Comparison of Two Electric Motors for Industrial Hoist
What would be the cost of electrical energy in cents per kilowatt-hour before the D-R motor is favored over the GE motor for an industrial hoist powered by these motors?
The D-R motor will be favored over the GE motor regardless of the cost of electrical energy. To determine the cost of electrical energy required for the D-R motor to be favored over the GE motor, we need to compare the total cost of ownership for both motors. The total cost of ownership includes the capital investment, annual maintenance cost, and the cost of electrical energy.
Total Cost of Ownership Calculation
Capital Investment: $2,500
Annual Maintenance Cost: $40
Cost of Electrical Energy: To be determined
GE Motor:
Capital Investment: $3,200
Annual Maintenance Cost: $60
Cost of Electrical Energy: To be determined
Now, let's calculate the cost of electrical energy for both motors:
D-R Motor:
Electrical Efficiency: 74%
Power Output: 90 hp
Power Input: 90 hp / 0.74 = 121.62 kW
Energy Consumption per Year: 121.62 kW * 500 hr = 60,810 kWh
Cost of Electrical Energy: To be determined
GE Motor:
Electrical Efficiency: 89%
Power Output: 90 hp
Power Input: 90 hp / 0.89 = 101.12 kW
Energy Consumption per Year: 101.12 kW * 500 hr = 50,560 kWh
Cost of Electrical Energy: To be determined
Now, let's calculate the cost of electrical energy in cents per kilowatt-hour for both motors:
D-R Motor:
Cost of Electrical Energy: To be determined
Total Cost of Ownership: Capital Investment + Annual Maintenance Cost + Cost of Electrical Energy
GE Motor:
Cost of Electrical Energy: To be determined
Total Cost of Ownership: Capital Investment + Annual Maintenance Cost + Cost of Electrical Energy
Since the MARR (Minimum Acceptable Rate of Return) is 10% per year, we can set up the following equation to determine the cost of electrical energy:
Total Cost of Ownership for D-R Motor = Total Cost of Ownership for GE Motor
$2,500 + $40 + Cost of Electrical Energy = $3,200 + $60 + Cost of Electrical Energy
Simplifying the equation:
$2,540 + Cost of Electrical Energy = $3,260 + Cost of Electrical Energy
Subtracting Cost of Electrical Energy from both sides:
$2,540 = $3,260
Since the equation is not true, it means that the cost of electrical energy for the D-R motor cannot be equal to the cost of electrical energy for the GE motor. Therefore, the D-R motor will be favored over the GE motor regardless of the cost of electrical energy.