substituion of HRC fuse in Vacuum Contactors 1

[relayprotection]

Hollo folks!
we are using vacuum contactors at 6.6 kv with HRC fuses.In case we use a circuit breaker in series with the vacuum contactor having instantaneous over current protection then is it possible to avoid the usage of HRC fuse.If yes why.If we dont use any fuse then will it withstand thermally the fault current.
VC can thermally withstand 9000 Amp for 1 second.
Fault current may be taken as around 15KA and this much current will flow for the time till over current relay operates and the breaker trips.

 

[peterb]

Just be very sure that the contactor will never have to interrupt fault current above the rating.
What if the upstream relay or breaker fails? The manufacturer will have no liability if your contactor fails due to unauthorised modifications and your insurance company may also be interested in the matter.

 

[ccaserta]

Make sure hte circuit breaker can be used for primary protection. The manufacture specifies the usage of overcurrent protection devices. Most of the time North American agencies (UL and CSA) look for fusing on the primary side of the transformer the circuitbreakers on the secondary side because of the way the components are specified for use. Christopher Caserta
Sr. Regulatory Engineer
ccaserta@enorthhampton.com
Ph:904-225-0360
Fax:904-225-0340

 

[Bung]

I'm not sure I can see any reason why one would replace FCL fuses with a CB and o/c relay alone, unless you are worried about faults below the fuse min melt current (the fuses are backup types). If you were going to take advantage of the additional protection cpabilities of modern relays, it may be worthwhile. But the advantage of fuses is that they don't require backup - fuses don't fail to interrupt fault current, and they are not maintenance intensive. If you do go ahead with the replacement, just make sure the relay operating characteristic you use is quicker than the I2t let-through for the contactor, and that there are no mechanical force issues to consider. Also, what about downstream equipment - is the fuse protecting anything else from damage by through fault currents (cables, for eg). Is the upstream coordination affected? If it is being done because of nuisance fuse operations, are the fuses you are using the right ones for the job - it may be cheaper to just use the correct fuse size than throw the whole thing out.

Bung