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Vfd


boby

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we have abb make acs 500 series vfd for 100hp motor for carrier application. we running the motoor with dive at 300 rpm and torque at 3%. at this motor taking a load of 24 amps. when i am checking the load at drive in coming it took 10 amp what is this load. i have observed zero voltageat drive out put(motor voltage) and while checking the frequency it varies over wide range from 20 mhz to......... we r maesuring the all with true rms clamp meter. is there any special meter to check drive out gonig voltage and frequency

and why i have observed zero voltage and variable frequency? we dont give any reference signal to drive to control the speed

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Measuring the output of a VFD is not an easy task for most meters. Even if it says "true RMS" it may not sample fast enough to get an accurate reading. Also, many "true RMS" clamp-on meters are not true RMS for voltage, only current. Even with true RMS current meters, the harmonics on the output can interfere with correct reading. The bottom line is that unless your meter specifically says it was designed to be used on the output side of a VFD, it is not to be trusted.

 

The best way to determine loading at the motor is to read the kW from the drive display, something I believe the ACS500 is capable of (depending on its age). The reason you read 10A on the input and 24A on the output (if that is even correct) , is because the voltage is different between them. the 10A is the current load at the line voltage. The 24A is the current load at whatever voltage was necessary to drive the motor at 300RPM.

"He's not dead, he's just pinin' for the fjords!"
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Well stated jraef, the out put of a drive can cause much head scratching. The best way is to trust the drive display (if available).

Ken

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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