Consulting Electrical Engineers
Association of Maharashtra
IGBT TECHNOLOGY IS A SYNONYM OF POWER QUALITY
Solutions and a Case Study to understand the uniqueness of IGBT Technology
for poor power quality. This drives the country for
having a better power quality in all the possible
ways to reduce the losses incurred in transmission,
distribution and utilization of the electrical power.
AUTHOR
In today’s scenario, the Power Quality is becoming
more and more a key element to meet end users
requirements successfully and economically. The
major Power Quality Problems faced by the Industries
are: (In the order of commonality)
¾¾ Power Factor or Reactive Power Problem
¾¾ Harmonics Problem / System resonances
Mr. Hasan Mydin J
¾¾ Unbalanced Loads
Manager - Power Quality Solutions
ABB India Ltd., Bangalore
¾¾ Voltage Dip/Sag or Swells
¾¾ Voltage Fluctuations
Email: [email protected],
[email protected]
¾¾ Interruptions etc.,
India, the modern and one of the expected super
powers of the world in 2030. Ten years before today,
our country didn’t have the power reach as high as
even 50% of the geographical area, but today we have
reached the highest availability of electricity even in
some remote areas of the country.(This still has to be
improved to a reach of 100%) Well, keeping that mind,
we know that the complexity of our Electrical Network
has become higher and higher, which in turn have
increased the requirement of high reliability and power
quality among all the levels of the electrical systems
including End Users and Distribution Authorities.
For example, ten years before there is hardly any
regulations imposed on the electricity users(Industrial)
for maintaining poor power quality in terms of Poor
Power Factor, High Harmonics etc., but today there is
almost all the electricity boards of Indian sub-continent
has the limits and regulations and penalty structures
In this article, the author discusses a simplified and all
in one solution using “IGBT Technology”
( Insulated
Gate Bipolar Transistor) to meet the above mentioned
challenges. This concept traditionally considered
as a very high end solution required only for the
distribution companies and high electricity utilization
users(Users having more than 500MW). But today
with the advancements in the IGBT manufacturing
industries it is possible for all the industries to afford
an IGBT Technology for a better power quality.
GENERAL
Now in this article the author discusses the major
power quality problems and IGBT Technology
Solutions to the same. The major problems faced by
most of the industries today are Power Factor/Reactive
Power and Harmonics Problems. Till date, there has
been a major trend of installing the capacitor banks
with or without reactors (Tuned/Detuned) for Power
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Factor and Harmonics problems at various levels of
the Electrical Network. (Typical installation shown in
Figure-1). But the complex applications today, are
opting for IGBT Based Technology.
IGBT Technology will rule the Power Quality
World
The versatile and adaptive design possibility of the
IGBT system has rolled them out in all the areas where
Power Quality is a mandatory requirement such as,
™™ Power Factor Improvement using Static
Condenser(STATCON) using IGBT Technology
™™ Harmonics Mitigation by Active Filter - Voltage
Source Converter using IGBT Technology
™™ Unbalance Compensation (Negative Sequence)
using IGBT Technology
™™ Active Front End DRIVES using IGBT Technology
™™ Active Front End UPS (Uninterrupted Power
Supply) using IGBT Technology
™™ Voltage Dip/Sag and Surge Protection using IGBT
Technology (Series Compensation)
™™ Industrial Power Automation solutions for Power
Supplies using IGBT Technology
™™ Special DRIVES for LOCO applications using IGBT
Technology
™™ High Frequency and Higher Power Quality
conversions for AVIATION Applications
™™ And many more..
In the Power Electronics Industry, IGBTs have entered
late after Diodes and Thyristor in the electrical world.
However with the better power quality output, the use
of IGBT technology has become more popular for the
high efficiency requirements in the electrical network.
At this juncture, the readers are also advised that
though the technology has entered in all the fields of
Power Quality, very few of them mastered the micro
level details on the technology. So it is highly important
to choose only a well proven solutions using IGBT
Technology.
