Parallel Operation
Parallel Operation
(OP)
Hi,
Could you kindly advise me about the thread, which had a very long discussion about the transformer connections by WAROSS and lot of other people contributed.
Thanks
Could you kindly advise me about the thread, which had a very long discussion about the transformer connections by WAROSS and lot of other people contributed.
Thanks






RE: Parallel Operation
I am sorry to say that I made some statements which were in error. Specifically in regards to running transformers in parallel with different tap settings.
With that warning, the thread is thread238-143892
Why don't you ask a specific question and we will be happy to help.
respectfully
RE: Parallel Operation
I was looking for your thread as that gives a lot of info about transformers and in regard to errors , people who know only they make mistakes. The idea of this question is to get the concept and I found many things I could not understand so I will ask in stages
Q1 I was looking at a single line diagram and the rating mentioned was 12/15 MVA OA/FA 220/6.6 KV
OLTC, Z=8.5 % and the NGR= 381 ohm 10 A 10 Sec.
When FA comes in to play, Is it automatic?
NGR- what does 10 A and 10 sec stands for.?
Most of the utility transformers in substations are solidly grounded, so when we do a short circuit study, how do we decide that we have to use a resistance grounded transformer as the fault current is higher than certain value.
Q2 At same location I found a switchgear, which had a NGR with an open fused disconnect rated 10 A, 30sec. I have never seen a resistance grounded switchgear.
Thanks
RE: Parallel Operation
The NGR ratings indicate that the resistor can handle 10A for 10 seconds safely (which means that the ground protection should be set to trip significantly before 10 seconds).
Your short circuit study must use the NGR in your transformer model, which limits the maximum GF current, if it is present. Multiple transformers may be modeled, solid or resistance grounded, but the maximum GF current through a NGR will not exceed its rating just because another solidly grounded transformer is present, even if paralleled.
Any NGR, by definition, should be connected between the transformer neutral and the ground point. The location of the NGR is typically at the transformer. Some switchgear systems have high-resistance neutral grounding, which is often located in the switchboard.
RE: Parallel Operation
respectfully
RE: Parallel Operation
thanks for earlier responses.
I was looking at a SLG done 10 yrs ago and the guy had
a 4.16 KV/600 V delta/STAR 2000 KVA transformer feeding an MCC and some HVAC auxiliaries.
The guy had the trasnsformer high resistance grounded.
Why would somebody ground a 600 V 3 ph transformer high resistance grounded. I do a lot of commercial building stuff but I have not come across 600 V sec t/f
high resistance grounded.
Thanks
RE: Parallel Operation
RE: Parallel Operation
Just a quick question on your comment, delta systems are ungrounded these days also. If this was done in old days, how do we counteract this situation these days. I would appreciate a comment.
Thanks
RE: Parallel Operation
RE: Parallel Operation
What exactly is it that you want to counteract?
RE: Parallel Operation
feeding an MCC and HVAC aux. with a 4.16KV/600 V transformer,we would not ground the sec. with a high resistance. So, the advantrages we could have with a High res. secondary neutral, how do we acheive that now.
Thanks
RE: Parallel Operation