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Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE) PDF Download

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
1. Single Line to Ground Fault
Ib = 0
Ic = 0
Va = IaZf
Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

(i) 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.

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

2. 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 + a2Ia1 + aIa2

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Fault current

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

(i) Line to Line Fault with Zf

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

3. 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

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

(i) Double Line to Ground Fault with Zf

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE)

The document Unsymmetrical Fault Analysis | Power Systems - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Power Systems.
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FAQs on Unsymmetrical Fault Analysis - Power Systems - Electrical Engineering (EE)

1. What are unsymmetrical faults in electrical engineering?
Ans. Unsymmetrical faults, also known as shunt faults, occur when one or more phases of a three-phase power system become shorted to the ground or to each other. These faults result in an imbalance of currents and voltages in the system.
2. How does an unsymmetrical fault analysis help in electrical engineering?
Ans. Unsymmetrical fault analysis is crucial in electrical engineering as it helps in understanding the behavior of the power system during fault conditions. It allows engineers to determine the fault current magnitudes, fault locations, and select appropriate protective devices to minimize damage and ensure system stability.
3. What are the main types of unsymmetrical faults?
Ans. The main types of unsymmetrical faults include line-to-line faults, line-to-ground faults, and double line-to-ground faults. Line-to-line faults occur when two phases of a three-phase system come into contact, line-to-ground faults occur when a phase comes into contact with the ground, and double line-to-ground faults occur when two phases simultaneously come into contact with the ground.
4. How is fault current magnitude determined in unsymmetrical fault analysis?
Ans. Fault current magnitude in unsymmetrical fault analysis is determined using the symmetrical component method. This method involves converting the unsymmetrical fault into its equivalent symmetrical components (positive, negative, and zero sequence components) and then calculating the fault currents for each component. The vector sum of these fault currents gives the total fault current magnitude.
5. What protective devices are used to mitigate unsymmetrical faults?
Ans. Various protective devices are used to mitigate unsymmetrical faults, including circuit breakers, fuses, and relays. Circuit breakers are designed to open the circuit and isolate the faulted section, while fuses are used to interrupt the current flow when the fault current exceeds a certain threshold. Relays are responsible for detecting faults and initiating the operation of the protective devices.
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