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Commentator

Join Date: Oct 2013
Posts: 62

Diesel under voltage

09/20/2022 4:13 AM

Dear all

Emergency diesel generator (400KVA,400V,1500RPM)when it starting up. the voltage

in three phase get to 350V then suddenly start to fall until generator become under

voltage trip,the speed its ok (1500RPM).please what are the possible causes for

this problem?

thanks for all

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#1

Re: Diesel under voltage

09/20/2022 4:32 AM

One of the solutions involves getting the original equipment manufacturer's Commissioning Engineer involved. Telephone?

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#2

Re: Diesel under voltage

09/20/2022 4:45 AM

What sort of load is connected?

What is the make and model number of the generator?

How old is it? Has it ever worked OK?

Does the diesel motor continue to run, when the generator side shuts down?

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Commentator

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#3
In reply to #2

Re: Diesel under voltage

09/20/2022 5:26 AM

diesel was no load,

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Guru

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#4

Re: Diesel under voltage

09/20/2022 8:04 AM

Maybe it's the exciter circuit or voltage regulator. Check your manual.

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#5

Re: Diesel under voltage

09/20/2022 9:34 AM

..."The most common causes of a generator producing no power are the loss of residual magnetism in the alternator and a failed AVR or another excitation component. If the voltage is around 50-70V on each phase, then it is likely the AVR needs replacement. if the voltage is 0-5V per phase, it is probably a loss of residual magnetism.

If your generator doesn't have a PMG system, then it is almost certainly a a self-excited alternator. These rely on the residual magnetism of the alternator, left from it being run previously, to build up its initial voltage. "...

https://support.wellandpower.net/hc/en-us/articles/360017916958-What-causes-a-generator-to-not-produce-any-power-How-can-I-fix-it-

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Commentator

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#6
In reply to #5

Re: Diesel under voltage

09/20/2022 5:22 PM

our generator have PMG, the voltage get to 350V in all three phase at no load,then the

voltage suddenly fall down gradually also in three phase then the generator shut down

because under voltage protection

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#7
In reply to #6

Re: Diesel under voltage

09/20/2022 9:48 PM

I would say you probably have a component failing in the PMG AVR system....

....but I'm just guessing

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#9
In reply to #6

Re: Diesel under voltage

09/21/2022 9:28 PM

There is a problem with the technical terms of your translation. You have a generator coupled to an engine.The generator shuts down implies the main circuit breaker opens, which then implies you have had load on the machine. There is no reason to shut down the prime mover, engine, on low generator voltage. So it would help if you clarified your terms, because they don’t make sense, what you report. Also, the make & model of the machine may help remote troubleshooting that you desire. It is likely a problem related to heat in your regulator package, it works while cold, but as it heats up, a small component could fail, even a bypass capacitor $0.25 part, could bias the regulator down to zero. Measure the excitation current with a dc clamp on ammeter, for example, and work from there.

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#10
In reply to #9

Re: Diesel under voltage

09/22/2022 5:21 AM

GA

ASSER

"in three phase get to 350V then suddenly start to fall until generator become under voltage"

What are the time scales for the above?

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#8

Re: Diesel under voltage

09/21/2022 2:58 AM

The voltage suppression on reaching 350V is probably triggered by a fault in main exciter windings that strikes an arc when the DC excitation voltage reaches a certain value.

It could also be that there is a short at 400V terminals / connections / CB / bus that is introduced during maintenance (prior to running up the DG set) and forgotten.

Try to check one by one and eliminate. If need be, take the OEM help. EDG set is a critical equipment and needs that much respect and care, if not more.

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