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Join Date: Feb 2012
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Loading on Different Capacities DG

08/31/2014 3:01 AM

how to load 2 DG set of different KVA working on paraller or with grid source without overloading the dg set and maintaning power factor

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Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

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#1

Re: loading on different capacitys DG

08/31/2014 7:23 AM

The DG sets should be loaded to about the same fraction of their respective capacities.

Woodward Governors would be a likely source of good literature on this topic. [non-interest disclaimer]

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Guru
Engineering Fields - Power Engineering - New Member

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#2

Re: loading on different capacitys DG

08/31/2014 12:25 PM

Learn what the terms "droop" and "cross current compensation" mean, then hire someone with experience to guide you.

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Location: Faridabad Near New Delhi India
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#3

Re: loading on different capacitys DG

08/31/2014 11:30 PM

Mr. Patel,

Hope my understanding is right that you already have synchronising and load sharing facility between the 2 DG Sets and you want to synchronise with Grid. In this case you have to take care of 3 things.

1. If there is dip in Grid Frequency your Engine will try to pump power in to grid to bring up the frequency - which your engine can not do and lug out.

Hence you have to safeguard your load, you will have to install df/dt based protection and probably some load shedding.

2. If There is dip in Voltage of Grid, AVR of your 3 phase alternator will try to restore system voltage resulting in heavy over load due to power factor going poor. Hence overloading of alternator, either damage to alternator or its AVR or excitation system depending upon which is relatively weaker.

To safe Guard the alternator you have to see either your AVR has this built in protection - if not then add to AVR if compatible is available or replace AVR.

3. There is always a Circuit Breaker at Remote end of Grid line (at sending end) to which you have synchronised (at receiving end).

If Remote (Sending end) Circuit Breaker Trips or is opened and is closed without check synchronizing interlock - you will loose either coupling or Crankshaft or Alternator.

To suggest protection scheme for Risk No. 3 above, one needs to study the system and suggest.

I am located in India and do all 3 of above. We have done in UAE and Sudan also. I can not give my e mail or phone contact on this site as not permitted. In case you do not find someone to do above for you and you are in India, you may get my reference from people in Power Field by asking for Ramesh Kapur from others in Power Business.

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Active Contributor

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#4
In reply to #3

Re: loading on different capacitys DG

09/01/2014 12:11 AM

sure sir

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Guru
Engineering Fields - Mechanical Engineering - New Member

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Location: CHENNAI, TAMIL NADU, INDIA.
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#5

Re: Loading on Different Capacities DG

09/02/2014 4:09 AM

Dear Mr.harshitpatel,

The DROOP CHARACTER of the DG SET Engines to be studied/matched. Similarly the VOLTAGE DROOP CHARACTER of Alternators to be studied/matched.

If the DGs are identical and equal capacity, load sharing will be equal. If DGs are not equal, the load sharing will be decided by the Voltage Drop i.e., in proportion to the Voltage Drop, with in the Alternator windings.

Get the details of the Droop Character of Engine Speed and Droop Character of Voltage Drop and study and decide.

DHAYANANDHAN.S

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