The magnitude of
earth fault current in the line to earth fault on an earthed system is
determined by

- Impedance from source to fault
- Impedance of earth return paths
- Impedance of Earthing transformer
- Resistors
- Reactors

The voltage
across resistor is nearly is equal to line to neutral voltage for single line
to earth fault on a resistance grounding system.

The resistor
current is equal to fault current for low resistance grounded system therefore
the current is practically equal to line to neutral voltage divided by the
resistance.

- This method is application only when earth fault current is small as compared to three phase fault current.
- The earth fault current is computed for resistance earthed system for line to earth fault.

I

_{G}= 3E / [ X_{1}* X_{2}+ X_{0}+ 3 ( X_{n}+ X_{GP})]
Where

E = Line to
earth voltage ( V )

I

_{G}= Earth fault current in ( Amp )
X

_{1 }= Positive sequence reactance in ohm / phase including sub – transient reactance of the rotating machines
X

_{2 }= Negative sequence reactance
X

_{0 }= Zero sequence reactance
X

_{n }= Reactance of neutral grounding reactor
X

_{GP}= Reactance of ground return circuits**You may also like**

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