Double Ended Substation / Kirk Key Needed?

[WastefulMiser]

No one, that I have ever seen anyways, and I see a lot of switchgear. That was a misconception.

In your opinion, who is the best of the major switchgear manufactures? Best power breakers?

I saw a job once in which the customer's oneline depicted a single 2000A incoming supplying two (2) 2000AT main breakers. The transformer was 1.5MVA, 480V secondary. Legal?

 

[quogueelectric]

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.

Question 1: It has been suggested to me that the kirk key system could be bypassed safely, since both sides of each substation are fed from the same source. This is desirable as I could test the main breakers and switches with no outages. Does anyone see any issues with bypassing the kirk key system, given this situation?

Question 2: Each main breaker is 4000A, and the tie breaker is 4000A. The feeder breakers on one side total 4000A. So if you have the tie breaker closed and one main open, 8000A of breakers will be fed from one 4000A main. Why would the founding fathers of this plant have not double sized the main breakers?

As an ex-controls guy who is just starting a new role as a facilities electrical engineer, any input is appreciated.

Do not repeat do not bypass safetys!!! Federal law prohibits this as you are probably not a qualified person to do this without an EE degree at minimum. Run it by an engineer but do not endanger inocent people by bypassing a safety intended for personell protection only to find out you killed a few people because you thought you knew what you are doing. You assume liability when you do something like this lawyers call it negligent homicide and gross negligence.You would probably only do 8 yrs but the wrongfull death lawsuits will keep you broke for the rest of your life. Is it worth the risk of a shutdown??

 

[jim dungar]

...Federal law prohibits this...

What Federal law are you talking about?

 

[zog]

Two 4000 amp mains supplying 4000 amp busing is a problem, the load those busses supply is irrelevant.

Two 4000 amp mains in parallel is a problem.

I think you are misunderstanding the configuration, no part of the bus will ever see more than 4000A. (Besides a fault condition).

 

[zog]

In your opinion, who is the best of the major switchgear manufactures? Best power breakers?

Current production stuff? It is all junk IMO, all the OEM's are making these breakers to last 5 or 10 years and be disposable, all part of the bean counters plan. If I had to pick one I guess GE is making the best new stuff today.

I see old breakers from the 1930's, 40's, 50's, and 60's everyday that still work great if properly maintained, they really dont make them like they used to. All time best power breaker, GE Magneblast, hands down, a tank built to last forever and a workhorse of many MV systems still today.

LV power breakers, GE AK series, ABB K-Line, Westinghouse/Square D DS series, all good. These 3 breakers make up over half of all the power breakers in existing plants today, and for good reason. If you look at the history of these lines they all were made for 30-40 years or so. Some power breaker lines were only made for 5 years, and for good reason, they were junk.

 

[iwire]

I think you are misunderstanding the configuration, no part of the bus will ever see more than 4000A. (Besides a fault condition).

It is irrelevant how much load the bus will 'see' you can not supply a 4000 amp buss with 8000 amps of OCP.

And .....

You can not operate OCPDs in parallel

Question 1: It has been suggested to me that the kirk key system could be bypassed safely, since both sides of each substation are fed from the same source. This is desirable as I could test the main breakers and switches with no outages. Does anyone see any issues with bypassing the kirk key system, given this situation?

 

[zog]

It is irrelevant how much load the bus will 'see' you can not supply a 4000 amp buss with 8000 amps of OCP.

You aren't. Look at the system.

And .....

You can not operate OCPDs in parallel

It is done all the time in my "Switchgear world", a very common system design, nearly all MV systems are like this. Heck, the entire power grid is made of OCPD's in paralell.

 

[iwire]

It is irrelevant how much load the bus will 'see' you can not supply a 4000 amp buss with 8000 amps of OCP.

Let me change that, what NEC section allows that?

 

[iwire]

It is done all the time in my "Switchgear world", a very common system design, nearly all MV systems are like this. Heck, the entire power grid is made of OCPD's in paralell.

No, they are not in parallel because the 'other' end is not joined together

If I understand your 'switchgear world' all these double ended gears are fed from two different sources. In the OPs situation both feeders now come from the same source, (transformer in this case) so they are in fact in parallel and a direct violation of 240.8

 

[zog]

Let me change that, what NEC section allows that?

No matter what the configuration every bus section will be protected by a 4000A breaker, what is the issue?

