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stevaux (Industrial) (OP)
26 Oct 05 9:46
I'm making a decision on whether to install a 400HP screw compressor with 4160V or 480V. In order to get to 4160 I would have to transform some of my available 480 to 4160. The original cost of the install would be more, but would there be any ongoing "gains" to offset the install price?
jraef (Electrical)
26 Oct 05 11:49
No. If you must transform UP from 460 to 4160, you will have more losses in the transformer. No point to that exercise unless it is a deep well submersible pump and the weight of the cables for 460V operation is a problem. If you already had 4160V available, then it would make more sense because you could avoid the 4160-460V transformer.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

BJC (Electrical)
26 Oct 05 12:08
The IEEE Red Book std 142 is a good reference on when to go 480 vs 4160.  One of the IEEE books that is worth the money.  The other source is Beemans book "Industrial Powere Systems"  IT's been our of print for years and is in need of an update and republishing.  Still if you can find an old copy it's worth picking up.  

Almost everthing you have to do to your system to connect a 480/4160 transformer you would have to do to connect the 480 volt motor. If your not allready committed to the 400 HP compressor you should look at actual load and wheather two smaller unit might have a lower total installed and operating cost.
stevaux (Industrial) (OP)
26 Oct 05 15:26
The compressor will be installed on the plant floor, so other than the cost of the 480 cable being more, weight is not a large factor. Our facility only has 480 available (today).

I checked with our local utility and they lean toward the 480 unit, stating that most every 400HP motor in the state is typically 480V. They also say that 480V is good for motors up to 600HP. Other issues they mention are considerations for who will work on the 4160 and the eventual cost of having to rewind/repair a 4160 motor.
jraef (Electrical)
27 Oct 05 1:10
In most areas, electricians must be separately qualified to work on medium voltage compared to low voltage (480), and that may cost you quite a bit if you don't already have anyone available. They typically demand more money as well.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

stevaux (Industrial) (OP)
27 Oct 05 9:52
jraef,
    I hear you loud and clear. Based on everything I'm hearing, 480 appears to be the prudent path forward.

Thanks.
benlanz (Electrical)
27 Oct 05 18:12
If you don't have extensive training and experience with medium voltage you are asking for reliability troubles.  The rules change at 1kV and higher.  I think you are not familiar with MV, you are making the right choice to stay with 480.

Benjamin Lanz
Vice Chair of IEEE 400
Sr. Application Engineer
IMCORP- Power Cable Reliability Consultants

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