Plant engineers need to change motor sizing approach, warns Softstart 21 December 2012

Plant and electrical engineers are being warned to take more care in sizing electrical motors in line with regulations and guidelines aimed at driving down emissions, fuel consumption and costs.

Motor control and automation equipment supplier Softstart UK makes the point that the EU's MEPS (Minimum Energy Performance Standard) is being phased in, with the first part already a legal requirement and the last due to be enacted in 2017, replacing the voluntary CEMEP scheme.

Under MEPS, the old EFF1 and EFF2 efficiency classifications are discontinued, with the sale of EFF2 rated motors illegal, while new testing procedures give engineers a better handle on motor efficiency.

The message for engineers, however, is that, whereas in the past designers routinely oversized motors by 10—20% jus in case – and many of these have been driving equipment via equally oversized and inefficient gearboxes, leadscrews, belt or chain drives, clutches or couplings – this practice needs to stop.

Stuart Harvey, managing director of Softstart UK (pictured), also makes the point that, given all motors' fairly narrow optimal efficiency sweet spot (typically 80—85% of full load), engineers need to take more care in motor system design.

"MEPS address this by measuring the efficiency of the whole drive system, rather than just the motor on its own. This means every installation has to be assessed individually, whereas in the past motors could be bought with an efficiency rating," advises Harvey.

This will matter next year when MEPS moves on from fans to pump drive systems. Softstart is advising OEMs "to make sure they are up to speed and comply with requirements".

The company is also urging plant engineers to take heed, as, over the next four years, all motor drive systems will be drawn into the MEPS regulations, requiring compliance.

"Engineers of a certain age, who were brought up over-specifying motors, need to move to a new paradigm," states Harvey. "This may be a simply matter of changing habits and assumptions, but it may also mean getting company policies and design procedures changed. Established OEMs may need to inform their regular customers of the changes."

End users are not obliged to change existing equipment, but it Softstart suggests that it may be worth modernising equipment in line with MEPS to improve energy efficiency enhance green credentials and cut costs.

"A rule of thumb would be that a new motor is 25—50% more efficient that one built before the turn of the millennium... The efficiency improvement gives the basic data for payback calculations – the simplest of which would be based on capital cost plus running costs. But you could also add in engineering costs of the swap out, offset this against the cost of routine maintenance and improved reliability."

Brian Tinham

Related Companies
Softstart UK Ltd

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