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.
