3 Phase Power Monitoring

BITS N BYTES

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Trying to find/understand how best to monitor the current in a three phase circuit with a PLC. Need an analog signal that can be monitored by an analog PLC input. Platform is OMRON NJ controller. Any suggestions/experience with suitable CT modules would be appreciated. THANX
 
Wago have a module specific for 3 phase power measurement. Works with a Rogowski coil around each phase conductor. Not cheap, works well (for decent currents, not for .5A ).

I do not know if other PLC manufacturers have similar modules.


Edit: would Omron KM1 fit your needs? http://www.ia.omron.com/data_pdf/cat/km1_n170-e1_8_2_csm1004013.pdf
I am not familiar with their PLC's and if it matches well with the KM1 modules in terms of connectivity, you may want to have a look.
 
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Lol, I even know better, but made a common error...

You said "power", many of us gave you current...:oops:

Thank goodness at least a few responders got that right...

And by the way that ABB unit is an ENERGY meter, also not the same.

Current = a component of power, along with voltage and power factor
Power = instantaneous reading of all of the above, a component of energy
Energy = power integrated across time

So as others posted, if you want power, you need a power transducer. You can in theory do it with a voltage transducer and a set of current transducers, but getting true power factor involves comparing wave form displacement and is difficult to do accurately in a PLC. Better to just get a power (kW) transducer that does that inside for you and gives you a simple analog output to go to your PLC.
 
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Wago makes several kinds of transducers (transformers and Rogowski coils) and corresponding input modules (750-493, 750-494, 750-495). For use with a different brand PLC you would need to apply a remote I/O setup that you read into your choice PLC through a fieldbus (e.g. Modbus/TCP).

Using with Wago software is pretty straight forward as there is a CoDeSys library with function blocks for getting power factors, current, voltage, cosinus phi, frequency, harmonics, active/reactive/apparent power etc. As far as I'm aware all processing is done in the input module, so with some leg work (specs of the module's process image) one can read the values from whatever PLC that "speaks" the same fieldbus.
 

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