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harakiri
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Join Date: Jan 2013
Posts: 6

SR4 VR6B Parallel Operation

02/11/2013 7:53 AM

We are using 2 SR4, 2000KVA, 600V, 60Hz generators.

Generators are equipped with VR6B voltage regulator.
DROOP CT transformer 2000/5A is connected on 5a and 6 (polarity mark on 6 on VR6B).
DROOP potenciometer is adjusted at 40% of full range on both generators.
STABILITY potenciometer is adjusted at 50% of full range on both generators.
Generator voltage at no load is adjusted on 605VAC on both.

Both generators when each is in island mode, with same load, have different response.
for example:
Generator 1:800A 607VAC
Generator 2:800A 594VAC

When working in parallel for same load like in example above the load sharing is:
Generator 1:900A 605VAC cosfi: inductive
Generator 2:200A 605VAC cosfi: capacitive

Please comment what could be a problem.
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RAMConsult
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Engineering Fields - Power Engineering - New Member

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 3230
Good Answers: 444
#1

Re: SR4 VR6B Paralell Operation

02/11/2013 11:23 AM

The problem could be the polarity of the Droop Compensation CTs. Although you have correctly corrected the secondary polarity mark to terminal 6 of the regulator you still need to ensure that the primary polarity marks are consistent across the generators. It is uncommon to find that the CTs are installed without regard to which end is closer to the generator, but when it happens it renders the CT's polarity mark irrelevant.

The other common error is the wiring from CT secondaries to the AVR input terminals. Any crossed connections will result in exactly the symptoms that you are experiencing. It is imperative that the entire secondary circuit path is traced from the polarity mark through each device and terminal block and back to the CT. Also make sure that every shorting link (if used) is open for proper operation and that there are no parallel paths.

Please let us know the result of your testing since there are other less obvious things that may be happening.

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CBlackwood
Member

Join Date: Feb 2013
Posts: 7
#2

Re: SR4 VR6B Parallel Operation

02/12/2013 10:07 AM

Check your polarity on the droop CTs, and the sensing wires on the regulator. Both are very important on proper paralelling. When checking the polarity it is important to use only resistive load. The regulators can only react to what they are told by the droop ct. The droop ct must lag the A phase of the regulator by 90 degrees. If the sensing wires are in the wrong place, the regulator will not react properly. You can use an oscilloscope with 1 lead on the A and C phase and one on the droop ct while transfered to a resistive load. If you dont have a oscilloscope, just use trial and error by moving the sensing wires until it works.
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LAA_Lucke
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Join Date: Feb 2010
Posts: 1013
Good Answers: 36
#3

Re: SR4 VR6B Parallel Operation

02/12/2013 1:09 PM

When in island mode, what was the power factor on each?

This should give you a clue on the wiring...
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harakiri
Member

Join Date: Jan 2013
Posts: 6
#4

Re: SR4 VR6B Parallel Operation

02/14/2013 1:07 AM

Thank you people on answers and I am sorry for late response.

We made all ass you have suggest and problem is solved.

The problem was on Generator 1. The leads on sensing transformers where switched and also one of sensing transformers was in malfunction (Secondary voltage of one sensing transformer was lower for 10% than other sensing transformer).

Once again thank you all till next topic.

Greetings, Marko.
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RAMConsult
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Engineering Fields - Power Engineering - New Member

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 3230
Good Answers: 444
#5
In reply to #4

Re: SR4 VR6B Parallel Operation

02/15/2013 8:53 PM

Thanks for the positive feedback, glad to be of help in pointing you in the right direction. RAM

__________________
 “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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CBlackwood (1); harakiri (1); LAA_Lucke (1); RAMConsult (2)

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