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Bisasa
Member

Join Date: Dec 2007
Posts: 7

Back-up Generator Problem

12/03/2007 8:10 AM

We have installed a back up generator.

We are running into following problem.

When we put the load on the whole system is going down. All is working fine during the testing stages. We have 100 KW Generator, we have 200AMP ATS. We are brining 200 AMPs from the main power into the ATS. From there we are going into 200AMP 277/480 panel. This panel is feeding two transformers one is 45KVA and the other is 75KVA. When we cut the main power off, the system is going for about 10 sec. and shutting down. The generator is giving us an error that the voltage is over. If I shut the 75KVA off, by shutting the breaker from the 277 panel. The system work perfectly, the 45KVA start and all is well on that side, but the when I run the 75KVA by itself the system goes down. The system is fine on the main power both transformers run fine and all is good. But when I shut the main to test generator the problem comes on.
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shogun7
Commentator

Join Date: Dec 2005
Posts: 92
Good Answers: 5
#1

Re: Back-up Generator Problem

12/03/2007 6:43 PM

The generator is too small for the load you seem to need about 40 more KW
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Bisasa
Member

Join Date: Dec 2007
Posts: 7
#4
In reply to #1

Re: Back-up Generator Problem

12/04/2007 6:17 AM

I have 100KW. My calculated load is 35KW.
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Bisasa
Member

Join Date: Dec 2007
Posts: 7
#8
In reply to #1

Re: Back-up Generator Problem

12/04/2007 7:52 AM

My calc load is 35KW. I'm only running a back up battery system, and two 3 Tons air conditioning units. But even if I shut those units off, I'm not running.
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chaterpilar
Power-User

Join Date: Aug 2007
Location: Bhopal India
Posts: 234
Good Answers: 5
#2

Re: Back-up Generator Problem

12/04/2007 1:30 AM

SOme more inputs...What is the load on Generator when it trips.? What is the peak load of your system when it is on Mains? The transformer inrush current could be causing the overcurrent trip. Good luck

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Bisasa
Member

Join Date: Dec 2007
Posts: 7
#5
In reply to #2

Re: Back-up Generator Problem

12/04/2007 6:21 AM

I notice that my rush current is high, but I get that on both transformers. Why I can run on one but not the other? that is when I shut the big transformer, I run fine.
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dgcabasa
Participant

Join Date: Dec 2007
Posts: 2
#3

Re: Back-up Generator Problem

12/04/2007 6:04 AM

Your Generator is not sufficient for this load of 45KVA plus the 75KVA specially during full load condition. Run your Generator below 1000 KW (Gen Capacity), I'm sure it will really fine.
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Bisasa
Member

Join Date: Dec 2007
Posts: 7
#6
In reply to #3

Re: Back-up Generator Problem

12/04/2007 6:24 AM

What do you mean by below 1000 KW? I have 100KW, my calc load is 35 KW.
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Bisasa
Member

Join Date: Dec 2007
Posts: 7
#7
In reply to #3

Re: Back-up Generator Problem

12/04/2007 7:50 AM

What do you mean? I have 100KW
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Anonymous Poster
#10
In reply to #7

Re: Back-up Generator Problem

12/04/2007 1:34 PM

Sorry....I mean below 100KW (Not 1000KW)
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CoronaCameraMan
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Join Date: Sep 2007
Location: Sheboygan, WI USA
Posts: 372
Good Answers: 13
#9

Re: Back-up Generator Problem

12/04/2007 10:08 AM

Where does the electrical control power for your ATS come from? Under each of the different modes of operation.

Does this come from one of the transformers?

Please look in the voltage sensing circuit of the ATS when you switch to the alternate configuration.

Electrical systems are sometimes funny that way, they tell you there problem.

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halibutA
Active Contributor

Join Date: Nov 2007
Location: Scotland
Posts: 20
#11

Re: Back-up Generator Problem

12/04/2007 2:30 PM

Your back up generator is far too small for the 75KVA transformer. The inrush current for this transformer can be up to 10x transformer full load current, irrespective of load. I would suspect that either the generator CB current overload, or undervoltage trip is operating on the generator, thus protecting the generator against damage. You could try adjusting the time delay on these trips, but this is not a safe option, just a "get you by" option. The solution is a bigger generator, or some fancy control gear to limit the inrush current. I have heard of control systems that will switch the input phases separately over a short period of time, but you really need the advice and expertise of an electronics/control engineer, of which I am not.
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Bisasa
Member

Join Date: Dec 2007
Posts: 7
#12
In reply to #11

Re: Back-up Generator Problem

12/04/2007 4:05 PM

Yes I found that today. My undervoltage trip, when I applied a load, 100KW. the system kicked in and was fine. But when I drooped the load, the system went down instantly and I got the alarm error. I tried to adjust the stability control, but i could not control it. My rush current was there, I need about 100AMP and I had that, but the voltage was the problem. I contacted the control manufacturer and after many hours of testing, they came to the conclusion that the control is defective and they are sending me a new one.

I hope that will work.

Thank you all for your input. it was great.
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coconutpete
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Hobbies - Fishing - New Member

Join Date: Feb 2007
Location: Suva Fiji Islands
Posts: 229
Good Answers: 3
#13
In reply to #12

Re: Back-up Generator Problem

12/12/2007 12:03 AM

Hopefully this will cure the problem. If it doesnt try connecting the transformers (ie close all switches manually from the generator to the transformers and disconect all load from them to the prior to starting the generator. This will allow the transformers to magnetise slowly as the generator builds up speed. preventing the inrush current. then as long as the load is less than 100 kW you should have no problems

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Users who posted comments:

Anonymous Poster (1); Bisasa (6); chaterpilar (1); coconutpete (1); CoronaCameraMan (1); dgcabasa (1); halibutA (1); shogun7 (1)

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