Difference between symmetrical and asymmetrical faults in power system
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Unsymmetrical Faults And Symmetrical Components
Unsymmetrical Faults
Unsymmetrical faults are the faults which leads unequal currents with unequal phase shifts in a three phase system.
The unsymmetrical fault occurs in a system due to presence of an open circuit or short circuit of transmission or distribution line. It can occur either by natural disturbances or by manual errors. The natural disturbances are heavy wind speed, ice loading on the lines, lightening strokes and other natural disasters.
The open circuit or short circuits of transmission or distribution lines will lead to unsymmetrical or symmetrical faults in the system. In case of tree branches falling on lines, a short circuit of transmission lines will occur.
These line faults are classified as,
1. Single line to ground faults (LG fault)
2. Double line fault (LL fault)
3. Double line to ground fault (LLG fault)

Single line to ground fault is the most frequently occurring fault (60 to 75% of occurrence). This fault will occur when any one line is in contact with the ground. Double linefault occurs when two lines are short circuited. This type of fault occurrence ranges from 5 to 15%. Double line to ground fault occurs when two lines are short circuited and is in contact with the ground. This type of fault occurrence ranges from 15 to 25% of occurrence.
Symmetrical Components:
Symmetrical components are derived to analyze unsymmetrical faults. The unsymmetrical network can be expressed in terms of three linear symmetrical components. The three symmetrical components are positive sequence component, negative sequence component and zero sequence component.
Figure 2 is the symmetrical components derived from an unsymmetrical or unbalanced network.

Unsymmetrical Faults
Unsymmetrical faults are the faults which leads unequal currents with unequal phase shifts in a three phase system.
The unsymmetrical fault occurs in a system due to presence of an open circuit or short circuit of transmission or distribution line. It can occur either by natural disturbances or by manual errors. The natural disturbances are heavy wind speed, ice loading on the lines, lightening strokes and other natural disasters.
The open circuit or short circuits of transmission or distribution lines will lead to unsymmetrical or symmetrical faults in the system. In case of tree branches falling on lines, a short circuit of transmission lines will occur.
These line faults are classified as,
1. Single line to ground faults (LG fault)
2. Double line fault (LL fault)
3. Double line to ground fault (LLG fault)

Single line to ground fault is the most frequently occurring fault (60 to 75% of occurrence). This fault will occur when any one line is in contact with the ground. Double linefault occurs when two lines are short circuited. This type of fault occurrence ranges from 5 to 15%. Double line to ground fault occurs when two lines are short circuited and is in contact with the ground. This type of fault occurrence ranges from 15 to 25% of occurrence.
Symmetrical Components:
Symmetrical components are derived to analyze unsymmetrical faults. The unsymmetrical network can be expressed in terms of three linear symmetrical components. The three symmetrical components are positive sequence component, negative sequence component and zero sequence component.
Figure 2 is the symmetrical components derived from an unsymmetrical or unbalanced network.

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