TB-254-357-005 Page No.1 of 12
FAULT LEVEL CALCULATIONS STUDY 1
INTRODUCTION NSPCL, A Joint Venture of NTPC and SAIL, is setting up an expansion of the Bhilai Power Project by 2x250 MW power generation at Bhilai, District Durg, Chhatisgarh. The installed capacity of existing Power Plants (Power Plant 1-PP1 and Power Plant 2- PP2) in Bhilai Steel Plant (BSP) is 110MW. The BSP load is 350 MW. In normal course, the Bhilai Power Project (Power Plant 3, PP3 consisting of G1 and G2) will work in parallel with Bhilai Steel Plant (BSP), existing Power Plants (PP1 and PP2) and PGCIL’s grid. PP3 will supply 240 MW to BSP. Around 40 MW are consumed by PP3 auxiliaries, the balance 220 MW will be exported to the grid at 400 kV. But during contingency conditions, there is a possibility of BSP together with PP1, PP2 and PP3 being islanded from grid. Under this islanding operation, PP3 shall be supplying power to Bhilai Steel Plant only through dedicated transmission lines connecting Bhilai Steel Plant to Bhilai Power Project. This report focuses on the development of a model of the electric power system in an expansion of the Bhilai Power Project by 2x250 MW power generation in order to perform short circuit study conducted on power system data as per TB-254-357-001- “Design Data, Load Flow and Island Mode of Operation Study” Report. The results of study serve to establish sequence data files to be used in further stability studies. SIMPOW, Power System Simulation Software is used for carrying out the Short Circuit studies.
2
Short Circuit Current Calculation A Short Circuit Study is critical for the safe, efficient, and economical operation of any electrical distribution system. A Short Circuit Study will help to ensure that personnel and equipment are protected by establishing proper short circuit current ratings. When an electrical fault exceeds the interrupting rating of the protective device, the consequences can be devastating, including injury, damaged electrical equipment, and costly downtime. Among the most important tasks, when planning and operating power systems, are the short-circuit current calculations (SCCs). Faults, i.e. short-circuits, can be minimized in the system through planning and design, and well-performed maintenance and operation of the system, but cannot be totally avoided. Protection settings and coordination and dimensioning of switchgear require accurate and detailed SCCs because switches and breakers have to be designed to switch off shortcircuits in a safe way and in short time. Short-circuits can cause mechanical oscillations in generators which can lead to oscillations in the power in the system, causing problems of stability in the power transfer. In the worst case this can lead to a blackout of the system. One last area to consider is that the installed equipment must be able to withstand the thermal and mechanical effects of short-circuit currents. Hence, it is very essential to conduct fault level calculation study for power system.
TB-254-357-005 Page No.2 of 12
3
Technical Requirements as per TS The maximum fundamental frequency short circuit current at the various 400 kV and 220 kV buses shall be limited to 40 kA for one second.
4
Input Data 1. Input data for the study is as per Report No: TB-254-357-001. 2. Single line diagram is taken to indicate the overall network around Bhilai Steel Plant for carrying out the short circuit studies.
5
Load Flow Cases The following load flow base cases [1] as described in Load Flow study were considered for calculating the Short Circuit levels. Case
CASE Name
Case Description
1
CASE 1
Parallel Operation of 2x250 MW PP3+PP2+PP1+BSP with Grid
2
CASE 2
Islanded Operation of 2x250 MW PP3+PP2+PP1+BSP no Grid
3
CASE 3
Islanded Operation of 1x250 MW PP3+PP2+PP1+BSP from Grid
No.
The power flow results for the above 3 cases are mentioned in Report No: TB-254-357-001.
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Fault Studies The power system is divided into several different voltage levels, where calculations are made for short circuits on the 400 kV, 220kV and 132 kV levels. Three different cases are set up in order to evaluate the system, so that the maximum and minimum currents can be determined. Fault studies were carried out to determine fault levels under the below three cases. Fault Cases Case No.
CASE Name
1
CASE 1
2
CASE 2
3
CASE 3
TB-254-357-005 Page No.3 of 12
6.1
Base Cases Three phase to ground (3PSG) faults are applied at the following buses in cases 1 to 3.
