Fault Level Calc.pdf

Calculations of Short Circuit Currents (by Impedence Mathod) Parameters Rated System Voltage VCB

11 kV

Power Plant Aux. Distn Swgr

11000

UoM Volts

Source Fault Level

40

kA

Source Fault MVA

762

MVA

Voltage factor

1.1 1.05

VCB

Impedance

ZQ

0.175

Ω

Resistance

RQ

0.035

Ω

Reactance

XQ

0.171

Ω

Cable 1 No. of runs

Cable 1

3x240 3

Route Length

VCB 11 kV

CHP . Distn Swgr

VCB Cable 2

11/3.5 kV 4000 kVA

Cable Resistance Cable Reactance Net Cable Resistance

1.2

kM

0.16 0.085 0.0640

Ω/km Ω/km Ω

XC1

0.0340 0.245

Ω Ω

Isc

28.51

kA

Cable 2 No. of runs Route Length Cable Resistance Cable Reactance Net Cable Resistance

RC2

3x240 1 0.1 0.16 0.085 0.0160

kM Ω/km Ω/km Ω

Net Cable Reactance

XC2

0.0085

Ω

ST

MVA kV kV

Net Cable Reactance Total Impedance Symmetrical S/C Current (rms) at 11 kV SWGR Bus

RC1

Remarks Assumed in the absence of the information For MV System up to 35 kV (In Accordance with IEC 60909) For 415 V System (In Accordance with IEC 60909) RQ = 0.2 ZQ (In Accordance with IEC 60909)

As per Cable Sizing Calculations Estimated Route lengths as per Plant layout Taken from Polycab Datasheets

Taken from Polycab Datasheets

ONAN, OCTC

Power Transformer Rated Capacity Rated Primary Voltage Rated Secondary Voltage

VT

4 11 3.5

Dyn 1

Rated Secondary Current

IT

659.8

Amp

% Impedance

uT

6.25

%

Full Load Cu Loss

QT

27000

W

As per CBIP Guidelines

Transformer Impedance

ZT

0.1914

Ω

(uT / 100)*(VT2 / ST)

Transformer Resistance

RT

0.0207

Ω

(Q / (3 * IT2)

Main CHP Trafo

Tap ± 5% @ 2.5

XT 0.1903 Ω Transformer Reactance (ZT2 - RT2) As two identical transformers are connected in parallel, its Impedance, resistance & reactance shall be divided by 2. RT1 0.0103 Ω Equivalent Transformer Resistance Equivalent Transformer Reactance

XT1

0.0951

Ω

The reactance & resistance calculated for HV Section must be recalculated for the LV network via multiplication by square of the voltage ratio of the transformer. N1 0.101 Square of the voltage Ratio Equivalent reactance up to Power Trafo

X1

0.1168

(XQ + XC1 + XC2) * N1 + XT1

Equivalent resistance up to Power Trafo

R1

0.0220

(RQ + RC1 + RC2) * N1 + RT2

Equivalent reactance up to 3.3 kV SWGR Bus

X1

0.1168

Equivalent resistance up to 3.3 kV SWGR Bus

R1

0.0220

Busduct Neglected for the purpose of calculation

Busduct

VCB 3.3 kV

CHP . Distn Swgr

Total Impedance Symmetrical S/C Current (rms) at 3.3 kV SWGR Bus

VCB Cable 3

HT JB on Ground

0.119

Ω

Isc

18.71

kA

Cable 3 No. of runs Route Length Cable Resistance Cable Reactance Net Cable Resistance

RC3

3x185 1 0.35 0.21 0.075 0.0735

Ω/km Ω/km Ω

Net Cable Reactance

XC3

0.0263

Ω

Cable 4

3x70

Cable Up to Center Pit JB

Taken from Polycab Datasheets

Cable from Center Pit JB to SR LBS Rev 0

Calculations of Short Circuit Currents (by Impedence Mathod) Cable 5 Trailing Cable

SR Machine HT LBS

No. of runs Route Length Cable Resistance Cable Reactance Net Cable Resistance Net Cable Reactance

RC4

1 0.22 0.354 0.093 0.0779

Ω/km Ω/km Ω

XC4

0.0205

Ω

VT

NA 0.63 3.3 0.433

MVA kV kV

840.0

Amp

Taken from Nicco Datasheets

630 kVA

Distribution Transformer Rated Capacity Rated Primary Voltage Rated Secondary Voltage

Dry Type, OCTC

Rated Secondary Current

IT

% Impedance

uT

5

%

Full Load Cu Loss

QT

8500

W

As per CBIP Guidelines

Transformer Impedance

ZT

0.0149

Ω

(uT / 100)*(VT2 / ST)

Transformer Resistance

RT2

0.0040

Ω

(Q / (3 * IT2)

Transformer Reactance

XT2

0.0143

Ω

(ZT2 - RT2)

3.3/.433 kV

SR Trafo

Dyn 1

ACB

ST

The reactance & resistance calculated for HV Section must be recalculated for the LV network via multiplication by square of the voltage ratio of the transformer. 433 V

SR MCC

Square of the voltage Ratio

N2

0.017

Equivalent reactance up to SR MCC Bus

0.017

Ω

(X1 + XC3 + XC4 ) * N2 + XT2

Equivalent resistance up to SR MCC Bus Total Impedance Symmetrical S/C Current (rms) at SR MCC bus

0.007 0.019

Ω Ω

(R1 + RC3 + RC4 ) * N2 + RT2

14.18

kA

Isc

Note: Motor Contributions are neglected in this calculations.

Rev 0