Study notes on Unsymmetrical Fault Analysis For Electrical Engineering Students

By Yash Bansal|Updated : May 22nd, 2021

In this article, you will find the study notes on Unsymmetrical Fault Analysis which will cover the topics such as Unsymmetrical Fault, Single Line to Ground Fault, Line to Line Fault & Double Line to Ground Fault.

In this article, you will find the study notes on Unsymmetrical Fault Analysis which will cover the topics such as Unsymmetrical Fault, Single Line to Ground Fault, Line to Line Fault & Double Line to Ground Fault.

Unsymmetrical Faults (Shunt Fault)

  • Single line to ground fault ( LG fault ),
  • Line to line fault ( LL fault ) and
  • Double line to ground ( LLG fault ) are unsymmetrical faults that may occur at any point in a power system.

To understand the unsymmetrical fault analysis, let us first, consider these faults at the terminals of an unloaded generator. This treatment can be extended to unsymmetrical fault analysis when the fault occurs at any point in a power system.

Consider a three-phase unloaded generator generating the balanced three-phase voltage. The sequence components of the terminal voltages are 

Single Line to Ground Fault

Ib = 0
Ic = 0
Va = IaZf

 image012

image013

Single Line to Ground Fault with Zf

The termination of the three-phase access port as shown in figure brings about a condition of single line to ground fault through a fault impedance Zf .Here, the fault tapes place on phase a.

image014

image015

Line to Line Fault

Here, the line to line fault takes place on phases b an C.

Ia = 0
Ib = -Ic
Vb = Vc + Zf Ib
Ib = -Ic = Ia0 + a2 Ia1 + aIa2

 image016

image017

Fault current 

 image018

image019

Line to Line Fault with Zf

image020

image021

Double Line to Ground Fault

The double line to go and fault takes place on phase b and C as shown in figure below

Ia = 0
Vb = Vc = ( Ib + Ic )Z

image022

image023

Double Line to Ground Fault with Zf

Fault-Analysis (24)

Fault-Analysis (25)

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