Faults and Relays.

TYPES OF FAULTS AND RELAYS

In power system only two types of faults are present

1.     Over-current Fault

2.     Earth Fault

In these two main categories  there are many types of faults present

Example:

1.     Over-current Fault

·        Line to Line Fault

·        3 phase fault  etc.

2.     Earth Fault

·           Line to ground Fault

·           Double Line To Ground Fault etc.

So relate with equipment and environment, we use so many types of relays used to protect the power system elements.

TYPES OF RELAYS:

1.O/C & E/F RELAYS

These relays are used for general protection.It give protection over earth fault and over current fault.The main thing we have keep in mind that it is used in short transmission lines up to 33KV limit(may be used in 66KV).

2.Distance Relays

This Relay is used as over current relay in long transmission high voltage lines. It is accurate than ‘O/C & E/F RELAYS’ and we can figure out the exact position of fault.So it is much helpful to locate the fault in long tx.line.

3.Restricted earth fault relay.

This relays are used in equipment protection mainly for transformer.It is connected to the C.T in the earthed neutral link,we called a Neutral C.T.It is actually a earth fault relay that find any internal insulation failure or heavy earth fault related with equipment surrounding.

4. Differential relays

The definition of such a relay is “one that operates when the vector difference of two or more similar electrical quantities exceeds a predetermined amount.That means in a trans former we know it primary and secondary voltages so the ratio of Pr. And Sec. Always constant so if any abnormality occur the ratio will change and relay will operate.This is also for equipment protection.

5.Master Relay  

All the above relays are connected to master relay in a panel board and it will operate the breaker.