Fault Calculation Duhail Annex 1

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ANNEXURE-I ANNEXURE-I for Doc. 13-3/14/SIE/16/0606

FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

Different cases are analyzed depending on the fault location. The values for various impedances which will restrict the fault current are calculated first and after determining the parameters the following net work for 132kV and 66kV system is obtained. 132kV Bus at Gharafa (Fault Level 17.48kA), ZS= 0.878 + j 4.267

X

X

Case- I (16.292KA)

Line # 2 ZL1= 0.209 + j 0.261

Line # 1 ZL1= 0.209+ j 0.261

132/66 kV 160MVA Transformer  ZT= 0.34 + j23.57 CT Location (Typ.)

132/66 kV 160MVA Transformer  ZT= 0.34 + j23.57

Case- II (0.114 kA on 132kV side) (0.228 kA on 66kV side)

X

X

66kV bus at Duhail (Fault level 9.38kA)

X X

Case- III (4.69 kA on 132kV side) (9.38 kA on 66kV side)

X

66kV Outgoing feeder 

66kV Outgoing feeder 

Source fault level at 132kV bus = 3996 MVA (17.48kA) (As informed by Client)

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ANNEXURE-I for Doc. 13-3/14/SIE/16/0606

FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

Source X/R ratio

= 4.86 (informed by the client)

Source Impedance (p.u.) = Base MVA / Fault MVA Base MVA

= 160MVA

Positive sequence impedance (Z s1) = System Voltage √3 x 17480 = 132000 (√3x 17480)

Min. Source resistance R s1

Rs1 Min. Source reactance X s1

=

( Zs1 )2 1 + (Xs1 / Rs1)2

=

(4.36)2 1+ (4.86)2

= 4.36 Ohms

= 0.878 Ohms = 4.86 x Rs = 4.86 x 0.878 = 4.267 Ohms

132kV power cable data (According to cable data) Positive sequence resistance (R L1) = 0.085 Ohms/Km Positive sequence reactance (X L1) = 0.106 Ohms/Km Line length = 2.466 km Positive sequence resistance (R L1) Positive sequence reactance (X L1)

= 0.209 Ohms = 0.261 Ohms

Transformer Data Voltage Ratio = 132/66 kV Rating = 160 MVA Zpu = 0.12 (at 96MVA) Zpu = 0.22 (at 160MVA)

Actual Impedance Z T = Zpu X Base kV2 X 1000 Base kVA

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

= 0.22 X 132 2 X 1000 160 X 1000 = 23.96 Ohms XT = Reactance of the transformer  RT = Resistance of the transformer  XT / RT = 69.33 (According to Transformer data)

RT

=

( ZT )2 1 + (XT / RT)2

=

(23.96)2 1+ (69.33) 2

= 0.34 Ohm XT

= 69.33 x R T = 69.33 x 0.34 = 23.57 Ohms

Detail calculations Source

0.878 4.267

0.209 0.261

0.34 23.57

0.209 0.261 0.34

23.57

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

Equivalent

Source

0.878

4.267

0.889

0.209 0.261

47.401

Equivalent Source

0.878 4.267

0.169 0.259

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ANNEXURE-I for Doc. 13-3/14/SIE/16/0606

FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

Three Phase fault condition Fault current will be limited by Source impedance (132kV Bus at Gharafa), impedance of  both of 160MVA transformers and Line #2 Impedance. Reactance X = Source reactance X s1 + (Line reactance X L2 + 2 X Trafo. Reactance XT) in parallel with (Line reactance X L1) = 4.267 + (0.261 + 2X23.57)//0.261 = 4.526 Ohms Resistance R = Source resistance R s1 + (Line resistance R L2 + 2 X Trafo. resistance R T) in parallel with (Line resistance R L1) = 0.878 + (0.209 + 2X.345)//0.209 = 1.047 Ohms Impedance

= 1.047 + j 4.526

Impedance Z 1 = √X2 + R2 = √(4.526) 2 + (1.047)2 = 4.645Ohms Fault current at the end of Feeder = 132000 ( If ) (√3x 4.645)

= 16407.4 Amp.

