Double Bus Bar switch gear 1

[Mbrooke]

What is double bus bar gear used for? Has anyone ever installed it or seen it in the field? I personally can not understand this concept or why its even being offered.

https://library.e.abb.com/public/22...04b9927/Leaflet_UG ZS1_DBB_Rev_2013_09_en.pdf

http://ms.schneider-electric.be/Main/PIX/catalogue/nrjed313574en.pdf

 

[piterpol]

I believe figures in the Schneider Catalogue explain by themselves.

 

[Mbrooke]

I am having a hard time understanding them. For example, "two busbars grant highest level of uninteruptible power supply" How? My understanding is that if one bus fault internally it could effect the other. In theory a main-tie-main would provide the same reliability with less complexity.

 

[7anoter4]

In my opinion, this article explains-generally-the advantages and disadvantages of the double busbar.

http://electrical-engineering-portal.com/abb-mv-switchgear-single-busbar-or-double-busbar

The supplied costumers sometime cannot be separated in a fault case, if you have
not a redundant busbar. In some instance-in very important installation in which the interruption of energy supply is more expensive than the equipment price as in a large steel complex-even a third busbar, namely a transfer bar, it could be required.

 

[Mbrooke]

Thank you very much!

Would you happen to know the behavior of this gear during a bus fault? Would it effect the other bus bar of be contained?

 

[Mbrooke]

I came across this as a good reference:

 

[ScottyUK]

Mbrooke,

That will very much depend on the protection employed and the type of fault. Bus differential would almost certainly clear the fault before it propagated to the second bar. Plain OC/EF might well allow an arcing fault to persist long enough to compromise both main and reserve bars. If an application is of sufficient criticality to justify the use of a double busbar board then it likely justifies the use of bus differential protection.

Note that repair to a faulted bar would still require the full board to be isolated to undertake repairs, or at least it would under our Safety Rules. The potential benefit of the double busbar is that supply could (possibly) be restored to the load until a convenient time was available to undertake repairs rather than having an unplanned forced outage at a hugely inconvenient time.

 

[Mbrooke]

Scotty, thank you! That makes perfect sense now. I was thinking of conventional over current and typical safety procedures which would not compliment double bus bar well. Wouldn't you still have to megger the unfaulted bus bar though to verify? In your country is double bus bar switch gear common? In the US it is a rarity with most critical applications being Main-tie-Main, hence my curiosity.

 

[ScottyUK]

Yes, in an ideal world you certainly would want to test as much as you could after a major event like that. It would probably come down to an assessment of the relative risks introduced by shutting down power to the loads versus the risk of potential damage to the second busbar.

In the UK dual busbar systems are very common in our transmission substations. Fifty / sixty years ago they were also common in power plants and the like for critical distribution, but today minimising capital cost has a higher priority than long term operability and maintainability and they are much less commonly seen. Improved switchgear reliability probably plays a part in that too, although I think we may soon be seeing a decrease in long-term reliability as a result of manufacturers designing out every last gram of non-essential material to the point where there is absolutely no margin left for wear & tear, operational degradation, or anything of that sort. Modern equipment seems to have far too many failures for which there is no excuse other than bare-minimum level of design and manufacture.

 

[Mbrooke]

At the transmission level I can certainly understand dual bus bars because any one can be safely shut down while all the circuits are transferred to the other without needing to pull the entire station out of service. Also a fault is unlikely to propagate into the other open air bus bar. Most of the HV and EHV stations that I have drawn up are double bus bar. However at the switch gear level the opposite is true making the extra cost less attractive.


In terms of decreasing reliability and maximizing capital cost I regret to say that is moving toward the transmission level; 400Kv not sparred. Single bus bar is actually now being contemplated at these voltage levels:

 

[Mbrooke]

Also, just to ask, in your work how many bus faults do you encounter in gear? Any ever been attributed to mice?

 

[RonShap]

Faults due to mice reduce based on voltage, since spacing between energized conductors are further apart.

 

[Mbrooke]

There is nothing to keep them out?

 

[ScottyUK]

MBrooke,


Actual busbar faults are very uncommon, I have only seen a couple first-hand on 11kV metalclad gear and both were phase-earth and limited by the NER to a relatively low current. Messy but repairable. Both were suspected to have been initiated by either contamination or PD on a polymer insulator which eventually resulted in flashover.

Most failures that I come across tend to be in or around the moving parts: disconnectors, circuit breakers, main disconnects on withdrawable gear, shutters, earth switches when they leave a pole closed and indicate open... not all on our site thankfully, but the Energy Networks Association in the UK operates a membership-based database of equipment faults which is available to suitable organisations including most of the distribution utilities and some private network operators.

 

[Mbrooke]

I agree, but in the US I have heard of stories (A texas utility for example) where a mouse cause a large number of customers going out that were served via MV switchboards at distribution substation. Open air aluminum tubes can be shielded with squirrel guards.

 

[rcw retired EE]

FAA facilities used to have 480V double-bus, double-breaker feeders for critical equipment at the air traffic control centers. Switchgear had an upper and a lower bus with two draw-out breakers in a single vertical section for each feeder. An A breaker was on top and a B breaker on the bottom and the common outgoing feeder bus was in the middle. That allowed breaker maintenance without de-energizing the load. But there still was the issue of energized components in every section and compartment.

That is the only place I've seen double bus at low voltage.

 

[Mbrooke]

Thanks, that is interesting and I was wondering if it was ever done at LV.