13.8kV Motors

dy11

Member
Location
PA
Occupation
Plant Electrical Engineer
We are out of 4.16kV capacity but have ample 13.8kV (impedance grounded) available. We have a need to add 3-5 2000-3000 HP motors to serve chiller compressors. One path we are considering is 13.8kV motors rather than new 4.16kV switchgear. I am hesitant to move in this direction, mostly from a lack of experience with motors of this voltage class. I've heard 13.8kV motors are more expensive, harder to source parts and are more susceptible to partial discharge. Does anyone feel those challenges are worth the savings of new transformers and switchgear?
 

dy11

Member
Location
PA
Occupation
Plant Electrical Engineer
Thanks, I did see that. I was wondering if maybe they caught on in the last years and possibly aren't as uncommon.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Like most things of this nature, the answer is probably not real obvious and will likely vary from plant to plant.

If you do an economic analysis, it may lead in one direction or another.

Other factors (some of which you mentioned) may make the economics less important.

You may also find that the people needed to maintain the higher voltage stuff are harder to come by.

It may not make all that much difference as long as you have adequate spares on hand. Having a plant shutdown because a motor has to be rewound is not pleasant. And storing some of this stuff is not as simple as sitting it on a shelf in a warehouse somewhere.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
At 2000 HP, finding someone willing to build the motors for you might be more difficult than you think. 15kV class motors generally start at around 5,000HP. In addition, all of the control gear jumps up to 15kV class as well, yet for a 2,000HP motor, you are looking at only around 80A and the smallest vacuum contactor for 15kV is going to be 200A, so you are going to pay for a 5,000HP controller whether you use it or not.

Conversely, 2000-3000HP motors at 4000V are common and readily available (comparatively). You might find that when it's all said and done, buying a new transformer and 4kV motors and gear will cost the same or less.
 

bwat

EE
Location
East Coast
Occupation
EE
They didn’t need 3-5, but one of my clients was in a very similar situation 7 or so years back. After doing cost analysis it became obvious very quickly that a new transformer and staying at 4160 for the new 3000hp ones was at least similar in price rather than going to 13.8kV, not to mention the lack of headaches with relative availability by staying at 4160. It was so much more standard at that size.
 
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