Say 16.407 kA Fault current in Case-1 Fault current through line 1

= I f * (47.409) (0.334 + 47.409) = 16.407 * (47.409) 47.743 = 16.292 kA (132kV base)

Fault current in Case-2 Fault current through line 2

= I f * (0.334) (0.334 + 47.409) = 16.407 * (.334) 47.743

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS = 0.114 KA (132kV base)

Case III: - Fault on the 66kV Bus of Duhail and Fault contribution from Source from Gharafa (Through fault current seen by 160 MVA transformers) Fault current will be limited by Source impedance (132kV Bus at Gharafa), Impedance of  both the Lines and impedance of both the160MVA transformers (Impedance of both the lines and transformers will act in parallel). Source

Rs

Xs

RL+RT

RL+RT

XL+XT

XL+XT

Three phase fault current calculation for 66kv Bus Reactance X= Source reactance X s + Line reactance X L /2+Transformer Reactance X T /2 = 4.267+ 0.261/2+ 23.57/2 = 16.183 Ohms Resistance R= Source resistance R s +Line resistance R L/2+Transformer Resistance R T/2 = 0.878 + 0.209/2 + 0.345/2 = 1.155 Ohms Impedance

= 1.155 + j16.183

Impedance Z 1

= √X2 + R2 = √ (16.183) 2 + (1.155)2

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS = 16.224 Ohms Fault current at the end of Feeder = 132000 = 4697.5Amp. (√3x 16.224) Say 4.69 kA Fault current seen by 66kV side CTs = 132000 x 4.69 = 9.38 kA 66000 132kV and 66kV systems are solidly grounded system. Therefore the current magnitude obtained above for phase fault current shall be used for earth fault relay settings also. Impedance for downstream of 66kV feeder is calculated based on 66kV Base voltage and 40MVA Base MVA and the following net work is obtained.

66kV Bus at Duhail (Fault level 9.38 kA), ZS= 0.289+ j 4.048 Line # 1 Impedance neglected due to small length

X

X

Line # 2 Impedance neglected due to small length

Case IV (9.38 kA on 66kV side)

66/11 kV 40MVA Transformer  ZT= 0.383 + j17.618 CT Location (Typ.)

X

X

66/11 kV 40MVA Transformer  ZT= 0.383 + j17.618

11kV bus at Duhail (Fault level 17.76 kA)

X X

Case V (2.96 kA on 66kV side) (17.76 kA on 11kV side)

X

11kV Outgoing feeder 

11kV Outgoing feeder 

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

Source fault level at 66kV bus = 1072 MVA (9.38kA) Source X/R ratio

=14.01(Derived from the calculations performed above in Case-III)

Base MVA

= 40MVA

Positive sequence impedance (Z s) = System Voltage √3 x 9380 = 66000 (√3x 9380)

Min. Source resistance R s

Rs Min. Source reactance X s

=

( Zs1 )2 1 + (Xs1 / Rs1)2

=

(4.062) 2 1+ (14.01)2

= 4.062 Ohms

= 0.289 Ohms = 14.01 x R s = 14.01 x 0.2 89 = 4.048 Ohms

Transformer Data Voltage Rat io = 66/11 kV Rating = 40 MVA Zpu = 0.13 p.u. (at 32 MVA base) Impedance at 4 0 MVA base = 0.13 x 40/32 = 0.1625p.u. Actual Impedance Z T = Zpu X Base kV2 X 1000 Base kVA = 0.1625 X 662 X 1000 40 X 1000 = 17.69 Ohms

