Gen Current Sharing

Why don't you share a little lot more information. Do you mean KVA or KVAR? What is the shared load amps and how is it divided? Both generators = 230 kw? What have you done to balance the load?

Important point when you will paralleling the sets are same phase rotation, freq and voltage. In freq and voltage not only same value but also droop. This will effect when you already parallel and load, changing in load will cause different loadsharing between gensets if the droop doesn't meet the same level.

Hope this help you

You should have the same rpm,freq.,voltage.these are the importance things for paralleling the generator.But you should use equalizer between the generator to ensure the proper load sharing between both generators.Then you will have nearly equal current.

Check if you can adjust the Voltage Regulator and balance amps with that adjustment on each Gen on line AFTER you get the best you can (look at KW's) with the Speed Regulator like Khi says.

In generator synchronizing we must look on three quantities ie. KW, KVA & KVAR shearing by each generator. If ur KW shearing is ok that means governor is ok, then for KVAR shearing check excitation voltage regulator (AVR) of both generators because for KVAR shearing we increase OR decrease excitation voltage.

If both generators are rated the same 230kW etc, and /or are of the same make, then:

1- Check the AVR settings: there is a DROOP setting usually, (a Potentiometer marked Voltage droop) which will be set the same on both generators. Also, a gain potentiometer, which is used to adjust the voltage gain when the load varies: Also, they must be the same. How:?

a) Run each genset separately and load it to ~75% if possible, and adjust the Voltage gain potentiometer to have the desired voltage without flickering (i.e. the voltage is stable, use an incandescdent lamp to see that it is not changing intensity periodically, or an analog voltmeter and look at the needle vibrations). if too much gain, the voltage will be varying (hunting) with more or less frequency: turn the pot to reduce the period until zero, and a little more. Also, adjust the main voltage pot to have the 440V at no load or low loading.

b) The droop setting: there are usually graduations to help setting. use then to set at the same graduation. Then check how much the voltage on each genset, will drop from no load to full load: It must be the same, otherwise adjust the droop for one of them to match the other.

2- The mechanical governor: They also have a droop setting screw if they are built for parallelling. This will adjust the rpm drop from no load to full load. They should be at the same setting for both engines if they are of the same capacity (similar engines and alternators). To set, run the engines from no load to near full load (~75%)separately and check that they keep the same rpm at each position from no to full. otherwise, adjust the One to match the other. Choice depends on the state of the engines (age and other variables) so that they will droop the same way and the minimum possible from the set Frequency.

If the above is done properly, both engines will share the load kW and kVAR. if the error in loading is +/- <10%, you are OK (you will look at the current Amps differential for that: ex: in your case ~30 to 35A difference).

I hop the above will help. this is not the 1st time in this forum. you can search for parallelling two generators...

Thank you so much for all your valuable info. appreciated very much. We tried to perform all hints, but the fault still persisted. the kw & hz are same both genies during running operation, but I wonder why the difference of current is too high, about 50 amps diff. anyway, we will try more solution.thanks again to all who respond.

One more thing: The Neutral of One machine is to be used preferably. The 2nd machine neutral can be isolated from the load busbar neutral. this might help reducing the excess current circulating ...

If you need to run each genset on its own from time to time, then a neutral switch/contactor should be provided for when the genset is running single.

You do realize that is ± 4.7%

And kW & Hz are the same ....

_{So what are the tolerances on your ammeters, CT's and/or shunts?}

Dear Mr. delta72924,

The Load sharing of Generator, mainly depends upon the VOLTAGE DROOP CHARACTER.

You consider two Generators, of 420 Volts, and same capacity. If 1st Generator Voltage Drop (known as DROOP CHARACTER) from No-Load to Full Load is ( for example) is 20 Volts, and for the 2nd Generator, Voltage Drop is 25 Volts, 1st Generator will share 25/45 = 0.55 or 55% and the 2nd Generator will share 20/25 = 0.444 = 44.4%, or rounded to 45%, to balance Mathematics, as 55+45=100.

The Generator with LESS VOLTAGE DROP, will SHARE MORE LOAD than the other Generator which has High Voltage Drop since the UNDER SYNCHRONISED CONDITION THE VOTAGE DROP at the GENERATOR Terminal SHOULD BE COMMON, for both Alternators which is achieved, by extra load sharing, by the Generator which has Less Voltage Drop from No-Load to Full Load.

This is a simple explanation/answer.

DHAYANANDHAN.S