FAULT CURRENT CALCULATION BY KVA METHOD for HT & LT LINES

Electrical Basic Calculators

FAULT CURRENT BY KVA METHOD for HT & LT LINES 

Fault current or short circuit fault current play important role to design earthing of system. It is based on KVA Method. The Fault current calculations are done on basis of Ohm's Law in which the current (I) equals the voltage (V) divided by the resistance (R). The formula is I = V/R. When there is a short circuit the resistance becomes very small, and that means the current becomes very large. Below Yellow Highlighted Data can be change by user and Green is output.

FAULT CURRENT CALCULATIONS (HT & LT )
Base MVA OF HT Side			:		MVA
Voltage of HT Side			:		KV
Base MVA OF LT Side			:		MVA
Voltage of LT Side			:		KV
Fault level of HT Side			:		MVA
1) Fault Level Calculation at HT Meter to DO-GO TOWER(breaker)
a) HT Cable up to Transformer				Run, length		meter
SELECTED CABLE:				11 KV, 3 Core, 240 mm2 Aluminium Cable
Resisitance of Cable -				ohm/km	Reactance of Cable-			ohm/km
b) Total Cable Resisitance (R) :			(Cable length*reisitance of cable)/Cable Run			=		ohm
c) Total Cable Reactance(X):			(Cable length*rectance of cable)/Cable Run			=		ohm
d) Total Cable Impedance (Zc1)				:	√ (R*R +X*X)
				:		ohm	:----------(1)
e) P.U. reactance at incoming side of breaker (X pu )= (Base KVA/Fault Level)
				:			:----------(2)
f) Total Impedance up to breaker (Z pu-a )= (Zc1)+ (X Pu)
				:			:----------(3)
g) Fault MVA at HT Breaker =BASE MVA/ Zpu-a
				:
h) Fault Current at HT Side= Fault MVA/ (√ 3*BASE KV)
				:		kA
2) Fault Level Calculation at HT breaker (GO-DO Tower) to Primary Side of Transformer
a) HT Cable up to Transformer				Run, length		meter
SELECTED CABLE:				11 KV, 3 Core, 240 mm2 Aluminium Cable
Resisitance of Cable -				ohm/km	Reactance of Cable-			ohm/km
b) Total Cable Resisitance (R) :			(Cable length*reisitance of cable)/Cable Run			=		ohm
c) Total Cable Reactance(X):			(Cable length*rectance of cable)/Cable Run			=		ohm
d) Total Cable Impedance (Zc2)				:	√ (R*R +X*X)
				:		ohm	:----------(4)
e) P.U. Impedance at primary side of Transformer (Z pu)= (Zc2 * Base KVA)/ (Base KV * Base KV*1000)
				:			:----------(5)
f) Total Impedance (Zpu)				:	(4) + (5)
				:			:----------(6)
g) Total Impedance up to Primary side of Transformer: (Z pu-b )= (Z Pu)+ (Z Pu-a)
				:			:----------(7)
h) Fault MVA atPrimary side of Transformer: =BASE MVA/ Zpu-b
				:
i) Fault Current at Primary side of Transformer: = Fault MVA/(√ 3*BASE KV)
				:		kA
3) Fault Level Calculation at Primary Side of Transformer to secondary side of Transformer
a) Transformer Rating:						KVA
b) Transformer Impedance						%
c)% Reacance at base KVA:			(Base KVA * % impedance at Rated KVA)/ Rated KVA			=
d) P.U. Reactance of Transformer (Z pu)=%reactance /100
				:			:----------(8)
e) Total Pu Impedanceof Transformer secondary winding: (Z pu-c )= (Z Pu)+ (Z Pu-b)
				:			:----------(9)
f) Fault MVA at secondary side of Transformer: =BASE MVA/ Zpu-c
				:		MVA
g) Fault Current at secondary side of Transformer:: = Fault MVA/ BASE KV
				:		kA
4) Fault Level Calculation at secondary side of Transformer to MAIN LT PANEL
a) LT Cable up to Transformer				Run, length		meter
SELECTED CABLE:				1.1 KV, 3.5 Core, 120 mm2 Aluminium Cable
Resisitance of Cable -				ohm/km	Reactance of Cable-			ohm/km
b) Total Cable Resisitance (R) :			(Cable length*reisitance of cable)/Cable Run			=		ohm
c) Total Cable Reactance(X):			(Cable length*rectance of cable)/Cable Run			=		ohm
d) Total Cable Impedance (Zc3)				:	√ (R*R +X*X)	=		ohm:-------(10)
e) Total Pu Impedance of Main LT Panel: (Z pu )= (Z c3 * base KVA)/(Base KV * Base KV*1000)
				:			:----------(11)
f) Total Impedance of Mail LT Pannel (Zpu -d)= (Zpu)+ ( Z Pu-c)= (11) +(9)
				:
g) Fault MVA at Main LT Panel: =BASE MVA/ Zpu-d
				:		MVA
h) Fault Current at secondary side of Transformer:: = Fault MVA/ (√ 3*BASE KV)
				:		kA