Download Improving Voltage Profile in the Egyptian National Power System

The Online Journal on Power and Energy Engineering (OJPEE)
Vol. (2) – No. (1)
Improving Voltage Profile in the Egyptian
National Power System (Enps) Using
Simultaneously Three Specific Remedial Actions
for Reactive Power Compensation (Part 1)
N. M. Abdel-Gawad A. S. H. Hamza
Benha University
H. M. Hassanin S. A. Mahmoud
Ministry of Electricity & Energy
Abstract-This Paper deals with the problem of voltage
instability that leads in some cases to voltage collapse and
complete blackouts. Voltage instability, being the absence
of voltage stability, results in progressive voltage decrease
(or increase). A power system at a given operating state
and subject to a given disturbance undergoes voltage
collapse if the post-disturbance equilibrium voltage is
below acceptable limits. Voltage collapse may be total or
partial blackout.[1]
Many major blackouts throughout the world have been
directly associated to this phenomenon, e.g. in France,
Italy, Japan, Great Britain, USA, etc. The analysis of this
problem shows that the major causes is the system’s
inability to meet the reactive power demands. The main
objective of this work is to find the most favorite methods
to assure the security of the system in terms of voltage
stability.[2]
In most case studies, using of one remedial action is not
enough to solve the voltage instability problem. This
paper declares that the usage of combined remedial
actions, specially during the peak load hours is a must
solution in most cases. Also it is declared that the usage of
normal capacitors to add reactive power together with the
other suggested methods helps much as being a cheap
tool.
It is known that the improvement of voltage levels on a
power system reduces the losses. In the present case,
specially at peak load, it is gained that the same energy
demand could be fulfilled with less power generation. In
addition to securing the voltage levels on a power system,
a feasible return is achieved.
I. INTRODUCTION
The voltage instability problem in power systems has been
demonstrated to be related to the overall stability of the
system and is closely associated with the proximity of a
system to a voltage collapse condition. as the system
approaches a voltage collapse point, its stability region
becomes smaller, resulting in a system that is less likely to
survive contingencies. Considering the continuous
development in the Egyptian Electricity Power System during
the past twenty years and the rapid increase of the electricity
Reference Number: JO-0002
S. El-Debeiky
Ain Shams University
demand, which was clearly shown by the technical studies to
predict the loads as a result of the continuous increase in
population, urbanization, industrial and service projects, the
problem of voltage stability gains more and more importance
and studies as in everywhere [3],[4],[5]. Special emphasis has
been given to the following items:
• Designed capacity to secure loads under standard (N-1)
contingency operation.
• Raising the voltage level of the electric grid or enhancing
the voltage levels in the grid.
• Reducing the losses in the grid.
The values of allowed voltages for the Egyptian national
network under different operating conditions (normal and
contingency) for the different voltage levels are shown in
Table (1):
Table (1) The Allowed voltage values for the Egyptian
National Network
Voltage in case of
Voltage in case of
Voltage
ordinary operation contingency disconnect
level
Higher
Least
Higher
Least
(K.V.)
Voltage Voltage
Voltage
Voltage
500
525
475
550
450
400
420
380
420
360
220
231
209
242
198
The criteria for (N-1) is used for studying the cases of
contingency disconnect for the Egyptian national grid. i.e.
disconnecting one element of the grid elements (transmission
line- generation unit) taking into consideration the following
factors:
• The power transferred through the transmission lines be less
than the rated capacity of these lines.
• The level of voltage for the various voltages should be
within the allowed values for operation, Table (1).
• Preventing any reduction for frequency levels in order to
prevent load shedding equipments from working.
• Preserving the stability of generation units while operating
within the range of their capability curves.
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The Online Journal on Power and Energy Engineering (OJPEE)
II.THE RECOMMENDED SIMULTANEOUS
REMEDIAL ACTIONS
A study and analysis of the most widespread methods to
solve the voltage instability problem were carried, out. Based
on these and on the experience of dealing with the Egyptian
National Power System (ENPS) and its technical and
economical conditions, three remedial actions have been
recommended to apply on the two selected systems in this
paper. The three remedial actions are the optimal usage of the
reactive power produced from generation units on the nodes
near the power stations, changing the tap points on the
transformers on the nodes near the sub-stations and injection
of reactive power at selected buses in various areas along the
system capacitors. Using these remedial actions could be used
in cascading or combining manners according to the
requirements of the system.
