Electric motor failures due to conductive liquids

[witchdoc]

We are experiencing an abnormally high failure rate with electric motors in our processing plant. We manufacture a salt that has a high pH (12+), a very high electrical conductivity, and very hygroscopic (it absorbs water from the air). It is also very corrosive to copper. Most of the failures result from windings shorting to ground. We have tried Mill and Chem duty as well as washdown duty motors. We specify motors with heavy, gasketed cast iron frames and covers. We also pack the conduit box with Dow Corning #4 non conductive grease.

Does anyone have any other ideas on how to reduce the number of failures?

 

[jbartos]

Suggestion: Have an electrical contractor or electrical engineer identify the cause of motor failures, i.e. it is necessary to perform a root cause analysis. It may be caused by the salty environment. It may also be caused by other detrimental phenomena and their combination.

 

[busbar]

Has transient overvoltage been ruled out, like that found in {480V} ungrounded distribution?

If 480V, it may be worth trying to operate lower-hp dual-voltage motors from a grounded 230Y/133V drive-isolation transformer.

Motor cycling may permit ingress during cooling periods.

 

[dadfap]

witchdoc

why not try epoxy impregnated windings as opposed to the VPI insulated windings?

It is a little more expensive and almost impossible to rewind them,but sounds like you have nothing to loose.

all the best

dadfap

 

[king144]

We have had some luck drilling small holes in the bottom of the motor T-box to drain moisture if and when it accumulates. We also use drains at conduit fittings near the motor t-box and local push button stations. We have also installed air fittings to some motors in extremely moist areas so that compressed air can be piped to the motor to cause a positive pressure diffrential for keeping moisture out of the motor and T-box...

Sounds counter productive, but seems to work well for us in high humidty/temperature areas of our paper mill...

Richard Anderson
GP mill - Camas WA.

 

[pablo02]

And how are the conduits and fittings sealed? I'm assumming that your motors are breathing as the heat up and cool down and pulling the salt dust in from somewhere?

 

[king144]

Our conduit is sealed with rubber gaskets under the fitting covers - we use RobRoy coated conduit in our Bleach Plant areas where Chlorine Dioxide can be a problem.

The condulet fitting drains I spoke of are designed to allow moisture to drip out yet discourage vapors from entering the conduit system. They are installed at the bottom of a conduit system usually using a TEE so that the motor lines are above the drains...

If your problem is extreme you might consider using explosion proof fittings and motors - though they are quite expensive...

Richard Anderson
GP Mill Camas, WA

 

[witchdoc]

The distribution system is a wye system, and we have surge arrestors installed. I don't think transients are the problem.

We plan to try the epoxy coated winding idea.

And yes, we suspect the heating and cooling of the motors is providing the driving force that pulls the salt into the motor.

We may look at installing the knockouts in the conduit -- it is worth a shot. However, one would assume that packing the motor conduit box with non-conductive grease would essentially eliminate the problem. It helps, but is not a cure-all.

thanks for all of your ideas. We are converting the worst offenders to air motors. All other ideas are welcome.

 

[jbartos]

Suggestion: This appears to be more chemical challenge rather than electrical one. The conducts, boxes and fittings are applied PVC or polyurethane coated. The motors are protected by various corrosion resistant layers depending on the environment.

 

[rshoultz]

Try paralene coating the motor inside and out.

 

[gpedens]

Have you tried

http://www.inpro-seal.com

?

Thank You,Radar. Duke Power

 

[chitown]

I've done some work offshore using air pressurizing/ purging on both control cabinets and electrical motors. These applications are used for classified areas but could be applied in this instance. By bring a good supply of air and pressurizing your motor you could avoid the caustic salt air entering the motor. Just a suggestion. Good luck.