Fault Level Calcn in 11KV & 415V

SAI SINDHU SPONGE IRON PVT LTD8 MW CAPTIVE POWER PLANT AT TADIPATRI

FAULT LEVEL CALCULATION

HIQ POWER ASSOCIATES PRIVATE LIMITED, CHENNAI

G

Y

D

11 KV bus

33 KV bus

DETAILS:1. Transformer - 8.6MVA, 11/33 KV, 8.5%

2. Generator - 8.0MW, 10.0 MVA

33Kv Grid SS

ACSR,O/H line

Isolater

11KV XLPE cable

1


FAULT LEVEL CALCULATION IN 11KV BUS BAR

I. Fault level at 33 KV: -

Fault level at 33KV Bus = 1000 MVA (considered)

Let the base MVA = 8.6 MVA

% Impedance of the system at source = 8.6/1000 = 0.0086 P.U = Z1

II. Fault level at 8.6MVA Transformer

Transformer KVA = 8600KVA

Voltage rating = 33KV/11KV

Impedance of the transformer = 10% = 0.1 P.U =Z2

III. Fault level at 10.0 MVA Generator

Sub transient Reactance of the Generator = 12. % (Considered)

Generator MVA = 10.0 MVA

Base MVA for generator = 8.6 MVA

Impedance of the Generator

= 0.12X (8.6 / 10)

= 0.1032 P.U = Z3

TOTAL FAULT IN 11KV BUS: -

Z1 and Z2 are in series

Total P.U in Transformer end (Z0) = Z1 +Z2


Z2 Z1

Z3

2


= 0.0086 + 0.1

= 0.1086

P.U in 11KV Bus = Z0 XZ3 /Z0+Z3

= (0.1086 X 0.1032) / (0.1086 + 0.1032)

= 0.0529 P.U

Fault MVA in 11KV End = 8.6/0.0529

= 162 MVA

Fault Current = 162/(1.732X11)

= 8.5 KA

FAULT LEVEL CALCULATION IN 415V BUS BAR

IV. Fault level at 11 KV: -

Actual fault level at 11KV Bus = 162 MVA Let the base MVA = 2.0 MVA

% Impedance of the system at source = 2.0/162 = 0.0123 P.U =Z4

V. Fault level at 2.5MVA Transformer

Transformer KVA = 2000KVA

Voltage rating = 11KV/0.433KV

Impedance of the transformer = 7%

= 0.07 P.U =Z5

TOTAL FAULT IN 415V BUS: -

Z4 and Z5 are in series

Total P.U in Transformer end (Z0) = Z4+Z5

= 0.0123 + 0.07


3


= 0.0823

Fault MVA in 415V End = 2.0/0.0823

= 24.3 MVA

Fault Current = 24.3/(1.732X0.433)

= 32.4 KA

Fault in motor end = 8 KA

Total Fault in 415V end = 40.4 KA


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Fault Level Calcn in 11KV & 415V

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