Advice for future connection provision on MV Switchgear

[philly]

I wanted to get some advice/suggestions from other here in providing a provision in a 4.16kV Switchgear lineup for connection of a future temporary feeder.

We are providing customer with a switchgear lineup that has a main 4.16kV feed from an upstream transformer and had (3) feeder breakers to downstream loads. The customer has requested that in the event they loose the transformer which feeds this switchgear they want to install a temporary feeder from a nearby transformer to power this gear. This nearby transformer has a dual voltage secondary of both 4.16 & 13.8kV that is selected via tap changer.

Connecting this other feeder to the switchgear properly would require an additional breaker in the switchgear lineup as well as all of the required protection and control (interlocking, transformer diff, bus diff, etc...). The customer does not want to pay for this additional breaker and associated P&C and is simply requesting a landing point provision (lugs or similar) to land these future feeder cables in the event of an emergency. They also do not want to pay for an additional structure to install this landing provision and are suggesting simply adding a set of lugs to the incoming section where the busduct from the normal source transformer comes into the switchgear.

As an OEM and engineer of record I have informed the customer that we cannot provide what they are requesting from a liability standpoint simply overlooking all the P&C that would be required to accomplish this safely and correctly. We have stated that we can provide them with an additional section with bus runbacks labeled for "future bus expansion" or provide them with an additional breaker provision labeled as "future" and what they choose to do with these sections after the switchgear is installed is on them.

Does anyone have any suggestions on how to approach this or see this any differently from a liability standpoint?

 

[zbang]

MV gear is so not my area, but it seems like anything more than the "Future expansion" section would be asking for trouble (especially the added breaker). At least with just the bus terminals, maybe they're more likely to make sure everything is safe before touching it and less likely to backfeed the main transformer.

(And really, how likely is it that they'd drag a set of MV cables from another transformer? Or even have them on hand? How long would it take to set this up? I have no idea.)

Problem is they've already said that they want to work around the usual P&C, so it would be a bit like handing them a suicide cord and saying "Don't use this to connect your generator".

(My opinion and $3 will get you a cup of coffee :happyyes

 

[petersonra]

It seems to me such an arrangement would require a transfer switch.

My personal opinion is that you cannot avoid liability by how you label the lugs or CB as since you clearly know their intended purpose and have now told the whole world that fact. But I am not a lawyer, so maybe you should ask your lawyer what he thinks about knowingly designing in such a hazard and then trying to shirk responsibility for it by such a label.

 

[Jraef]

Your instincts are correct. Any future feed into or out of a switchgear lineup must be handled with the same protection elements as everything else, and then some! To accommodate them in the way they request would set up a possible scenario in which someone “forgets” to disconnect the primary feed and energizes the back-up transformer, killing someone at or near the failed transformer. Sure, you would have “procedures” in place, but Kirk-key interlocks are the belt and suspenders approach that everyone has used. With no second feed device, you can’t interlock anything. As their “engineer of record”, you would own that.

The exception however would be the Transfer Switch approach that Bob mentioned; i.e. it can only be in one state at a time. So both transformers feed one or the other side of the Transfer Switch, the Transfer Switch common feeds the gear. But really, that’s what a Main-Main interlocked feed system is accomplishing too.

 

[Tony S]

Looking at the situation from this side of the pond, I would go for the Kirk Key (Castell) interlock. A MV transfer switch is going to be expensive by comparison. If they’re bitching about price already I can’t see you have an option.

My background:
Before I retired I was the companies SAP (Senior Authorised Person), legally responsible for the management of our MV distribution networks.

 

[pv_n00b]

The code does not provide an exception for what your client wants. NEC Art. 590 covers what exceptions are allowed for temporary installations such as maintenance and replacement of the transformer. Sometimes, clients want to do stupid things, it's the PEs job to provide a safe alternative and not facilitate a client's death wish.

 

[JFletcher]

I somehow doubt the gear is more expensive then the million-dollar + lawsuit that is filed by the family of the poor guy who makes the temporary connections and makes one slight mistake.


Of all the extremely bad ideas I have heard, what your customer proposes is solid Darwin Award material, and I personally would not hesitate to tell them that

 

[electrofelon]

I certainly dont know the layout and wiring methods, but what about installing the transformer secondary conductors through a padmount switch or other enclosure where they could use seperable connectors to provide the option to connect to a different transformer? I would think one could put something together inexpensively with some load or deadbreak bushing inserts and elbows.

 

[zog]

I wanted to get some advice/suggestions from other here in providing a provision in a 4.16kV Switchgear lineup for connection of a future temporary feeder.

We are providing customer with a switchgear lineup that has a main 4.16kV feed from an upstream transformer and had (3) feeder breakers to downstream loads. The customer has requested that in the event they loose the transformer which feeds this switchgear they want to install a temporary feeder from a nearby transformer to power this gear. This nearby transformer has a dual voltage secondary of both 4.16 & 13.8kV that is selected via tap changer.

