Generally, a single line-to-ground fault on a transmission line occurs when one conductor drops to the ground or comes in contact with the neutral conductor. Such types of failures may occur in power system due to many reasons like high-speed wind, falling off a tree, lightning, etc.

### Circuit diagram of single line-to-ground fault

Suppose the phase **a** is connected to ground at the fault point F as shown in a figure below. I_{a}, I_{b} and I_{c} are the current and V_{a}, V_{b} and V_{c} are the voltage across the three phase line a, b and c respectively. The fault impedance of the line is Z_{f}.

Since only phase **a** is connected to ground at the fault, phase b and c are open circuited and carries no current; i.e fault current is I_{a} and I_{b} = 0, I_{c} = 0. The voltage at the fault point F is V_{a} = Z_{f }I_{a}.

The symmetrical component of the fault current in phase “a” at the fault point can be written as

This relation can also be found by matrix method as follows:-

In the case of a single line-to-ground fault, the sequence currents are equal. The sequence voltage at the fault point is determined by the equations:-

Where, E_{a0}, E_{a1}, and E_{a2} are the sequence voltages of phase a, and Z_{a0}, Z_{a1} and Z_{a2} are the sequence impedances to the flow of currents I_{a0}, I_{a1}, and I_{a2} respectively. For a balanced system

On substituting the I_{a0} = I_{a1} = I_{a2} = I_{a} in above equation we get,

The sequence current is given by equation,

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Jayson Leethank you. very helpful

habtamuGreat Article

ThiyaneshPls elaborated the 3 phase symmetrical fault .

types

Archana TYou can study here the types of symmetrical fault http://circuitglobe.com/types-of-faults-in-power-system.html

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Arun kauravVery very good site

YKKimThanks for explanation

KashishReally appreciate it!