A fault in an electrical equipment is defined as a defect in the electrical circuit due to which current is
diverted from the intended path.
General Faults
> Over current
> under voltage
>unbalance
>reversed power
>surges
>unbalanced fault
>short circuit or shunt fault
>short circuit or shunt fault
The faults that may occur in 3-Phase power system
1> single phase to earth
2> phase to phase
3>two phases to earth
4> phase to phase and at the same time from third phase to earth
5>all three phases to earth
6>all the three phases short circuited.
The first four types of faults give rise to unsymmetrical fault ,while the other two types give rise to
symmetrical short-circuit currents.
Sources of Fault Power
1>Generators
2>Synchronous motors and synchronous condensors.
3>Induction motors.
Necessity for proctection system
modern power systems are growing fast with more generators, transformers, and large networks in the systems . There are many abnormal conditions like
>overloads
>under-voltage
> open-phase
> unbalanced-phase currents
> reversal of power
>under-frequency
>over temperature
>power swings
>instability
to prevent these things protection is required .
Basic requirements of Protection System
1>reliability
2>selectivity
3>sensitivity
4>speed of operation
without selectivity and reliability the protection is largely ineffective and could even become liablity.
Typesof Protection
1>main or primary protection
2>back up
3>auxilary protection
