A two machine power system is shown below. Transmission

A two machine power system is shown below. Transmission line XY has positive sequence impedance of Z_{1_{Ω and zero sequence impedance of Z₀ Ω.

An ‘a’ phase to ground fault with zero fault impedance occurs at the centre of the transmission line. Bus voltage at X and line current from X to F for the phase ‘a’, are given by V_a Volts and I_a Amperes, respectively. Then, the impedance measured by the ground distance relay located at the terminal X of line XY will be given by}}

Impedance measured by ground distance relay

=	Bus Voltage	=	V_a	Ω
	Current		I_a

Z₁	Ω
2

Z₀	Ω
2

(Z₀ + Z₁)	Ω
2