Is it healthy to maintain the rated current for motor during running condition??

Dear,

Temperature and current both are not normal.

Check out both quantities reponse during no load condition.

Kind regards,

no load amp = 28.1A at 48degC caging temp.

The body temperature of motor should not be above ambient temp by 40 deg C.

I would suggest reducing the load by throttling the damper ( if present)

cheers.

originally, its damper (suction side only) is throttled at 75% opening, but since we had installed a vfd for it, we opened it to 100% and reduced speed of fan to obtain the required suction. But still, at 50Hz, 440VAC, the current drawn by the motor is at 69.43A and the temp of caging is at 80 degC.

It causes frequent breakdown on our VFD and affects our process..

maybe there is someone who could help me on this one.

Thanks a lot. Your response are highly appreciated.

Is the motor designed to run at lower speed through the use of a VFD. If not then its temperature will rise above the one observed during running under normal load as its heat dissipation largely depends on the air draft being circulated through it because of the motor rotation.

You may have to change your motor or try to install an additional fan apart from the shaft mounted fan on the motor.

Does the VFD trip because of sensing of higher temperature of motor.

have you checked the vfd program ,settings ,why did you go for vfd ? what was the original start/run equipment.

maybe the motor is not suitable to run at lower speed ?

I would suggest checking the parameters at VFD .

What is your VFD rating ? I always suggest to install VFD one size bigger than the motor size ( If motor is 30 Hp, i install VFD of 40 hp)

The drive manfacturers have lot derating factors ( normally writen in fineprint...) like ambient temperature, altitude etc.

Is your motor inverter duty rated?

cheers.

Also check to see if your motor has accumulated a lot of dust. Air flow and a clean motor are very important near full load.

What is the air temperature near and around the motor?

Everything (including insulation) degrades faster at elevated temperatures.

You have probably already checked this but,

1) Is the overheating there without the VFD? Is this the same motor that has always been there? You can expect some extra heat just from the nonsinusoidal output of the inverter, but nothing that will eventually peel the paint. If the motor runs normally without the VFD, guess where the problem is.

Check to make sure the windings of the motor are connected correctly. Sometimes in a multiwinding motor, when the configuration is delta, if the unused delta windings are not open induced voltages in this winding will cause overheating.

This sounds like a european application from the kW rating you mentioned. Was there a star-delta starter before the VFD installation? Make sure the VFD is configured correctly for the motor.

That is about all I can think of at the moment

Thanks guys, i appreciate all your inputs.

Even without the VFD, the values that i had mentioned at the top of this topic had been seen.

Wye-delta start is in parallel with the VFD but not simultaneous, in case of VFD failure we switch from VFD to direct line connection.

We also changed the motor with the same capacity, but i still get the same result.

We already checked the parameters and all parameters are ok.

Is it possible to size up the capacity of the motor while retaining the existing VFD.

The motor sounds hot and if the current is near full load but the applied load is much less it means you are applying too much (overfluxing or 'pushing current')or too little voltage (partial stalling)at the reduced frequency.

If no load is 28A and full load is 74A for the motor then 75% is about 65A.

You do not mention the rated motor voltage / Hz and also your mains supply voltage.

Some VFDs scale the output by input supply, others are definitive voltages.

If the motor is 440V/3ph/60Hz then 5/6 of this voltage would be OK at 50Hz output (i.e.365V at 50Hz)simplistically

If you have a 460V mains and the inverter is outputting 5/6 you may be overvolting which would explain your first postion when D-o-L.

If so, find out how to set the VFD scaling of v/f to get a better result.