Switchgear Bus Rating

[MeinKaun11]

Hi I have a existing old 4.16 kV switchgear which i need to replace. It is fed from two main transformers 5/6.67 MVA @ 27.6/4.16 kV.

I dont have a way to find out the existing bus rating but on 4.16 kV, We have been buying a 2000 A bus switchgear but those transformers are smaller.

This is a special case and total ampacity for both transformers at full load is 1852 A at 4.16 kV.

Any suggestions, a 2000 A would do the job or I need a 3000 A bus, what would be the traditional approach.

 

[collies99]

I only get 922A at 4160 on 6.67 MVA.

However if you max FLA x SF is less that 2,000A, yes you can use 2KA bussing. Just chevk it is within max short curcuit curtent rating.

 

[MeinKaun11]

Thanks Collies but I have two transformers feeding the same bus simultaneously, so my max. current will be 1852 and bus will be 2000 A if I go with it.

I could not find any literature on bus sizing. My next option is 3000 A but I want to make sure I have some kind of scientific justification to buy a 3000 A rated switchgear rather than 2000 Amps.

Appreciate your input !

 

[waross]

Two transformers @ 6.7 MVA

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

What is the cost difference? It might be less than you think. If the maximum load will be 1852 A, then 2000 A is adequate. That is the science. The art is in determining the possibility of future load growth, replacement of transformers with larger units, etc. As mentioned above, short circuit bracing must be considered as well.

 

[collies99]

Yes, DPCs recommendation should be considered. Thank you

 

[jase28]

Have you considered the load considerations further back to best align your protection standards as the change of TX will require upscale protection changes, is this part of a radial or ring distribution network, there are many things to consider if you cannot perform a like for like change.