Single Phase Heating of 3 Phase Motor 1

[BigMotorGuy]

What are the generally accepted rules for drying out a 3 phase motor that has gotten wet by applying a low voltage single phase power supply to create heat and thus remove the water? I have a spare stator that needs to be put into service and evidently got rained on to some degree. An oven is not available to dry it out, so what are the calcs to determine the voltage/current/power so as to dry the water, but not burn up the coils? The motor is basically an F class motor. I assume monitoring the coil temps with a probe in various spots is prudent, but what outer surface temp of the coil would limit any internal temps to class F?

 

[dpc]

I don't know about drying, but we used to sometimes use trickle voltage in lieu of space heaters and I have a tech paper from US Motors that states that a 10 deg C RISE in motor winding temp requires about 25% of motor FLA. This generally requires about 7% to 10% of the motor nameplate voltage.

You'll probably want more heat than that, but this will give you a starting point.

 

[jraef]

Information on what to do after water damage faq237-1157



"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[edison123]

If you have a variable voltage supply with enough ampacity, you could apply about 10% voltage to the stator (with rotor removed) that could get you about 30% of FLA, which could warm up the stator. Use to a temp gun to monitor winding surface temp and keep it below 90 deg C.


Muthu

http://www.edison.co.in

 

[LionelHutz]

Ensure the stator insulation won't be damaged when you apply this voltage.

 

[BigMotorGuy]

thanks for all the advice on this.....my only exerience with this was a preheat and subsequent cure for trickle varnish applications on small universal motors. Makes sense about starting low on the voltage and ramping up slowly while monitoring the coil temps. I will also follow up with a 65% hipot test to insure low moisture, but since the stator was double VPI dipped in epoxy, I assume we'll be fine after a good dry out.

BigMotorGuy

 

[waross]

You may want to avoid currents close to full load current. With the motor stopped, there is little air movement and cooling is less than it is when the motor is running.

Bill
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Jimmy Carter