Equipment -
Motor 10 HP 480V 3 phase
Emerson Commander SK (brand new)

Motor was checked out by a rebuilder after it started tripping out the old drive and / or breaker.

No issues found except worn bearing seats which were re-machined.

Looked like the old Hitachi drive was history so a Emerson was purchased. Installed and programmed - try to start drive and instant DC bus overvoltage faults.

Disconnect motor and drive "runs" flawlessly.

Wired motor direct runs great with 7.6 / 7.8 / 6.9 amp readings. (fla is 13.3)

Voltages are 483 / 487 / 484.......

Any ideas ???

 

A couple of comments:

1. There seems to be a bit of unbalance on your motor. Measure the inductance of the motor between the three phases, and see whether this unbalance is reflected in these readings.

2. You did not mention what is the length of cable between the drive and the motor. Are you respecting the drive's requirements vis-a-vis length of cable, type of cable, etc? Drives produce voltage waveforms on motors which result in higher than normal voltage peaks on the motor insulation and reflections which go back to the drive, unless the system is designed properly.

3. You did not mention whether you performed the same test with the old drive as you did with the new drive, and at what point in its lifetime did the old drive fail.

4. Were you operating the motor and the drive at relatively slow speeds possibly resulting in excessive temperature rise on the motor, which in turn damaged the motor windings (and thus the possible unbalance)?

 

Dschmatzhagen... the measured values result in Voltage-Unbalance-Factors (VUF)of 0.48%/0.50%. The first number is based on NEMA; the second, IEC.

The corresponding Ampere-Unbalanced-Factors (AUF)are 7.2%/7.3%!

However, before any meaningful conclusion can be reached, it would be helpful to know where the measurements were made, that is, were they made on the source-side of the drive, or on the motor-side? Or without the drive?

It would be helpful to know the phase-to-neutral voltages on both the source-side and motor-side of the drive!

Regards, Phil Corso (cepsicon [at] aol [dot] com)

 

Thanks for the reply

I should explain that I am working on this piece of equipment as a contractor and do not have many details on running history etc.

To answer the questions

I will test the motor as suggested - I have not done so as I had faith in the motor rebuilder and his stating the motor had no issues.

The cord to the motor is only about 3 feet long - 10 AWG SEO type cord.

I did not test the old drive - I was called in to install a new one and relied on the maintenance departments assessment of the old drives' failure

The motor was not run at low speeds but a pulley size change was done somewhere in thee machine's history resulting in a higher demand on the motor and yes, the motor did run hot. This was changed back to original configuration but the motor could have been damaged.

This motor and drive is on a "high shear" mixer - the company decided to put a larger mixing blade on without doing any research. The higher demand actually resulted in the need for a 30 HP motor to drive the larger blade. Again, this could have caused damage too the motor and again this was changed back to OEM.

I am now thinking that the motor received further damage after being at the rebuilder.

 

Dschmatzhagen... Feedback?

Phil Corso