How to find high current flow?

[dhanasingaraja]

Hi,
In my village, 3 phase supply comes for 4 hours, and single phase supply comes for remaining hour. I wanna switch 5HP,30amps motor for every time phase changing.My problem is how can i sense 3 phase supply.can i use resistors? If power comes i should control the connection with relay

 

[FvM]

The best method, also to protect the motor against damage, is a phase loss monitoring relais.
FINDER|72.31.8.400.0000|RELAY, PHASE FAILURE | element14 India

The relais closes a contact, when the three phase mains is up with correct rotation. It can control the power contactor.

 

[dhanasingaraja]

I want to monitor/control this switching through gsm.so i should use micro controllers.How can i sense/control this with micro controller?
pls help me

 

[FvM]

You can either use a ready-made phase loss monitoring relay, or learn how these devices work and design your own one.

My measuring all three phase-to-phase voltages, you can test if a three phase voltage is present. Usually, the phase sequence is checked in addition.