Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
(OP)
I have no experience with fuses (other than some fuses on radial distribution lines); I need some help coming up with the fuse size to protect a 3.75/4.68 MVA distribution Transformer. The fuses obviously are on high side (Delta 23kV) and the low side is Wye-grounded 4.16kV. I have looked into using 125E, 150E, and 175E S&C fuses, but don't know what the actual criteria is for coming up with the fuse size based on Transformer data. Transformer Z=6%
Since there is no other form of protection (breakers, relays, etc) on this transformer, I am a little more concerned. Your help would be really appreciated.
Since there is no other form of protection (breakers, relays, etc) on this transformer, I am a little more concerned. Your help would be really appreciated.






RE: Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
According to NEC Art.450.3 [Table 450.3(A)]:
If it is a unsupervised locations if Z<=6% the primary fuse rating has to be not more than 3*Irated[300%].Here is a note:
"1. Where the required fuse rating or circuit breaker setting does not correspond to a standard rating or setting, a higher rating or setting that does not exceed the next higher standard rating or setting shall be permitted."
The rated current has to correspond to S[rated apparent power]used to state the short-circuit impedance Z.I think S has to be 3.75 MVA and 300 A has to be the fuse rating.
RE: Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
Also do some searching on the S&C site, they have great references on fuse sizing.
Check with your utility for coordination and possibly the building insurance company if the transformer will be indoors. I believe some insurance companies such as FM Global require current-limiting devices in order for the liquid-filled transformer to contain the FM label.
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla
RE: Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
RE: Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
RE: Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
If you wish to have some type of overload protection on the transformer, add some type of protection to the fuses.
Bill
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"Why not the best?"
Jimmy Carter
RE: Fuse Sizing for 3.75/4.68 MVA Transformer 23/4.16kV.
Also, this TXfmr is feeding only one feeder which has a recloser on it, so I think overload protection will be done by that feeder on the 4.16kV side. The only other protection that I proposed for this unit other than fuses were 63FP and 71Q. Are those enough or do I need to add some more?