Curent Transformer to Monitor Amperage
Curent Transformer to Monitor Amperage
(OP)
I want to monitor amps on a 75 hp 480 volt 3 phase motor with a remote digital ammeter. Does it matter if I install the current transformer (doughnut) on the load side or line side of the VFD? Thanks.






RE: Curent Transformer to Monitor Amperage
RE: Curent Transformer to Monitor Amperage
An ordinary CT doesn't work well below rated frequency (50 or 60 Hz, depending on where you are). So, if you go down with motor frequency, it is very probable that the CT will saturate and introduce significant errors. On the other hand, the mains current is rather distorted and an RMS meter will probably show too high a value if you put the CT there.
Most frequency inverters have have an output where you can read the motor current as a 4-20 mA or 0-10 V analogue signal. That is what I would use in the first place.
Gunnar Englund
www.gke.org
RE: Curent Transformer to Monitor Amperage
As Gunner has also pointed out, use the analog output of the drive to feed the meter, likely a 4-20mA loop.
RE: Curent Transformer to Monitor Amperage
----------------------------------
Sometimes I only open my mouth to swap feet...