 

[zog]

No, they are not in parallel because the 'other' end is not joined together

And they are not here either, the tie breaker sperates them form being directly joined together.

If I understand your 'switchgear world' all these double ended gears are fed from two different sources.

Yep

In the OPs situation both feeders now come from the same source, (transformer in this case) so they are in fact in parallel and a direct violation of 240.8

I just am not seeing how, not trying to argue with you here Bob but one of us is missing something here, if this violates 240.8 then I could find this violation in nearly every large industrial plant in the country.

 

[iwire]

And they are not here either, the tie breaker sperates them form being directly joined together.

I 100% agree, as long as the tie breaker is open then there is no problem.

But removing the Kirk key system allows the closing of both ends and the tie.

I just am not seeing how, not trying to argue with you here Bob but one of us is missing something here, if this violates 240.8 then I could find this violation in nearly every large industrial plant in the country.

The breakers are not in parallel in regards to 240.8 when they are supplied from different sources, as soon as both breakers come from the same supply and feed the same equipment they are in parallel and in violation of 240.8.

Of course I agree that if the tie breaker is left open we would not have an issue but it is apparent the OP wants to have all three breakers closed at some times to do 'testing'.

the kirk key system could be bypassed safely, since both sides of each substation are fed from the same source. This is desirable as I could test the main breakers and switches with no outages.

The only way he will have 'no outage' is if the tie breaker is closed before he tests either main.

BTW; You did not really just try the 'We always do it that way argument' did you?

 

[iwire]

No matter what the configuration every bus section will be protected by a 4000A breaker, what is the issue?

Until he closes the tie breaker as well for testing as he described.

 

[weressl]

Nothing would ever see 8000A. Not sure where you get that from. Maybe the OP's statement of the total frame size ratings of the breakers?Me thinks he was a little confused on that part.

The Mains are 4000AF so nothing will ever see more than that, no matter what the configuration. Relax codemaster

Bob's question is legitimate, but I think he phrased the question with the wrong emphasis.

If the two mains are the secondary mains of the transformer - and nowhere in the writeup did I see evidence ot the contrary - then nothing prevents the overloading of the transformer. Each main would sing along untill each sees 4000A before starts paying attention. NOTHING prevents the installation of 4000A worth of loads on each side of the double ended SS.

Since overloads develop over time, there would be nothing wrong with paralleling the mains for a short time, provided that the total load does not exceed the transformer rating before paralleling and you have control over that no additiona loads are switched ON while you're doing your testing.


I think one of the original question was phrased in reverse. It is the tie-breaker that could be half the size of the mains. Could be, but shouldn't be.

1. the full size tie assures that you have a spare on hand for the mains,
2. There is no way to assure that each half of the gear is exatly half the load, eg. 2000A,
3. Most of the times this scheme is employed when the majority if not all the equipments are A and B, in other words there are 100% installed standby spares that are continually switched around to provide for equal wear and maintenance downtime.
4. Often times the laoding is sized that when a single transformer is out the full OAFA dual rating of the single transformer is considered to be available for use, approx 25-33% over nameplate laoding, depending on the transformer seize and type.

 

[zog]

Of course I agree that if the tie breaker is left open we would not have an issue but it is apparent the OP wants to have all three breakers closed at some times to do 'testing'.

I am assuming (Yeah I said assume) that this would be for a short duration during switching to allow for isolation of a main breaker for testing. I agree that the system should never be left with both mains and the tie closed for any duration beyond the few seconds it takes for closed transition switching.

 

[zog]

I think we are all in agreement there there were just some commincation issues as far as what assumptions were being made. Bob and Laszlo agree?

 

[weressl]

I think we are all in agreement there there were just some commincation issues as far as what assumptions were being made. Bob and Laszlo agree?

Yep, that's a change WE ALL CAN BELIEVE IN!

 

[iwire]

I think we are all in agreement there there were just some commincation issues as far as what assumptions were being made.

I agree. :smile:

 

[billsnuff]

Bob and Laszlo agree?

:grin:

good thread !

 

[iwire]

I am assuming (Yeah I said assume) that this would be for a short duration during switching to allow for isolation of a main breaker for testing. I agree that the system should never be left with both mains and the tie closed for any duration beyond the few seconds it takes for closed transition switching.

What part of 240.8 allows this for any duration?