VFD increasing the motor winding temperature

[edison123]

I tested a 415 V, 350 KW, 2 pole motor on no-load (open shaft).

With utility supply at 50 Hz, the motor winding temperature was 64 deg C with 130 A current.

With VFD supply at 50 Hz, the winding temperature went up to 97 deg C with the same 130 A current.

The drive is Yaskawa GA 700 model.

Where is the additional heat coming from? From the stator iron due to drive switching frequency?

Will using a sine filter on VFD output reduce the winding temperature?

 

[jhnblgr]

Did you check the hz independently of each other? Also what was the shaft speed? Could be poor wave form on the vfd output otherwise.

 

[mparenteau]

Distance from drive to motor? Is the motor inverter duty rated?

Mike

 

[edison123]

Shaft speed is directly measured as 3000 RPM in both cases by independent digital non-contact speed sensor.

The motor is VFD duty rated, and the distance is 5 meters.

 

[jhnblgr]

Ok so shaft speed rules out ineffective cooling. What were the voltages? Might want to check your sine waves

 

[waross]

Have you ruled out measurement error?
The switching frequency may be affecting your temperature measurement.
Check the temperature immediately after stopping the motor as a quick check.