Answer / sudheer

if two generators synchronised and are punning parallel,
the total load divided and generator takes half of the
total load upon it.
some times because of load unbalancing one generator
shifts his total load on second generator and run as a
motor . before this condition the generator is taking load
upon him and now it will became as a load and it will run
as a motor insted of generator.
in this condition the second generator winding can be
damage, so we use reverse power relay. because the
direction changed of power , so we called it reverse
power .

Answer / pundlik wanwe

Generator is normally feeds power to the infinte grid which
is having a number of generators connected.
If by some reson turbine gets tripped but if GCB not get
opened in that case there will be a reverse flow of power
from grid to stator wdg and the generator will behave as a
induction motor. In this case there will be a heating of
rotor end ring and and outer wedges of the same which will
in turn damage the rotor winding. To avoid this reverse
power flow is resricted by tripping the generator on
reverse power flow.

Answer / abdul nazir

Normally reverse power relay is used for generator side.
when ever we will synchronise the generator with grid or
other generator, immediately we will increase the generator
load other wise the generator will take load from the other
side(grid or other generator). So the generator will run as
a motor.
to avoid these conditions,the reverse power relay will act
& trip the generator circuit breaker.

Answer / kk

A reverse power relay is a directional power relay that is
used to monitor the power from a generator running in
parallel with another generator or the utility. The function
of the reverse power relay is to prevent a reverse power
condition in which power flows from the bus bar into the
generator. This condition can occur when there is a failure
in the prime mover such as an engine or a turbine which
drives the generator.
The failure can be caused to a starvation of fuel in the
prime mover, a problem with the speed controller or an other
breakdown. When the prime mover of a generator running in a
synchronized condition fails. There is a condition known as
motoring, where the generator draws power from the bus bar,
runs as a motor and drives the prime mover. This happens as
in a synchronized condition all the generators will have the
same frequency. Any drop in frequency in one generator will
cause the other power sources to pump power into the
generator. The flow of power in the reverse direction is
known as the reverse power relay.

Another cause of reverse power can occur during
synchronization. If the frequency of the machine to be
synchronized is slightly lesser than the bus bar frequency
and the breaker is closed, power will flow from the bus bar
to the machine. Hence, during synchronization(forward),
frequency of the incoming machine is kept slight higher than
that of the bus bar i.e. the synchroscope is made to rotate
in the "Too fast" direction. This ensures that the machine
takes on load as soon as the breaker is closed.

Answer / shambhu sharan prabhat

Suppose generator is synchronysed with grid and is
supplying power to the grid. If suddenly turbine trips and
gcb of generator does not open then there wil be reverse
flow of power from grid to generator stator windings as
generator will be on low potential side.Generator will now
act as induction motor and therewill be a heating of rotor
end rings and wedges damaging the rotor windings also.
Considering turbine, as stop valves are closed and there is
now no cooling media (steamflow ) for rotaing turbine at
synchronous speed there will be overheating of blades
causing damage to last stages of turbine.

Answer / rajendra mane

generator intended to operate
in parallel must have reverse
power protection.
A reverse power relay monitors
he direction of power flowing
between the generator & the
load .If prime mover failure
occured the generator will act
as motor.The reverse power
relay detect this fault & act to
trip the generator circuit
breaker.

Answer / s.m imran alam

  A reverse power relay using semiconductor components is
provided to sense the phase relationship between current
and voltage in an electric circuit and to trip a circuit
breaker controlling that circuit in the event of reverse
power conditions. The reverse power relay comprises an
amplifier and current multivibrator circuit, an amplifier
and potential multivibrator circuit, a comparator circuit,
and a timing and output circuit. Current and voltage
condition signals from the two multivibrator circuit are
compared in the comparator circuit and, if a reverse power
condition exists, an output signal from the timing and
output circuit operates a trip coil which trips the circuit
breaker. The reverse power relay is powered from the same
power supply as a known type of overcurrent trip device.

Answer / sivaraju

if two generators synchronised and are punning parallel,
the total load divided and generator takes half of the
total load upon it.
some times because of load unbalancing one generator
shifts his total load on second generator and run as a
motor . before this condition the generator is taking load
upon him and now it will became as a load and it will run
as a motor insted of generator.
in this condition the second generator winding can be
damage, so we use reverse power relay. because the
direction changed of power , so we called it reverse

Answer / edwin

generator intended to operate
in parallel must have reverse
power protection.
A reverse power relay monitors
the direction of power flowing
between the generator & the
bus.If prime mover failure
occured the generator main MCCB did trip/ open it will act
as a motor.The reverse power
relay detect this fault & act to
trip the generator circuit
breaker

Answer / sivagurusgs

Suppose if there is any problem in excitation voltage the
generator will take power from Grid side. that is current
angle will be shifted from 180 degree. At that time this
relay is used to Trip this function and isolate the equipments.

what is meant by vector group in transformers? wy we r using that?

1 Answers  

Why do we mostly prefer to generate and distribute electricity in 3 phase and not in 4 phase or 5 phase?

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