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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
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