Single Phase preventer

[suma.n]

How does the phase preventer circuits works? How does it stops the motor rotation when phase reverses.?

 

[chuckey]

The problem with a three phase motor is that once its rotating, breaking a phase to it will result in the motor generating the missing phase (google rotary phase converters). So you need a very tight window detector on the phase to phase voltages, say 95% or some form of current monitoring, as when a phase is missing, the motor generates voltage but the current in that phase will be zero.
Frank

 

[FvM]

The problem with a three phase motor is that once its rotating, breaking a phase to it will result in the motor generating the missing phase (google rotary phase converters). So you need a very tight window detector on the phase to phase voltages, say 95% or some form of current monitoring, as when a phase is missing, the motor generates voltage but the current in that phase will be zero.

True, but the missing phase won't be a problem at low load, as long as the rated motor current isn't exceeded. Industry standard thermal motor circuit breakers or monitoring relays will provide sufficient protection in this case.

Decicated phase failure/reversal monitoring relays are appropriate for sites with unreliable power supply, e.g. mobile machines.