MV motors & Vacuum contactors 1

[RRaghunath]

Vacuum contactors for motors are specified to be non-latched type normally.

Have any one come across latched type ones for maotor duty.
If so, what circumstances require such use.

Thanks in anticipation.

 

[Lakey]

Hi,

Does it have to be a vacuum contactor? Or will any sealed type (IP66) do - to prevent the ingress of contamination.

To my knowledge, Bi-stable or latched type contactors are NOT generally used for motor applications because they are NOT fail safe.

Regards,

 

[ScottyUK]

Many MV motors are controlled by vacuum circuit breakers (VCBs), rather than contactors. VCBs are inherently bistable devices.

I can't speak for overseas practice, but in the UK there are some quite distinct differences in the way motors are switched at MV when compared with LV, the use of circuit breakers instead of contactors being one of the main ones.

 

[gordonl]

I've seen both widely used at MV. Generally larger motors get latching breakers because contactors just aren't available. One thing to watch out is under voltage protection, with a breaker it wont open on it's own when low system voltage occurs like contactors and control transformers do, making undervoltage protection even more important.

 

[ruelvb]

We had MV motors switched on by latching type vacuum contactors. We replaced it with non latch type due to power failure problems with our utility. Contactor is still latched when power fails, and when power is restored it will run immediately causing huge problems. Our MV motors are controlled by reduced voltage starters using autotransformers.

 

[gordonl]

This problem is exactly why I mentioned UV protection, but I failed to say a secure source of control potential should be used, such as DC battery system, or a capacitor system with enough juice to trip on loss of potential.

 

[xabproject]

Dear RRN,
Recollect that fantastic presentation by M/s TOSHIBA about the use of Fuse backed up VAC Contactor for motor feeders back in TCE? I will arrange a copy for you. Send me the e-mail address.
Best regards

 

[rbulsara]

I have had used 6.6 kV nonlatching type vaccum contactors (in 80's) without any problems. These were DOL starting and we had 33 kV service so starting current was not an issue.

As ruelvb pointed out there may be more problems with the latching type contactors than benefits.

Latching type contactors (MV or LV) would only be used for manual starters and if restaring the motor upon restoration of power after an outage is not a problem. IMHO any process that requires quick restarts, shall still be controlled by a seprate control/automation system and not rely on a latching type starters/contactors.

If you are worried about chattering type of issue for a electrical held contactor, then provide a stable source of control power (for example 110V DC baked up by batteries or UPS).