III. PROPOSED SYSTEMS FOR APPLICATION AND
SIMULATION
To apply the recommended remedial actions, two power
systems were proposed. The first one is the known (IEEE)-30
bus system [6].the second one, the main power system under
study is the Egyptian National Power System (ENPS) of
Extra-High Voltage 500 KV and High-voltage 220 KV levels.
ENPS contains 44 power stations with a total installed
capacity of about 25000 MW, 14 substations of 500 KV and
134 substations of 220 KV The total number of buses are 25
and 275 on the 500 and 220 KV respectively[3]. Fig. (1):
presents the single line diagram of the network parts under
study.
The simulation tool used in this paper is the Power System
Simulation for Engineering (PSS/E) as an known software
package. This package was preferred due to its wide usage in
the world, especially in the grand utilities in the field of
electricity as similar as the Egyptian Electricity Holding
Company (EEHC).and as it is an interactive program for
simulating, analyzing and optimizing power system
performance. The program contains a set of modules which
handle a number of different power system analysis
calculations.[7]
IV. CONTINGENCY ANALYSIS
System Static Security encompasses the ability of the
power system to withstand steady-state conditions, some
unforeseen, but reasonably expected, unscheduled outages of
network elements, with the minimal disruption of the service
or its quality. Contingency analysis method is based on
simulation of element outages by a deterministic approach.
Complete analysis of the N-1 situations has been carried
out for both 500 K.V, 220 K.V. transmission networks for the
Egyptian National Power System (ENPS) for each target year
and for selected characteristic hour load conditions. The
network constraints and violations have been detected and
reported giving the number of overloads for lines and
transformers and the number of nodes with voltage levels out
Reference Number: JO-0002
Vol. (2) – No. (1)
of limits. As well, cases of generation units contingencies
have been studied.
IV.1 Transmission Line Contingencies:
Case Of One 500 K.V Circuit Tripped
Table(2) presents the voltage levels calculated in case of
outage of one circuit of 500 K.V. line for 500 K.V. nodes the
following results are obtained:
Case 1: The outage of one circuit of 500 K.V. line High
Dam(B#293) – Nag Hammadi(B#292) caused many critical
500K.V. contingencies that lead to post contingency
situations characterized by very low voltage levels with
probable risk of widespread voltage collapse. It is cannot be
analyzed due to non-convergence of load-flows. This
contingency causes a generalized low voltage profile in Upper
Zone of Egypt.
Case 2: Another case, the outage of one circuit of 500K.V.
line Assuit (B#291) – nag hammdi (B#292). This case also
cannot be analyzed due to non-convergence of load-flows.
This contingency causes a generalized low voltage profile in
Upper Zone in Egypt too.
Case 3: The third case, the outage of one circuit of 500K.V.
line SAML 500 (B#235 - Cairo 500 (B#30) causes small
voltage drop in the 500 K.V. network so, the convergence of
load flows is existing in this case.
Case 4: The outage of one circuit of the 500 K.V. line
Nobaria (B#192) - Cairo 500(B#30) cannot be analyzed due
to non-convergence of load-flows. This contingency causes a
generalized low voltage profile in Cairo and Delta Zones.
Case 5: The outage of one circuit of 500 K.V. line A.Zabbl
(B#233) - Bassous500 (B#180) causes small voltage drop in
the 500K.V. network.
Case 6: The outage of one circuit of 500 K.V. line O.Moussa
(B#305) - Suze500 (B#303) causes small voltage drop in the
500K.V network.
Table (2): The p.u voltage levels calculated in case of outage
of one circuit of 500 K.V line on the 500 K.V. nodes.
Voltage (p.u.)
Bus
Normal
No.
Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
condition
30
0.914 0.907 0.911 0.905 0.888 0.911 0.914
180
0.916 0.911 0.913 0.908 0.894 0.911 0.915
192
0.969 0.968 0.968 0.967 0.972 0.968 0.969
229
0.920 0.914 0.917 0.913 0.901 0.926 0.918
233
0.935 0.928 0.932 0.930 0.920 0.938 0.935
235
0.938 0.900 0.924 0.933 0.924 0.937 0.938
238
0.917 0.911 0.914 0.909 0.894 0.912 0.916
291
0.918 0.858 0.896 0.912 0.909 0.917 0.918
292
0.907 0.816 0.877 0.902 0.904 0.906 0.907
293
1.001 0.990 0.987 0.999 1.000 1.000 1.001
303
0.957 0.956 0.955 0.953 0.944 0.961 0.954
305
0.962 0.961 0.961 0.958 0.950 0.966 0.963
306
0.944 0.945 0.942 0.939 0.931 0.948 0.945
320
0.957 0.947 0.953 0.952 0.943 0.957 0.957
950
0.977 0.977 0.976 0.975 0.974 0.976 0.977
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The Online Journal on Power and Energy Engineering (OJPEE)
Figure (2) illustrates the voltage profile in case of outage
of one circuit of 500 K.V. line on the 500 K.V. nodes for
different cases.
IV.2 Generation Unit Contingencies
At Peak Load conditions, it is difficult to lose generation
unit(s) as the Power reserved is so little. Loss of generation
unit(s) need re-dispatch the output power from all generation
units which have reserve active power to compensate the loss
of generation. In this section, the outage of Generation units is
carried out in different zones in Egypt and recording of the
effects of these events on the Voltage Profile on both the 500,
220 K.V networks are presented.
Case 1: The outage of Generation unit at bus North West
South Gulf (N.W.S.G) (B#206) of 340 MW. In this case, the
ENPS loses the Generation unit at bus N.W.S.G(B#206)
which is located in the Canal Zone with maximum active
power of 340 MW. There are some 220 K.V. substations that
suffer from low voltage levels such as SHARM (B#915),
NABK (B#917) and GHARD (B#804), which may lead to
voltage collapse.
Case 2: The outage of Generation unit at bus GN.WALID
(B#507) of 320 MW. In this case, the ENPS loses the
Generation unit at bus GN.WALID (B#507) which is located
in the Upper Zone with maximum active power of 320 MW.
There are some 220 K.V. substations suffering from low
voltage levels such as SAML220 (B#5038), SAFAGA
(B#5051) and QENA220 (B#5046) and other 220 K.V.
substations located in the Canal Zone will suffer from low
voltage levels such as SHARM SH (B#915), NABK (B#917)
and GHARD (B#804), which may lead to voltage collapse.
Case 3: The outage of Generation unit at bus GN.KURIM
(B#530) of 625 MW. In this case, the ENPS loses the
Generation unit at GN.KURIM (B#530) which is located in
the Upper Zone with maximum active power of 625 MW.
The outage of GN.KURIM (B#530) unit cannot be analyzed
due to non-convergence of load-flows. This contingency
causes a generalized low voltage profile in Cairo and Upper
Zones, as it is one of the largest units in the ENPS.
Case 4: The outage of Generation unit 330 MW at bus
GN.CW.1 (B# 516). In this case ,the Egyptian power system
losses the Generation unit at GN.CW.1 (B#516) which is
located in the Cairo zone with maximum active power 330
M.W.
Case 5: The outage of Generation unit at bus G.NOBAR
(B#538) of 250 MW. In this case, the ENPS losses the
Generation unit at GN.KURIM (B#538) which, is located in
the Delta Zone with maximum active power of 250 M.W.
Table (3) presents the voltage levels calculated in case of
outage of Generation units on the 500 K.V. nodes for
different cases.
Reference Number: JO-0002
Vol. (2) – No. (1)
Table (3): The p.u voltage levels calculated in case of outage
of Generation units for 500 K.V. nodes for different cases.
Voltage (p.u.)
