Double Ended Substation / Kirk Key Needed?

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don_resqcapt19

don_resqcapt19

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iwire said:
What part of 240.8 allows this for any duration?
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It is my opinion that the rule in 240.8 is talking about a direct physical paralleling of the breakers. We don't have that here as there is a tie breaker between the two main breakers. Yes, if you close it, the mains are electrically in parallel but I don't see that as a violation of 240.8. There may be other issues here, such as the seconday protection of the transformer if that is required and the protection of the bus when the tie breaker and both mains are closed.
 
iwire

iwire

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don_resqcapt19 said:
It is my opinion that the rule in 240.8 is talking about a direct physical paralleling of the breakers. We don't have that here as there is a tie breaker between the two main breakers. Yes, if you close it, the mains are electrically in parallel but I don't see that as a violation of 240.8.
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I am at a loss to find anything in 240.8 that would indicate it is OK if there is an additional switch between the two OCPDs.:confused:



(Regarless, thanks for jumping in:smile:)
 
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io748

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Zog, your assumption is correct that all 3 breakers will be closed for a short period of time. Just long enough to go from the tie after it is closed to one of the mains and open it. (iwire I agree with your point that if it is not safe/not compliant with code, it does not matter how short the time is)

Also it can be assumed that the system is correctly designed for one side to carry the load of both sides indefinitely. This has been done before for extended periods of time in the past (so I am told) when the switches on one side have needed maintenance.

I am attaching a quick sketch of the system, please pardon its crudeness. Let me know if I have left out any needed information.
 
weressl

weressl

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io748 said:
Zog, your assumption is correct that all 3 breakers will be closed for a short period of time. Just long enough to go from the tie after it is closed to one of the mains and open it. (iwire I agree with your point that if it is not safe/not compliant with code, it does not matter how short the time is)

Also it can be assumed that the system is correctly designed for one side to carry the load of both sides indefinitely. This has been done before for extended periods of time in the past (so I am told) when the switches on one side have needed maintenance.

I am attaching a quick sketch of the system, please pardon its crudeness. Let me know if I have left out any needed information.
Click to expand...

As far as the switchgear bus concerned there is no practical danger allowing all the breakers to be closed for an indefinite time. (The bus is rated 4000A and from any potential inflow direction of energy the flow of energy is limited to 4000A by 'a' breaker.)

  1. We has a single power source that is capable to deliver 4000A.
  2. Ground fault on either busses = the appropriate breakers, both tie and main would open,
  3. Overload on either busses = see 1
  4. Short circuit on either busses = see 1
As I said, if there is no independent secondary main protection for the transfomer, the transformers secondary protection is compromised.

If anything is violated it would be the parallel feed issue, where the feeders should be following the same route, be the same type and same length. Since they terminate on two different device on one end they do not meet routing requirement and potentially violate others. They probably violate the tap rule also.
 
zog

zog

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The sketch is not what I expected to see. You still have 2 transformers (13.2kV/480V) feeding the LV switchgear. The concern here is the availabe fault current with both mains and the tie closed exceeding the AIC rating of your LV breakers. That is likely the reason they (Kirk Keys) in the first place.

After seeing this drawing I would not recommend removing the key interlocks. Not at least until you do a SC study and investigate further.
 
weressl

weressl

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zog said:
The sketch is not what I expected to see. You still have 2 transformers (13.2kV/480V) feeding the LV switchgear. The concern here is the availabe fault current with both mains and the tie closed exceeding the AIC rating of your LV breakers. That is likely the reason they (Kirk Keys) in the first place.

After seeing this drawing I would not recommend removing the key interlocks. Not at least until you do a SC study and investigate further.
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The sketch shows how it was originally configured.

He stated that one of the transformers were removed and both mains ar feed by the same trasnformer. I do not see separate mains for the switchgear and the transformer secondary and that is a problem when trying to parallel as I stated before, but only from the trasnformer overload point not the bus.
 
zog

zog

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weressl said:
The sketch shows how it was originally configured.

He stated that one of the transformers were removed and both mains ar feed by the same trasnformer. I do not see separate mains for the switchgear and the transformer secondary and that is a problem when trying to parallel as I stated before, but only from the trasnformer overload point not the bus.
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I dont read it that was Laszlo, I think one of the 138kV/13.2kV utility transformers was removed.

io748 said:
My facility has 9 double ended substations (M-T-M) that have kirk key interlocks. When our facility was constructed it was fed from two substation transformers, whose primaries were connected to the same feed from the utility. Some time later one of the transformers was removed, and both main feeds into the plant were connected to the same source.
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At least that is my understanding.

So here we are again, back to misreading and disagreeing. That was a sweet few minutes that you, I , and Iwire were all in agreement, I knew it couldn't last long. :)
 
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io748

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Nashville, NC
It was one of the 115kv/13.2kV utility transformers that was removed. All of the low voltage double ended substations are unchanged.

The sketch I attached shows the current configuration.
 
zog

zog

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io748 said:
It was one of the 115kv/13.2kV utility transformers that was removed. All of the low voltage double ended substations are unchanged.

The sketch I attached shows the current configuration.
Click to expand...

In that case you want to keep those key interlocks there, they are still needed unless you prove otherwise (SC Study) and even then still a good idea.
 
weressl

weressl

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zog said:
In that case you want to keep those key interlocks there, they are still needed unless you prove otherwise (SC Study) and even then still a good idea.
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Absolutely.

I just couldn't fathom the question in the first place if the issue was NOT the elimination of one of the Secondary Unit Substation Transformers. The replacement of main incoming would have hardly anything to do with it, unless they were operated parallel and the common SC source would make such difference.
 
zog

zog

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Charlotte, NC
weressl said:
Absolutely.

I just couldn't fathom the question in the first place if the issue was NOT the elimination of one of the Secondary Unit Substation Transformers. The replacement of main incoming would have hardly anything to do with it, unless they were operated parallel and the common SC source would make such difference.
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Good, we are in agreement again. Iwire? Will the stars align tonight? Should I go buy a lottery ticket? :)
 
iwire

iwire

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Pierre C Belarge said:
240.1 Scope.
Parts I through VII of this article provide the general requirements for overcurrent protection and overcurrent protective devices not more than 600 volts, nominal.
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OK, I can get behind that, but the OPs installation is ( I believe) under 600 volts, I think only Zog has brought Medium voltage into this thread.
 
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io748

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Nashville, NC
Let me throw another purely hypothetical scenario out here. Say production was shut down, and each side of the LV gear was supplying only 200 amps. If both main breakers were adjusted to 1000A, could all three breakers then be closed, and be in copliance with code? Or is that still in violation due to the parallel feed issue?
 
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philly

Senior Member
Even with the current configuration ignoring the SC thing for a minute, both mains and the tie could not be closed at the same time if the bus was only rated for 4000A due to the fact that with both mains closed and the tie closed it could put 8000A onto the bus.

At least that what I got out of the discussion.
 
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