Answer / deepak patidar

When the load on the generator becomes unbalanced, negative
phase sequence currents flows. The negative sequence
components produce a rotating magnetic field which rotates
at synchronous speed in a direction opposite to the
direction of rotor field. Hence effectively the relative
speed between the two is double the synchronous speed. Thus
double frequency currents are induced in the rotor. These
currents cause sever heating of the rotor and can cause
damage to the rotor. The unbalanced stator currents also
cause sever vibration and heating of stator. Hence it is
necessary to provide the negative sequence protection to
the generators against the unbalanced load condition.

The negative phase sequence filter alongwith the
overcurrent relay provides the necessary protection against
the unbalanced loads.

Answer / alee xain

We use a negative sequence filter to filter out negative
sequence component, its characteristics are similar to that
of Inverse overcurrent or over voltage relay. we operate
such a relay on the basis of these negative sequence
component of fault current.

Answer / j.venkatesan

In case of the numeric relay the negative phase sequence
current is calculated bu NPS=Ir+a2Iy+aIb.
Where a is an 120 degree phase shift opeator.
This calculated NPS is used for operation of the relay.

Answer / 32r

deeepak patidar the questin is regarding syn. motor so pls make it clear

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