate emission limits
and immunity requirements, also aiming at reduction of complaints about mal-operation (both
of loads and of system components) to a minimum. By definition, compatibility levels do not
represent rigid limits, but are expected to be exceeded with a low probability and only to a
small percentage of places.
Compatibility levels for the 3rd respectively 5th order of harmonic voltage are 5 % respectively
6 % and 8 % for the Total Harmonic Distortion Factor (THD).
Note: Additionally to the compatibility levels, so-called planning levels have been defined;
they represent levels, set by the network operator for their single supply network, which
is aimed at not getting exceeded, being lower than the standardised compatibility
levels.
IEC 61000-3-6 [43] establishes planning levels for MV, HV and EHV networks as well
as the conditions for connecting disturbing loads producing harmonics.
Emission limits are given in:
-
IEC 61000-3-2 [14], which specifies limits for harmonic current emissions applicable
to electrical and electronic equipment having an input current up to and including 16
A per phase, and intended to be connected to public low-voltage distribution systems.
The tests according to this standard are type tests.
-
IEC 61000-3-4 [16], which specifies limits for harmonic current emissions
applicable to electrical and electronic equipment having an input current
greater than 16 A per phase, and intended to be connected to public lowvoltage distribution systems. This document is a technical report.
-
IEC 61000-3-12 [15]: the recommendations of this -- at present -- draft standard, are
applicable to electrical and electronic equipment with a rated input current exceeding
16 A, up to 75 A per phase and intended to be connected to public low-voltage ac
distribution systems.
-
IEEE 519 [44]: establishes limits on harmonic currents and voltages at the point of
common coupling (PCC) or at the point of metering.
Immunity levels are defined in:
-
IEC 61000-4-13 [45], which proposes different immunity levels in accordance with
different performance criteria.
2003-030-0769
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November 2003
F.2
Flicker
A flicker value is also given in EN 50160 [1], with Plt lower or equal to 1 during 95 % of the
time.
Compatibility levels are given in
-
IEC respectively EN 61000-2-2 for LV networks [13] and
-
IEC 61000-2-12 for MV networks [25]
Note: Additionally to the compatibility levels, so-called planning levels have been defined;
they represent levels, set by the network operator for their single supply network, which
is aimed at not getting exceeded, being lower than the standardised compatibility level.
IEC 61000-3-7 [38] establishes planning levels for MV, HV and EHV networks as well
as the conditions for connecting disturbing loads producing harmonics.
For emission, the limits for equipment connected to the LV supply network are given in:
-
IEC 61000-3-3 [20]
IEC 61000-3-11 [46]
Immunity requirements as well as performance criteria and the immunity measurement
method are specified in IEC 61000-4-14 [47] and IEC 61000-4-15 [41].
F.3
Voltage Dips
EN 50160 [1] gives some indications including indicative values1:
“Voltage dips are generally caused by faults occurring in the customers’ installations or
in the public distribution system. They are unpredictable, largely random events. The
annual frequency varies greatly depending on the type of supply system and on the
point of observation. Moreover, the distribution over the year can be very irregular.
Also IEC 61000-2-2 [13] deals with the voltage dip issue.
As far as voltage dips are concerned, this standard has been completed by IEC TR 61000-28 [22], which proposes a clear definition of voltage dips and short interruptions and contains
statistical measurement results about voltage dips and short interruptions. Concerning voltage dips, the present PQ Report reflects mainly this Technical Report.
EN 61000-6-1 [48] and EN 61000-6-2 [49] specify minimum immunity requirements:
-
1
For a 10 ms duration and 30 % depth of a dip, the apparatus shall continue to operate
as intended after the test. No degradation of performance or loss of function is
Indicative values: Under normal operating conditions the expected number of voltage dips in a year
may be from up to a few tens to up to one thousand. The majority of voltage dips
have a duration less than 1 s and a depth less than 60 %. However, voltage dips
with greater depth can occur very frequently as a result of the switching of loads in
customers’ installations.”
2003-030-0769
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November 2003
allowed below a performance level specified by the manufacturer. During the test,
degradation of performance is however allowed. No change of actual operating state
or stored data is allowed. This is called performance criterion B.