Bus
No. Base Case 1 Case 2 Case 3 Case 4 Case 5
Case
30 0.914 0.904 0.906 0.898 0.906 0.915
180 0.916 0.904 0.908 0.901 0.907 0.917
192 0.969 0.964 0.966 0.965 0.966 0.967
229 0.920 0.907 0.912 0.903 0.912 0.921
233 0.935 0.924 0.928 0.911 0.931 0.937
235 0.938 0.930 0.916 0.906 0.938 0.948
238 0.917 0.905 0.909 0.901 0.907 0.918
291 0.918 0.913 0.892 0.883 0.921 0.933
292 0.907 0.906 0.888 0.871 0.915 0.927
293 1.001 1.002 0.996 0.978 1.005 1.010
303 0.957 0.941 0.952 0.946 0.952 0.958
305 0.962 0.946 0.957 0.952 0.957 0.963
306 0.944 0.923 0.937 0.933 0.938 0.945
320 0.957 0.949 0.949 0.924 0.954 0.960
950 0.977 0.970 0.972 0.973 0.972 0.975
Figure (3) illustrates the voltage profile in case of outage of
Generation units on the 500 K.V. nodes for different cases of
outages.
V. REMEDIAL ACTIONS
V.1 Impact of the recommended Remedial Actions
The three remedial actions are the optimal usage of the
reactive power produced from generation units on the nodes
near the power stations, changing the tap points on the
transformers on the nodes near the sub-stations and injection
of reactive power at selected buses in various areas along the
system. These Remedial Actions have been selected to
improve the voltage profile. In the previous sections, the
analysis for the effect of losing one element of the network
(N-1) were carried out in case of normal conditions without
using any remedial actions.
In this section, the selected remedial actions will take
place. Once again, the analysis for the effects of (N-1) for the
same cases in the previous sections are repeated in the
presence of the remedial actions. The results and the
improvement in the voltage profile are shown in the following
subsections.
V.2 Optimal Usage Of Reactive Power Produced From The
Generation Units
The schedule voltage (Vsch.) of certain generation units of the
ENPS, which have reserve in the reactive power, is changed
to produce more reactive power to improve the voltage profile
as possible as can. Changing Vsch. has the largest effect on the
500 K.V. and 220 K.V. profiles of the ENPS. All 500 K.V.
substations which are suffering from low voltage levels are
going to be in the permissible limits. Some of the 220 K.V.
substations are still suffering from low voltage levels, as the
voltage is not within the permissible limits such as SHARM
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The Online Journal on Power and Energy Engineering (OJPEE)
(B#915), NABK (B#917), QENA220 (B#5046) and GHARD
(B#804). Table (4) illustrates the Changing the schedule
voltage at certain generation units of the ENPS.
Table (4): The changing of Vsch. at certain
generation units of the ENPS
Bus
No.
Pgen
(MW)
440
415.4
Qgen
(MVA)
at base
case
227.3
315
Vsch
(p.u.)
base
case
1.015
441
525
240.7
330
1.015
442
525
240.7
330
443
525
240.7
530
600
531
600
624
625
Vsch
(p.u.)
New
Qgen
(MVA)
New
1.04
294.8
1.04
306.1
1.015
1.04
306.1
330
1.015
1.04
306.1
326
400
0.95
0.98
359.4
326
400
0.95
0.98
359.4
330
127.1
200
1
1.03
140.9
330
127.1
200
1
1.03
140.9
Qmax
MVA)
Table (5) reports the voltage levels calculated in case of
changing Vsch at certain generation units of the ENPS on the
500 K.V. nodes.
Table (5): The voltage levels calculated in case of changing
Vsch at certain generation units of the ENPS on the 500 K.V.
nodes.
Bus
Vsch (Base case)
Vsch (New) (pu)
No.
(pu)
30
0.914
0.957
180
0.916
0.957
192
0.969
1.021
229
0.920
0.958
233
0.935
0.974
235
0.938
0.992
238
0.917
0.958
291
0.918
0.977
292
0.907
0.970
293
1.001
1.042
303
0.957
0.984
305
0.962
0.988
306
0.944
0.976
320
0.957
0.998
950
0.977
1.017
Figure (4) illustrates the voltage profile in case of changing
Vsch at certain generation units of the ENPS on the 500 K.V.
nodes.
V.3 Changing the Tap Points of Transformers
Case 1: Change the tap of Cairo 500 (B#30)
Case 2: Change the tap of Cairo West 500 (B#238)
Vol. (2) – No. (1)
Case 4: Change the tap of Nobaria 500 (B#192)
Case 5: Change the tap of kurimtt 500 (B#320)
Reactive power limits on generators and the tap limits on tap
changing transformers have a significant effect on voltage
collapse. The tap ratio of certain 500/220 K.V. transformers is
changed to control the reactive power flow in order to get the
most suitable voltage profile for the 500 K.V. and 220 K.V.
networks. Different scenarios of changing the tap ratio are
carried out. Table (6) reports the voltage levels calculated in
case of changing the tap ratio of certain 500/220 K.V.
transformers on the 500 K.V. nodes in different cases.
