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3608
Journal of Applied Sciences Research, 8(7): 3608-3612, 2012
ISSN 1819-544X
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLES
Project Based Learning of a Test Distribution System and its Configuration: A Case
Study
K.A. Karim, N.C. Cheow and L.K. Onn
1
Department of Electrical, Electronic and Systems Engineering Universiti Kebangsaan Malaysia, 43600Bangi,
Selangor, Malaysia.
ABSTRACT
This paper describes the application of the project based learning (PBL) on the test distribution system. The
methodologies and the real time simulation are developed for the audit base case load flow, short circuit and
electromagnetic transient analysis. The control and protection scheme, generator, capacitor switching, protective
relay setting and coordination are designed such a way that the system losses are reduced. Besides, the analysis
of the system is able to maintain the reliability and quality of the power system.
Key wrods: PBL, Test distribution system, demand, system loss, simulation.
Introduction
Generation, transmission and distribution are the main parts of the power system. The electricity is
generated in the power station, which is installed with generators, control and instrumentation equipments,
switchgears and other associated plants and equipment for quality power distribution (Hannan et al., 2005,
Salam et al. 2010). Transmission lines are required to transport the bulk electricity from the power stations to
various locations to enhance supply reliability as well as to achieve effective utilization of power (Hannan et al.,
2009). Transmission of electricity is usually at high voltage so as to reduce transmission losses, substations
equipped with transformers are required to step down electricity from high voltages to low voltages to suit the
requirements of the various categories of consumers such as commercial, industrial and domestic (Sallehhudin
et al., 2009, Hannan et al., 2011, Ghani et al., 2012). At consumer sides, there are various sensitive equipment
and devices whose operation might be affected by the quality level of the power system (Subiyanto et al., 2011,
Ghani et al., 2012, Hannan et al., 2012, Subiyanto et al., 2012). Therefore, power quality mitigation is important
issue (Hannan et al., 2006, Hannan et al., 2009, Hannan et al., 2012). At present the transmission system in
Malaysia is at voltages of 66kV, 132kV, 275kV. Electrical energy is distributed to consumers via distribution
system. The distribution system represents the final linkage between the consumers and the power stations. The
distribution process starts at the termination of the transmission lines at distribution substations. The voltage is
then stepped down by step down transformers to supply to the load centers via the distribution network. The
distribution voltages used in Malaysia are 33 kV, 11 kV and 415/240.
This paper deals with the test distribution system that was given as project based learning (PBL) task.
Methodologies and a real time simulation of the given task has been developed for audit base case load flow
analysis. In the simulation, control and protection scheme, generator, capacitor switching, protective relay
setting and coordination have been designed to reduce the system losses and it analysis to maintain the
reliability and quality of the power system (Hannan et al., 2004, Yorkshire Electricity, Benmouyal, 1999, Verma
et al. 1979). However, this paper highlighted only the system configuration, load demand, duration and losses.
Test Distribution System:
A test distribution system is shown in Fig. 1. It comprises of network operating at medium voltage (MV)
and low voltage (LV) levels to obtain power from the transmission network or the grid. In some cases, the
distribution network may also have embedded generators connected to it. Most customers are connected to the
distribution network at MV or LV levels. In this project, the distribution network is connected to the grid with
some loads being supplied by a generating unit. The following sections describe a distribution network and to
complete the project tasks, it will be necessary for modeling the network and obtain the correct load flow and
short-circuit results.
Corresponding Author: K.A. Karim, Dept. of Electrical, Electronic & Systems Engineering, Universiti Kebangsaan
Malaysia, 43600 Bangi, Selangor, Malaysia; E-mail: [email protected]
3609
J. Appl. Sci. Res., 8(7): 3608-3612, 2012
Fig. 1: Test distribution system
System Configuration:
The main step down substation is connected to the grid at nominal voltage of 132 kV, i.e., the source. The
maximum 3-phase and 1-phase-to-ground fault currents at the source are given with a 3-phase solid fault on the
132 kV bus. The 132 kV is stepped down to 11 kV using 2 x 30 MVA transformers whose parameters are also
indicated in Fig. 1. The main intake substation has another voltage transformation, i.e., 132/33 kV. Parameters
for the two 45 MVA transformers are also indicated in Fig. 1. The two transformers are also sized in accordance
to the same principle as for the 132/11 kV power transformers. The 11 kV and 33 kV buses are arranged in
single-bus single-breaker scheme with two buses connected through a bus-coupler breaker.
Feeders and Substations:
On the 11 kV side of the main intake substation, there are 2 x incoming feeders from the two power
transformers and 8 x 11 kV outgoing feeders. On the 33 kV side, there are also 2 x incoming feeders from the
two power transformers and 4 x outgoing feeders supplying a series of PPUs (Main Distribution Substations).
Typically an 11/0.433 kV substation (red box) comprises of switches for incoming and outgoing feeders as well
as for distribution transformer feeder as indicated in Fig. 2. The Ring Main Unit (RMU) with capability to break
only on load, the transformer feeder is provided with a switchable fuse with the use breaking the fault current
and subsequently opening the switch on no load or the load current. Ring Main Unit or RMU is a unit to make
up a distribution substation comprising at least a minimum of two load break switches and one switch fuse unit.
It is installed in ring as well as radial circuits.
A main distribution substation (PPU) has incoming voltage at 33 kV or 22 kV and stepped down to 11 kV
and typically arranged as shown in Fig. 2. The switches are all circuit breakers.
