ONE of my diesel generator 1400kva trips down, showing the reverse power 200kw indication during synch... why is that so ?

Hussain,

If it had 200kW of reverse power then either the prime mover was turning too slow or the it was an out of phase closure.

Was this the first time the machine was synced to the grid, was it after any kind of maintenance, or was it just a routine sync gone bad? Assuming that all the instrumentation had the correct polarities; if it was an autosync then it was poor settings, if it was manual sync then it was operator error.

Alan

Check connections of CT, if that is ok.
while synchronizing momentary there are chances of generator act as motor because of voltage level, voltage selection to be done before synchronizing.

Satish,

Differences in voltage cause reactive current (kVAR) to flow, real power (kW) flows due to difference in phase/torque angle and/or frequency/speed.

Alan

when i say voltage i mean its phase angle, frequency and magnitude

sounds like manual error went bad. this should never happen.

Hard to imagine the prime mover was not at sync speed when the sync was attempted, so the likely issue is phase. If the phase angle error is greater than 90 degrees, then your generator is in the motoring quadrant, not the generating quadrant.

ALan
its totally a new generator 1400 kva diesel Perkin .... and one of the operator operated it for 2nd time ....

if you are using the Auto synchronizer relay then either relay setting is not correct or some issue with relay/relay wiring.

If it done by manual.....lets take one relevant example .Accepted Angle selection for the a synchronous is +_30 degree means 60 degree.

Suppose you have difference in frequency between the grid and DG is 10mHz,means one vector will be in line with another vector at 100sec.

Time window, for which vectors are meeting CB closing criterion of ±30° = 60°, are valid for a period of 16.67s.
CB will take 20 ms(approx.) in closing ,means that actual closing command is issued when vector have come closer to for additional 7.2°, what means that at the moment when manual system have issued a command to close the CB, voltages may be at ±22.8° away.

Because of this 22.8 degree it is technically possible to have a reverse active power flow during manual synchronization .

To avoid this condition ,operator need to do some calculation before issue any close command or he must try to close the CB when the angle difference between the voltage is less than 10degree.
I have taken 30 degree in my example as it v common setting for the A synchronous network auto synchronizer relay.