Sample Short Circuit Calculation

Calculation Sheet

Calculation for Short Circuit Fault Current PROJECT:- STEP ERC office

Fault Location:

At the Main Switchboard.

Service Voltage:

400

Volts

Generator No-Load Voltage:

420

Volts

Supply Cable Parameters:

From Generator to Main Distribution Board

Busbar Length:

15

mtr

Busbar CSA:

400

sqmm

No. of bars per Phase:

1

+5% of the Service Voltage

Transformer Impedance: Transformer kVA:

1500

kVA

For a 1500kVA Transformer: Usc = 6%

Transformer Impedance:

7.06

mΩ

(Based on only 1No. Transformer feeding the Main Board)

Elements contributing to the Fault:

X (mΩ)

R (mΩ)

Transformer: (Reactance)

7.06

Transformer: (Resistance)

X trafo = Z trafo 1.41

R trafo = X trafo x 0.2

Circuit Breaker:

0.15

Average Reactance for an MCB = 0.15mΩ

Busbar: (Reactance)

2.25

Average Reactance per Metre of a Busbar = 0.15mΩ

X cable = 0.15 x Length

Conductor Resistivity per Metre (with an MCB) = 0.023Ω

R cable = (23mΩ x Length) / (Phase CSA)

Busbar: (Resistance)

0.86

Sum of the Fault Elements:

X (mΩ)

Total Reactance:

9.46

Total Resistance:

R (mΩ)

2.27

9.726

mΩ

Short Circuit Fault Current (Steady State):

24.93

kA

Steady State Fault Current Isc

Isc = No Load Voltage / (sqrt (3) x Impedance)

Calculated value of k:

1.50

Short Circuit Fault Current (Peak):

52.76

kA

Peak Asymmetrical Fault Current Iscpk

Iscpk = Isc x k x sqrt (2)

Total Impedance:

Short Circuit Fault Currents:

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Calculation Sheet

Calculation for Short Circuit Fault Current PROJECT:- Camp Accommodation and Recreation

Fault Location:

Sub Main Distribution Board 0S-EDB82C01.

Service Voltage:

400

Volts

Transformer No-Load Voltage:

420

Volts

Supply Cable Parameters:

From the Generator to Main Distribution Board

Cable Length:

70

mtr

Cable CSA:

95

sqmm

No. of Cores per Phase:

1

Elements contributing to the Fault:

X (mΩ)

Circuit Breaker:

0.15

Average Reactance for an MCB = 0.15mΩ

Cable: (Reactance)

5.6

Average Reactance per Metre of a 3 Phase Cable = 0.08mΩ

X cable = 0.08 x Length

Conductor Resistivity per Metre (with an MCB) = 0.023Ω

R cable = (23mΩ x Length) / (Phase CSA)

Cable: (Resistance)

R (mΩ)

16.95

Average Reactance for an MCB = 0.15mΩ

Circuit Breaker:

0.15

Upstream Values at the Main SWB:

0.00

0.00

Sum of the Fault Elements:

X (mΩ)

R (mΩ)

Total Reactance:

5.90

Total Resistance:

+5% of the Service Voltage

Refer to the S/C Calculation for the Main SWB

16.95

17.945

mΩ

Short Circuit Fault Current (Steady State):

13.51

kA

Steady State Fault Current Isc

Isc = No Load Voltage / (sqrt (3) x Impedance)

Calculated value of k:

1.02

Short Circuit Fault Current (Peak):

19.50

kA

Peak Asymmetrical Fault Current Iscpk

Iscpk = Isc x k x sqrt (2)

Total Impedance:

Short Circuit Fault Currents:

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Calculation Sheet

Calculation for Short Circuit Fault Current PROJECT:- STEP ERC Building

Fault Location:

Distribution Board 0S-EDB82C10 in the Recreation Block.