-
F.4
For a 100 ms duration and 60 % depth, temporary loss function is allowed, provided
the function is self-recoverable or can be restored by the operation of the controls.
This is called performance criterion C.
Further Phenomena
F.4.1 Voltage Level, Voltage Variations
-
IEC 60038.…. [50]
-
HD 472 S1 … [23]
-
EN 50160 …... [1]
F.4.2 Overvoltages
-
EN 50160 [1] gives indicative values for temporary power frequency overvoltages between live conductors and earth as well as for transient overvoltages between live
conductors and earth
-
IEC 60664-1 [24] specifies requirements for the insulation.
F.4.3 Interharmonics
No standardized levels or limit values specified for interharmonics. IEC 61000-2-2 [13]
gives indicative values for interharmonic voltage levels.
F.4.4 Unbalance
EN 50160 [1] gives values for unbalance in LV and MV supply networks.
Compatibility levels are given in IEC 61000-2-2 [13] for LV networks, for MV networks and in
IEC 61000-2-12 [25] for MV networks.
Due to these three standards, for LV and MV systems, in normal operating conditions, 95%
of the 10 minutes values of τ (over the week) shall be less than 2%. In some areas where
single or bi-phase lines are existing, the limits could be 3 %.
IEC 61000-2-4 [42] specifies compatibility levels for harmonic voltages at the IPC (in-plant
point of coupling) for industrial installations, establishing three classes according to the
required immunity of equipment.
IEC 61000-4-27 [51] defines the immunity levels of equipment from unbalance as well as the
measurement method.
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F.5
Network Impedance
IEC 60 725: 1981 [39]
F.6
Power Quality Measurement Methods
IEC 61000-4-30 [27]
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ANNEX G
BIBLIOGRAPHY
[1]
CENELEC EN 50160:11-1999 “Voltage characteristics of electricity supplied by
public distribution systems”
[2]
CENELEC Application Guide to the European Standard EN 50160 on “Voltage
Characteristics of Electricity Supplied by Public Distribution Systems”, 2003
[3]
CEER-Report “Quality of electricity supply: Initial benchmarking on actual levels,
standards and regulatory strategies”, April 2001
[4]
UNIPEDE DISNORM 12, “Definitions of the Physical Characteristics of Electrical
Energy Supplied by Low and Medium Voltage Public Systems”, September 1989
[5]
UNIPEDE Report “Measurement Guide for Voltage Characteristics”, 1995
[6]
UNIPEDE Report “Voltage Dips and Short Interruptions in Electricity Supply Systems”, Ref.: 91 en 50.02
[7]
UNIPEDE Report on “Expected Harmonic Distortion in LV Networks”, October
1995
[8]
UNIPEDE: “Harmonic Distortion in Public Electricity Distribution Systems: Contribution of Class D Equipment,” February 1997
[9]
UIE - Guide to Quality of Electrical Supply for Industrial Installations. Part 5 : Flicker
and Voltage Fluctuations
[10] UIE-Guide to the Quality of Electrical Supply for Industrial Installations. Part 4: Voltage
unbalance.
