Sizing up your motor strategy
With more emphasis than ever about how energy is produced and managed in a manufacturing plant, the focus turns to the intelligent management of motors and drives. Plant Engineering discussed these trends with Jim Clark, a 25-year veteran of the low voltage and frequency drives business and the director of ABB’s low voltage motor operations in the United States, and Mark Kenyon , who is part of ABB’s Global Reference Group responsible for defining ABB’s next generation products.
PE: As customers talk to you about their motors inventory and operation, what are they most concerned about right now?
Clark : Customers are expecting motor vendors to be able to deliver replacement motors off the shelf. For most any given installation, the cost of downtime outweighs any energy saving benefit.
PE: Have the economics of energy costs and the politics of sustainability changed that equation in the past few years?
Clark : I don’t think so, at least not at the replacement level. I think it is more so with new installations. It will certainly be brought front and center with the new efficiency minimums being enacted into law in December of this year.
PE: What’s most often overlooked about motors? Are there one or two things customers can and should do to improve the efficiency of motors?
Clark : What’s most overlooked would be the sizing and application details of motors %%MDASSML%% making a proper selection based on the actual needs of the application. In many cases, larger than necessary motors are installed with the idea it will increase service life, but if not of optimum sizing, it could be energy inefficient.
PE: Motors and drives are often seen as two parts that work together. Is that the correct approach, or is there something else manufacturers can do to improve the operation of their entire network?
Clark : One of the most immediate and significant ways to improve operational efficiency is to look at the entire process rather than the individual components. Using the classic example of centrifugal pumps or fans as a guide, similar results can be achieved in other applications as well by controlling the speed of the motor (and its energy usage) to just what is needed at any given point in a process rather than trying to throttle the output while the motor runs at full speed continuously. In constant torque applications the savings will not necessarily be of the same magnitude nor realized as quickly but the energy usage benefit will be greater than that of just replacing a motor with one of a higher efficiency rating.
Kenyon : While every motor doesn’t need a drive every drive needs a motor.
It is reported that 63% of all energy used in the United States is consumed by motors. The majority of these motors, however, are still being operated at fixed speeds. While there are some applications where using a drive wouldn’t save energy, there are more benefits to using adjustable speed drives than just saving energy.
Manufacturers should consider using drives to increase productivity, decrease maintenance costs, remove cost from their processes, etc. There’s much more to drive use than just saving energy on a variable torque load.
PE: The use of dc drives seems to be rising? Where are you seeing growth for use of dc drives?
Kenyon : The sales of dc drives have actually continued to flatten as some manufacturers pull out of the dc drives market. In 2008, dc drive revenue increased by an estimated 7%, because of new orders for retrofit projects following a contraction in 2007.
AC drives grew by almost 15% from 2007 to 2008. The dc drives market is expected to be most effected by the recession that began in the latter months of 2008. Forecasts of dc drive revenue for 2009 show a contraction of up to 14.5%.
Several key industries where dc drives are used are printing, steel and rubber and plastics. These industry segments have been severely impacted by the recent recession as well as off-shore competitors. As such, sales of dc drives will not grow dramatically.
PE: What is the single biggest factor a plant manager and/or plant engineer should consider when looking at using drives in their plants?
Kenyon : Rather than just looking at the purchase price of a drive the plant manager or engineer needs to look at the total cost. By this, I mean weigh the cost of the drive against the energy it will save, the scrap material that won’t be generated, the cost savings of not having motors reworked so frequently, the lower demand charges from the utility, the decreased down time due to brown outs caused by voltage sags resultant of line starting large motors, cost savings of removing mechanical means of changing process speed, etc.