We have 2 No. frame 6B generators both connecting to the same grid. occasionally one will not auto sych on the first attempt but will always auto synch on the second attempt (stopped and run up again). Fail to synch has happened on each machine on occasion with the other machine auto synchronising ok. Only once did both machines fail.

We have checked the following:
- auto/manual sych switch in the auto position

- difference in volts <2.2% we have an auto tap changer on our generator transformer limiting difference grid voltage to +/-0.75% from nominal 11.5kV

- difference in freq - grid is generally very stable at 50Hz

- variation in PT's (signaling Mark V) between machines is negligible, variation in two 11.5kV sets of windings of generator transformer is negligible

On the synch control screen on Cimplicity we generally leave the synch mode at 'auto' so our operators do not always note the status of any red lights (permissives not made).

We have noticed that an alarm 'loss of compressor discharge bias' occurs when the auto synch fails but does not occur when auto synch is successful. Does this alarm lead to the 'turbine incomplete sequence' alarm? is this alarm linked to the permissive (red light) 'sequencing sync permit'?

We found some logic that would seem to suggest that if the compressor discharge pressure was lost the control reverted to discharge temperature - could this be responsible for a fail to auto synch (when cold) but allow auto synch on second attempt (when warm)? Is there a flow diagram for this sequence?

Also, the auto synch seems to lock out - is this normal? after how many attempts / how long?

If we wanted the operator to check the status of the permissives prior to synch would it just be a matter of selecting synch mode 'manual' on the synch screen and then check all of the permissives were made/green (except 'auto sync permit') and then select sync mode 'auto' and it should auto synch?

Any advice on this issue would be appreciated as start reliability is critical to us.

Thanks in advance,
David

 

1)Your idea of monitoring the Sync. page to see what may be holding you out is a good one initially.

2) You say all voltages and frequencies are OK but if you can monitor the status of L3SYNC you can be sure that this signal is allowing the Auto Sync to run

3) The Sync. Lockout is a bit of a worry, see if you can check the status of L30AS1 & L30AS2, either of these will cause a Sync. lockout because they see a failure of a TCEA card in the <P> core.

4)Any Diagnostic Alarms at the same time?

5) From software that I have, I cannot see a connection between CPD Bias failure and Auto Sync. Maybe someone else has some experience of this one

6)Drop me an Email to [email protected] and I'll send you some info on Temperature control vs. loss of CPD bias

 

Thanks for your suggestions Bob, we'll follow up on them.

We also had a suggestion from outside control.com that it could be to do with the lube oil system as we had ALARM: 103 AUX LUBE OIL PUMP MOTOR RUNNING indicating that the aux lube oil pump was still running (should stop at 95% full speed when pressure is ok L63QA2L and temperature is ok L26QL) which would prevent signal L3 (Complete sequence) to become '1' and after 30 mins cause the 'incomplete sequence alarm' but we would never run for 30 min without synch due to cost of fuel.

This may also explain the intermittent nature and why the second run up is always successful eg. if the lube oil temperature was insufficient on the first run up.

Any thoughts on this?

I'll email directly to receive the info you have but wanted to continue this thread on control.com for the benefit of others who may have a similar problem.

regards,
David

 

The fault is now resolved. The cause was that the aux lube oil pump command (which comes on along with the lube oil heater if the ambient temperature is low) was still active when the machine was at speed. We modified the logic and used L4QAZ to stop the aux lube oil pump at 95% speed which allowed the conditions for L3 to be satisfied and a successful synch resulted. Thanks to Bob who gave advice on the possible causes.

 

Thanks very much for the feedback!