Switchgear Fault Level 3

[Deansharafi]

What is the remedy for a switchgear when its fault capacity is exceeded? Let's consider a case where generators are added to a busbar without considering the fault capacity of the board.
Is there anything that can be done to rectify the situation?
Thanks for your thoughts.

 

[neps3]

Dean

Yes ABB has come up with a fusing device for HV that can be added to the switchboard to protect the aparatus from excess fault level.

I do not have full details but you can contact your local ABB and they should put forward a proposal.

For large generators it is proper for them to consider adding limiting devices to limit fault levels.

If in house, then you should consider ABB. There are a few installations that I know who have installed.

 

[ScottyUK]

Hi Dean,

What voltage is the board in question? LV or MV?

What elements of the board rating are exceeded? Bars, breakers, etc?



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[peebee]

There was a very similar thread to this on this site within the last year or so.

Anyway, aside from current-limiting devices mentioned above, the other solution would be to add impedance. That is, additional cable length, transformers, reactors -- anything that will increase the impedance of the system will help limit the fault current.

Or, you could replace the gear. . . .

 

[dpc]

If you go with a fuse type device, you will be sacrificing any notion of selectivity and coordination for high-level faults, since the fuse must melt in order to limit current.

 

[charlierod]

If generators neutrals are earthed it would be good to consider adding grounding reactors or resistors.

 

[Deansharafi]

ScottyUK,

The voltage level is 3.3KV and the bars are exceeded.
Regards,

 

[ScottyUK]

Some good suggestions above. A fault-limiting reactor may be best option at MV but may cost you additional breakers if you need the ability to remove the reactor from service while maintaining supplies to the board. Charlierod's suggestion helps with phase-ground faults but offers no improvement for phase-phase faults.

The transformers feeding the bar will be of lower capital cost than the generators assuming they are of similar rating. Can you replace the transformers with a higher impedance design? This will cost more than adding a reactor, but will consume less space overall than adding a reactor to the existing installation and will not require the extra costs of bunding and foundation plinths, etc.

Can you use a Castell or similar interlock scheme to limit the number of infeeds to the board to say two from three or three from four?



----------------------------------

If we learn from our mistakes,
I'm getting a great education!