AC Generator

You said the AVR is working properly. How did you come to that conclusion? I see an apparent contradiction in your statements. Therefore either I misunderstand you or you misunderstand what is actually happening.

Thanks for sharing

I switched the AVR to the other generator as I mentioned there its behaviour is as good as the other. it is maintaining 450 volts in all load conditions. then I swithed the other generators AVR to this one but result was the same i.e voltage drops to 435 volts at 100 kw load

Just trading working circuit boards does not mean the AVR system of a generator is working properly. It only indicates that the problem is probably not the AVR circuit board. Higher rotor winding resistance due to a loose connection, or failing brushes can reduce the maximum exciter current. A break in an isolating bearing can cause a parasitic load on the generator. The load may simply be too heavy for one or all phases causing the magnetic cores to saturate. You could even find that the voltage at the AVR sense point claims that the voltage is fine due to a different wiring path magnetic coupling or just failing output wiring.

You must do some more methodical troubleshooting than just board swapping.

Good Luck

thanks REDFRED

some more intresting facts are here. I started with the checking of exciting circuit componants one by one, then diode assembly then I swaped AVR but it did not work. Then We were having one brand new generator of the same kind. My boss advised to replace that. I replaced brand new generator and was happy that it will work but unfortunately when we run that the same problem was there. Then we decided to check the switchboard instruments and its Breaker. all those are working perfectly. we run two generators in parallel most of the time but with this defect we are unable to do that cause having load sharing problems. So after putting my all efforts I decided to get advice from this forum. Again thanks for understanding such defect.

This makes even less sense to me now. If having one generator ON produces the expected voltage at load then why add a second generator? What protocols or circuitry keep the two generators operating synchronously? If replacing the whole low voltage generator with a factory new identical model produces the exact same undesired result then I doubt there is anything wrong with the generator. More than likely something is wrong in how you are using the generator.

We have a fundamental problem, as demonstrated by this question from the OP.

"Can I use 230 volt 50 hz electric cooking range on 230 volt 60 hz supply."

Not sure OP is highly qualified for electrical work.

as cooking range has resistive load so it does not matter if you use 50 or 60 hz supply.

You obviously had no clue of that when you asked, "Can I use 230 volt 50 hz electric cooking range on 230 volt 60 hz supply. The available ranges in market are mostly 50 hz. I could not find electric cooking range for 60 hz."

Well, if your directions say cook your roast for 60 minutes, you better set the timer for 72 minutes.

The load on your generator can also be responsible for what you are seeing. Run the generator connected to a resistive test load bank and see how the voltage drops or not. You may be looking for a trouble in the generator that is not there.

Thank you for taking intrest in my GEN defect. Once it came to my mind that any load may be cause of this defect but when I run the same load with the other generator that works fine. I mean voltage did not drop and maintain at 450 volts.

You really need to fine someone knowledgeable in troubleshooting/electricity/power-plants/paralleling/gen-sets.

Anything less, your wasting and money.

Are you measuring the terminal voltage by your multimeter, or you are viewing the voltage at the control panel which has some digital meter?

I am wondering maybe if using digital meter at the control panel of the genset has some defect in the voltage sensing circuitary, because you said you have changed the generator and changed the AVR and still having the same problem.

It sounds like there is a problem with the breaker, have you tested the components with IR heat sensing tool....I would look for elevated temp....

You did not mentioned that does the voltage drop to 435 and stay there or it goes back to 450volts. I always find question posted on Diesel genset problems that they do not read it up how an genset works(all answer is in the net). Any problems as suggested should always check the health of the alternators by measuring its DC excitation, amps, volts and the running speed, which will tell a story.

I think we need a clear defination of the problem.You have stated the generator is running separately and then later it is in parallel.How are u running the set.Secondly 174KVa and then you switch to Kw. 174 KVA is abouy 139 KW.Generator name plate rating is what?Normally ratings go as 125, 160,180 kva and not 174 KVA.Is it the load Kva?What are the connected loads.The load and voltage drop occurs automatically or when something is started.Pl clarify so that the problem can be solved.

..........speed control is also in good working condition.

I take it, that by this statement, the gen set is maintaining its correct rpm under all conditions of load and is not dropping at all in speed. Did you check the accuracy of your rev counter. The reason I ask this is there could be a problem with the engine governor.

Also are the Hertz remaining stable or is that inconsistent as well?

Could be the type of load that is causing the trouble!

I know a case where the load that puts a lot harmonics in the system caused this kind of problem. The load was fine on the grid supply but when the load had to be supplied exclusively by the generator the voltage used to dip.

HI, thanks all those shared their experiance and knowlege about AC Generators.today my problem solved. Generator was dropping its terminal voltage from 450 volts to 435 volts at load. Its AVR settings (some pots) was such that it was dropping voltage from noload to ful load by 3.6 percent. when I changed the other generator having same type of AVR that was also dropping the same value of voltage. Then we decided to reset the pots and configured again step by step. we reached the solution.

Pl see one of your replies where you have clearly stated that when u switch the AVR to another Generator it worked well and another AVR swicthed from a diffrernt generator also behaved in the same way ie drop in voltage to435V.If you have adjusted the POT the AVR should have given the same drop when tried on a different generator.Your statements are contradictory.pl clarify.

Both AVRs pots settings were the same. It has S,U,K,T and R47 pots.when I switched the defective generator's avr to the other generator it worked well there. when I put the other generator AVR to this particular generator , It was also droping voltage whereas it was working well on its own gen set.when closely monitored the settings of the pots, that was the same. Then replace the original avr and run the generator first at noload. its noload voltage was 450 volts. then put the 25 percent load and checked the voltage, it droped to 443 volts. I then changed the setting of S pot in lower direction and observed the voltage it changed from 443 to 447 volts and then I changed the setting of U pot a bit and voltage set to 450 volts, then Increased the load to 50, and then 75 percent and observed the terminal voltage which was maintained at 450 volts.After generator was synchronized with other generator and tested the load sharing. Allworked well.

Great work done !!!

You must have adjusted DROOP pot on the AVR, this potentiometer is used for kVAR sharing of the Load between the alternators, when the generators are synchronised.

If you want to run the Gensets in SOLO mode, just put a switch which will short circuit the secondary of the QDCT (Quadrature Droop Current Transformer) connected in W phase of the alternator...

Now the voltage will not droop in SOLO mode, in Sync mode put the switch otherway..