Generator Load Sharing

Are you sure the zero load speed of the generators are set correctly ?

Suppose the zero load speed of the generator 4 is highr than others, then the other generators starts working as motors, till the droop of the generator 4 (by taking extra load) brings the system to the un-balanced loding pattern ?

Just a thought

Check the droop characteristics of the generators.

May be after the load (>2/3) the droops are dissimilar - Gen 4 has a flatter curve so it is trying to compensate for the others.

The suggestions by SB to check the droop settings on each machine and the no load speed setting are right on.

If the droop setting is smaller for #4 it will load faster than the other machines causing it to pickup proportionately more of the system load as load is applied and the speed droops below setpoint. There is also a droop setting in the AVR which could be causing you trouble. If the droop setting on one machine's voltage regulator is appreciably tighter than the others it will load picking up KVARs faster as the system load increases.

My guess is that you will find your trouble in either the AVR settings or Speed governor settings. If the settings are correct then you may have a malfunction in one or the other of those systems or an operator with fiddly fingers.

It would also be a good idea to make certain that the AVR for #4 is set up for droop or parallel operation.

Work Safe!
TT3

Thank you TT3 for Your suggestions,

we are gona try to see droop setting on each AVR, our AVR is analog so is very hard to put the switch on each AVR at same position.

The droop setting on AVR is 5% for full load, our frequency is 50Hz, and all AVR are set up for droop mode. Hopefully without ' fiddly fingers '.

Does anybody had come kind of experience with the Basler Electric, digital voltage regulator DECS-100? We are planning ti install them.

While re-reading your original post, I noticed that the machines track up to a certain load. If I understand correctly, past that load, #4 begins to pickup more of the KVAr leading to it going into current limiting before the others. This could be due to a metering problem caused by a faulty CT. I have seen similar problems before. In my case it was found by using a clamp on Amp meter to read the CT currents for each phase and comparing them to measurements made on the leads leaving the generator. IF you have other CTs on the same phases, it is probably safer to measure the current on the second set of CTs and compare them to the CTs that provide current measurement to the AVR.

A CT replacement is usually a lot cheaper than an AVR retrofit.

I suppose a PT problem could lead to a similar problem but that is not what was found on the particular job I was working to resolve. While you have the tools out and the safety gear on, it might be a good idea to check that side of things also.

Work Safe!
TT3

When you said "gen.No.4 is trying to take most of the load", I am assuming it is KW load, however I don't understand what you meant by "sharing the kW is no problem but the kVAr is".

Though I am not an expert of Woodward 2301A but it seems that the governor of the 4^th generator is set for Isochronous and other 3 generators are set for Droop. You can verify Droop/Isochronous setting details from the Woodward 2301A manual.

If the droop setting of a generator is Isochronous, it automatically shares the total changes of load. The load sharing of the generators with Droop setting has to be done with manual intervention with increase/decrease speed control switch or a separate load sharing system.

I think the droop setting of the 4 th Machine is not matching with other machines for loads upto 66 %.

May be settings are alright for loads beyond 66 %.

Pls confirm #4 is under Droop Mode.

- make sure droop setting for all gensets are same.

- there should be a load gain potentialmeter besides the droop potentialmeter. Make sure the load gain setting should be similar with others.

My suggesttion:

apply full load for the genset and measure the dc voltage at terminal load signal. This must be done for only 1 genset. Then using the same method to adjust another 3 genset.

At full load, load signal should read 6Vdc. If unable to reach 6v, try to adjust load gain until load signal reach 6Vdc. If there is impossible to apply full load to genset, you may try to get 50% load and the load signal should be adjusted to get 3Vdc.

This is to ensure all the genset having the load capacity.

If you have solved the problem, can you share your solution?