Fig. 2: Typical arrangement of PPU
3610
J. Appl. Sci. Res., 8(7): 3608-3612, 2012
Network Circuits Connections:
Table 1 lists the kVA size of transformers at each substation and the corresponding static loads connected to
its secondary. At 433 V, loads are to be connected in grounded-star while at 11 kV loads are delta connected.
Table 2 is the motor specification for each substation.
Table 1: Substation transformer and static loads
Transformer 1 (T1)
Substation
Size
Load
(kVA)
(kVA)
Paper Mill
2500
400
Jaya
Sun
Puchong
Hospital
Samua
Aloe
RTM
Disk
Jong
Shield
Cowan
Chem
500
2500
2500
750
2500
2000
2500
750
300
300
1000
1500
Table 2: Motor specification
Substation
Rated
Voltage
(kV)
Paper Mill
3.3
Transformer 1
327.23
595.45
480.44
393.3
284.44
2041.2
313.47
451.1
175.88
300.55
751.06
813.23
Load P.F.
0.88
Transformer 2 (T2)
Size
Load
(kVA)
(kVA)
2500
600
Load
P.F.
0.85
0.9
0.82
0.91
0.87
0.86
0.87
0.95
0.86
0.83
0.81
0.82
0.9
Remarks
Refer to Table 3 for motor loads
on T1 and T2
Refer to Table 4 For motor load
on T2
Rated
Power
(kW)
2000
Loading
(kW)
NEMA
Code
Lock-Rotor
Reactance (p.u.)
R (p.u.)
X (p.u.)
Sub-transient
Transient
1200
Type B
0.0753
0.149
0.119
0.1958
Paper Mill
Transformer2
0.433
2000
1500
Type D
0.161
0.104
0.0991
0.0991
Chem
3.3
2000
1000
Type B
0.0753
0.149
0.119
0.1958
Results And Discussion
Reducing system losses to optimal level for the given test distribution system, annual demand and loads are
simulated and shown in Table 3. Table 3 concludes that the annual loss for the original test distribution system
is 1.0587 MW (40.86-39.8013). The annual cost of losses is (.0587 MW x RM0.29/kWh x 24 hours x 365 days)
RM 2,689,521.48. Therefore, the annual cost of losses for original system is RM 2,689,521.48. Table 4 shows
the simulated demand, power loss and the power factor of the system.
Table 3: Annual demand and load for test distribution system
Original test distribution system
Load (%)
Duration (%)
100
5
90
10
80
25
75
20
60
20
50
10
40
10
Annual Total
Index
0.05
0.09
0.2
0.15
0.12
0.05
0.04
Table 4: Original test distribution system demand and system losses
Power Before Capacitor installed
Demand
Loss
P(MW)
Q(MVAR)
P(MW)
58.372
32.465
1.513
Power(MW)
Demand
2.919
5.253
11.674
8.756
7.005
2.919
2.335
40.860
Load
2.84295
5.11731
11.3718
8.52885
6.82308
2.84295
2.27436
39.8013
PF (%)
Q(Mvar)
-3.397
87.39
From the load flow analysis result as shown in Fig. 3 for 33 kV network and all 11 kV, where load buses
are under the voltage limit. Capacitors are installed to increase the voltage limit to achieve the desire level (90100%).
3611
J. Appl. Sci. Res., 8(7): 3608-3612, 2012
Fig. 3: Load Duration for test distribution system
To get the minimum power losses analysis, the changes of losses of various generating is shown in Table 5.
Result show that the 1200 kW generating unit does not incurred additional system losses. Terminal voltage at 11
kV bus varies between 11.074kV to 11.123kV. The maximum and minimum voltage limit for 11 kV is 11.55kV
(105%) and 10.45kV (95%) respectively. Therefore, it can be considered that there is no voltage limit for 1200
kW generating unit.
Table 6: Change of Losses for Variation of Generating Unit
Generator
After generator set up
Before generator set up
Output
System Loss
System Loss
P (MW)
P (MW)
Q (Mvar)
P (MW)
Q (Mvar)
3000
1.537
-3.83
1.513
-3.397
2500
1.608
-3.715
1.513
-3.397
2000
1.562
-3.789
1.513
-3.397
1800
1.546
-3.816
1.513
-3.397
1700
1.539
-3.828
1.513
-3.397
1600
1.532
-3.838
1.513
-3.397
1550
1.529
-3.843
1.513
-3.397
1530
1.528
-3.845
1.513
-3.397
1500
1.526
-3.847
1.513
-3.397
1450
1.524
-3.852
1.513
-3.397
1430
1.523
-3.854
1.513
-3.397
1350
1.519
-3.86
1.513
-3.397
1300
1.517
-3.863
1.513
-3.397
1250
1.515
-3.866
1.513
-3.397
1200
1.513
-3.869
1.513
-3.397
Change
∆P
0.024
0.095
0.049
0.033
0.026
0.019
0.016
0.015
0.013
0.011
0.01
0.006
0.004
0.002
0
∆Q
0.433
0.318
0.392
0.419
0.431
0.441
0.446
0.448
0.45
0.455
0.457
0.463
0.466
0.469
0.472
Voltage
11 kV
11.103
11.176
11.123
11.111
11.104
11.097
11.093
11.093
11.091
11.087
11.086
11.081
11.077
11.074
11.074
Conclusion
In the paper, theoretical and practical approaches have been learned and applied in the project based
learning (PBL) on the test distribution system. The system design such as the control and protection scheme,
generator, capacitor switching, protective relay setting and coordination have reduce the system losses. Besides,
the analysis of the system can maintain the reliability and quality of the power system.
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