Fault Level Calculations
Transcript of Fault Level Calculations
Fault Level Calculations
Fault Level Calculations 2
What is ahead?
• Overview of transmission network.
• What is mean by fault level
• PU Concept
• Network Modeling
• Fault Level Calculation
• Example
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Step-1Overview of power system
grid and transmission network
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Typical State Level Power System & our area of interest
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Typical State Level Power System & our area of interest
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400kV
220kV
220kV
132kV
33kV
33kV220kV
132kV
11kV33kV
S/S - A
S/S - F S/S - E
S/S - B
S/S - C
S/S - D
Local Network – or – Sub-Transmission System
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Step-2What is mean by fault level
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What is fault level
ABC Transmission Co. Ltd.
3 Ph Fault Levels For 2010-2011
14530 MVA
18290 MVA
9700 MVA
8400 MVA
11300 MVA
4630 MVA
5800 MVA
6400 MVA
7200 MVA
2700 MVA
1185 MVA
3670 MVA
9730 MVA
S/S - B
S/S - A
S/S - C
14530 MVA
8400 MVA
9730 MVA
S/S - B
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What is fault level-Continued….
14530 MVA
9730 MVA
S/S - B
2200 MVA 2200 MVA 2300 MVA
2450 MVA 2450 MVA
1465 MVA1465 MVA
8700 MVA
1030 MVA
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Step-3Understanding Per-Unit
Measurements
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PU Concept
• PU impedance values are calculated by
– For Transformers
• %Impedance = Ohmic Value * ( Base MVA / Name Plate MVA )
– For Lines
• %Impedance = Ohmic Value * ( Base MVA / BasekV2 )
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PU Concept
• PU impedance values are calculated by
– For Transformers
• %Impedance = Ohmic Value * ( Base MVA / Name Plate MVA )
– For Lines
• %Impedance = Ohmic Value * ( Base MVA / BasekV2 )
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PU Concept
400/220 kV
15% 315 MVA
12 Ohm
Sec DSec CSec B
0.4 ohm/Km 200 Km
0.4 ohm/Km 50 Km220/132 kV
14% 200 MVA
132/33 kV
9.33% 25 MVA
0.4 ohm/Km 30 Km
Sec A
Base MVA = 200 MVA
400kV 33kV132kV220kV
T1 L1 T2 L2 T3 L3
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PU Concept
400/220 kV
15% 315 MVA
L3T3L2T2L1T1
0.4 ohm/Km 200 Km
0.4 ohm/Km 50 Km220/132 kV
14% 200 MVA
132/33 kV
9.33% 25 MVA
0.4 ohm/Km 30 Km
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Short Circuit Current
• 3 Phase Short Circuit MVA at fault point
Base MVA x 100 = ----------------------------------------------------
Percentage Impedance (from source to fault point)
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PU Concept-Continued
9.52% 33.05% 14% 22.96% 74.64% 220%
XT1 XL1 XL2 XL3XT2 XT3
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PU Concept
400/220 kV
15% 315 MVA
12 Ohm
65 Ohm20 Ohm34 Ohm80 Ohm75 Ohm
0.4 ohm/Km 200 Km
0.4 ohm/Km 50 Km220/132 kV
14% 200 MVA
132/33 kV
9.33% 25 MVA
0.4 ohm/Km 30 Km
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Step-4Finding Source Impedance
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Typical State Level Power System & our area of interest
4630
Base MVA=Xs(pu)
MVA
100 Xs(pu)4630
Xs (pu) = 0.0216
Or
Xs% = 2.16%
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Solved Example
2850 MVA
8 Km
0.4 Ohms / Km
5 Km
0.4 Ohms / Km
50 MVA 10.21%
50 MVA 10.88 %
25 MVA 9.73 %
25 MVA 10.04 %
50 MVA 10.21%
50 MVA 10.88 %
25 MVA 9.73 %
25 MVA 10.04 %
50 MVA 10.03%
25 MVA 10.52 %
25 MVA 10.21 %
25 MVA 9.84 %
220/132kV Padegaon
132/33-11 kV Harsool
132/33-11 kV Chikalthana
132kV 33kV
11kV
132kV 33kV
11kV
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Solved Example
2850 MVA
668 MVA
2257 MVA
220/132kV Padegaon
132/33-11 kV Harsool
132/33-11 kV Chikalthana
132kV 33kV
11kV
132kV 33kV
11kV
1998 MVA
538 MVA
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Unsymmetrical Faults-Sequence Network
• Up till now we have discussed 3 Phase faults which are rear. Most of the fault in power system are single line to ground faults.
• To find out the short circuit MVA due to single phase to ground fault it is necessary to use Sequence Network
• Let us have a closer look of sequence network
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Unsymmetrical Faults-Sequence Network
M1
M2
T2 L GT1
Xg1XT11XL1XT21
XM21XM11
Xg2XT12XL2XT22
XM22XM12
Xg0XT10XL0XT20
XM20XM10
F
FF
SLD
+Ve Sequence Network
-Ve Sequence NetworkZero Sequence Network
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Single Line to Ground Fault-Sequence Network Connections
Xg1XT11XL1XT21
XM21XM11
F
Xg2XT12XL2XT22
XM22XM12
F
Xg0XT10XL0XT20
XM20
F
X1
X2
X0
Ia = 3 / (X1 + X2 + X0)
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Single Line to Ground Fault-Solved Example
3Ph 2850 MVA
8 Km
0.4 Ohms / Km
5 Km
0.4 Ohms / Km
50 MVA 10.21%
50 MVA 10.88 %
25 MVA 9.73 %
25 MVA 10.04 %
50 MVA 10.21%
50 MVA 10.88 %
25 MVA 9.73 %
25 MVA 10.04 %
50 MVA 10.03%
25 MVA 10.52 %
25 MVA 10.21 %
25 MVA 9.84 %
220/132kV Padegaon
132/33-11 kV Harsool
132/33-11 kV Chikalthana
132kV 33kV
11kV
132kV 33kV
11kV
1Ph 2230 MVA
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Single Line to Ground Fault-Solved Example
3Ph 2850 MVA
3Ph 2850 MVA
1Ph 2230 MVA
3*BaseMVA*100
( XS0 + (XL10 || XL20) )2*( XS1 + (XL11 || XL21) )( )+
1 Ph Short Circuit MVA
at 132kV Harsool Bus
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Solved Example220/132kV Padegaon
132/33-11 kV Harsool
132/33-11 kV Chikalthana
132kV 33kV
11kV
132kV 33kV
11kV
1998 MVA
538 MVA
3Ph 2850 MVA
1Ph 2230 MVA
3Ph 2257 MVA
1Ph 1662 MVA
3Ph 668 MVA
1Ph 604 MVA
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