protective devices

[sahelrahman]

I have a question regarding the protective device voltage. The utility is 34.5kV and the relay connected to the S&C vista SWGR is rated at 23000V. I always thought that the protective device voltage should always be higher than the bus voltage. Please advise...

Thanks

 

[magoo2]

Did you mean relay or was it perhaps a fuse rating? I've never heard of a relay rated very high.

A 4-wire multigrounded neutral system has a line to neutral voltage of around 20 kV (19.92 kV). If the exposure for faults is all cable, then it is customary to use 23 kV fuses because you'll get just phase to ground faults. If however the exposure is overhead line, where phase to phase faults are possible, then you'll need a 38 kV rating.

 

[sahelrahman]

It is a Vacuum fault interrupter.

 

[alehman]

Vista gear has a special 'voltage sensor' device that detects presence of voltage and provides a low voltage signal for phasing. Is this what you're referring to?

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[davidbeach]

Relays typically have a voltage rating of 300V and 5A. To paraphrase Walt Elmore "A breaker is a device used to increase the withstand rating of a relay." There is no protective relay rated 23kV.

 

[TZilla]

The S&C Vista has three voltage ratings; 15.5, 29, and 38 kV max. I believe the 23,000V rating you are referring to is the voltage rating in the SKM library. Since the standard SKM library does not have a relay rated 38,000V it's probably getting flagged when you run the Equipment Evaluation module. The overcurrent control (relay) in the Vista is adequate for for all voltage classes.

 

[EEIre]

Have a look at the single line diagram and you will Should see a Voltage Transformer (VT) between protection relay and the busbar