Generator Issue - 22KW Motor and 1500 RPM on Steam Engine

Pardon my ingnorance, i am perplexed. i thought steam turbines DRIVE generators which produce electricity. Here you are using a motor to drive a turbine? Assuming you will explain and i will understand...

OK, 18A @ 380V implies a 10HP/7.5kW motor. The generator is 1000kW. It probably should not even notice this piddly little motor.

However you do have genuine problems. So let me ask :

• Is the phase sequence correct?

• Generator and mains neutrals should be different, and the changeover switchgear should be 4-pole. Are they?
  

When you remove the steam from a Turbine, the Turbine is very hot. The rotor will sag while cooling, so to prevent this, the turbine is turned for sometimes many hours till completely cold.....

I think that is the motor he is talking about....

Oh thank you. It is clear now, i learnt something new.

Perhaps the OP thought this stupid guy is not worth responding to, no issue there

I am sure he was not being rude.....

Being extremely charitable by nature, i endorse your view. But i am sure he has still not read my post

I'm sure he read it - but the first bit indicates you do not have great familiarity with the installation - so the two end observations may not be pertinent. They are - but still a doubt would exist - which is why others have asked the same questions.

Ah, ok. i see what you mean. Yes, that is what i would have done myself, i guess, to be honest. Thanks for opening my eyes

this can't be happen for a motor of such small specs but may be your generator cannot bear the starting surge produce by this motor while running on government source you are connected to a large system thats why starting surges of motors like these doesn't makes any difference.you should check this motor separtely on runing on generator donot atach any other load to generator,in this way you will come to know wheather your generator is cabale for running this load or not.

It sounds to me you may have the phases on one supply miss-sequenced compared to the other. Meaning the motor tries to reverse when switched over. This would "overload after 5 sec", also cause the "abnormal sound" in the 1MW generator, due to the massive current drawn. Also major switch contact sparking so short life.

See if the motor slows or stops when switched. If so, swap two lines on generator feed.

Alternatively; you are not completely switching out the other supply (and the generator is out of sync with the government supply) and still fully or partly connected.

Check the switch over circuit diagram is fully switching out the other supply and check that the diagram has been followed in the actual wiring.

However, I may not be understanding your question, so if the above is not answering, please explain further.

thanx for all of your interest guys.

Actually the turning gear motor is required for turning the turbine shaft when it is stopped or it is moving upto 169 RPM. This is necessary for the turbine to make its shaft rotating because of high temperature of 525 degree celsius and 96 Bar Steam Pressure that the turbine takes while running on load. If the turbine shaft is not being rotated then there is a fear of jamming it or sticking the rotor to the stator of the generator coupled to the turbine. I think it will clear all of your queries. We are using Siemens Sirius softstarter 3RW3036-1AB14 of 22 KW rating. The supply sequence is right and we have checked that since for the first try the motor run smoothly. In the second try the problem occurred and I contacted you.

For further discussion I will wait for your feedback and queries.

Best Regards,

How long between tries? Enough for some maintenance on the standby generator to maybe change output wiring?

Or has starter failed on one phase on alternate supply - so trying to run on 2 not 3 phase?

Dear 34Point5,

Actually the government source gave no problem and the motor was running smoothly. On one night 2 days before the government supply failed and the back up supply of 1MW generator was there to run the same motor. But this motor used to trip again and again in that night shift. We came in the morning and traced back the actual problem. When we tried to run the motor on the generator for the first time it run smoothly taking only 18.5 A load.But after sometimes we stopped it. In the second try it tripped after 5 sec and the generator sound was also changed.The time between the two tries was hardly 3 minutes. We asked the generator's operator to check it from the maintenance point of view to change any air filter,fuel filter or oil filter. Then from our side we checked the soft starter.It used to trip the motor again and again. The motor was overheated and burnt. We replaced it with a new one. Then we checked it again. Increased the setting of overload. After that it was working ok. The previous setting was 35A now it is 40A.

I hope the answer of your question is received.

Best Regards,

Ok, this now suggests standby generator is "hunting" due to small load (11 kW vs 1MW) and resonance with load.

This surging gives a slave motor a hard time; 50 Hz = go 1500 rpm, 70Hz go 2100 rpm. Can't follow, so it burns out.

This may be a generator governor problem (only 10% of duty)

Make the governor less sensitive or put more load on generator to make the output more stable.

Amps can be measured "per phase" or total. 18 per phase is equal to about 31 amps total. The extra amps may be due to generator surging. If so, you must address that or many motors will die.

Dear 34Point5,

What do you mean by governor less sensitive? and 10 percent duty?Does it mean that the generator's abnormal sound on load is due to the low load on it.

Best Regards,

Very few governors respond proportionately to light loads changes. They expect a big load to happen and over react to a small change. In this below 30% load zone you can get "surge" - over power then under power...... "varoom.. die... varoom"

It can synchronize sympathetically with the mechanical inertia's and make serious problems in frequency changes. Together they can make very 'harsh' sounds.

But I can't hear what you say is "abnormal".

Try locking the governor on the generator and see if it all settles out to 'normal'.

You don't need to be on an exact Hz for this - I.e. steady within ±10Hz is ok for the motor.

If this solves; add a resistive load to the motor feed to break the 'resonance' of governor and mechanical inertia. Try, say lifting load to 20% of generator output, but do it so if another unit comes on line, that the ballast load switches out.