inverter duty motors quote

[electricpete]

Attached is an excerpt from “Motors and Drives A Practical Technology Guide” by Dave Polka

These motors are designed with insulation systems that are able
to handle the over-voltage stress. Figure 4-45 indicates the construction of
a random wound versus a form wound motor. [in the figure, both show round conductors in semi-closed slot] The concentric wound or form wound motor is designed to handle spike voltages generated.

Motors that meet the MG1 standard are concentric wound and are termed
inverter duty motors. These motors contain stator windings that are carefully
formed around the stator slots, so that the first winding turn is not
next to the last winding turn

First there is some entertainment value - I am sure he has mis-used the term form wound motor and the figure 4-45 is not a form wound motor.

The term concentric winding seems to be equated to form wound in an unnatural way. Using the normal definition of concentric winding, I don’t think it does anything to minimize turn to turn stress and don’t see why it would have a unique role for vfd motors, do you?

Beyond that, I wonder if there is anything at all true in this quote (maybe something I’m not aware of):
Is there anything different about placement of conductors in inverter duty motor such as attempt to control placement of the first/last conductor?


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(2B)+(2B)' ?

 

[ScottyUK]

Not what I recognise as a form-wound coil. They're normally the preserve of HV machines where the cost of manufacture can be justified.

Regarding coil positioning the only suggestion I can offer for his statement is that high dv/dt impulses tend to affect the first few turns of the winding most severely, and perhaps he is suggesting positioning them to minimise the inter-turn and turn - stator core stress on the insulation? I struggle to see that level of care in the VFD-grade LV motors I've looked at - I guess it's easier to use a wire with better insulation than to precisely wind the coil.


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If we learn from our mistakes I'm getting a great education!

 

[Smokerr]

What I do know is that if you are going to run them on a VFD, you need to get ceramic hybrid bearings on each end at the very least. If not, the VFD causes arching in the balls/races, eating them up and destroying the grease with it.

If its belt driven that seems to do the trick, at least up to 40 hp in my experience.

If in direct drive (pump) you may also want to or need to add the Aegis Brush system to ground out the voltage build up in the rotor.

I get a cotter wire, atach it to my meter and get it on the shaft, then the other lead to the frame to see how much voltage build up there is. 50 is pretty common.