Unbalanced current outputs at ATV38 driver.

[mhans]

Hello all.

I have 200 kW ATV38 driver and this driver runs a 160 kW motor. It is a fan application.

Problem is :

There are big current differences at output. 120 - 160 - 200 A.
When I run the motor with the soft starter , everything seems O.K. Currents are balanced. When I turn back to driver I have big unbalanced currents.

I sent it to service , and service said there was no wrong thing in the driver and they said they tested it with 110 kW motor and it was O.K. They sent it to me again.

I made auto-tunning but the problem is still going on. Any idea for this ?

 

[jraef]

You are measuring the current on the output side? With what? Most common multimeters are incapable of correctly interpreting the complex psuedo-sine wave output of a PWM drive. I would not trust any readings from a meter that costs less than $1,000 US and states unequivocally that it was specifically DESIGNED for use on the output of a PWM inverter. And don't be fooled by the use of the term "True RMS", it is basically meaningless when it comes to this.

Most good quality VFDs provide you with the ability to read the output phase currents using the VFD display. The VFD itself must have that ability to monitor current correctly, because it is protecting the motor, so the display reading is what you need to know. Unfortunately that is not a "good" drive, it is a cheap drive, so it does not monitor individual phase currents, it only looks at average current to the motor. Still, if it was severely off like that, the average current would be affected. But if you sent it in and they said it is fine, that's likely because they had a better meter than you.