Answer / sath

relays are classified into

under current, voltage, power relay,
over current, voltage, power relay,
distance relay,
directional or reverse current relay,
differential relay.
based on any one of the catageries the relay will
operate.Based on the application of the motor relay will
selected.

These are the device which direct the abnormal condition in
the electrical system by measuring the electrical quantity
like voltage, current, frequency, phase angle.Due the
abnormal condition any one of the above mentioned values
are changed.After detecting the fault relay will complete
the trip circuit and energised the circuit breaker.Hence
isolate the fault current.

Answer / ramesh

1st part of the Question is not clear...

Now come to the function of the relay...

It is a device which continuously compares the electrical
quantities in a line (i.e. voltage, current etc.. different
types of relays are provided for different purposes) which
are the output of sensing devices like INSTRUMENT
TRANSFORMERS (CTs & PTs) and if these values in line are
exceeded or reduced to the SET VALUE in the relay (this set
value can be said as normal operating values beyond/below
which the load/consumers connected to the line will not be
safe or equipment gets damaged for different reasons...).
If there is any difference in these two values (values from
the line and set values in the relay) relay senses this
abnormality and sends a signal to the circuitbreaker to
break the circuit. So these abnormal values will not be
reached to the end users/loads. So they are safe....
Is it clear...

Answer / santhoshkumar

single phasing preventer. If it happens motor winding may
get burn

If we says that current is flow only when there is closed path & neutral work as a return path for the same. Then how circuit is closed in three phase as no neutral available ??

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