Generator Voltage Dip 2

[Gene1203]

Our client reported that they are experiencing an unpredictable and irregular voltage dip with their power supply. They have their own power plant using diesel engine generators. On a particular single-unit operation, they reported that the dip occurs once a month, after two months and twice a month. The genset is still new. It was a brand new unit started-up and operated 6 months ago. The dip occurs only on this new unit.

The voltage dip, according to the report, occurs for a duration of about one second. However, the motor loads stopped/tripped off. They observed that the voltage meter almost registered "zero" during the dip and recovers. One report indicated that after the recovery of the voltage, the meters registered 58Hz and 450V. (The system is 3-phase, 480V, 60Hz.)

Has anybody experienced such occurrence? What is/are the possible causes of this dip?

Any inputs are appreciated. Thanks.

 

[RAMConsult]

I would start monitoring the voltage regulator/excitation system/field current for intermittent operation. If voltage goes to zero on all three phases it may be an intermittent open in the field circuit; easy to find with a recording ammeter & voltmeter if there are brushes. Intermittents are frustrating to chase, usually they become permanent at the worst possible moment.

 

[Gene1203]

The generator is brushless.

 

[e5fornow]

I have had this problem before, usually the cause is the voltage regulator is losing power. I would check the fuses and fuse holders first. Pay attention to the PM fuses that power the regulator and also the sensing input fuses. If you do not find any loose connections or bad fuses. I would replace the voltage regulator.

 

[Gene1203]

RAMconsult and e5fornow:

Thank you very much for the insights. I will follow your advice. Will let you know the results. I really appreciate it.

 

[Sett]

Hi Gene!

I have some question: How many generators are connected?
There are feeding the same bus?

I said this because, when one generator (connected in parallel with others generators)loose (for any reason) the excitation current; the terminal voltage do not fall to zero immediatly, Why? because the gen when loose the excitation, behave like a Induction Generator. I mean the generator will absorb the reactive power that need and the speed down (slip).

Excuse my English!

Regards!

 

[jbartos]

Suggestion: It may be a good idea to use the more time effective approach, i.e. record voltages and currents on the generator output.

 

[Gene1203]

Sett:

The unit in question is running as single unit - not synchronized with the other units. There are 3 units one of which is new where the problem occurs. Synchronizing is used when transferring the load from one unit to another.

jbartos:

I agree with you. Actually, the operators are logging the volts, amps and kw hourly. However, since the dip as reported is unpredictable and lasts only for a second, they have no record on the exact values during the actual dip.

Thanks to both of you.

 

[EddyEE]

Recording/logging parameters might prove the problem but may not solve it. And, waiting for the problem to happen again is not a good idea at all. Since you have 3 units (assuming similar), then you must have spare voltage regulator, rectifier assembly, potentiometer, fuse, etc. Why not use them? If you don't have, then buy. Replacing a suspected defective part might solve it.

Regards

 

[RAgrawal]

Voltage dip is generator operating in isolation indicates the problem in Field circuit, as already explained by ohtres. Dont you have recording charts / devices, which record parameters on continuous basis automatically? because with this, apart fro the routine check, atleast you can pin point the problem at the time of occurance.

 

[edison123]

Gene1203,

You should also check the rotating rectifier diodes and also the semicondutor fuses, if any in that ckt for any damages due to dynamic forces.

 

[EddyEE]

Gene1203,

Are you the supplier of this unit? I suppose this unit is still under warranty. Then, the supplier should provide the services to determine the problem and the appropriate solution.

In addition to previous suggestions, I noted from the information you provided, "One report indicated that after the recovery of the voltage, the meters registered 58Hz and 450V".

If the problem is on electrical/generator side, the frequency/speed of the engine should have remained stable during voltage dip. Intermittent overloading or high starting currents may cause the voltage to dip more so if the engine can't respond fast enough. Please check engine side also, governor gain setting, fuel lines, etc. And be sure no overloading.

Regards