Heating of motor by using frequency converter

[wiks]

For checking of operation of frequency converter (4kW 3 phases 400V)we use 0.75kW motor. Unfurtonately motor heats more than it could be.
The frequency converter on my opinion was programmed correct. The rated current of the motor is 2.3A, but measurings shows that it is 3.2A.
Is this converter's programm's mistake or something is doing wrong?
Or this is motor fault?

 

[CHDean]

Have you looked for an overload? The drive you have is greatly oversized for a .75kw motor and will give the motor all the power it can handle plus some more. You may wish to double check the current limit you have programmed.

 

[CB2]

What kind of amp meter are you using to measure amperage? The output of the VFD is not a standard syn wave and can not be measured with the common digital meters. Use either an old style iron movement meter or a true RMS meter.

What does the VFD say the output current is?

 

[acadien]

Check the motor specs, most motors cannot tolerate low Freqencies unless they are designed for it. Typically if the application calls for less than 20Hz I would use a speciallised motor for VFD application.

 

[AFab]

I agree with acadien, the cooling fan on the motor is sized for the designed speed. If you run the motor at a much slower speed it will require an external cooling blower.

 

[jbartos]

Suggestion: The frequency converter in lightly loaded condition may be noticeably less accurate than for the rated conditions.

 

[mishlove]

What type of load: Constant Torque or Variable Torque ?
What is the operating speed range: ?Hz to ?hz
Are you getting hi current at all speeds ?
Is the VFD a regular V/Hz drive ?
What is the carrier frequency ?
What is the output voltage ?(use a true RMS meter)
Is this a new application or retrofit ?

 

[avigodner]

Motor efficiency is essentially hit by frequency converter / inverter / PWM amplifier operation that causes additonal loss / heating.

Of additional PWM losses mechanisms - copper ohmic, iron eddy current and hysteresis loss - eddy current PWM induced loss is likely dominating for conventional iron machine (this is not the case of pancake ironless brushless motor).

More info is supposed to be found at

http://www.drbrushless.com/articles/ironloss/

-Alex V.

 

[Marke]

Hello wiks

The most common cause of a problem like this is because the motor is being driven overspeed with a load that increases with speed. (Fans pumps etc) The second most common cause is because the output voltage setting of the drive does not match the motor, and the third most common reason is the measurement of the current. It must be measured on the output of the drive (not the input) using an instrument that is not affected by harmonics. i.e. it must be a true RMS measuring device.

Best regards

Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion: The motor may draw more current if the motor input experiences a higher harmonic content than the one it was used for setting the motor nameplate rated current.