Voltage and current zero crossing

[leonel]

I need to measure the V-I displacement on a 3phase, without neutral, and i don´t know which circuit to use.
I´m thinking to use optocouplers to detect the zero voltage and corrent crossing and in a microcontroller determine the diference between them.
If the circuit was 1phase I would know, but with 3phases!???
Anybody can help me!?

 

[Russlk]

I would use a current transformer and comparitor to find the current zero crossing. If the 3 phases are equally loaded, you only need to measure one. If the loads are not equal, it is just like measuring 3 single phase circuits.

 

[leonel]

Corrent transformer!!??

Insatead using a corrent transformer, can I use a current sensor resistor?

 

[Russlk]

Opening the lines to insert a resistance would be a problem, and if it is a high power system, the power disapation could be a problem, plus you still need a way to isolate the 3 phases.

 

[leonel]

I´m thinking to use this circuit (see the attachement). What do you say? Should I do some changes? Where?
Or you advise other kind of circuit?