XT = Reactance of the transformer  RT = Resistance of the transformer 

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

XT / RT = 46 RT

=

( ZT )2 1 + (XT / RT)2

=

(17.69) 2 1+ (46)2

= 0.383 Ohm XT

= 46 x RT = 46 x 0.383 = 17.618 Ohms

Case IV :- Fault on the 11kV Bus of Duhail and Fault contribution from Source (Through fault current seen by both of the 40 MVA transformers) Fault current will be limited by Source impedance (66kV Bus at Duhail) and parallel impedance of both of the 40MVA transformers. Source

Rs Xs

RT

RT

XT

XT

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS Three phase fault current calculation for 11kV Bus Reactance X= Source reactance X s + Transformer Reactance X T /2 = 4.048+ 17.618/2 = 12.857 Ohms Resistance R= Source resistance R s +Transformer Resistance R T /2 = 0.289 + 0.383/2 = 0.4805 Ohms Impedance

= 0.4805 + j12.857

Impedance Z 1

= √X2 + R2 = √(12.857) 2 + (0. 4805)2 = 12.86 Ohms

Fault current at the end of Feeder = 66000 (√3x 12.86)

= 2963.1 Amp.

Say 2.96 kA (66KV base)

Fault at 11KV bus

= 66000 x 2.96 = 17.76 kA 11000

Earth fault current magnitude for 11kV system is limited to 750A due to Earthing transformer. The same will be used for relay settings. Various impedances for 11kV system are calculated based on 11kV Base voltage and 500 kVA Base kVA and the following network is obtained.

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

11kV Bus at Duhail (Fault level 17.76kA), ZS= 0.013+ j 0.348

Line # 1 Impedance neglected due to small length

Case VI (270A on 11kV side) (7.15kA on 415V side)

11/0.433 kV 500KVA Transformer  ZT= 0.6565 + j2 3.22

CT Location (Typ.)

X 415V bus at Duhail

X

415V Outgoing feeder 

Source fault level at 11kV bus = 338 MVA (17.76 kA) Source X/R ratio

= 26.76(Derived from the calcula tions performed above in Case-IV)

Base MVA

= 500kVA

Positive sequence impedance (Z s) = System Voltage √3 x 17760 = 11000 (√3x 17760)

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= 0.357 Ohms

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ANNEXURE-I for Doc. 13-3/14/SIE/16/0606

FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS

Min. Source resistance R s

Rs Min. Source reactance X s

=

( Zs1 )2 1 + (Xs1 / Rs1)2

=

(0.357)2 1+ (26.76) 2

= 0.013 Ohms = 26.76 x R s = 26.76 x 0.013 = 0.348 Ohms

Transformer Data Voltage Ratio = 11/0.415 kV Rating = 500kVA Zpu = 0.096 p.u. Actual Impedanc e ZT = Z pu X Base k V2 X 1000 Base kVA = 0.096 X 11 2 X 1000 0.5 X 1000 = 23.23 Ohms

XT = Reactance of the transformer  RT = Resistance of the transformer  XT / RT = 35.37

RT

=

( ZT )2 1 + (XT / RT)2

=

(23.23)2 1+ (35.37) 2

= 0.6565 Ohm XT

= 35.37 x R T

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FAULT CURRENT CALCULATIONS FOR RELAY SETTINGS = 35.37 x 0.6565 = 23.22 Ohms

Case V: - Fault on the 415V Bus of Duhail and Fault contribution from Source (Through fault current seen by 500 kVA transformer) Fault current will be limited by Source impedance (11kV B us at Duhail) and impedance of 500kVA transformer.

Three phase fault current calculation for 415V bus Reactance X= Source reactance X s + Transformer Rea ctance XT = 0.348+ 23.22 = 23.568 Ohms Resistance R= Source resistance R s +Transformer Resistance R T = 0.013 + 0.6565 = 0.669 Ohms Impedance

= 0.669 + j23.5 68

Impedance Z 1

= √X2 + R2 = √(23.568 )2 + (0.669)2 = 23.577 Ohms

Fault current at the end of Feeder = 11000 = 269.45 Amp, say 270 Amp (√3x 23.57)

Fault current seen by 415kV side CTs

= 11000 x 270 = 7.15kA 415

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