single busbar or double busbar 1

[vikkyarora]

Please can anyone tell me where it is preferable to have double bus bar over single busbar switchgear panels in power distribution? How does the double bus bar sytem work?

 

[mpparent]

Obviously there are two buses per phase in this case. The benefit is that you can use two smaller buses rather than one larger one, assuming you might have some space constraints in the construction of the electrical equipment. Can you tell us your application?

Mike

 

[dpc]

Medium-voltage switchgear can be purchased with a double bus arrangement that allows a feeder to be fed from either bus - this is typically used by utilities in distribution substations to allow a feeder to be placed back in service in the event of a breaker failure or bus fault.

In a typical switchgear assembly, the bus itself is subject to a common-mode failure - a bus fault causes a total failure of the entire lineup until it can be repaired. The double bus arrangement provides for transfer bus that can be used in the event of a bus failure.

I've never seen these used except in utility substations.

 

[vikkyarora]

Thanks for the info and the quick response. But what I am looking for is:

If I am to sell both double busbar (dbb) panels and single busbar (sbb) panels to a utility company - for which application would they prefer to have a dbb panel and not a sbb panel? Ofcourse they wouldn't want to purchase dbb panels through out their distribution system inspite of their redundancy benefits, as the costs of dbb are higher. Then which place in the distribution system, will the utility industry prefer to have a dbb panel over a sbb panel?

 

[RRaghunath]

Vikkyarora,

Double busbar arrangement in indoor switchgears is not all that popular considering the additional cost vis-a-vis the little benefit.

Double bus bars are still preferred in big industrial plants for their main switchgear that cannot be shutdown even when the complete plant is under shut down for carrying out periodic maintenance activity.

Double bus bar enables planned shut down of one bus bar at a time for carrying out cleaning and othet periodic maintenance activity.

This means if the plant is highly polluting and would call for regular cleaning of even the switchgear busbars to avoid flashovers (without shutting down the complete power supplies), double bus bar switchgear will be natural choice.

I have come across a chemical plant with captive power generation (in addition to grid power) with double bus bar switchgear. The voltage level was 6.6kV and generation comprising DG sets rated 6MW each.

Present day industrial plants are quite environment conscience and thus the switchgears do not require that frequent cleaning. Further, the switchgears with insulated bus bars are available now as a gaurd against flashover. Thus, as I said earlier the switchgears with double bus bars are becoming a rarity these days.

 

[PaieMan]

Dear rraghunath,

Hi, I'm new here.

Regarding the double busbar system, you mentioned it's a rarity these days. I think Utility company still considered a double-bus system don't u think?

Anyway, just to check from all people's experience, how do you do BUSBAR EXTENSION work for the double-bus switchgear WITHOUT needing to shutdown the whole electrical system connected to it?

FYI, my new cogen plant will have a 33kV double-bus GIS WITH a bus coupler between the two bus but WITHOUT any bus sections. So, in future if i need to add more generators to it, do you have any idea how is this normally done? Again, without needing to shutdown the entire plant.

Thank you!

 

[dpc]

Don't even think about trying to do this with an energized bus. Schedule an outage to do the bus extension.

 

[RRaghunath]

Paieman,

Welcome to you.

Double bus system is ideally suited to meet the requirement of extension without any need to shutdown any of the connected feeders / sources. This is how it is done,

Shift all the feeders connected to a bus to the second one. This done one at a time after keeping the bus coupler closed and closing one bus isolator and opening the other sequentially. It is important to check if the bus coupler is provided with any protections such as over current / earth fault and disable the trip output from the same during bus changeover.

Thus, all the feeders and sources are shifted from the particular bus, open the bus coupler. Now, the bus is free /dead and allows you to work on extension.

Make sure you follow all safety precaustions for your own sake as well as for the sake of production.

Trust you find the above useful.

 

[matwong]

Paieman,
As you may notice, the double-bus switchgear has two separate compartments for its main & reserve busbar where you are completely safe to de-energize one busbar at a time for the extension work as described by rraghunath above. Care shall be taken when handling with gas.

 

[PaieMan]

Dear all,

Thank you all for the replies.

Yes, of course, I have to make sure EITHER one of the gas insulated double-bus switchgear to be in DEAD condition, protections are disabled accordingly.

Yes, I believe there are two different compartments for each main and reserve bus.

I really hope OEM design caters for shutting down one bus and do the extension work at the far end of the bus, while the other bus remains energised and loaded. And continue on the other bus after completing all works on first bus.

And I think all agree that such work requires STRINGENT procedure and control, right?

Mr rraghunath, I think you have such experience in doing this bus extension work? May be I will contact you again in future for info sharing. TQ!

 

[dpc]

If the two buses are fully separated by metal barriers and suitable safety grounds can be installed, then work on de-energized bus can be done. Not all double-bus switchgear has fully isolated bus sections.

 

[Bung]

Vikkyarora, if other utilities are anything like mine, you won't be given the option of which you want to sell. It will all be tied up tight in the specification, and they will decide what they want to buy. I haven't come across a utility yet that lets an equipment supplier have the final say on system design philosophies.

As for extensions on existing GIS boards - good luck! You'll probably end up with joggle chambers and all sorts of integration issues because nothing matches the old switchgear any more. Or brand C is cheaper than the existing brand B and purchasing didn't ask engineering...

Bung
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