Figure(5) illustrates the voltage profile in case of changing
the tap ratio of certain 500/220 K.V. transformer on the 500
K.V. nodes in different cases. This agrees with previous
findings[8].
Table (6): The voltage levels calculated in case of changing
the tap ratio of a certain 500/220 K.V. transformers on
the 500 K.V. nodes
Bus
No.
30
180
192
229
233
235
238
291
292
293
303
305
306
320
950
Voltage (pu)
Actual
Tap
0.914
0.916
0.969
0.920
0.935
0.938
0.917
0.918
0.907
1.001
0.957
0.962
0.944
0.957
0.977
Case
1
0.944
0.937
0.985
0.936
0.946
0.954
0.939
0.933
0.920
1.005
0.965
0.970
0.954
0.968
0.989
Case 2
0.925
0.929
0.983
0.929
0.942
0.947
0.930
0.926
0.914
1.003
0.963
0.968
0.951
0.963
0.988
Case
3
0.922
0.925
0.983
0.923
0.939
0.944
0.925
0.924
0.912
1.002
0.957
0.962
0.943
0.961
0.987
Case 4
0.915
0.916
0.988
0.919
0.935
0.938
0.917
0.917
0.906
1.000
0.956
0.962
0.943
0.957
0.988
Case
5
0.920
0.921
0.983
0.924
0.940
0.944
0.922
0.924
0.912
1.003
0.960
0.965
0.947
0.963
0.988
V.4 Injection of Reactive Power at Certain Nodes According
to the System Requirements
Thus, the reactive Power output from generation plays a very
important role in assuring successful transactions of electric
energy[9]. However, The experience with the ENPS shows
that the average power factor is 0.85 at the peak load which
causes low voltage level at many substations. To improve the
average power factor, it is important to select suitable
locations for adding capacitors in order to obtain good
results[10]. Figure (6) illustrates the voltage levels on the 500
K.V. nodes after improving the power factor from 0.85 to
0.92. Table (7) shows the optimal locations of the reactive
power which will be added to improve the power factor from
0.85 to 0.92 to avoid the voltage collapse
Case 3: Change the tap of Bassous 500 (B#180)
Reference Number: JO-0002
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The Online Journal on Power and Energy Engineering (OJPEE)
Vol. (2) – No. (1)
Table (7): The impact of improving the power factor on the
voltage levels on the 500 K.V. nodes.
Bus
Voltage (pu)
No
PF=0.85 PF=0.88 PF=0.89 PF=0.90 PF=0.91
30
0.914
0.928
0.935
0.942
0.947
180
0.916
0.930
0.938
0.946
0.952
192
0.969
0.974
0.976
0.979
0.981
229
0.920
0.935
0.944
0.953
0.963
233
0.935
0.949
0.957
0.964
0.969
235
0.938
0.977
0.995
1.009
1.010
238
0.917
0.931
0.938
0.945
0.951
291
0.918
0.970
0.996
1.017
1.015
292
0.907
0.972
1.006
1.039
1.031
293
1.001
1.025
1.038
1.049
1.048
303
0.957
0.979
0.994
1.010
1.036
305
0.962
0.985
1.001
1.018
1.046
306
0.944
0.993
1.029
1.069
1.126
320
0.957
0.971
0.978
0.984
0.988
950
0.977
0.982
0.985
0.988
0.989
Voltage (pu)
Change Vsch, change tap
Base Case
ratio and add reactive power
306
0.944
1.048
320
0.957
1.020
950
0.977
1.021
Figure (7) illustrates the voltage levels on the 500 K.V. nodes
after changing Vsch. , changing tap ratio and adding 950
MVAR.
V.5 Using One or More of The Recommended Remedial
Actions In A Combined Manner.
Table (9): The voltage levels on the 500 K.V. nodes in case of
tripping one circuit 500 K.V. T.L with and without remedial
actions.