Parallel Compensation using IGBT
Technology
Figure 1: Typical Capacitor Bank at HV Level with Tuned/
Detuned Reactors
IGBT based compensator used in parallel to the
load is the compensation method for the reactive
power(PF), Unbalance compensation and Harmonics
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Figure 2: Typical IGBT Based Compensator connection
diagram (Parallel to Load(s))
Mitigation. This is the common configuration used in
all the STATCON and Active Filter Technologies.
This arrangement is similar for both Reactive Power
and Harmonics are same, there are some minor
changes are employed internally based on the
frequency of operation of the IGBT converter. The
compensation for the reactive power is explained in
the next section.
Water Tank Analogy (Reactive Power
Compensation by IGBT System)
For understanding the reactive power compensation
of the IGBT based compensator consider the following
set-up as shown below in Figure-3.
Let us assume there are two water tanks namely
Vs(Source Tank) and (Wish Tank) Vi, both connected
by tube with a tap as shown in Figure-3. The wish
tank, from the name itself it is understood that, it can
increase or decrease the level of the water, whereas
the source tank’s water level is constant.
Now when the Wish Tank(Vi) water level is higher
than the Source Tank(Vs) Water level, the direction of
Water current will be towards the source(Vs), which in
electrical terms, a capacitive current. Similarly when
Figure 3: Water tank analogy for understanding the reactive
power compensation of the IGBT based compensator
the Wish Tank(Vi) water level is lower than the Source
Tank(Vs) water level, the direction of the water current
will be towards the Wish Tank(Vi), which in electrical
terms, an Inductive Current.
The analogy is, in any IGBT based compensator, the
IGBT converter acts as a Wish tank to increase or
decrease the voltage and thereby causing a potential
difference between the Source and the IGBT Voltage
Source Converter(VSC). So whenever the converter
voltage is higher, the compensator delivers a capacitive
current and whenever the converter voltage is lower,
the compensator delivers an Inductive Current.
Hence the compensator achieves both inductive and
capacitive current compensations in the system.
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Figure 2: Installation of 6
at Sabarkantha, Gujarat
Figure-4: 50% Line Losses reduction by IGBT based compensator by negative sequence compensation
Un-Balanced Load Compensation
IGBT based compensators can compensate for the
line unbalance due to negative sequence components
in the system. To understand the compensation, one
should understand the anatomy of the Unbalance
current. Any unbalance current is combination of
Positive Sequence, Negative Sequence and Zero
sequence components of current in together. And out
these three the Zero sequence component is assumed
Zero because of the Three-phase three wire system.
And hence there are only two components present in
the Unbalance current (Positive & Negative Sequence
components only).
There are number of ill effects present due to
unbalanced currents in the electrical system. Out of
which the biggest savings can be attained is in the
reduction of the Line losses (Cu Losses) as shown in
the figure-4. Considering the article sizing, the author
decided to remove the effects of Unbalance currents
in details.
To compensate for the unbalanced currents is by
adding a IGBT compensator, this can supply the
negative sequence components in to the system and
thereby making your electrical network experience
Balanced currents above the point of coupling of the
IGBT system.
Harmonics Compensation by IGBT Based
Compensator
Harmonics Mitigation is one of the recent topics
of discussions among most of the industries and
electrical authorities in India. In fact some of the states
in India are planning to impose Harmonic Penalty
for the industrial customers having Harmonics limits
beyond the CEA (Central Electrical Authority). The
details are as mentioned below,
(1) The total harmonic distortion for voltage at the
connection point shall not exceed 5% with no
individual harmonic higher than 3%.
(2) The total harmonic distortion for current drawn
from the transmission system at the connection
point shall not exceed 8%.
(3) The limit on total harmonic distortion mentioned in
clause (1) and (2) above shall come into effect from
01.01.2011 and the limit on individual harmonic
distortion for voltage mentioned in clause (1)
above shall come into effect from 01.01.2012.
