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liukawa
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Join Date: Jun 2009
Location: Singapore
Posts: 36

Grounding Parallel Generators

12/17/2009 1:44 AM

Hi guys,

My customer has just requested me to design a grounding system for his generators.

Basically, he has 6 generators ( 6.6kV) which will operate in parallel.

From his single line diagram and specifications, he wants the grounding to be done indivually for each generator with a NGR of 254 ohms for each generator.

I find it rather costly to have a NGR for each generator.

Therefore, i was thinking of proposing to him to incorporate a neutral busbar to connect all the 6 generators and from the neutral busbar connect to a common NGR panel .

Will it be possible for me to design a common NGR panel instead? What will be the value of this NGR then in this case?

Also, what are the pros and cons of indiviual grounding of each generator versus a common NGR for all 6 generators?

Would really appreciate if any kind soul are able to help me solve my problem.

Need to give an answer to my customer by this week .

Engineer in dismal

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Siswanto
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Engineering Fields - Power Engineering - Siswanto

Join Date: Mar 2008
Location: JAKARTA. INDONESIA
Posts: 73
Good Answers: 15
#1

Re: Grounding of parallel generators

12/17/2009 6:54 AM

Dear. liukawa

pls check the following link

Re: What is the formulla for calculating the resistance value of a NGR.

Rgds

Siswanto

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anand.mandarapu
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Join Date: Nov 2009
Posts: 39
Good Answers: 4
#2

Re: Grounding of parallel generators

12/17/2009 7:56 AM

It is the correct method for NGR, You can use one common NGR Panel and 6 NGR isolators.

In my most of the projects I have disigned the common NGR Panel. It is fulfilling the requirement
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rasam.syamsudin
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Join Date: Dec 2009
Location: Jakarta 12130 Indonesia
Posts: 76
Good Answers: 1
#3

Re: Grounding Parallel Generators

12/17/2009 8:04 PM

Dear Sir,

This information presneted below is related with NGR instead of NGT.

You can apply one common resistor for 6 generators but you have to consider the following conditions to meet the safety and maintenance requirement.

1. Each connection between neutral point of star winding to a common bus grounding must be provided with repectively CT. To protect generator against groundfault individually.

2. You have to provide a breaker between generator neutral point to common grounding bus to isolate a faulty generator to a common grounding bus when a groundfault occurred. A disconnecting switch or breaker alsos hall be provided between common bus and NGR.

3. One common NGR problem, a possibility to shutdown all generators is possible. A spare neutral grounding resistor completed with panel and auxiliary shall be provided in ready for service upon required.

4. When one common bus grounding is to connected to earth, all generator become solidly grounded. So you have to consider the bus rating shall meet single phase to ground. The short circuit capacity may different if the generator connected directly to synchronizing bus or throu transformer.

Comprehensive study shall be done by the engineer who have authority to conduct this job.

I have not experience yet with one common grounding but I have seen before. They provide a grounding breaker and bus (connected to each other to form a common bus for indoor installation) in a several cubicle panels one Gen one panel. When a groundfault occured in generator or within zone protection, the main GCB and neutral CB open. Most of oil & gas that I know is implementing individual NGR.

During maintenance for one generator we have to consider that other generator still running, so any posibility feed back voltage from running generator through common grounding bus is possible, except you have to provide a grounding truck for earthing the neutral generator and isolated from common grounding bus.

May be this information can help you.

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liukawa
Associate

Join Date: Jun 2009
Location: Singapore
Posts: 36
#7
In reply to #3

Re: Grounding Parallel Generators

12/21/2009 1:58 AM

Awesome Info !

Exactly what i need !

Thanks alot rasam !

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electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#4

Re: Grounding Parallel Generators

12/18/2009 8:28 AM

Check this link: www.i-gard.com
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mlimberg
Active Contributor

Join Date: Feb 2008
Posts: 11
#5

Re: Grounding Parallel Generators

12/18/2009 10:55 AM

liukawa,

It's a nice gesture to want to save this customer money, but if you redesign and install anything other than what the customer requests and problems develop, the customer is going to suggest you are responsible, even if the problem is unrelated to the grounding system.

I'm assuming that the customer is qualified to design the grounding system, and it is according to local codes?

Sometimes saving money is costly.

Hope this helps....
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Patrick Whowha
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Join Date: Nov 2009
Location: Nnewi,Anambra,Nigeria
Posts: 146
#6

Re: Grounding Parallel Generators

12/18/2009 11:56 AM

Since yr customer has not complained about the cost of the NGR,and u know well that the job will be fine with the NGR,why not do what he wanted.Its like he is technically inclined and seems to know what he wants.

Patrick Whowha

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#8
In reply to #6

Re: Grounding Parallel Generators

02/03/2010 11:10 AM

Could it be that he wants to save money not for the customer but for his company?
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Users who posted comments:

anand.mandarapu (1); Anonymous Poster (1); electricalexpert65 (1); liukawa (1); mlimberg (1); Patrick Whowha (1); rasam.syamsudin (1); Siswanto (1)

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