Fuses operating 12 KV sub station,the natives are getting restless.

[kwatt108]

Out of one of our 12.47 substations, 20a type T fuses are causing dips or operations that are seen breaker wide. These are generally fuses near enough to the station to have a high fault current. Our system engineer has a "deer in the headlights" look, is unresponsive, and I have no experience with current limiting fuses.Guidance,resources,or just good stories appreciated.

 

[zog]

Here is a little primer on MV fuse operation. But not sure what you mean by this "fuses are causing dips or operations that are seen breaker wide" View attachment fuseoperation.pdf

 

[Hv&Lv]

Out of one of our 12.47 substations, 20a type T fuses are causing dips or operations that are seen breaker wide. These are generally fuses near enough to the station to have a high fault current. Our system engineer has a "deer in the headlights" look, is unresponsive, and I have no experience with current limiting fuses.Guidance,resources,or just good stories appreciated.

Type T expulsion fuses aren't current limiting. Fusing coordination will blink the breakers once before blowing, depending on recloser curves. Here are the T curves. That close to the station, I believe I would opt to fuse for load rather than coordination. You can look at the curves and set the fusing as high as possible without the blinks.

http://www.cooperindustries.com/con...ystems/resources/library/Kearney/K51000AB.pdf

 

[mivey]

If you give some relay settings, station size, available fault, relay types, protection scheme, differential settings, etc. we can help you out. Excluding the instantaneous, I would expect the fuse to clear 1st when close in to the station because of the inverse nature of typical relay curves (close in for me is in the 5-20k range on the far right).

If the faults are that close in, you may be tripping on instantaneous. Could even be a differential if the settings are off or the CTs connected wrong. Does one feeder trip or the whole station? What kind of operation flags are you getting?