So the harmonic mitigation in industries have become
one of the top priorities in India subcontinent and
authorities of electricity distributions. The Harmonics
is “Multiple frequency components of Fundamental
Frequency (50Hz)” For example when a harmonic
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Association of Maharashtra
components frequency is 200Hz then the Order of the
Harmonics is 4th Order
Harmonic order (n) =
Frequency of the Harmonic Component (Fh)
Frequency of the Fundamental Frequency (F1)
Here considering the focus on the IGBT compensation
the author has decided to shorten the article by
removing the effects of Harmonics and other analysis
from the detailed explanations.
To remove the harmonics in the system, by far IGBT
based technology is the most effective way. In IGBT
compensator this is achieved by the injection of
negative harmonics into the system. For example if you
have 10 Ampere of 5th Order harmonics(250Hz), then
the IGBT compensation equipment injects 10Ampere
of 5th Order harmonics in the perfect opposite phase
to the original harmonics in order to cancel out each
other at the point of coupling of the IGBT system as
shown in the Figure-5.
Figure-5: Harmonics Mitigation by IGBT Based Compensator
Figure-6: IEEE-519:1992 Harmonic Levels
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IEEE-519:1992 Standard for Allowable Limits
of Harmonics
One of the other commonly followed regulation is
IEEE-519, This is another regulation for harmonics by
an international Standards organization IEEE (Institute
of Electrical and Electronics Engineers). The IEEE-519
states the following limits for harmonics with respect
to different voltage levels and short circuit capacity of
the system as shown in Figure-6.
Whether you are following an IEEE-519:1992 or CEA
regulation, in either case the Harmonics Mitigation
in the system will always reduce the risk of failures
which is the major reason for DOWN-TIME losses in
the industries.
Series Compensation using IGBT Technology
Series compensation is mainly used for Voltage Dip/
Sag or Surge applications in the Electrical Network.
And this is again achieved using an IGBT based
compensator with an injection transformer in series
as shown in Figure-7. In this article we are not going
to discuss in detail the operation of the compensator
only.
The series compensator takes feedback from the
Secondary side of the series transformer and injects
the difference in voltage caused due to Voltage Dip
Instantaneously and thereby avoiding the down time
due to the tripping of the critical and sophisticated
equipment in the network.
Case Study – Power Quality Compensation F\
for a Steel Rolling Mill Application
Executive Summary
This case study involves, a Power Quality Study,
Project Proposal, Execution of the Solutions, and
Power Factor improvement for a highly fluctuating
loads using IGBT Based Compensator in a Steel Hot
Rolling Mill in Andhra Pradesh. The end user could
not able to achieve PF improvement with classical
compensation equipment where their power factor is
going as low as 0.55(lag). Here the key is, in Andhra
Pradesh, the billing system is in kVAh not in kWh.
Which indirectly drives all the customers to maintain
unity PF to achieve maximum savings in the electricity
bills.
kVAh Billing System
In most of the States in India the billing structure is in
kWh(Active Energy only) based system with a Penalty
for PF below a certain level. This penalty level varies
from State to state, typically from 0.85 to 0.90. That
Figure-7: Voltage Dip / Surge compensation using IGBT based series compensator
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is if the end user’s average monthly PF is lesser than
0.90 then they will be paying a surcharge/penalty to
the electricity board. In some of the electricity boards
there are REBATES for having a better Power Factor
as high as 7% of their entire energy charges. Recently
the electricity authorities understood the importance
of having a unity PF in the system, hence states like,
Andhra Pradesh, Delhi NCR, Haryana, Uttar Khand,
Uttar Pradesh and Himachal Pradesh etc., the Billing
system is in kVAh(Apparent Energy). This means
irrespective of the PF, in kVAh billing system the bill
will always include both kWh(Active energy) and kvarh
(Reactive Energy).
Since the billing system is in kVAh, it is very uneconomical for the customer to pay for the reactive
power consumption in the system makes it even worse
by adding another almost 40-50% of the electricity
cost in to the production cost of the rolled steels. The
end user requested for an IGBT based compensation
by understanding the possibility of improving the PF
to 0.90 and above. ABB have conducted the PQ study
with the specialized team of Engineers and proposed
a +/-3600kar IGBT based compensation with some
base compensation of Fixed Capacitors to the end
user for the above mentioned applications.
