4.18 kV BUSDUCT

[bobziva]

Company is suggesting to install 4.18 kV busduct connected to existing switchgear , and feeding a special load – 4180 kV, another busduct from another switchgear ( 2 side supply)
Can I do that ? What is your experience about that ? How to make a proper protection ?

 

[peebee]

First of all, it's highly unlikely that your special load is 4180 kV, which would be 4.18 megavolts, which would be unusual to say the least. It's more likely 4180V, which is the same thing as 4.18kV, which is the same voltage you stated you're using for your other system. That may answer your question right there. If I'm mistaken here, let me know.

So far as double-ended switchboards go, they are rather common, particularly for industrial installations, data centers, and generally anwhere that you're looking for high reliability power. Most any power engineer worth his salt should be vaguely familiar with the concept, and any major electrical manufacturer will definitely be familar with this.

A couple key issues on double-ended boards, at any voltage:
+ Open vs. Closed transition. This is a CRUCIAL difference. Open transition boards require only some means to prevent simultaneous closure of both sources, such as a Kirk-key lock (do a Google search or call your manufacturer before you start asking what Kirk keys are unless you want to get smacked around on this board). I've seen a few installations that didn't even have such preventative devices, but I would STRONGLY recommend that you DO NOT decide to save a couple bucks there, at least not without first speaking to your AHJ, your insurance company, your lawyer, etc. YOU HAVE BEEN WARNED ON THAT ONE. So long as you put the Kirk key or similar in, you're set.
+ Closed transition: these are trickier. The key issue here, is that if the sources are out of phase, your board could violently explode, destroying your building and killing people in the process. No joke. This typically means that protective relaying is employed to prevent an out-of-phase closure, this is somewhat similar to generator synchronization equipment at least in general concept. There's two sub-categories here, momentary closed transition and normally-closed (parallelled). Gear which normally parallels both sources is unusual unless you're a utility or have a rather sophisticated on-site engineering staff. Also, beware that during the closed transition, you're fault current is roughly double what it would be on a single source. You are STRONGLY urged to consider rating your board for the full 2x fault current (many would argue that NEC requires this beyond any doubt).
+ Regardless of open vs. closed transition, a tie breaker should be considered as this can greatly facilitate maintenance. Better yet, provide two tie breakers and cable or busduct between them to facilitate complete isolation of one half of the board while maintaining power to the other.

One last recommendation: you should DEFINITELY get someone who knows what they're doing to engineer this for you. And 95% of the contractors out there do NOT fall into that category. Get a PE. Medium-voltage equipment does NOT have a sense of humor about these things.

 

[peebee]

One more idea:

If reliability is priority #1, provide two equipment rooms or other physical separation between the two halves of your board rather than putting them in close proximity to each other. That way, even if one side of the board burns to the ground, you'll still get power out of the other side. Such an installation is usually reserved for places like NORAD, bank headquarters data centers, and other money-is-no-object types.

 

[jbartos]

Suggestion: It appears that more information is needed in terms of load nature, emergency load, critical load, life safety load, essential load, etc.
Normally, two power supplies may be used for non-essential load. In this case the double ended switchgear/substations are used. If the two power supplies are used for essential loads, then the double ended switchgear/substations should not be used. One power supply should power one substation and the second power supply should power the second substation. If there are unique loads, not train A and train B loads, then they will have to be individually aligned to the emergency switchboard/switchgear/substation via automatic transfer switches. Some electrical safety codes permit to have one emergency generator to be used for the emergency situation to power one emergency switchboard/switchgear/substation.
This has a disadvantage in the single failure which may cause a blackout and all emergency loads will be without power.

 

[kssschsekhar]

In stead of using busduct you can use HT cables provided your load is 4180v (your load voltage is 4180kv or 4180v please confirm)

then use a circuit breakers ( required ampere capacity)with interlocks. for reliable power supplies use always both breakers in ON condition and protected with a fast acting relays for isolating the faulty zone by switch off the on breaker incase of supply failure in one Board