3-Phase Earth-Neutral measurement

[smitchell]

Hi,

I need to measure the voltages and currents of a 5 wire 'Y' connected 3 phase system. Professional energy meters have turned out to be too expensive, so I'm thinking of just using stepdown transformers, rectifying the signal, then feeding it to an ADC.

My problem is, how do I measure the voltage between earth and neutral, when I am already using neutral as my ADC ground reference for the other measurements?

I'd really appreciate any idea's, or general advice on measuring 3-phase power using ADC's.

Thanks a lot,

Sam

 

[batdin]

Measuring the neutral-to-earth voltage is not a problem.The problem is that you are going to use a rectifier whose rectifying curve is by no means linear,i.e. you will have a certain error (unless you use a look-up table,of course).

 

[smitchell]

How would I go about measuring the earth-neutral voltage? how would I configure the transformers, and what will be fed to the ADC?

The non-linearity of the rectifier shouldn't be too much of a problem, as the voltages I'm measuring will not vary that much. Also, before the voltages are displayed remotely, software adjustments can be made to counteract the non-linearity. Well, thats my dodgee plan anyway...

Will that work?

I'm still baffled about the actuall circuit configuaration to measure all of these voltages with the same ground reference on one ADC chip. well actually its an AVR micro with 8 channels of ADC.

Thanks heaps,

Sam