Results of the PQ Improvement
kWh=Active Energy only
kVAh=kWh+kvarh (Active Energy + Reactive Energy)
The Problem for the Rolling Mill Application
In case of a rolling mill the load fluctuations are very
high, which makes it highly challenging for a classical
capacitor based solutions to maintain the Power
Factor. In this case study the total rolling mill load is
around 5-7MW. Even though the customer was already
having a classical capacitors for the Power Factor
Improvement, the power factor was not improving,
because the load dynamics very high. The reactive
Power Fluctuations are from 900kvar to 5000kvar in
seconds and the cycle repeats every few seconds.
This fluctuations of the kvar and the PF without having
a compensator is shown in Figure-8.
The delivery, installation and commissioning of the
system took about two months. And Thanks to the
IGBT based instantaneous and stepless reactive
power compensation with a rugged design of the
compensator, now the end user is maintaining an
astounding PF of 0.999 which is VERY near to the
Ideal conditions of an Electrical System. Please review
the graphs of PF before and after installation of the
IGBT based compensation in Figure-9.
SAVINGS for the END USER
The timely actions of the end user and the technical
capability on the customized solution by the solution
provider (ABB) using IGBT Compensator, the customer
is enjoying the benefits of the Unity PF for rolling mill
Figure-8: Dynamics of the Rolling Mill Load without IGBT Compensation
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AVERAGE PF = 0.999
Figure-9: Dynamics of the Rolling Mill Load without IGBT Compensation
with a reduced productions costs and high reliability
of the system.
Savings by IGBT Compensator – 16-Hours and 25days
Savings by IGBT Compensator
CASE kVA
Plant Running
Savings
Hours / Days/
Day
Month
Yearly Savings
(Rs.6.4/ Unit)
MAX
1,209
16
25
Rs. 37,145,815
AVG
563
16
25
Rs. 17,300,529
Figure-10: Savings to the End Customer for ROLLING MILL
Applications
From Figure-10, it is very clear to understand that the
end user will be saving as high as Rupees 3.7 Crores
in a year with the IGBT Based compensator. This is one
of the very typical and most common application for
IGBT Based compensator in Rolling Mills, Railways,
Furnaces, Automobiles and other process industries.
At this juncture, the author would like to emphasis
that with this kind of techno commercial benefits, it
is very easy for any industrial customer to use IGBT
Compensator for Power Quality Applications.
Conclusion
From the Power Factor improvement and Drive
application to Voltage Dip / Surge correction, the
IGBT Technology has it all. And like mentioned in the
starting of this article, India is focusing on a Better
Power Quality more than any other country in the
world currently. The recent google analysis shows
that, in 2005 the countries that mostly looked for
Power Quality is Americas and from 2011 onwards,
the trend changes, the highest ratings stays with India
from 2011 onwards. This is shown in Figure-11.
Please see the differences in searches for Power
Quality in 2005 and 2011, which clearly indicates
that our country(India) is on the right path to achieve
maximum efficiency by improving Power Quality. And
this also proves that India is getting ready to step up,
and to achieve the “Super Power“ Status by saving the
wastage of “Electrical - Power”, and IGBT Technology
will lead the way to it!
REFERENCES & WEBSITE LINKS
http://www.pqindia.in/power-quality.html
[1] Power Quality India – Google Results & Power Quality
Analysis
http://www.cea.nic.in/reports/regulation/reg_grid_draft.pdf
[2] CEA – Central Electricity Authority Web Link above
http://ieeexplore.ieee.org/xpl/mostRecentIssue.
jsp?punumber=2227
[3] IEEE-519 Weblink above
[4] Power Quality Solutions – by Duggan
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Figure-11: Google Analysis for Power Quality Search Volumes in Year 2005 and 2011
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