Problem with CHP synchronus generator - help please

[morticelock]

I have a CHP engine with 400 Volt 3 Phase synchronus generator that connects to our main busbars and runs in parallel with the incoming power. This generator has started to give problems, and I am at a loss as to why it is happening or the cause. When I start the CHP, the engine runs up to speed and I can leave it idling (off load) and the alternator is generating 400 Volts, 50 Hz. The synchronising breaker is still off at this stage. The busbar voltage (mains voltage) is also at 400 Volt, 50 Hz. Now when I switch on automatic synchronisation, the synchronisation process starts. After a few seconds, my alternator voltage drops to 350 Volts, but my frequency stays at 50 Hz. The synchronising breaker has not closed at this stage and the generator is still off load. Shortly aftre this, the generator shuts down on undervoltage.
My initial thoughts were maybe a faulty AVR, but the excitation voltage seems normal. The alternator is a Leroy Somer and is fitted with a R452 AVR and R726 PF controller.

Appreciate any help on this.

 

[dpc]

Sounds like the auto-synchronizer may be jacking the voltage down? Does the auto-synch have an interface to the AVR to allow it to adjust the voltage for synchronizing?

I would monitor that signal or pulses during auto-synch to see what is happening.

 

[iop995]

I think it's an error in automatic synchronisation circuit; it sense too high voltage and send to AVR to reduce voltage and this is in conflict with undervoltage monitor circuit. Check generator voltage sensing wires and T2 from R726 PF controller.

 

[catserveng]

The Leroy Somer AVR's seem to have sensitive remote voltage adjust circuits, at least in my experience. I have had a couple of similar issues with LS AVR's interfaced to Woodward DSLC and GCP30 controllers where the voltage bias output over drove (put to high a voltage) into the remote voltage adjust of the AVR, causing it to not respond properly afterwards. As suggested above. take a look at what ever circuit interfaces your automatic synchronizer to the AVR, it if is a voltgae bias output make sure it cannot supply a higer voltage than what the LE AVR is rated for. Also, has any recent work been done that could have caused the interface circuit to be incorrectly reinstalled? Does your synchronizer have a manual raise/lower volts feature you can test the interface before trying to parallel?

Maybe if you provide more details on what synchroniser you have you can get some better help. ALso, is this a new installation? Old installation with new problem? How well did the VAR control work before this problem?

Mike L.

 

[morticelock]

There is a Woodward Synchroniser on this generator, not sure of the model. At home now, so will get more info tomorrow and see what the interface is.

 

[catserveng]

If it is a Woodward SPM or SPM A with voltage matching it is likely working thru motor operated potentiometer. If that is the case details on the MOP would also be helpful, as sometimes problems with them can result in your issue.

Mike L.

 

[morticelock]

The Woodward Synchroniser is an SPM-D10, the only controls being used from the D10 is the raise/lower speed relay (terminals 8,9 & 10). The voltage control terminals (11,12 & 13) are not connected.