[11] Phase 1 Report on European Residential Harmonics, 2001, The Low Frequency Emission Industry (LFEIC)
[12] Council Directive 85/374/EEC of 25 July 1985 on the approximation of the laws,
regulations and administrative provisions of the Member States concerning liability for
defective products
[13] IEC/EN 61000-2-2:2002: “Electromagnetic compatibility (EMC) - Part 2-2:
Environment - Compatibility levels for low-frequency conducted disturbances and
signalling in public low-voltage power supply systems”
[14] IEC 61000-3-2 (1995) Ed. 2.1 (Consolidated Edition 2001-10): “Electromagnetic
compatibility (EMC) - Part 3-2: Limits for harmonic current emissions (equipment
input current ≤ 16 A per phase)”
[15] Draft IEC 61000-3-12 Ed. 1.0 (2003-08): “Electromagnetic compatibility (EMC) – Part
3-12: Limits for harmonic currents produced by equipment connected to public lowvoltage systems with input current < 75 A per phase and subject to restricted
connection” (77A/426/CDV)
[16] IEC 61000-3-4 TR (1998-10): “Electromagnetic compatibility (EMC) - Part 3-4:
Limits - Limitation of emission of harmonic currents in low-voltage power supply
systems for equipment with rated current greater than 16 A”
[17] Council Directive 89/336/EEC on the approximation of the laws of the Member States
relating to electromagnetic compatibility, amended by Directives 91/263/EEC,
92/31/EEC, 93/68/EEC, 93/97/EEC
Revision under way
2003-030-0769
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November 2003
see also:
Guidelines on the application of Council Directive 89/336/EEC of 3 May 1989, European Commission DG III – Industry, 23 May 1997
[18] IEC 60050 - International Electrotechnical Vocabulary (IEV)
[19] IEC/TR2 60868 (1986-09): “Flickermeter – Functional and design specifications” +
IEC/TR2 60868-am1 (1990-06), IEC/TR2 60868-0 (1991-05) “Flickermeter – Part 0:
Evaluation of flicker severity” (see also [41])
[20] IEC 61000-3-3 (2002-03): “Electromagnetic compatibility (EMC) - Part 3-3: Limits Electromagnetic compatibility (EMC) – Part 3: Limits –Section 3: Limitation of voltage
fluctuations and flicker in low-voltage supply systems for equipment with rated current
≤ 16 A”
[21] “The Power Quality in Denmark”. P. Jorgensen et al. CIRED 1999
[22] IEC 61000-2-8 TR (2002-11): “Electromagnetic compatibility (EMC) - Part 2-8:
Environment - Voltage dips and short interruptions on public electric power supply
system with statistical measurement results”
[23] CENELEC HD 472 S1 (1988-11): “Nominal voltages for low voltage public electricity
supply systems” + Corrigendum 2003
[24] IEC 60664-1 Ed. 1.2 (2002-06) + Corr.1 (2002-11) “Insulation coordination for
equipment within low-voltage systems - Part 1: Principles, requirements and
tests”
[25] IEC 61000-2-12 (2003-04): “Electromagnetic compatibility (EMC) - Part 2-12:
Environment - Compatibility levels for low-frequency conducted disturbances and signalling in public medium-voltage power supply systems”
[26] “Study of the extra cost due to harmonics in HQ networks and equipment”.
R. Bergeron. 1998.
[27] IEC IS 61000-4-30 Ed. 1.0 (2003): “Electromagnetic compatibility (EMC) – Part 4-30:
Testing and measurement techniques -- Power quality measurement methods”
[28] „PQ in Switzerland“. M. Levet, UCS, 1998
[29] „Spannungsqualität. Koordinierte Messungen österreichischer EVU”, VEÖ-Journal
11/2000, 7/2001, 8/2001, 8/2002, 2-3/2003, 10/2003
[30] Belgian measurement campaign
[31] Harmonics measurements on French public LV systems. EDF. Luc Berthet.
October 2000. Ref. 77AWG1-001026Berthet01
[32] Slovakian measurement campaign
[33] “Harmonic Distortion Levels in UK Distribution Networks”. EA, May 2000. Ref.
77AWG1-000518Sinclair01.
[34] “Initial results of the harmonic measurement campaign on the French LV networks”.
