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Re: CAT SR4 Voltage Regulation Problems

To properly diagnose this we'd need a lot more information.

 

On Gen 2, what AVR was used to replace the VR3?

 

While in parallel, how is VAR sharing done, in cross current or droop?

 

Does each unit have its own Woodward synchronizer? What kind and how connected, like an SPM-A with contact outputs to an MOP or what?

 

Its rare the have an AVR problem cause a diode fault, unless it happens while the unit is paralleled and results in a loss of excitation.. Was a set of generator electrical tests done or were the diodes just changed out?

 

On your interface, are these units equipped with EMCP II control panels?  Are you using a CIM (Customer Interface Module) to interface with your BAS system?  It may be that the CIM module if used is losing comms signal, this causes all the outputs to "flash", indicating the comms loss issue.

 

Some more details could get you better answers, MikeL. 

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CAT SR4 Voltage Regulation Problems

I work at a data that is backed up by 3 CAT 3516 diesel engines with SR4 generators and VR3 voltage regulators.  Two years ago in our 2nd generator we experienced a voltage regulation issue that was resolved by replacing the voltage regulator.  We are now again having voltage regulation problems.  After the problem started again a CAT service technician determined that one set of diodes was bad (a known issues for that model) and the problem seemed to have been resolved.  A little over a month later the problem has returned.  Here's the scenario:
While load bank testing, the generators are given a start signal to come online and the first one to 90% rated frequency and voltage closes to the bus and the other 2 sync through a Woodard synchonizer.  During this time generators 1 and 3 come online and properly sync.  Generator 2 however ramps up to 600V then drops to well below 480V.  The breaker for the generator closes at approximately the same time as generator 1 and 2, staying closed with the engine continuing to run.  The generator cubicle panel shows an over crank alarm and through our building automation system we recieve a day tank high fuel (although we have no day tanks), low oil pressure, and high water temp alarms.  
Has anyone had problems similar to this?