6.6kV Vacuum Contactor (Latched) Opening time

[RRaghunath]

We have a problem with 6.6kV Vacuum contactors (VCUs)-latched type.
The contactor closing time is about 60ms and opening time is about 25ms. There is no issue with that.
When the trip command came while motor is starting, the contactor takes ~400ms to open. This time the trip was from process (O&G industry), But, it could have been from earth fault protection.
As we know the likelihood of faults during inrush (whether it is motor or transformer) is high statistically and it is important that the VCU opens without additional delay when commanded by earth fault protection.
In VCU feeders, short circuit protection is not enabled in feeder protection relay (fuse is expected to clear large current faults) but earth fault protection is enabled. 6.6kV system is resistance earthed with earth fault current limited to 300A.


Rompicherla Raghunath

 

[ScottyUK]

It sounds like there's an intentional delay somewhere, but without knowing which relay you've got any comments here are going to be conjecture and speculation.

 

[krisys]

raghun,

It is not clear whether you want to trip (open the contactor) with minimum delay or you want to delay intentionally.

For the earth faults where the earth fault current is low (maximum 300A, in your case) half a cycle or a couple of cycles doesn't matter. The extent of burn out will not be much. Nevertheless earlier is the better.