480V Motor HP rating
480V Motor HP rating
(OP)
Hello. I have a question on selection of voltage level for a group of motors. What is the maximum allowed HP ratings for 480V? In other words, when a motor have a larger size than that, it has to be rated at the next higher voltage level. I was told 200HP might be the number. But I could not find the basis in the standards, like IEEE. Please help. thanks.






RE: 480V Motor HP rating
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 480V Motor HP rating
In general, if you have a large number of motors over 200 hp, it is going to be more economical to use a higher voltage.
RE: 480V Motor HP rating
First of all I agree with all above.
I think is not a direct problem of voltage level but a problem of supply transformer size. Usually is limited to 2500-3000 KVA.
So you have to check if when starting the most powerful motor the voltage drop through the transformer [ loaded 80% or more ] is not too high and the voltage at the other still consumer terminals does not fall under the permissible[let us say 10% under the rated] .
A thumb rule is the transformer KVA > 3*maxMotor HP.
Regards
RE: 480V Motor HP rating
Then you must consider maintenance. Is your staff trained on medium voltage? Would training be a significant cost or inconvenience? Also look at lead time for procurement of the equipment (and maybe future maintenance replacements).
RE: 480V Motor HP rating
But what you may have heard is an individual plant's assessment, which is not uncommon. I know of several facilities who have 4160V systems already running throughout the plant, who have internal edicts that all motors 200HP and up shall be 4160V. I even know one plant that draws the line at 150HP. They do it because they can. In most places, going to MV for such small motors is impractical and the cutoff is generally 500 - 600HP.