S. No.
Bus Name
1
BESCL220
2
BESCL400
3
MSD5Ͳ220
4
MSD6Ͳ220
5
BP1TG1Ͳ6
6
BP1TG2Ͳ6
7
BP1TG0Ͳ6
8
MSD1Ͳ132
9
MSD2Ͳ132
10
MSD3Ͳ132
11
MSD4Ͳ132
12
MSD5Ͳ132
13
MSD6Ͳ132
14
M4SEC1Ͳ1
15
M4SEC2Ͳ1
16
M4SEC1Ͳ6
17
M4SEC2Ͳ6
18
M2DR1Ͳ6
19
M2DR2Ͳ6
20
M2VADͲ11
21
M2SMSͲ11
22
M2SEC1Ͳ1
TB-254-357-005 Page No.4 of 12 S. No.
Bus Name
23
M2SEC2Ͳ1
24
M2SEC1Ͳ6
25
M2SEC2Ͳ6
26
M2SEC3Ͳ6
27
M2SEC4Ͳ6
28
M6SEC1Ͳ1
29
M6SEC2Ͳ1
30
P2Ͳ1Ͳ132
31
P2Ͳ2Ͳ132
32
P2SEC1Ͳ6
33
P2SEC2Ͳ6
34
P2Ͳ21TͲ6
35
P2Ͳ22TͲ6
36
P2Ͳ23TͲ6
TB-254-357-005 Page No.5 of 12
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MODELING & SIMULATION 7.1
Different cases
The different cases analyzed are a number of network configurations that are of interest to investigate. Three different cases are set up, where each case has a specific objective which is important to examine.
7.1.1
Case 1
Case 1 is set up at Parallel Operation of 2x250 MW PP3+PP2+PP1+BSP with Grid, with contribution from the 400 kV and 220kV grid and from the generators G1 and G1 respectively. PP3 generators are assumed to be operating at 1.05pu voltage in order to ensure the voltages in the study system within the limits. Both PP3 generators are supplying their rated power (250MW each). The short circuit current levels in the network are tabulated in Table.1. The short circuit current values obtained in the study system are within the limits, i.e. less than 40kA for one second. The 3 phase to ground and single phase to ground fault currents at each of the 400kV, 220kV and 132kV buses for case 1 are tabulated in Annexure A.
7.1.2
Case 2
Case 2 is set up at Islanded operation of 2X250 MW PP3, PP2, PP1 and BSP without grid connection. PP3 generators are assumed to be operating at 1.05pu voltage in order to ensure the voltages in the study system within the limits. Generator G1 is supplying 143 MW and generator G2 is supplying 142 MW to meet the reduced load requirement in the absence of export to grid. The short circuit current levels in the network are tabulated in Table.2. The short circuit current values obtained in the study system are within the limits, i.e. less than 40kA for one second. The 3 phase to ground and single phase to ground fault currents at each of the 400kV, 220kV and 132kV buses for case 2 are tabulated in Annexure B.
7.1.3
Case 3
Case 2 is set up at Islanded operation of 1X250 MW PP3, PP2, PP1 and BSP from grid connection. Only one PP3 generator (G1) is assumed to be operating at 1.03pu voltage and supplying 250 MW to BSP. The short circuit current levels in the network are tabulated in Table.2. The short circuit current values obtained in the study system are within the limits, i.e. less than 40kA for one second. The 3 phase to ground and single phase to ground fault currents at each of the 400kV, 220kV and 132kV buses for case 3 are tabulated in Annexure C.
.
TB-254-357-005 Page No.6 of 12
For each case, reported in Annexure A to C, the maximum fault current (fault KVA level) out of the fault currents on the selected 36 buses is shown in bold letters. Similarly, the minimum fault current (fault KVA level) out of the fault current on the selected 36 buses are shown in bold italics for each operating scenario.
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Conclusions
The short circuit studies were conducted for the various base operating conditions and contingencies.
Maximum fault currents were then determined at M2DR1-6 bus for case 1,BP1TG1-6 bus for case 2 and M2DR1-6 bus for case 3.
The fault levels at various buses of 400kV, 220kV and 132kV were found to be lower than 40 kA as stipulated in Technical Specifications. Out of the reported fault levels, the minimum and maximum fault levels at the 400 kV, 220kV and 132kV buses in cases 1 to 3 are as shown below: CASE No.