Connecting this other feeder to the switchgear properly would require an additional breaker in the switchgear lineup as well as all of the required protection and control (interlocking, transformer diff, bus diff, etc...). The customer does not want to pay for this additional breaker and associated P&C and is simply requesting a landing point provision (lugs or similar) to land these future feeder cables in the event of an emergency. They also do not want to pay for an additional structure to install this landing provision and are suggesting simply adding a set of lugs to the incoming section where the busduct from the normal source transformer comes into the switchgear.

As an OEM and engineer of record I have informed the customer that we cannot provide what they are requesting from a liability standpoint simply overlooking all the P&C that would be required to accomplish this safely and correctly. We have stated that we can provide them with an additional section with bus runbacks labeled for "future bus expansion" or provide them with an additional breaker provision labeled as "future" and what they choose to do with these sections after the switchgear is installed is on them.

Does anyone have any suggestions on how to approach this or see this any differently from a liability standpoint?

Our guts agree on the liability issue. I think the most economical way to do this would be a duplex load break switch upstream of the main breaker (And key interlocked with the main breaker)

 

[zbang]

This nearby transformer has a dual voltage secondary of both 4.16 & 13.8kV that is selected via tap changer.

Even with a load-break switch or mechanical interlock on breakers, how will they ensure that the 4.1kv gear isn't going to see 13.8? (And, what about that transformer's usual loads?)

The client needs to rethink their requirements, risks, and costs.

 

[electrofelon]

I can't help but think there is a little "overthinking" going on. Full disclosure, I am not a MV guy, but are tap changers, extra lugs, loop feed bushings, etc not allowed because someone might use them improperly for something stupid? Someone who is not qualified can find a way to kill themselves no matter how hard you try.

 

[JFletcher]

I can't help but think there is a little "overthinking" going on. Full disclosure, I am not a MV guy, but are tap changers, extra lugs, loop feed bushings, etc not allowed because someone might use them improperly for something stupid? Someone who is not qualified can find a way to kill themselves no matter how hard you try.

It would be a little different if the client spec'd the gear with an extra set of lugs and did not say why... the OP no longer has plausible deniability if and when those lugs are used as the client intends.

It's a little bit like asking your mechanic to rig your car so that the heated seats come on automatically when the key is turned. He would probably do it unless you also told him you intended to wire a bomb to the seat circuit and give the car to your wife as a present.

And if the original poster can design something safe and effective for the client without all the usual associate gear, he should patent what he designs and make a mint off of it

 

[electrofelon]

It would be a little different if the client spec'd the gear with an extra set of lugs and did not say why... the OP no longer has plausible deniability if and when those lugs are used as the client intends.

It's a little bit like asking your mechanic to rig your car so that the heated seats come on automatically when the key is turned. He would probably do it unless you also told him you intended to wire a bomb to the seat circuit and give the car to your wife as a present.

And if the original poster can design something safe and effective for the client without all the usual associate gear, he should patent what he designs and make a mint off of it

Certainly if it has been documented on paper or emails that client wants to do XYZ and it is stupid and dangerous then I could see it being a bad idea of "endorsing" the plan by providing what they wanted. I dont really know enough MV gear and the specifics of the setup to know if that is the case or not. Seems like a letter from the client stating that any such use of the supplied equipment will be done per codes and osha requirements would suffice.

 

[JFletcher]

Full disclosure, I'm not a medium voltage guy either. Zbang's post brought up a couple of key points I thought of after I made my post and was past the edit time.

The other things I was thinking is that one, none of the stuff is needed, because the odds of losing a transformer are pretty small. The second, more pressing issue, is that the connections to the other transformer sound like they would more than likely be done while it is live, and also possibly under rush / emergency conditions, the thought of which makes my skin crawl, but nowhere near like getting hit by 4160 would.

Last thought: the warning sign "DANGER!!! Not only will this equipment kill you, it will hurt the whole time you're dying" is intended to be funny, however it would be deadly serious and completely applicable to what the customer wants

 

[electrofelon]

Full disclosure, I'm not a medium voltage guy either. Zbang's post brought up a couple of key points I thought of after I made my post and was past the edit time.

The other things I was thinking is that one, none of the stuff is needed, because the odds of losing a transformer are pretty small. The second, more pressing issue, is that the connections to the other transformer sound like they would more than likely be done while it is live, and also possibly under rush / emergency conditions, the thought of which makes my skin crawl, but nowhere near like getting hit by 4160 would.

Last thought: the warning sign "DANGER!!! Not only will this equipment kill you, it will hurt the whole time you're dying" is intended to be funny, however it would be deadly serious and completely applicable to what the customer wants

Yeah I dont know what they are thinking of doing. Swapping the transformer with the cables and elbows back fed and energized? How would that work? Shove a insulated standoff bushing into the elbows? Seems pretty sketchy. Maybe there is another cabinet where the cables can be isolated. I guess my point was just that just because you can come up with an incorrect way they could do it, doesnt necessarily mean you have to provide for it. You cant brother in law proof enything.