MV Transformer Fusing

[zooby]

Sorry for the pic. I couldnt seem to get the "file" to load. Anyway---I am updating info on our transformers and I wanted to ask or confirm that the links in the bayonet fuses are sized based on the load that was calculated and the xfmr size has nothing to do with it? T12 might be a good example since it was a 112.5kva but was replaced with a 500kva. Gonna piggyback another question here....
With roughly 14 xfmrs on south loop and 8 on north loop, is it a sure thing that someone does their homework in regards to the loads being added to either loop? Likely irrelevant but there are 500kcmil all thru our loop. I will be the first to admit when I dont know or understand. I appreciate this forum!

 

[jim dungar]

MV transformer fuse selection tables almost never protect loads and quite often do not even protect transformers. Their sizing is typically chosen to remove a faulted transformer in order to protect the MV grid. Many tables are probably 70 or 80 years old and were originally intended for utility transformers fed by overhead conductors.

 

[zooby]

MV transformer fuse selection tables almost never protect loads and quite often do not even protect transformers. Their sizing is typically chosen to remove a faulted transformer in order to protect the MV grid. Many tables are probably 70 or 80 years old and were originally intended for utility transformers fed by overhead conductors.

Thanks Jim. I did find an article from Maddox that went thru the sizing and yep....boils down to what you said. appreciate it.

 

[Elect117]

There are some really good coordinating tools these days like S&C has a online app that you can select MV transformer values and cable types to see if the fuse selection will protect things. That would be a okay quick and dirty way to verify but if you are looking for coordination, then you might want to talk to an Engineer and replace the set up with CT / PTs with relays. Like a SEL-751. Then you can modify some of the values around to get a more desired effect.