Voltage (pu)
Trip of one ct.
Normal condition
Bus
(B#293)–(B#292)
No.
without
with
without
with
Remedial
Remedial
Remedial Remedial
Actions
Actions
Actions
Actions
30
0.914
0.997
0.907
0.990
180
0.916
0.993
0.911
0.987
192
0.969
1.029
0.968
1.027
229
0.920
0.990
0.914
0.984
233
0.935
0.997
0.928
0.990
235
0.938
1.029
0.900
0.996
238
0.917
0.993
0.911
0.987
291
0.918
1.022
0.858
0.969
292
0.907
1.026
0.816
0.942
293
1.001
1.050
0.990
1.028
303
0.957
1.023
0.956
1.019
305
0.962
1.028
0.961
1.025
306
0.944
1.048
0.945
1.044
320
0.957
1.020
0.947
1.011
950
0.977
1.021
0.977
1.020
In this case taking into consideration the following:
• The value of (Vsch.) is the same as in subsection (5.2).
• In addition to changing the tap ratio of CAI500(B#30)
500/220 K.V. transformers in subsection (5.2) from step
No. 2 to step No. 6, changing the tap ratio of
Bassous(B#180) 500/220 K.V. transformer from step No.
14 to step No 9".
According to the above scenarios the voltage profile on the
500 and 220 K.V. networks has occurred, however not to the
desired values. This improvement helps to reduce the value of
the reactive power injected by added capacitors. Table (8)
shows the results of the voltage levels on the 500 K.V. nodes
after changing Vsch., changing tap ratio and adding 950
MVAR.
Table (8): The improvement of the voltage after changing
Vsch, Changing tap ratio and adding reactive power.
Voltage (pu)
Bus No.
Change Vsch, change tap
Base Case
ratio and add reactive power
30
0.914
0.997
180
0.916
0.993
192
0.969
1.029
229
0.920
0.990
233
0.935
0.997
235
0.938
1.029
238
0.917
0.993
291
0.918
1.022
292
0.907
1.026
293
1.001
1.049
303
0.957
1.023
305
0.962
1.028
Reference Number: JO-0002
Bus No.
VI. CONTINGENCY ANALYSIS AFTER APPLYING
THE RECOMMENDED REMEDIAL ACTIONS
VI.1. Cases of One 500 K.V. Circuit Tripped
In between the contingency cases of one circuit 500 K.V.T.L.
shown in subsection (4.1), the most critical case is the outage
of H.D.(B#293) - N.H.(B#292). This case has been repeated
after applying the remedial actions. and there is no low
voltage problem. Table (9) shows the voltage levels on the
500 K.V. nodes in case of tripping one circuit 500 K.V.T.L
with and without the remedial actions.
Figure (8) illustrates the voltage levels on the 500 K.V. in
case of tripping one circuit 500 K.V.T.L with and without
remedial actions.
VI.2. Generation Unit Contingencies
The outage of Generation unit of 625 MW at bus
GN.KURIM (B#530) is the most critical Generation outage in
the ENPS, After applying the remedial actions, the ENPS can
deal with this outage and there is no low voltage problem.
Table (10) shows the voltage levels on the 220 K.V. nodes in
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The Online Journal on Power and Energy Engineering (OJPEE)
case of tripping Generation unit of 625 MW at bus
GN.KURIM (B#530) with and without the remedial actions.
Figure (9) illustrates the voltage levels for 220 K.V in case of
tripping the generation unit of 625 MW at bus GN.KURIM
(B#530) with and without remedial actions.
Table (10): The voltage levels on the 220 K.V nodes in case
of tripping Generation unit of 625 MW at bus GN.KURIM
(B#530) with and without the remedial actions
Voltage (pu)
Bus
No.
