Yet these hidden costs are almost never taken into consideration by machine builders, plant managers or engineers when they specify an electric motor for production machinery. This can result in motors that are oversized or over engineered, and as a result consume too much energy and could require more frequent maintenance and repair interventions than necessary. These additional costs have an impact on production levels, with outages causing significant downtime, directly lowering output and puts profits at risk for many manufacturing facilities.
Maximum up-time, reliability and energy efficiency should be the basis for motor choices on applications that run continuously as these applications will have the highest cost of ownership ratio.
How do you calculate the cost of ownership ratio? There is a simple formula, developed by ABB that looks at the true cost of running an electric motor over its operating life. It looks at the costs of purchasing the motor, the cost of running it in terms of energy costs and running hours and the costs of not running including maintenance costs and unexpected downtime costs.
Getting motor choices right in terms of lower overall acquisition and running costs can provide a welcome cut in component costs, maintenance costs and thus overall motor running costs.
For example*, a 45 kW motor costing £1,700, with 94.1 percent efficiency and running for 6,000 hours per annum would cost £2,105,454 over a 20 year life. This assumes an average electricity price of £0.08 and the downtime cost per annum of around £80,000.
When expressed as purchase price over total cost of ownership the resulting ratio is very small. For example, if the ratio was one, then this would mean that the purchase price was the same as the cost of ownership. But in the above example, you end up with a ratio of 0.0008.
Given such a high ratio, the true cost of owning a motor in a critical continuous process application is far more important than the initial purchase price. Buyers should therefore focus on the efficiency and the reliability of the motor.
The biggest risk, and the highest cost, for the motor owner is the cost of not running and unplanned outages through motor failure. High efficiency alone is not necessarily a guarantee of high reliability.
Consideration must be given when choosing a motor to the full load operating temperatures of the windings and the bearings.
End users and OEMs need to also think about how motor manufacturers can assist to predict when critical motors will fail thus, through on-site or remote condition monitoring and analysis, so that service interventions can be planned during scheduled plant outages. And if the worst comes to pass and the motor fails between planned outages consideration should be given to how the manufacturer can get you running again as quickly as possible.
To understand how best to calculate the cost of ownership ratio for your motor applications, talk to the ABB motors team on 07000 MOTORS, that’s 07000 668677