Over Heating 1000KVA Alternator

Use Thermo vision camera to identify the real source of heat.

Suppose the defect is in the core , it will be identified.

Thorough testing can lead to identify the currect defect

Best wishes

Dear,

The 65 degree centigrade i got by IR gun thermometer.

Thanks for comment

The temperature you described is I suppose to be 65 degrees Celsius. But this is the temperature measured on the surface of the alternator. But in the nameplate, the 65degrees temperature rise is based on the temperature rise which is based on the insulation class of the equipment. Now if the ambient temperature is 30 degrees , then you add this you have 95 degrees. If you can still touch the surface then it is still quite alright.

Now, since you already had it repaired, then it is assumed that it is clean already. So no issue on ventilation and air cooling.

The problem may be elsewhere. Do you have harmonics issue which can be the culprit?

This particular gen set was H class before rewinding and now it is F Class. But I afraid the temp may rise beyond that(65 DC) if loaded!

65 degrees where?? Cooling air exit? Winding buried sensor? Rotor?

Did you rewind stator or rotor? High field current to get normal volts off-load seems like rotor problem at first glance.

65 degrees on the alternator body, and also it is not uniform.. I used IR camera for temp reading.

The rewinding was done only on the Stator.

Also please be informed that this generator is using for stand-by support.

Thanks for Comments..

Since the excitation voltage seems to you higher than similar genset (30V instaed of 11.8V ??), then I would check the Exciter winding at the end of the alternator. If the higher temperature is measured in that area of the body, then more confirmation to check it.

I hope this will help.

Exciter (PMG) stator winding was checked for continuity (resistance values) and found ok. Also the out put from PMG are also balanced and within limit as per the manufacturers document (180V)

You may like to run the generator at no load and monitor the temperature of same point (which has 65 degree rise). If this point still attains high temperature, then it is most probably due to core short. In that case you may like to perform ELCID test and locate the shorted core packet and attempt to repair the same.

If the temperature rise is not high, then you may perform short circuit run from reduced circulating current and then go on increasing the current till limiting temperature is reached. If it is at reduced load then there is problem with cooling of the generator.

I also suspect the core short here. But expert comments were that is a very rare chance. And also the repair will be very costly. Thats why trying to eliminate other probable chances.

Now the only point remaining is rotating diode assy. As it is very within the alternator i couldnt do that till now. What is the chances for diode fault in this case?

Thanks LAA Lucke for comment,

In this case exciter rotor widing are not accessible(correct me if I am wrong). At the non driving end of the genset there is a cover and by opening it the PMG exciter is visible. But only terminals are those of stator (three cables) where I measured the out put of exciter (180V).

I can see the diode assy thru the main alternator terminal box, but being very within, not accessible. Any way if need to test it I need to remove the Alternator from the engine. I couldnt check this when I removed for rewinding.

Yesterday I did a lamp test on AVR as said in the Stamford mannual and found the AVR is healthy.

The main exciter: (1) stator field winding , (2) rotor winding, (3) the rectifierbridge diodes assembly.

The AVR can be OK. The problem is that if the main exciter has a problem in any of its 3 components, it will start to compensate by supplying more current into the stationary exciter field in order to generate a higher voltage in the exciter rotor windings and maintain the same required current into the MAIN alternator rotor field and thus the maintain the Main Output Voltages.

The 1^st item: Exciter Field winding should be accessible, but apart from visual or obvious leak to the body, it is difficult to realise any minor faults within. But on the long run, the winding will deteriorate relatively fast while in use.

The exciter rotor windings and the diode assembly will need physical checks and cannot be checked without removing them out.

If the Main Alternator Rotor Field was faulty, the fault would snowball quickly when running and more so if loaded.

Your best bet is to remove the Alternator and get access to the internals: Exciter windings and diodes.

If you can remove the alternator and slide out the stator body, that will be the easiest way to reach all the components for examination without removing them from the rotor shaft. But I think that you should know or maybe have some manual with instructions.

Hi,

Let me clear one thing, I could check only PMG, not exciter. The exciter stator terminals coming to AVR are checked for correctness of resistance, its ok. To check the exciter further or to check rectifier I need to ditach Alternator again.

hi guys... I'm also facing the same problem.... power g did u solve your problem and what actual the problem...

PowerG may not be checking this thread any more. If you click on PowerG's name (bold text) in his post, you will go to a screen which has "Send PowerG a message" button.