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Join Date: May 2013
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DG Generator Unable to Run Machines

04/15/2014 8:58 AM

On running 125 KVA Swan DG set, there is a problem of no output voltage. The alternator has no other electronic components other than diodes and AVR. I changed the AVR available in the market which can be used for upto 500 KVA alternator. On running the DG set, I got the rated output voltage of about 230V per phase at no load.The DC voltage at AVR terminal F+ and F- gives about 12 V at no load.

But,as the 3-phase welding machine is tried to run,the voltage as shown in the voltmeter drops and fluctuates and the machine does not turn on. While trying to turn on a grinder,the grinder produces a noise and stops.

This shows that the load is unable to draw current from the alternator.

Three different AVRs have been changed but the result is the same.One of the AVRs is attached herewith.

So, what might be the problem? Is any faulty in field winding or other windings can cause such problem? Or, any problem in excitation can cause such problem?

Why the alternator cannot deliver current though it gives rated output voltage.

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#1

Re: DG Generator Unable to Run Machines

04/15/2014 9:33 AM

What did the folks at Swan say when you called them?

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#2

Re: DG Generator Unable to Run Machines

04/15/2014 12:32 PM

Please state the insulation and continuity readings taken on the windings.

With the thing not rotating and disconnected from the load yet "ready to rock" when the diesel starts up, when one measures ohms at the output terminals, please state the readings found.

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#3

Re: DG Generator Unable to Run Machines

04/16/2014 2:21 AM

you hav to check the excitation circuit and diode ...due to loose connection ,dry sold on diode,are possible conditions and check on output and their connection ...and weather the DG sets are taking load ..or it hav problem on actatur..or on excitation or on out put circuit...most probable problem is ...loose connection...or short circuit or leakage problems...

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#4

Re: DG Generator Unable to Run Machines

04/16/2014 4:24 AM

Since no indication of the voltage when load is applied, try not to have guess work. the best way to determine whether diode is faulty or winding problem, use a 12 Volts battery and connect it to the excitation wire, and start the genset it should produce full voltage from there you can safely says the diodes are ok, if voltage is there check all the phase voltage to be balance( this can also determine health of winding). All others can be obtain from manual.

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#5

Re: DG Generator Unable to Run Machines

04/16/2014 9:47 AM

If you are sure that 12 volts is the correct level of excitation voltage for maximum generator output I would start with the brushes and brush rigging.

Look for worn out brush rigging, improper brush spring pressure, and loose connections.

If I did not find anything irregular with these components I would then check the diodes for a high resistance condition across the anode-to-cathode junction.

If none of the above yields a viable solution/answer I would surge test the generator windings and armature using an appropriate test set.

If you are not experienced in perfroming the surge test or any other part of this testing, it would be in your best interest to contact Swan field services and get a technician on site to help.

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#6
In reply to #5

Re: DG Generator Unable to Run Machines

04/16/2014 10:31 AM

Surely this is self exciting and brushless....

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Guru

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#7
In reply to #6

Re: DG Generator Unable to Run Machines

04/16/2014 10:43 AM

Yes, good point as it could well be but maybe not.

I did not see where/if the OP stated how old or what type of DG it is.

If it is a "brushless" unit then I would suggest:

1. Test the diodes for a high resistance and/or shorted junction condition.

2. Perform a surge test on the excitation winding(s) and the generator windings.

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