Service Voltage:

400

Volts

Transformer No-Load Voltage:

420

Volts

Supply Cable Parameters:

From Main Distribution Board to DB1

Cable Length:

30

mtr

Cable CSA:

25

sqmm

No. of Cores per Phase:

1

Elements contributing to the Fault:

X (mΩ)

Circuit Breaker:

0.15

Average Reactance for an MCB = 0.15mΩ

Cable: (Reactance)

2.4

Average Reactance per Metre of a 3 Phase Cable = 0.08mΩ

X cable = 0.08 x Length

Conductor Resistivity per Metre (with an MCB) = 0.023Ω

R cable = (23mΩ x Length) / (Phase CSA)

Cable: (Resistance)

R (mΩ)

27.60

Average Reactance for an MCB = 0.15mΩ

Circuit Breaker:

0.15

Upstream Values at MDB

5.90

16.95

Sum of the Fault Elements:

X (mΩ)

R (mΩ)

Total Reactance:

8.60

Total Resistance:

+5% of the Service Voltage

Refer to the S/C Calculation for 0S-EDB82C01

44.55

45.370

mΩ

Short Circuit Fault Current (Steady State):

5.34

kA

Steady State Fault Current Isc

Isc = No Load Voltage / (sqrt (3) x Impedance)

Calculated value of k:

1.02

Short Circuit Fault Current (Peak):

7.71

kA

Peak Asymmetrical Fault Current Iscpk

Iscpk = Isc x k x sqrt (2)

Total Impedance:

Short Circuit Fault Currents:

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Calculation Sheet

Calculation for Short Circuit Fault Current PROJECT:- Camp Accommodation and Recreation

Fault Location:

Distribution Board 0S-EDB82C11 in the Recreation Block.

Service Voltage:

400

Volts

Transformer No-Load Voltage:

420

Volts

Supply Cable Parameters:

From 0S-EDB82C10 to 0S-EDB82C11.

Cable Length:

10

mtr

Cable CSA:

25

sqmm

No. of Cores per Phase:

1

Elements contributing to the Fault:

X (mΩ)

Circuit Breaker:

0.15

Average Reactance for an MCB = 0.15mΩ

Cable: (Reactance)

0.8

Average Reactance per Metre of a 3 Phase Cable = 0.08mΩ

X cable = 0.08 x Length

Conductor Resistivity per Metre (with an MCB) = 0.023Ω

R cable = (23mΩ x Length) / (Phase CSA)

Cable: (Resistance)

R (mΩ)

9.20

Average Reactance for an MCB = 0.15mΩ

Circuit Breaker:

0.15

Upstream Values at 0S-EDB82C10:

8.60

44.55

Sum of the Fault Elements:

X (mΩ)

R (mΩ)

Total Reactance:

9.70

Total Resistance:

+5% of the Service Voltage

Refer to S/C Calculation for 0S-EDB82C10.

53.75

54.616

mΩ

Short Circuit Fault Current (Steady State):

4.44

kA

Steady State Fault Current Isc

Isc = No Load Voltage / (sqrt (3) x Impedance)

Calculated value of k:

1.02

Short Circuit Fault Current (Peak):

6.40

kA

Peak Asymmetrical Fault Current Iscpk

Iscpk = Isc x k x sqrt (2)

Total Impedance:

Short Circuit Fault Currents:

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Calculation Sheet

Calculation for Short Circuit Fault Current PROJECT:- Camp Accommodation and Recreation

Fault Location:

Distribution Board 0S-EDB82C12 in the Recreation Block.

Service Voltage:

400

Volts

Transformer No-Load Voltage:

420

Volts

Supply Cable Parameters:

From 0S-EDB82C10 to 0S-EDB82C12.

Cable Length:

10

mtr

Cable CSA:

16

sqmm

No. of Cores per Phase:

1

Elements contributing to the Fault:

X (mΩ)

Circuit Breaker:

0.15

Average Reactance for an MCB = 0.15mΩ

Cable: (Reactance)

0.8

Average Reactance per Metre of a 3 Phase Cable = 0.08mΩ

X cable = 0.08 x Length

Conductor Resistivity per Metre (with an MCB) = 0.023Ω

R cable = (23mΩ x Length) / (Phase CSA)

Cable: (Resistance)

R (mΩ)

14.38

Average Reactance for an MCB = 0.15mΩ

Circuit Breaker:

0.15

Upstream Values at 0S-EDB82C10:

8.60

44.55

Sum of the Fault Elements:

X (mΩ)

R (mΩ)

Total Reactance:

9.70

Total Resistance:

+5% of the Service Voltage

Refer to S/C Calculation for 0S-EDB82C10.

58.92

59.715

mΩ

Short Circuit Fault Current (Steady State):

4.06

kA

Steady State Fault Current Isc

Isc = No Load Voltage / (sqrt (3) x Impedance)

Calculated value of k:

1.02

Short Circuit Fault Current (Peak):

5.86

kA

Peak Asymmetrical Fault Current Iscpk

Iscpk = Isc x k x sqrt (2)

Total Impedance:

Short Circuit Fault Currents:

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