DC Motor Stator Grounding & Corrosion

[sdk_imported]

I am designing a small 2.5" stator OD, 250W, internal- rotor, permanent magnet, brushless DC motor. The motor is driven by a PWM based variable speed inverter that will see a 435VDC on the bus.

(1) Is it critical that the motor stator be grounded to the blower frame? there is no way for a person to touch the stator and the blower frame is earth grounded.

(2) Since each lamination is has an insulation coating, how do ensure that each lam is grounded to the frame?

(3) If I rely on the OD of the motor stator for the grounding, then I need to make sure this surface is conductive. Does anyone have a specific recommendation for a good corrosion protective coating that is electrically conductive?

Thank you in advance.

 

[nbucska]

1.) no
2.)-3.) never mind

<nbucska@pcperipherals DOT com> subj: eng-tips

 

[aolalde]

For LOW VOLTAGE machines the frame is grounded only for safety reasons. If eventually an insulation failure puts electric potential to the frame, the ground current will allow trip off the circuit. It is not necessary to ground the internal lamination core stack as far as the external case is grounded. There are lots of hand tools double insulated (the stator lamination is insulated from the frame or external encase) to reduce the potential risk of electric shock.

For HIGH VOLTAGE machines there is an additional partial discharge (PD) phenomenon. If the potential between the copper conductors and ground has air gaps, partial discharges will be developed and eventual failure of the insulation will be developed. For those cases it is important to keep the laminations grounded, which by the way is a compromise since eddy currents must be kept reduced to the minimum. There are special semi conductive varnishes to treat the core laminations. If interested visit VRI (Von Roll Isola) site

http://www.vonroll-isola.com/products/eim.htm.