Fuse Rating for Short Circuit
Fuse Rating for Short Circuit
(OP)
Hi,
I need to hook up 138kV, 1ph ssvt (inductive type) to a bus via fuse link disconnect. The maximum SLG fault current at that bus can be 20kA (symmetrical) from my study. But, the maximum fuse rating available in the market is only 12.5kA (symmetrical). Can I still use this fuse to protect the SSVT. The insulator and the remaining structure can withstand 20kA for sometime.
I learn that typically the 138kv ssvt units are hard bus connected without any fuse or disconnect switch. Considering that, I thought what I propose is definitely a better solution if not better.
Will a fast acting fuse serves better than normal speed fuse? After all this fuse is meant to blow anything more than 5 amp current
I need to hook up 138kV, 1ph ssvt (inductive type) to a bus via fuse link disconnect. The maximum SLG fault current at that bus can be 20kA (symmetrical) from my study. But, the maximum fuse rating available in the market is only 12.5kA (symmetrical). Can I still use this fuse to protect the SSVT. The insulator and the remaining structure can withstand 20kA for sometime.
I learn that typically the 138kv ssvt units are hard bus connected without any fuse or disconnect switch. Considering that, I thought what I propose is definitely a better solution if not better.
Will a fast acting fuse serves better than normal speed fuse? After all this fuse is meant to blow anything more than 5 amp current






RE: Fuse Rating for Short Circuit
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Fuse Rating for Short Circuit
RE: Fuse Rating for Short Circuit
Regards
Marmite
RE: Fuse Rating for Short Circuit
Marmite - In this case the fuse is actually underrated for short circuit fault. Its never meant for overcurrent.
Available short circuit at the bus - 20kA
Fuse capability - 12.5kA
RE: Fuse Rating for Short Circuit
The fuse SCC rating has to be equal or greater than the available max. fault current, which is 20kA in this case.
Rafiq Bulsara
http://www.srengineersct.com
RE: Fuse Rating for Short Circuit
I thought the fuse will anyways blows off much less than 12.5kA...
RE: Fuse Rating for Short Circuit
So you are saying the fuse should blow just fine, except it may not be able to interrupt the current during a fault (since it is rated well below the availble fault current)?
RE: Fuse Rating for Short Circuit
Where did I say that?
Rafiq Bulsara
http://www.srengineersct.com
RE: Fuse Rating for Short Circuit
Sure, I will not recommend it
RE: Fuse Rating for Short Circuit
What Marmite said...., politely.
Rafiq Bulsara
http://www.srengineersct.com
RE: Fuse Rating for Short Circuit
RE: Fuse Rating for Short Circuit
Depends on how sensitive the 138kV differential is set to trip. The SSVT is only 100kVA @ 138kV = 0.73Amps. That's too small a current for differential to pick - up.
RE: Fuse Rating for Short Circuit
Regards
Marmite
RE: Fuse Rating for Short Circuit
RE: Fuse Rating for Short Circuit
Marmite - I agree that the fault current will be more than 0.73Amps. I take back my statement, I gotta get back to my basics. Thanks for the correction!