Prince Mohammad Bin Fahd University
College of Engineering
Department of Electrical Engineering
Internship Report
at
[Saudi Electricity Company]
Reporting Period:
[16/06/2012 - 19/06/2012]
Submitted by:
[Sultan Hamed Al-Mutairi]
[200800298]
[submission date (29/06/2012)]
Electrical Engineering Department
Summer 2012
My name is Sultan Hamed AL-Mutairi, and my major is Electrical
Engineering. I am seiner student. I have Internship course with Dr.Omar
Ouda in this summer.
Summary
The progress report concerns with the engineering aspects that face the underground
medium voltage in the Saudi Electricity Company.
A power supply project is of two types, one is the low power supply and the other is the
high power supply. A low power supply project is when dealing below an apparent power
below 4 MVA whereas the high power supply is above 4 MVA.
A system improvement project is a project that deals with the company network to make it
more reliable and secure. The system improvement projects usually come when the load in
a 13.8 KV feeder/ cable is close to 8 MVA which is the maximum apparent power that the
feeder withstands in order not to be damaged. The report starts with a background of the
company medium voltage electrical equipment. Then, introducing the single line diagram,
where each project depends on.
1. Background
The first day of my training was in 16\6\2012 at SAUDI ELECTRICITY COMPANY
(SEC) in AL-Kobar. The SAUDI ELECTRICITY COMPANY (SEC) was established
in 2000. The company main job is to provide comprehensive electrical services
starting from the high voltage until reaching the low voltage.
The company can be divided in accordance to the power into three parts which are the
power planet, power transmission, and operation areas. In the power planet, a standard
voltage is generated and converted to higher voltages using step up transformers. The
power transmission is responsible to transmit the higher voltages to a desired region.
In operation areas, the high voltages are converted to a standard medium voltage
using step down transformers. This medium voltage is the interface between the
company and customers.
Training supervisor information:
Distribution Planning Section Head
Name: Fahad H. AL-Talhi , phone: 0504697173, Email: [email protected]
The company's training schedule:
During the summer training period, four divisions will be attended in the medium
voltage which are the Maintenance, Operation, Engineering, and Planning and
Construction Division. The duration of the training period in each division is two
weeks.
The Engineering Division deals with the distribution of substations and mini pillars
among a new region. This includes also the exemption from a substation or a mini
pillar when customers objecting to have a substation or a mini pillar to be funded in
their lots. The training within The Engineering Division was completed and the next
training will be within The Maintenance and the Operation Divisions.
2. The Single Line Diagram SLD
The single line diagram (SLD) is a representation that is used for the 13.8KV electrical
equipment and how the company network is arranged. It is important because it has all
the information that makes the work easier for engineers and operation people. It is used
to locate a substation, a mini pillars, identify from where the substation is energized. In
system improvement and power supply, the single line diagram must be used because it
is the place of designing. The single line diagram is a standard that engineers and
operators, understand and use widely.
2.1 The Single Line Diagram for the 13.8KV Electrical Equipment
The single line diagram includes substations and its components. Fig.2.1 shows that
each substation has a special drawing representation in addition to the auxiliary
transformer. Also, three oil switches are in the figure and the load break switch with two
drawing representations. The normally open point in the figure represent where the
current of the cable stops. The figure introduces all parts of the single line diagram
including grid station breakers, substations, oil switches, load break switches, and the
normally open point. Substations in the single line diagram contain numbers, i.e. a 300
KVA substation can be identified in the single line diagram from its drawing. Also, the
substation unique number is written inside the drawing. The figure does not represent
any number of a substation. In the next sections, there will be a clear representation of
substations in the single line diagram.
Figure 2.1: Operation single line diagram.
Sometimes when dealing with bulk customers with loads higher than 4 MVA, the
drawing of the substation will be the same as the street light in addition to some note
to indicate the specifications of the substation. The single line diagram for the
substation components is shown in Fig.2.2. The transformers and the low voltage
panels are repented by the single line diagram. The ring main unit has the incoming,
outgoing, and local cable. Also, the figure shows the circuits from the low voltage
panel for each type of transformer.
Figure 2.2: The single line diagram for the substations' components.
For projects, when a single line diagram is presented, some modification may be
applied to the single line diagram in accordance to the desired design. There are three
basic drawings that are used in designing to be applied on feeders. The drawing
operations are cable diversion, cutting, and jointing shown in Fig.2.3. The diversion is
an operation of connecting a cable to switchgear and applied when the cable is to be
used totally by the switchgear, whereas joining is an operation that is used when
connecting a cable to another cable. The cutting operation indicates that the locus of
the feeder will not be used anymore.
Figure 2.3: Designing drawings applied in the single line diagram for cables.
2.2 The Company Network
For better customer services, substations are joined together in a ring topology. The
ring topology starts from the grid station through a breaker which has a feeder
connected to the first substation and from the first substation to the second one and so
on. This continues until reaching to the last substation in which it is also connected to
another breaker from the grid station, establishing a loop that started from a breaker
and ended at another breaker. Each loop in the ring topology must have a normally
open point in the feeder locus. The advantage of the ring topology can be understood
from Fig.2.4. In the figure there are two breakers from different buses at the same grid
station. The first breaker B-1 is energizing the substations S/S a1, S/S b1, and S/S c1
while the other breaker B-2 is energizing the substations S/S a2, S/S b2, S/S c2. The
normally open point is between the substations S/S c1 and S/S c2 and achieved by
switching off an outgoing feeder from either S/S c1 or S/S c2. Now, if a cable fault
occurs between S/S a1 and S/S b1, the breaker B-1 will be energizing only the
substation S/S a1. However, because of the ring topology, the other substations which
are S/S b1 and S/S c1 can be energized by B-2 when the normally open point is
closed.
Figure 2.4: The ring topology in the company network.
There is sometimes a radial substation which is a substation that stops the ring
topology and its outgoing feeder is not yet connected to another substation and this
happens in new regions.
The ring topology makes the network more reliable. To improve the reliability,
instead of using the same grid station for a two breakers in the same loop, the
company uses two breakers from different grid stations in case where one of the grid
stations is off for any reason.
3. Load Estimation
The load is classified into three major elements which are the contracted load,
connected load, and the demand load. The contracted load (CRL) is the capacity of
power supply equivalent to the circuit breaker provided to the customer. The
connected load (CL) is the sum of the nameplate ratings of all present and future
electrical equipment installed by a customer. The demand load (DL) is the maximum
load drawn from the power system by a customer at the customer’s interface and can
be estimated or measured. The demand load is important in designing because the
connected load does not give a real estimate of the consumed power. Also, it is
difficult for customers and not true to run their applications all in the same time. So,
the demand load gives an approximation of an instantaneous consuming of power.
There is an important factor which is the demand factor (DF). The demand factor is
the ratio of the maximum demand to the total connected load.
The demand factors for different type of customers are introduced in Appendix D.
The contracted load can be calculated from the following equation for the low voltage
127V/220V:
Also, there is another important factor which is the diversity factor (DvF). The
diversity factor is the ratio of the sum of individual maximum demands of customers
to the maximum demand of the whole system. Appendix C introduces the diversity
factors in accordance to the number of customers. Also, this appendix can be used for
the number of circuit breakers.
When dealing with a number of customers, the demand load can be calculated, using
the diversity factors in Appendix C, from the following equation:
Also, when calculating the demand load for a group of one circuit breaker , the
demand load is calculated from the following equation:
These equations are widely used in planning and designing. The demand load is the
load of concern instead of using the contracted load or the connected load because it
gives a considerable consume of power and approximately equivalent to the real
consumption.