Answer Posted / vijay
Vector surge relay compares the previous cycle with the
latest. If there is a considerable import or export ( say
20 % ) of the genrator capacity then a sudden disconnection
of the grid supply will cause either a load throw off in
case of export and load on in case of import. This will
cause the generators either underloaded or overloaded (
over accelerated or deaccelerated ) . This loading and
unloading on the generator will shift the cycle of the
genrator by some degrees. If this difference in cycle is
within the trip setting of the relay the relay will
generate a tripping command.
For example
50 HZ frequecy cycle means 50 Cycle / Second
so 1 cycle will take 20 msec
20 msec = 360 deg ( Angle for 1 full cycle )
1 msec = 18 Deg
If the relay setting is at 9 deg means a time delay of 0.5
msec in crossing of previous cycle happen then the relay
will trip.
If the cycle measurement repetation is of 4 cycle then the
relay will compare the previous 4 cycles.
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