Figuring cost of ac and dc motors

[kbinion]

I need some help on figuring the cost to run a 200 HP DC 230 volt motor vs a 300 HP 480 volt ac motor. The DC Motor is an old Westinghouse looks to be a 1964 model. It is a shunt wound 230 volt 720 amps. It is feed from a 230 volt 3 phase drive that has an amp rating of 800 amps. The 300 hp is a new upgrade and is 480 volt and 311 amps. I have some figures and wanted to know if what I am showing is correct. Any input will help.

 

[petersonra]

I need some help on figuring the cost to run a 200 HP DC 230 volt motor vs a 300 HP 480 volt ac motor. The DC Motor is an old Westinghouse looks to be a 1964 model. It is a shunt wound 230 volt 720 amps. It is feed from a 230 volt 3 phase drive that has an amp rating of 800 amps. The 300 hp is a new upgrade and is 480 volt and 311 amps. I have some figures and wanted to know if what I am showing is correct. Any input will help.

You will need the same amount of Hp from both motors to do the work required.

It is likely the AC motor is at least somewhat more efficient than the old DC motor.

However, the AC motor is larger than the DC motor HP wise so it may well be running at a far less efficient point on its HP curve.

I do not know any reliable way to calculate what you want from the minimal data you have provided. it would not surprise me if the DC motor was actually more efficient if it was running at close to full load if the AC motor is only running at 2/3 of full load.

 

[Jraef]

Why was the AC motor sized higher, because of torque requirements?