Base Case
Tripping M/C at (B#530)
804
915
917
5038
5039
5040
5042
5043
5044
5045
5046
5047
5049
without
remedial
actions
0.832
0.802
0.822
0.867
0.869
0.909
0.829
0.819
0.838
0.808
0.821
0.841
0.804
with
remedial
actions
0.977
0.988
0.988
0.950
0.958
1.011
0.963
0.966
0.991
0.983
0.996
0.952
0.966
without
remedial
actions
0.801
0.790
0.810
0.837
0.837
0.872
0.791
0.781
0.801
0.768
0.783
0.807
0.766
5051
5052
5053
5062
5070
0.826
0.852
0.852
0.841
0.862
0.980
0.954
0.952
0.995
0.981
0.794
0.818
0.818
0.805
0.825
with remedial
actions
0.970
0.985
0.985
0.943
0.952
1.005
0.955
0.957
0.982
0.972
0.986
0.943
0.956
0.972
0.946
0.944
0.985
0.975
VII. CONCOLUSION AND RECOMMENDATION:
With reference to the previous studies, analysis of the
methods used in the world to avoid voltage instability and
from the background about the technical and economical
Reference Number: JO-0002
Vol. (2) – No. (1)
conditions relevant to ENPS, three remedial actions have
been recommended in this paper to be applied
simultaneously. These remedial actions are the optimal usage
of reactive power produced from generation units, changing
the tap points of transformers and the reactive power
compensation at certain locations in the power system. Also,
an economical analysis carried out in this work verified that
the optimal localizing and qualifying of capacitors is a most
feasible mean to reactive power compensation beside the
other two..
Benefiting from the obtained results, the main application
was on the ENPS. The voltage profile for ENPS in normal
conditions clarified that the voltage level in many locations is
under the permissible secure limits (0.95 p.u. ≤ voltage level
≤ 1.05 p.u.). The ENPS was put under many contingency
cases for outages of extra-high voltage 500 K.V. transmission
lines and grand generation units. A comparison between the
voltage profile in the base case and the cases of using
remedial actions verified the necessity of using remedial
actions to improve the voltage levels in ENPS. The following
are some specific results:
• Increasing the reactive power produced from generation
units (i.e. raising the schedule voltage Vsch. From 0.98 to
0.99 p.u.) causes an increase in the voltage levels but not
to the desired values.
• Changing the tap ratio on all transformers to 0.92 causes
an increase in voltage with permissible values above the
critical voltage collapse limits (about 0.86 p.u.).
• Injection of reactive power at certain locations (i.e.
increasing the power factor to 0.90) causing a discrete
improvement of the voltage profile, however there is one
node has an over voltage (V> 1.05 p.u.).
• Once more, injection of reactive power to raise the power
factor to 0.91 did not solve the problem of over voltage,
however redistributing the qualified reactive power caused
all the voltage levels to be maintained.
• Using combination of the recommended remedial actions
simultaneously presents an effective remedy to the voltage
instability problem.
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The Online Journal on Power and Energy Engineering (OJPEE)
Vol. (2) – No. (1)
Figure (1): Single Line Diagram of The Network Parts Under Study
Reference Number: JO-0002
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The Online Journal on Power and Energy Engineering (OJPEE)
Vol. (2) – No. (1)
Figure (2): The voltage profile in case of outage of one circuit of 500 K.V. line
on the 500 K.V. nodes for different cases.
Figure (3): The voltage profile in case of outage of Generation unit
on the 500 K.V. nodes for different cases of outages.
Figure (4): The voltage profile in case of changing V sch. at a certain generation units
of the ENPS on the 500 K.V. nodes
Reference Number: JO-0002
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The Online Journal on Power and Energy Engineering (OJPEE)
Vol. (2) – No. (1)
Figure(5): The voltage profile in case of changing the tap ratio of certain 500/220 K.V. transformers
on the 500 K.V. nodes for different cases.
Figure(6): The voltage levels on the 500 K.V. nodes after improving the power factor from 0.85 to 0.92
Figure(7): The voltage levels on the 500 K.V. nodes after changing V sch & changing
tap ratio and adding 950 MVAR
Reference Number: JO-0002
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The Online Journal on Power and Energy Engineering (OJPEE)
Vol. (2) – No. (1)
Figure(8): The voltage levels on the 500 K.V. in case of tripping one circuit 500 K.V. T.L with
and without remedial actions.
Figure (9): The voltage levels on the 220 K.V. in case of tripping generation unit of 625 MW at bus GN.KURIM(B#530) with
and without the remedial actions.
Reference Number: JO-0002
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The Online Journal on Power and Energy Engineering (OJPEE)
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