Current limiting fuses for momentary protection

[jstelly]

I have several vacuum switches used for cap banks that have recently been found to be over-dutied. The momentary for the switches is 15kA, and currently there is roughly 25kA of fault duty available.

The switches are protected by SMU-20 fuses, which initally was thought to protect the switch. After looking at the TCC curves however, it was discovered it would take between two to three cycles for the fuse to clear. This would likely damage the vacuum switch and cause a safety concern.

I was wondering if it would be feasable to apply a current limiting fuse in this instance? Also, are there any 34.5kV current limiting fuses that would fit this application?

 

[ePOWEReng]

You can check S&C fault tamer current limiter. It applies at this voltage level.

 

[alehman]

But only if you have S&C switchgear. They won't sell it to other manufacturers. I don't think it's available for 34.5kV anyway.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[Marmite]

You might want to check out the making duty of the switch also. The inrush current to a capacitor bank is of high frequency and magnitude. The rate of increase in current dI/dt can exceed the rate of increase in contact pressure, causing burning of the contacts. The current switchgear standards from IEEE and IEC specify capacitor bank switching duty in terms of both current and frequency. The inrush can be mitigated by the use of series reactors.
Regards
Marmite

 

[rbulsara]

Just curious, who makes 15kA momentary rated vacuum switch?

Rafiq Bulsara

http://www.srengineersct.com

 

[jghrist]

I'd check with Cooper Power for availability of 34.5 kV CL fuses. CL fuses ahead of the switch should be a feasible solution, since you are not trying to interrupt the fault current with the switch. With that high a level of available fault, you probably need CL fuses to prevent capacitor tank rupture anyway.

 

[ePOWEReng]

The fault tamer applies at 34.5kV in an outdoor cut-out type....also checkout Eaton's selection of CL fuses. I haven't seen anyone advertising that high of an interrupting rating for 34.5kV CL fuses though...