Torque from 280KW Motor & VSD 1

[Ant2004]

Is there any other way to prove the torque being produced at a motor shaft is correct, apart from using tha torque / current diagnostic on a VSD HMI?

I have a situation where the customer has replaced a old DC system with a closed loop VSD / Motor. The drive has autotuned offload correctly. However when running the machine it runs at approx 100% torque and @ FLC.

Obviously on a DC system a quick check of IA and VA will give you some indication however is somewhat more difficult on AC.

 

[Skogsgurra]

The standard way of doing it is to measure absorbed active power (watts) and divide by shaft speed (rad/second). That will give you a rough newtometer value. Correction for losses will give you a quite accurate value.

A normal motor is symmetric so you need only measure one phase. The problem usually is that phase current and phase-phase voltage is available. So you probably have to measure with a two (or three) wattmeter system.

Gunnar Englund

http://www.gke.org

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

 

[waross]

If you just want to prove that the torque is correct, look at the load. If the torque is too much the load will be turning too fast. If the torque is too little the load will be turning too slow.
respectfully

 

[DickDV]

Assuming the motor is seeing proper voltage and phase balance, it seems to me the easiest way to find running torque is to determine rotor slip.

Since there is an essentially linear relationship between slip and torque, a simple strobe light on the shaft and a calculation of % slip should give you torque.

For example, in the 50Hz world, a four pole motor has a sync speed of 1500rpm. Let's say the motor is nameplated 1460rpm.

At no-load the motor will turn very close to 1500rpm. At 100% rated load, the shaft speed will be 1460rpm. At 25% load the speed is 1490, at half load it is 1480, at 75% it is 1470, and at 50% overload it is about 1440.