Phase Rotation Detector

[Katy1163]

Can anyone fill me in on how a phase rotation detector works? I need to alter an existing design, but I'd like to understand how they works before attempting to do that. Any help would be great!

 

[Skogsgurra]

It depends on what type you have. Is it a electromechanical device or a passive one, using RC combinations? Or is it an electronic one, using chips or a micro?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[edison123]

Ordinary electro-mechanical phase indicator has a small 3 phase motor inside.

Beware that changing the phase sequence of your system will also change the direction of rotation of all your 3 phase motors presently in the system.

*Why a man thinks he outrun a chasing dog when it has twice as many legs?*

 

[Katy1163]

It's a passive circuit using resistors and caps.

 

[Skogsgurra]

OK, that type works with the principle of creating a phase-shifted voltage between one phase and neutral. If you draw a vector diagram with three equally long and spaced vectors (120 degrees apart) and put an RC combination from one of the vectors to neutral, you will get a voltage across the capacitor that is lagging the vector voltage.

Since you now have created an asymmetry, the distance from this lagging voltage to the next vector is smaller than the distance to the preceding vector. Using purely resistive voltage dividers in the other two phases, you can get a significant difference, which is dependent on rotation direction. Sometimes two simple neon lights are used to show rotation direction - the one connected to the preceding vector is always the brightest.

A relay with dual coils is sometimes used to close a contact when rotation is right.

What is it that you need to change?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Katy1163]

Well, this unit that we have is only good for 12 volts....I think this is only because the meter that we use on this unit is only good for 1mA.....and so i think if I play with some resistor values, that may work to draw a little less current at a higher voltage....any ideas? And thank you by the way!

 

[Skogsgurra]

You have 12 V three phase? And an instrument instead of the neons? That should also work.

You just play around with what you have. Cannot do much harm if you remember to have enough series resistance so you do not peg the instrument.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...