Hi HiSet:
I have never seen a trip coil on a fuse unit assembly for 22 kv applications. I do not believe what you are inquiring about is possible.
Is there an upstream switching device that can be modified for this application?
It is about busbar proptection of HV(22kV) board ,where all circuits except station service transformer circuit have dedicated CTs for high impedance based bus protection scheme. Station service trf bay is switch fuse unit without CT. Appropriate fuse can be choosen to make sure that BZ scheme do not operate for external fault(i.e. on station service trf HV or LV side) but for real internal bus fault , how do you make sure that fuse blows to isolate faulty bus ?
Replace the fuse/switch combination with a circuit switcher or circuit breaker. - Expensive
Add a motor operator to the fuse switch. - Sllooooowwww
Add a high speed ground switch after the fuse to ensure enough fault current to clear the fuse fast. - Make a little fault a big fault
Coordinate your bus protection with the fuses so that you'll never trip the bus for anything the fuse would clear. Bus faults generally draw lots and lots of current while your fuse is probably pretty small. - Best option in my opinion.
David,
Thanks for that.Your last option seems most prudent but how do you make sure that busbar is physically isolated after genuine bus fault. All other circuits(CBs) will trip by virtue of trip signal emanating from Bus prot scheme but station service bay will remain connected and potentially could back feed low amount of fault current (if there is a source to do so) on to the faulty bus
Never seen a station services transformer that could back feed a faulted bus; never seen one with a source. Not to say that it couldn't happen but you'd just have to make sure there was no source that could be switched in.