9
Minimum Fault Level
Maximum Fault Level
At Bus
Fault MVA
At Bus
Fault MVA
1
MSD6Ͳ132
2.424
BESCL220
10.287
2
MSD6Ͳ132
0.8466
BESCL400
1.4743
3
MSD4Ͳ132
0.03576
BESCL400
5.5377
The study summarises the results of short circuit levels under various conditions.
References: 1. TB-254-357-001- “Design Data, Load Flow and Island Mode of Operation Study” Report.
TB-254-357-005 Page No.7 of 12
Annexure A CASE 1
S.No.
Bus Name
1 PSG Fault
3 PSG Fault Short
Isc (kA)
Isc (kA)
circuit KVA
1
BESCL220
10.132
26.997
10287.24
2
BESCL400
4.685
12.998
9005.279
3
MSD5Ͳ220
9.817
26.278
10013.26
4
MSD6Ͳ220
9.803
26.317
10028.12
5
M3SEC1Ͳ1
0.365
21.827
434.7629
6
M3SEC2Ͳ1
0.337
28.71
571.8626
7
M3SEC3Ͳ1
0.376
28.711
571.8825
8
MSD1Ͳ132
4.047
10.366
2369.986
9
MSD2Ͳ132
5.385
13.175
3012.21
10
MSD3Ͳ132
4.75
12.206
2790.666
11
MSD4Ͳ132
3.307
9.059
2071.166
12
MSD5Ͳ132
0.587
14.247
3257.302
13
MSD6Ͳ132
1.788
10.604
2424.4
14
M4SEC1Ͳ1
0.081
13.26
264.1204
15
M4SEC2Ͳ1
0.081
13.26
264.1204
16
M4SEC1Ͳ6
0.145
8.523
97.43098
17
M4SEC2Ͳ6
0.145
8.52
97.39668
18
M2DR1Ͳ6
1.03
37.312
426.5334
19
M2DR2Ͳ6
1.171
37.179
425.0131
20
M2VADͲ11
0.816
7.367
146.7402
TB-254-357-005 Page No.8 of 12 21
M2SMSͲ11
2.04
13.918
277.2269
22
M2SEC1Ͳ1
0.143
23.05
459.1234
23
M2SEC2Ͳ1
0.143
23.05
459.1234
24
M2SEC1Ͳ6
1.03
37.131
424.4643
25
M2SEC2Ͳ6
1.034
37.124
424.3843
26
M2SEC3Ͳ6
1.03
37.159
424.7844
27
M2SEC4Ͳ6
1.017
37.151
424.693
28
M6SEC1Ͳ1
0.682
13.809
275.0557
29
M6SEC2Ͳ1
0.682
13.809
275.0557
30
P2Ͳ1Ͳ132
4.765
12.383
2831.134
31
P2Ͳ2Ͳ132
2.932
8.576
1960.737
32
P2SEC1Ͳ6
4.067
12.163
139.0418
33
P2SEC2Ͳ6
4.07
12.162
139.0303
34
P2Ͳ21TͲ6
1.138
3.416
39.05012
35
P2Ͳ22TͲ6
1.138
3.416
39.05012
36
P2Ͳ23TͲ6
1.125
3.347
38.26135
TB-254-357-005 Page No.9 of 12
Annexure B CASE 2
S.No.
