Medium vs low voltage and HP ratings 1

[buddy91082]

What is the break point where you would consider using medium voltage(above 600v) in lieu of low voltage (below 600v) for motor HP ratings?

Thanks.
b

 

[dpc]

This has been discussed a few times before - you might try a search. There are too many variables to be able to generalize. If the facility already has a 2400 V or 4160 V system, then making any motor above 100 hp medium voltage is a pretty common approach. But if going medium voltage requires adding a new transformer and distribution system, it's probably more cost-effective to stick with 480 V up through maybe 500 hp, unless of course you would need to add a new 480 V transformer to serve it.

If you are looking purely at bare motor costs, I'd guess the breakover point is somewhere around 300 hp, but others with more recent experience can correct me.

Other factors - constant speed versus adjustable speed. Full voltage start versus soft starter. Frequency of starts. The list goes on.

 

[waross]

I have heard one rule that states that if the HP exceeds the voltage consider a higher voltage. That agrees well if not perfectly with your suggestions dpc.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

The available medium voltage is a factor also. If 4160V is available and if there is an empty cell in the MCC then 100 HP may well go on 4160V.
If the medium voltage available is 13kV then the 100 HP motor will probably stay on 480V or 600V.

Bill
--------------------
"Why not the best?"
Jimmy Carter