Random vs. Form-wound stator coils for IFDs.

[jgbg]

Hi to all of you,

You make a very good forum (helpfull and clear). I'm new and have a lot of questions (hopefully not too much to get you bored).

I would like to open a question regarding the random wound electric motors, and their suitability for inverter fed drives (IFDs).

In my opinion they are not to good with a standard execution but I have found information about new wire materials that could improve their behaviour against the dv/dt and the voltage peaks in these aplications.

Any comments would be higthly appreciated.

 

[electricpete]

I agree about the part that there are now commonly available insulation materials which will address dv/dt concerns for ifd random wound motors

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[edison123]

Form wound and random wound decisions are based on the machine voltage not on whether they are vfd operated.

In both types, turn insulation and ground insulation used now-a-days can survive dv/dt issues.

*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[DickDV]

Simply buy a motor that is rated for the service it is to perform. In North America, that would be a motor with an MG1 Part 31 endorsement on the nameplate. I'm not familiar with similar endorsements in the IEC world but there may well be one or more.

Having bought a good motor does not resolve all other issues regarding motor operation on inverters, particularly issues related to lead length. You will want to familiarize yourself with those limitations before you proceed further.

Search this forum for lead length threads and you will be off to a good start.

 

[jgbg]

edison123,

You say that the turn insulation in both types can survive dv/dt issues, but as far as I know there is no turn insulation in the random wound motors apart from the insulation of the magnet wire. That means that the form wound motor will have a better turn insulation, apart from less air between the conductors that could lead to partial discharges (PDs).

 

[petronila]

Hello jgbg,

The Inverter duty windings(random or form coil) are different from the standard due to a wide factors:1.The magnet wire is coated with high dielectric strength film and capable to resist the fast rise time pulses.2.Due to the small Wire sizes tend to enhance nonuniform stress distribution they are wuindded with Larger Wire sizes. Example: prefer a 15 AWG than Two Wires 18 AWG .3. Some manufacturers add Phase and ground Protection using stronger dielectric materials or applying sleeving over the first turn at the line end of motor.4. Be sure about the NEMA Design and prefer the A or B than the C or D, because the rotor looses are higher and will heat up more in this NEMA C or D design motors.5. The Insulating material have a higher temperature rating. 6 .The Inverter Duty Motors winding are Treated with resins applied with VPI in order to eliminate the voids.

You could find in some ID motors Insulated bearings and if they are operating at very low speed they will have a Forced air ventilation.



Regards

Petronila