Luc Berthet, Denis Boudou, Xavier Mamo, June 2001. 16th CIRED
[35] “State of play of the harmonic levels on the French LV networks”. Luc Berthet,
Denis Boudou, Xavier Mamo, Philippe Eyrolles, Jean Martinon. May 2003. 17 th
CIRED
[36] Plan de Medidas de Perturbaciones de UNESA
[37] “Some Problems of Power Quality in the Czech Distribution Networks”. K. Procházka,
P. Santarius, M. Schneider, Z. Hejpetr, P. Vašenka. CIRED 1999
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November 2003
[38] IEC 61000-3-7 (1996-11): “Electromagnetic compatibility (EMC) – Part 3: Limits –
Section 7: Assessment of emission limits for fluctuating loads in MV and HV power
systems”
[39] IEC/TR3 60725 (1981-01): “Considerations on reference impedances for use in determining the disturbance characteristics of household appliances and similar electrical
equipment”
[40] IEC 61000-4-7 (2002-08): “Electromagnetic compatibility (EMC) – Part 4: Testing and
measurement techniques – Section 7: General guide on harmonics and interharmonics measurements and instrumentation, for power supply systems and equipment connected thereto”
[41] IEC 61000-4-15 Consolidated Edition 1.1 (2003-02): “Electromagnetic compatibility
(EMC) – Part 4: Testing and measurement techniques – Section 15: Flickermeter –
Functional and design specifications” (superseding IEC 60868 and IEC 60868-0 (see
[19]))
[42] IEC 61000-2-4 (2002-06): “Electromagnetic compatibility (EMC) – Part 2: Environment
– Compatibility levels in industrial plants for low-frequency conducted disturbances”
[43] IEC/TR3 61000-3-6 (1996-10): “Electromagnetic compatibility (EMC) – Part 3:Limits –
Section 6: Assessment of emission limits for distorting loads in MV and HV power
systems”
[44] IEEE 519 “Recommended Practices and Requirements for Harmonic Control in Electric
Power Systems”
[45] IEC 61000-4-13 (2002-03): “Electromagnetic compatibility (EMC) – Part 4-13: Testing
and measurement techniques – Harmonics and interharmonics including mains signalling at a.c. power port, low frequency immunity tests”
[46] IEC 61000-3-11 (2000-08): “Electromagnetic compatibility (EMC) – Part 3-11: Limits –
Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage
supply systems – Equipment with rated current ≤ 75 A and subject to conditional
connection”
[47] IEC 61000-4-14 (1999-02) + IEC 61000-4-14-am1 (2001-07): „Electromagnetic
compatibility (EMC) – Part 4-14: Testing and measurement techniques – Voltage fluctuation immunity test“
[48] IEC 61000-6-1 (1997-07): “Electromagnetic compatibility (EMC) – Part 6: Generic
standards – Section 1: Immunity for residential, commercial and light-industrial environments”
[49] IEC 61000-6-2 (1999-01): “Electromagnetic compatibility (EMC) – Part 6-2: Generic
standards – Immunity for industrial environments”
[50] IEC 60038 Consolidated Edition 6.2 (2002-07): “IEC standard voltages”
[51] IEC 61000-4-27 (2000-08): “Electromagnetic compatibility (EMC) – Part 4-27: Testing
and measurement techniques – Unbalance, immunity test”
[52] CIGRE: Electra No. 208, June 2003
-
“Why it is necessary to control harmonic and flicker emission”. E.A. G. Finlay. July
1999. Ref. TF5a-9925
-
“Indices for Assessing Harmonic Distortion from Power Quality Measurements: Definitions and Benchmark Data”. D.D. Sabin et al. CC02-9821 (1998).
-
Results of EEI Harmonic Survey for IEC
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-
Draft IEC 61000-1-4 Ed. 1.0: „Electromagnetic compatibility (EMC) – Part 1-4: Rationale for limiting power-frequency conducted harmonic and inter-harmonic current
emissions from equipment, in the frequency range up to 9 kHz” (77A/339/CD: 2000-9)
-
IEC 61000-3-1 TR Ed. 1.0: Electromagnetic compatibility (EMC) – Part 3-1: Overview
of emission standards and guides” – Technical Report (Draft revision: 77A/226/NP)
-
„Empfindlichkeit von elektrischen Geräten gegenüber Spannungseinbrüchen und Kurzzeit-Unterbrechungen“, Studie, im Auftrage des Verbandes der Elektrizitätsunternehmen Österreichs (VEÖ) durchgeführt an der TU Wien, Institut für Elektrische Anlagen
