DOL Motors operated with a VFD 1

[balaji28]

Hi

I recently received a quote for a motor and states that the starting method is "Direct on line". I had requested a motor to be suitable for it to VFD driven.
When I checked with the motor manufacturer, they conveyed that the same motor is suitable for VFD start as well.
I was under the impression that DOL start motors and VFD start motors are different.
Is the motor manufacturer correct in his claim ?

Regards
Bala

 

[edison123]

VFD duty motors have a different winding insulation system when compared to standard duty motor and are stamped as such. And they should have an independently driven fan for cooling due to speed variation. And they are costlier.

Muthu

http://www.edison.co.in

 

[waross]

HP? Application? Required speed range? Voltage?
VFDs may produce very high voltage transients.
Inverter drive motors have more robust insulation to withstand the higher voltage harmonics.
Generally the longer the leads to the motor the higher the voltage transients.
Some applications require filters to reduce the harmonics even for inverter duty motors.
In some applications a standard duty motor may be used with a VFD with suitable filtering.
If an application does not require very low speeds an external cooling method may not be required.
It depends.
Need more input.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Unfortunately, there are no officially enforced standards for what constitutes a motor being suitable for operation on a VFD, so motor suppliers can and often do just tell you what you want to hear. There are standards, such as IEEE and NEMA here in North America and if you write those standards into your RFQ then you can (hopefully) get a response from suppliers that is more truthful. So for example if you said "Motor must meet NEMA MG 1 Section IV, “Performance Standards Applying to All Machines,” Part 31, “Definite-Purpose Inverter-Fed Polyphase Motors.” This creates a minimum standard for issues such as the motor's ability to withstand voltage stresses encountered in the PWM output of the VFD, temperature rise limits that might be different from GP motors, and minimum requirements to mitigate the risks of bearing damage due to EDM from capacitance between the stator and rotor that can take place. I know there are similar IEC guidelines as well, I just don't know what they are so hopefully someone else can fill that in. The only ones I know of are IEC 60034-18-41 and IEC 60034-18-42, but they only cover the winding insulation issues (two standards based on random would or form wound coils used inside of the stator).


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Skogsgurra]

A few curves from the British association of drive and motor manufacturers. Al major makes are represented. And a few less known.

The peak voltage increases with cable length, as Bill said. But when cables get longer than around 100 m, the dispersion reduces that influence.

But it is obvious that a motor that isn't designed for PWM and that doesn't have a filter, will suffer from Ozone (caused by partial discharge in narrow air gaps) between magnet wires and sometimes wall insulation. Ozone deteriorates the insulation. Not good.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[che12345]

Dear Mr balaji28 (Civil/Environmental)
I noticed that all the learned response are relevant to your question.

However, I also noticed that you are in the civil/environment and perhaps not? trained in electrical engineering from the question you had asked, " I was under the impression that DOL start motors and VFD start motors are different".

I am looking at your doubt in a different angle. Perhaps you should seek the advice from your electrical trained colleges.
- Why do you "requested a motor to be suitable for it to VFD driven" ?
- Is the motor going (to be/must) be operated with a VFD?
- are you aware that unless the motor speed is to be varied (continuously) in responds to the load variation would need to be operated with a VFD, otherwise a standard motor would do the job (with DOL starting) at very much lower in price and far more reliable than a (VFD+VFD rated motor).

However, if the motor [is going to be VFD operated], then the above learned advice are relevant.

Che Kuan Yau (Singapore)

 

[dpc]

I agree with all of the comments, but just want to point out that there are no fundamental differences between motors running across the line or running on an AFD. The differences relate to modifications made to reduce the failure probability when running on a drive for all of the reasons stated previously.

There must be thousands and thousands of standard motors running on AFDs in service around the world. They will run, but under some situations can have a short service life.