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Fluctuating KVAR Reading
Genset doesn't maintain a stable KVAR reading while in parallel


As an upgrade to our power plant which consist of 4 caterpillar 1250KVA gensets, we have added a 850KVA caterpillar genset which we are currently having issues with. All sets get synchronized to a main bus depending on the load (load demand). What is happening is: once the new genset (850KVA) gets synchronized to the bus, its KVAR reading goes crazy and starts hunting. For example if i have 150KW on it, the KVAR reading will be hunting up to 170KVAR+ 170KVAR-.

What we have checked so far is running the genset alone and bringing the load on it up to 100%, and it runs perfect no problems at all. But, when it gets on the bus which usually has a PF of 0.86 while other sets are present on the bus, it makes the reading go havoc. Take the genset (850KVA) out off the bus and everything runs fine, and the KVAR reading is beautifully stable. since the KW reading is all ok... it has to do with the exaction system but exactly what is a mystery.

I've taken the AVR and hooked it to one of the 1250kva gensets, and it ran without any issues. I took the AVR off one of the 1250KVA genset, installed it on the 850KVA and same issue (KVAR hunting). I've done the same exact thing to the synch controller, swapping the controller and still got the same result. This tells that these parts are working perfect. The CT's are outputting a correct reading as this have been confirmed using clamp meters to verify the readings, signal wires has no noise on them and are grounded on one side.

I am unsure of what else can be checked? so what do you guys think?

Thanks in Advance


The most likely problem--given the information provided--is in the metering CT circuit for the newest generator control system. There is something amiss with the polarity of the signals being provided to the new excitation control system.

The "excitation droop compensation" circuit is misfired or reconfigured.

Please write back to let us know what you discover!!!