How Negative Phase Sequence Relay works in case of
Synchronous Motor?

Answer Posted / 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.

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