Shut off 3 phase supply

[Guest 004]

^ ok E54 Here is is the set up.

My client has an combined undervoltage transient device, so in in effect when the supply voltgae goes +- 10%, on any given phase that phase will shut down, and then switch an invertor for required cicuirts.
One of the circuits that is not required under such said conditions is a 3 phase ceiling void fan, which in effect runs all the time. My client was worried that with the other 2 phases still trying to turn the motor, this would genereate heat, and possibly cause a fire, or burn out the motor. Why would a muti phase MCB (which is already installed) trip? So this is why IMO that a phase failure relay would work really well.

If you have an easier suggestions I will gladly read them.

Thanks

 

[Engineer54]

^ ok E54 Here is is the set up.

My client has an combined undervoltage transient device, so in in effect when the supply voltgae goes +- 10%, on any given phase that phase will shut down, and then switch an invertor for required cicuirts.
One of the circuits that is not required under such said conditions is a 3 phase ceiling void fan, which in effect runs all the time. My client was worried that with the other 2 phases still trying to turn the motor, this would genereate heat, and possibly cause a fire, or burn out the motor. Why would a muti phase MCB (which is already installed) trip? So this is why IMO that a phase failure relay would work really well.

If you have an easier suggestions I will gladly read them.

Thanks

See what a difference it makes, when you give the relavant details!! Looking at things in the dark or with only half the story on a forum can be confusing to say the least!!

We didn't know what you were trying to protect against, i was assuming you lost a fuse, from a downstream fault when you were talking about losing a phase.

To be honest, i can't see the point of the UTD only dropping out the offending phase, usually they will drop out all the phases and switch in a 3 phase inverter/stand-by generator or the like, especially where you have a mixture of single and 3 phase equipment connected after the UTD.


Anyway you have found a solution that suits your needs, so all's well that ends well as they say. ...lol!!

 

[Knobhead]

From the OP i'm still not sure what he's trying to do. If all he wants to do is shut down a 3 phase supply when losing a phase, say due to a fault down stream, and the supply has fuse over current protective devices, then all that's required is to replace the fuses with a multi phase MCB/MCCB. Anyway if he's happy that he's found a solution in the way of a phase failure relay, all's good!! lol!!


One of the reasons i don't like fuse protection for poly phase motors, unless those fuses are of the striker release type, where when any fuse ruptures, is releases a striker to disconnect all the phases.

The motor O/L will protect against single phasing. So where’s the problem with fuses for motor protection?

 

[Engineer54]

You would think so, If set correctly. ...But seen far too many starter O/L modules fail to protect in a timely manner. It's just become a preference for me now to use poly phase MCB's/MCCB's for motor supplies now.

 

[Knobhead]

If either the fuses blow or MCB trips there’s an underlying fault.
Over the years I’ve had very few O/L units fail in relation to the number installed.
When it comes to the old dashpot relays then I would agree. I can’t remember the last time I installed one of them!