Synchronizing Checks
Synchronizing Checks
(OP)
We tried this idea to verify synchronizing a 15KV 120 MVA generator across an SF6 Breaker. Note: we also did all the usual checks, backfeed etc.
We constructed six metal plates with insulated backs and taped them to the breaker pole frame right next to the insulators on each pole, for each phase, line side and generator side. We ran six wires from the plates outside the enclosure and using a 4 channel oscilloscope we were able to see the waveform at about 4V P-P induced. We were able to see that, when all phases are in phase, the synchroscope was at 12 and the synchronizer was sending the signal to close (breaker close command was disabled)
My question is - good idea or really, really dangerous and stupid?
PS we already did it with two units, OK I admit it, I've done it a few times before, once in a 230kV yard.
We constructed six metal plates with insulated backs and taped them to the breaker pole frame right next to the insulators on each pole, for each phase, line side and generator side. We ran six wires from the plates outside the enclosure and using a 4 channel oscilloscope we were able to see the waveform at about 4V P-P induced. We were able to see that, when all phases are in phase, the synchroscope was at 12 and the synchronizer was sending the signal to close (breaker close command was disabled)
My question is - good idea or really, really dangerous and stupid?
PS we already did it with two units, OK I admit it, I've done it a few times before, once in a 230kV yard.





RE: Synchronizing Checks
An alternative method for checking synchronisers:
Check the phase rotation on the bus VT and record for later comparison (see note below if no 3-phase VT).
Close the generator onto a dead bus, and confirm that with the breaker closed, the synchroscope and any sync-check relays etc are showing 12 o'clock/synchronised. Check the phase rotation on the same bus VT as previous and confirm that it is the same as the first check.
Rack the breaker into the test position (or if not possible, disable the close command in some other way) and run through a dummy sync. Check that the synchroniser does sensible things (raises/lowers the speed and voltage appropriately, closes the breaker at the right phase angle and slip frequency, etc). If you have any sync-checks, etc, this is a good time to confirm that they properly block a close signal as well.
Rack the breaker into the connected position and synchronise the unit. Your unit is now online and your synchroniser is commissioned.
Note, if a three-phase VT is not available on the bus, or if the bus cannot be taken out of service, it is also acceptable to remove the stator links and back-energise the generator cables etc from the bus. The generator 3-phase VT is then used for phase rotation comparison.
This method is not affected by VT wiring errors, and does not expose test personnel to anything more dangerous than VT secondary voltage.
RE: Synchronizing Checks
RE: Synchronizing Checks
I like very much the method of checking actual voltages phase angles across the breaker that will make the final closure. That gives very good safety in the matter of taking possible PT wiring errors out of the picture as they relate to out of sync closures.
As for safety of persons using this method, that would depend on insulation methods and creep and flash-over distances. Could be very good, could be bad. Not enough information as to the physical details.
I will be filing this method away in my memory under possible test methods. Thanks for the tip.
Bill
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"Why not the best?"
Jimmy Carter
RE: Synchronizing Checks
RE: Synchronizing Checks