Bus Name
1 PSG Fault
3 PSG Fault Short
Isc (kA)
Isc (kA)
circuit KVA
1
BESCL220
0.089
3.388
1291.001
2
BESCL400
0.745
2.128
1474.322
3
MSD5Ͳ220
0.016
3.377
1286.81
4
MSD6Ͳ220
0.751
3.382
1288.715
5
BP1TG1Ͳ6
4.018
30.076
343.8149
6
BP1TG2Ͳ6
3.779
30.074
343.792
7
BP1TG0Ͳ6
4.365
24.876
284.3709
8
MSD1Ͳ132
0.422
4.408
1007.804
9
MSD2Ͳ132
1.455
4.772
1091.026
10
MSD3Ͳ132
0.03
4.586
1048.5
11
MSD4Ͳ132
0.82
4.091
935.3282
12
MSD5Ͳ132
0.809
4.22
964.8216
13
MSD6Ͳ132
0.557
3.703
846.6195
14
M4SEC1Ͳ1
1.779
10.483
208.8065
15
M4SEC2Ͳ1
1.78
10.483
208.8065
16
M4SEC1Ͳ6
0.007
7.532
86.10232
17
M4SEC2Ͳ6
0.005
7.529
86.06803
18
M2DR1Ͳ6
0.683
26.374
301.4953
19
M2DR2Ͳ6
0.681
26.302
300.6722
20
M2VADͲ11
0.939
6.3
125.4871
TB-254-357-005 Page No.10 of 12 21
M2SMSͲ11
1.877
11.066
220.4191
22
M2SEC1Ͳ1
0.191
16.168
322.0437
23
M2SEC2Ͳ1
0.215
16.168
322.0437
24
M2SEC1Ͳ6
0.146
26.274
300.3522
25
M2SEC2Ͳ6
0.126
26.269
300.295
26
M2SEC3Ͳ6
0.401
26.291
300.5465
27
M2SEC4Ͳ6
0.117
26.287
300.5008
28
M6SEC1Ͳ1
1.528
10.307
205.3008
29
M6SEC2Ͳ1
1.528
10.307
205.3008
30
P2Ͳ1Ͳ132
1.71
4.658
1064.962
31
P2Ͳ2Ͳ132
1.376
4.034
922.2963
32
P2SEC1Ͳ6
1.945
10.602
121.1971
33
P2SEC2Ͳ6
1.947
10.6
121.1743
34
P2Ͳ21TͲ6
0.506
3.181
36.36371
35
P2Ͳ22TͲ6
0.506
3.181
36.36371
36
P2Ͳ23TͲ6
0.551
3.131
35.79214
TB-254-357-005 Page No.11 of 12
Annexure C CASE 3
S.No.
Bus Name
1 PSG Fault
3 PSG Fault Short
Isc (kA)
Isc (kA)
circuit KVA
1
BESCL220
0.143
8.316
3168.822
2
BESCL400
2.117
7.993
5537.713
3
MSD5Ͳ220
0.004
8.249
3143.291
4
MSD6Ͳ220
1.053
8.256
3145.959
5
BP1TG1Ͳ6
3.59
28.622
327.1934
6
BP1TG2Ͳ6
3.535
28.62
327.1705
7
BP1TG0Ͳ6
3.943
23.811
272.1963
8
MSD1Ͳ132
0.423
6.802
1555.146
9
MSD2Ͳ132
1.955
7.916
1809.841
10
MSD3Ͳ132
0.044
7.534
1722.504
11
MSD4Ͳ132
1.107
6.206
1418.882
12
MSD5Ͳ132
1.544
8.33
1904.494
13
MSD6Ͳ132
1.039
6.945
1587.84
14
M4SEC1Ͳ1
2.271
12.486
248.7034
15
M4SEC2Ͳ1
2.273
12.486
248.7034
16
M4SEC1Ͳ6
0.01
8.332
95.24755
17
M4SEC2Ͳ6
0.007
8.328
95.20183
18
M2DR1Ͳ6
0.992
33.899
387.5176
19
M2DR2Ͳ6
0.974
33.79
386.2716
20
M2VADͲ11
1.152
7.145
142.3183
TB-254-357-005 Page No.12 of 12 21
M2SMSͲ11
2.266
13.051
259.9574
22
M2SEC1Ͳ1
0.275
20.875
415.8004
23
M2SEC2Ͳ1
0.318
20.875
415.8004
24
M2SEC1Ͳ6
0.215
33.75
385.8143
25
M2SEC2Ͳ6
0.192
33.743
385.7343
26
M2SEC3Ͳ6
0.116
33.743
385.7343
27
M2SEC4Ͳ6
0.186
33.743
385.7343
28
M6SEC1Ͳ1
2.445
13.116
261.2522
29
M6SEC2Ͳ1
2.445
13.116
261.2522
30
P2Ͳ1Ͳ132
2.457
7.614
1740.794
31
P2Ͳ2Ͳ132
1.83
5.939
1357.838
32
P2SEC1Ͳ6
1.968
10.826
123.7578
33
P2SEC2Ͳ6
1.971
10.824
123.7349
34
P2Ͳ21TͲ6
0.512
3.204
36.62664
35
P2Ͳ22TͲ6
0.512
3.204
36.62664
36
P2Ͳ23TͲ6
0.547
3.129
35.76927
