# Diesel Generator MCCB tripping after few minutes with NO LOAD



## Bird dog (Oct 27, 2015)

What kind of genset is it? FG Wilson seemed to have great customer support in that part of the world. Do you have a good set of manuals? Under what conditions will the main breaker on the genset trip? You may have to have a test set up on the genset as it operates & sit there and watch it until it trips. Are all the parameters set properly? You may have a bad sensor.


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## RePhase277 (Feb 5, 2008)

If multiple generators are connected, I would suggest you isolate the generator in question and test it by itself. If generators are in parallel, they absolutely MUST be in phase, otherwise the larger generator will pull the smaller one as a motor. This means current will be supplied to the set and it might be enough to trip the overcurrent.


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## Southeast Power (Jan 18, 2009)

RePhase277 said:


> If multiple generators are connected, I would suggest you isolate the generator in question and test it by itself. If generators are in parallel, they absolutely MUST be in phase, otherwise the larger generator will pull the smaller one as a motor. This means current will be supplied to the set and it might be enough to trip the overcurrent.


All was a great mystery until the word grid was read.
That's a game changer.


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## syed.nifty (Mar 16, 2014)

Thanks everyone for feedback.
Sorry for late reply as i was busy at work. 
The generator configuration is 220 kw ,450 volts and 60 hz. . Its model number is scania dsi9. There is AVR connected to it . There is reverse power relay and over current relay. Finally generator breaker and also there engine controller. This engine controller is okay as there is no error indications in it. 
Now i have tested it alone. It runs for few minutes after breaker closed and then trips. There is no overcurrent . Then i connected parralel the another generator to the grid which is sharing same load after syncing them. Then still the problematic generator trips. There is no over current or low frequency . 
I have doubt with only the breaker which might tripping. I will need to test this breaker.


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## Southeast Power (Jan 18, 2009)

syed.nifty said:


> Thanks everyone for feedback.
> Sorry for late reply as i was busy at work.
> The generator configuration is 220 kw ,450 volts and 60 hz. . Its model number is scania dsi9. There is AVR connected to it . There is reverse power relay and over current relay. Finally generator breaker and also there engine controller. This engine controller is okay as there is no error indications in it.
> Now i have tested it alone. It runs for few minutes after breaker closed and then trips. There is no overcurrent . Then i connected parralel the another generator to the grid which is sharing same load after syncing them. Then still the problematic generator trips. There is no over current or low frequency .
> I have doubt with only the breaker which might tripping. I will need to test this breaker.


Syed,
Can you post the breaker make and model? We have at least two breaker gurus here on the forum


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## syed.nifty (Mar 16, 2014)

I dont have the model number yet but the photos. I will try to find out the details.


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## telsa (May 22, 2015)

Those CTs -- any numbers off of them ?


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## RePhase277 (Feb 5, 2008)

Does it trip with no load connected at all? If so, your breaker needs to be checked.


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## syed.nifty (Mar 16, 2014)

Yes it trips under no load as well after the breaker is closed. I will have to check details of those CT.
Is there anyways to test the breaker to confirm its faulty.


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## Bird dog (Oct 27, 2015)

Syed, we are all in the US. There is a Scania dealer in Dubai. If they have a good genset department, might help if you gave them a friendly call for advice and confirm what needs to be done.


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## active1 (Dec 29, 2009)

The label seems to have 220-240v @ 50-60 htz or 208-277 @ 60 htz.
It does not have 480v or your 450v listed, but can't see the entire.

Sometimes there are safety switches on doors covering energized areas that when opened trip the shunt in the breaker. If some screws are missing or not tightened with a tool, they can rattle loose to trip the safety. The E-stop would trip the breaker. 

Loose / bad connections on the line, load or crimps will cause the breaker to prematurely overheat and trip. An IR camera helps identify overheating spots in and around the breaker.


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## RePhase277 (Feb 5, 2008)

I didn't even look at the breaker pics... yeah it might be freaking out because it's seeing a voltage higher than its rated for.


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