# Set up of a melting shop

#### matttrix

Joined Mar 6, 2009
11
Need some help on how to start this question.

A 50 HP motor needs to be installed in a melting shop. A nearby substation is able to transmit any
supply voltage less than or equal to 4096 V. Using your knowledge of: cables, safety, and relative costs,
determine the most cost-effective implementation by: selecting cables sizes and supply voltages and
appropriate insulation. Assume Copper wire is 3x as expensive as Aluminum wire and every AWG size
increase corresponds to a 1.5x increase in wire price. State any other relevant costs.

#### KL7AJ

Joined Nov 4, 2008
2,208
Need some help on how to start this question.

A 50 HP motor needs to be installed in a melting shop. A nearby substation is able to transmit any
supply voltage less than or equal to 4096 V. Using your knowledge of: cables, safety, and relative costs,
determine the most cost-effective implementation by: selecting cables sizes and supply voltages and
appropriate insulation. Assume Copper wire is 3x as expensive as Aluminum wire and every AWG size
increase corresponds to a 1.5x increase in wire price. State any other relevant costs.

I suppose the first order of business is to determine whether this is 3 phase or single phase. I would presume three phase. But in any case, start out with what you know.

Power consumption at a bare MINIMUM is 50 hp x 746 watts/hp= 37.3KV. I think motors are assumed to have about 90% efficiency, so crank that up by 10%=41 KV. You're going to need a three phase step down transformer on site. It will be aluminum between the substation and your on-site transformer, and copper from there to your shop. You want your on-site transformer as close to the shop as possible, of course.

Hope this gets you started.

eric