PROTECTION
OBJECTIVE : To quickly isolate a faulty section
from both ends so that the rest of the System can function satisfactorily.
THE FUNCTIONAL REQUIREMENTS
OF THE RELAY:
i) Reliability : The most important requisite of protective relay is reliability since
they supervise the circuit for a long time
before a fault occurs; if a
fault then occurs, the relays must respond
instantly and correctly.
ii) Selectivity : The relay must be able to discriminate(select) between
those
conditions
for which prompt operation is required and
those for which no operation, or
time delayed operation is required.
iii) Sensitivity : The relaying equipment must be sufficiently sensitive so
that it
operates reliably when required under the
actual conditions that
produces least operating tendency.
iv) Speed : The
relay must operate at the required speed. It should neither be too
slow which may result in damage
to the equipment nor should it be too fast which may result in undesired
operation.
IMPORTANT ELEMENTS
:
Switch gear: Circuit breaker Bulk oil, Minimum
oil, SF6, Airblast, Vacuum etc. depending on medium used for quenching the arc.
Different operating mechanisms such as solenoid, spring, pneumatic, hydraulic
etc. are employed.
Protective gear: Relays (current, voltage, impedance,
power, frequency, etc. based on operating parameter, definite time, inverse
time, stepped etc. as per operating characteristic, logic wise such as
differential, over fluxing etc.
Station Battery : A Station battery containing a number
of cells accumulate energy during the
period of availability of A.C supply and discharge at the time when relays
operate so that relevant circuit breaker is tripped.
POWER STATIONS
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