Large Motor Reliabity -- Better at 480V or 4160V?
Tom Rhodes
I have a customer running two each 500 HP air compressors who has been
experiencing unexplained motor burnouts. The motors are shorting one or two
phases to ground.
Each compressor is located on a different 480V service, although both services
are fed from a common 14kV substation. Each motor is fed from a 1200A feeder
from a 2000A panel. Each compressor motor starter includes a softstart SCR
module that transfers to a bypass contactor once the motor is up to speed.
The failures began about 4 years ago, with each compressor blowing up its motor
twice. The motors are rewound and returned to service. One failure was traced to
single-phasing, but the other 3 failures had no reasonable explanation.
My expertise is in PLC controls, not large motors. I wondered if anyone can
compare the reliability of motors operated at 480V versus 4160V? The customer is
considering a third compressor installation and could go either way.
I would also be interested in any power system tests that could be recommended
to help prevent the catastrophic failures.
Thanks in advance,
Tom Rhodes
Pyxis Engineering Corp., Redwood City, CA
e: t...@pyxiseng.com v: 415/365-2694 f: 415/365-2695
"Industrial Electrical Engineering Services"
Paul Hartung
Tom Rhodes wrote:
> The failures began about 4 years ago, with each compressor blowing up its motor
> twice. The motors are rewound and returned to service. One failure was traced to
> single-phasing, but the other 3 failures had no reasonable explanation.
>
> My expertise is in PLC controls, not large motors. I wondered if anyone can
> compare the reliability of motors operated at 480V versus 4160V? The customer is
> considering a third compressor installation and could go either way.
It appears that you may not have appropriate protection on the motor if
the single-phasing was not detected and terminated before damage was
done. There are many good manufacturers for these protective relays.
I used 4160V extensively on a water system. The cost is much greater
for 5kV as opposed to 600V but you do save a lot of copper because of
the higher voltage. In my personal experience I have not experienced a
failure of a motor at the 4160V level but I am sure it does occur. At
the 480V level I often hear of motor failures. At an different water
utility they rewound one of their two 400HP motor every year.
--
Paul J. Hartung, P.E.
Tom Rhodes
Paul Hartung <phar...@annainc.com> wrote:
>It appears that you may not have appropriate protection on the motor if
>the single-phasing was not detected and terminated before damage was
>done. There are many good manufacturers for these protective relays.
>
>I used 4160V extensively on a water system. The cost is much greater
>for 5kV as opposed to 600V but you do save a lot of copper because of
>the higher voltage. In my personal experience I have not experienced a
>failure of a motor at the 4160V level but I am sure it does occur. At
>the 480V level I often hear of motor failures. At an different water
>utility they rewound one of their two 400HP motor every year.
>
>--
>Paul J. Hartung, P.E.
Funny that you mention protective relays. The last failure occurred when the
electrician pushed the STOP button after installing the new voltage sensor and
the new current imbalance detector. Neither device is capable of blowing two
phases to ground inside the motor, but the electrician feels he is cursed.
Dwight Hebert
t...@pyxiseng.com (Tom Rhodes) wrote:
>I have a customer running two each 500 HP air compressors who has been
>experiencing unexplained motor burnouts. The motors are shorting one or two
>phases to ground.
>Each compressor is located on a different 480V service, although both services
>are fed from a common 14kV substation. Each motor is fed from a 1200A feeder
>from a 2000A panel. Each compressor motor starter includes a softstart SCR
>module that transfers to a bypass contactor once the motor is up to speed.
>The failures began about 4 years ago, with each compressor blowing up its motor
>twice. The motors are rewound and returned to service. One failure was traced to
>single-phasing, but the other 3 failures had no reasonable explanation.
>My expertise is in PLC controls, not large motors. I wondered if anyone can
>compare the reliability of motors operated at 480V versus 4160V? The customer is
>considering a third compressor installation and could go either way.
>I would also be interested in any power system tests that could be recommended
>to help prevent the catastrophic failures.
>Thanks in advance,
>Tom Rhodes
>Pyxis Engineering Corp., Redwood City, CA
>e: t...@pyxiseng.com v: 415/365-2694 f: 415/365-2695
>"Industrial Electrical Engineering Services"
I don't have any solid data that indicates that either a low or
medium voltage is more reliable, but most technical people, maint &
engrs, have told me that medium voltage is more relable at 300 HPs and
above. Usually med voltage motors will be form wound rather than
random wound. Additionally, 500 hp med voltage motors are easier to
find on the shelf when needed quickly. Equipment price for med
voltage may be higher but can be offset by smaller conductor and
conduit size and installation costs.
I'd be glad to furnish budget prices for both voltage motors.
Dwight Hebert
NEMSCO
National Electric Motor and Supply
Houston TX
(P) 713-467-8682
(F) 713-467-0095
email - dwig...@iamerica.net
Santiago Barcon
I agree that over 300 HP is better to go to a 4,160 volt system. But here now 2 motors
already exist. Maybe is better to have the same motors, provided that the cause of the
failures is founded.
I would like to know if the motors are connected to a variable speed drive. The failure
seems typical of that cause.
Either way a Power Quality study will be useful at the site.
We are located in Mexico and dedicated to the Power Quality field. Please feel free to
contact me at
Inelap, S.A. de C.V.
Lago Tana 43-7
11290 Mexico D.F.
MEXICO
TEL 011 52 5 399-6606
FAX 011 52 5 399-6488
sba...@spin.com.mx
ine...@spin.com.mx
Regards
Santiago Barcon