Bushing Ampere Rating
Bushing Ampere Rating
(OP)
Our Transformer standard specifies that Bushing ampere rating shall be at least 20% higher than the respective transformer winding ampere rating at maximum transformer nameplate rating.
Does anybody have a basis for this standard? I checked c57.19 series on bushings but couldn't find anything on this. Our vendor is committing to 19% over the LV winding ampere rating and we want to know if that is okay or not. The bushing in question is LV bushing – 25kV class, 150 kV BIL for a GSU transformer 25kV-230kV (750 MVA Transformer).
Thanks in advance.
Does anybody have a basis for this standard? I checked c57.19 series on bushings but couldn't find anything on this. Our vendor is committing to 19% over the LV winding ampere rating and we want to know if that is okay or not. The bushing in question is LV bushing – 25kV class, 150 kV BIL for a GSU transformer 25kV-230kV (750 MVA Transformer).
Thanks in advance.






RE: Bushing Ampere Rating
I personally don't think that 19% O/L capability is significantly worse that 20% O/L capability, but I live in a climate where we won't ever see +40°C ambient so in reality I would always have a little more in hand than indicated by the standard ratings. If you are in a hot location then maybe it would be a problem.
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RE: Bushing Ampere Rating
Anybody has any idea if there is a standard that dictates the ampere (current) rating of the bushing as compared to the transformer winding? Like I mentioned, ours says it should be 120% compared to the winding.
RE: Bushing Ampere Rating
RE: Bushing Ampere Rating
I'd have preferred a reference in IEEE or even NEMA document to IEC (specially since we don't follow it and we don't have access to those documents), but still I am thankful.
Wouldn't this also depend upon what is the fault availability in the area? I mean, if the max short circuit current that the transformer sees is much less than this value (120% of winding ampere rating which is around 21kA, as opposed to the vendor proposed bushing which is 18KA) then we really shouldn't be worried? I guess the short ckt current would be much much higher than the rated current, but 21kA is pretty high.
RE: Bushing Ampere Rating
No, short circuit current has nothing to do with the current rating.Normally bushings are very strong to SC currents.
Being inside the busduct, rating may have to be derated.This depends on design of bushing etc. Manufacturer will be able to guide you.
RE: Bushing Ampere Rating
Thanks for the help.
RE: Bushing Ampere Rating