und Energiewirtschaft, November 2001
-
ERA Technology “How to improve Voltage Dip Immunity in Industrial and
Commercial Power Distribution System”. ERA Report 99-0632R, August 1999
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ANNEX H
ABBREVIATIONS
CEER
CENELEC
DFT
DPQ
EDP
EHV
EMC
EMF
EN
EPRI
EURELECTRIC
GDP
HV
IEC
IEEE
IPC
IS
IT
ITE
LV
MV
PCC
PQ
SVC
THD
TR
TV
UIE
UNIPEDE
UPS
VDU
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Council of European Energy Regulators
European Committee for Electrotechnical Standardisation
Digital Fourier Transform
EPRI System Power Quality Monitoring Project
Electronic Data Processing
Extra High Voltage
Electromagnetic Compatibility
Electromagnetic Fields
European Standard
Electric Power Research Institute, USA
Union of the Electricity Industry
Gross Domestic Product
High Voltage
International Electrotechnical Commission
The Institute of Electrical and Electronic Engineers, USA
In-plant point of coupling
International Standard (IEC)
Information Technology
Information Technology Equipment
Low Voltage
Medium Voltage
Point of Common Coupling
Power Quality
Static var Compensator
Total Harmonic Distortion (Factor)
Technical Report (IEC)
Television
International Union for Electroheat
International Union of Producers and Distributors of Electric
Energy
Uninterruptible Power Supply
Visual Display Unit
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November 2003
ANNEX I
LIST OF FIGURES
2-1
2-2
2-3
2-4
2-5
2-6
Distorted wave: fundamental, 5 th harmonic
Typical example for the development of 3 rd , 5 th and 7 th harmonic and THD in a
substation in a residential estate LV (UK)
Typical example for the development of 3 rd , 5 th and 7 th harmonic and THD in a
substation in a residential estate MV (UK)
Maximum 95 % level of 3rd and 5 th harmonic voltages (NL)
Example for the 5 th harmonic distribution at 400V-, 30-kV and 110-kV- busbar
over one week (AT)
Typical mean Plt values in urban and rural distribution networks (DK)
B-1
Development of the odd harmonics 1979 – 1997 in Swiss LV networks
B-2a Evolution of the 95% 5 th , 100% 5 th harmonic, LV, 2000 - 2003 (AT)
B-2b Evolution of the 95% 5 th , 100% 5 th harmonic, HV, 2000 - 2003 (AT)
B-3
Evolution of the 95% 5 th , 7 th , 11 th harmonic and THD 1996 – 2002 (BE)
B-4
Evolution of P lt 1996 – 2002, Belgium, Site A, residential = 50%, industrial =
50%
B-5
Evolution of P lt 1996 – 2002, Belgium, Site B,residential = 95%, industrial = 5%
B-6
Evolution of P lt 1996 – 2002, Belgium, Site C, residential + industrial
B-7
Distribution of the 5 th harmonic during 12 consecutive days in a substation
(French winter sports resort)
B-8
Harmonics on 110-kV-level close to an arc furnace (SK)
B-9
3 rd , 5 th and 7 th harmonic and THD in UK residential estate over 24 hours
B-10 3 rd , 5 th and 7 th harmonic and THD in UK industrial area over 24 hours
B-11 3 rd , 5 th and 7 th harmonic and THD in a UK plastic extrusion factory over 24 hours
B-12 50-% level of the 5 th harmonic in French LV networks. Status 1991, 2000, 2001
B-13 95-% level of the 5 th harmonic in French LV networks. Status 1991, 2000, 2001
B-14 Max. level of the 5 th harmonic in French LV networks. Status 1991, 2000, 2001
B-15 Harmonics up to order 13 in 79 Spanish MV substations, 1987 - 1989
B-16 Frequency distribution of 95-%- and 100-%-values of 5th harmonics in Austrian
LV networks
B-17 95-%-values of the 5 th harmonic vs. fault level in Austrian LV, MV and HV
systems
B-18 THD values in Danish rural and urban LV networks
B-19 THD and 5 th harmonic in different locations of Prague with different specific
types of loads
B-20 Flicker values in Belgian LV networks, 1994
B-21 Counts of measurement results per P lt class in Austrian LV networks
B-22 Distribution of voltage dips in Austrian LV networks, 2000 - 2003
B-23 Distribution of (10-minutes average) minimum values of the voltage in Austrian
LV networks
B-24 Distribution of (10-minutes average) maximum values of the voltage in Austrian
LV networks, 2000 - 2001
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