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Can engineers adapt to new demands? – from Stuart Harvey of Soft Start UK

Tuesday, February 26th, 2013

Engineers are leading the charge for energy efficiency, and they are very good at innovative new ideas such as wind turbines, micro-generation and electric cars. But we are likely to gain more by improving the efficiency of existing systems and techniques, so need to rethink commonly held ideas and change some old habits. Stuart Harvey of SoftStart UK looks at motor selection.

As the millennium turned electrical engineers were focused on cutting carbon emissions. A few years later the global economy collapsed and attention turned to cost cutting.Fortunately these two goals are very closely related!

The EU’s new Minimum Energy Performance Standard (MEPS) is born out of green issues, but serves equally well to help contain costs. So how does it affect drives engineers?
Motor efficiency classifications have been redefined and only high efficiency motors can now be installed. Motors typically have a long operating life, so the total running costs far exceed purchase prices, and even a small improvement in efficiency will provide long term savings.

However, in the past engineers have routinely oversized motors by 10-20 percent. And these motors may have been driving equipment via equally oversized and therefore inefficient gearboxes, lead screws, belt or chain drives, clutches or couplings. Added to this is the fact that motors have a fairly narrow optimal efficiency band of typically 80-85 per cent full load, and many will not be running within the range. The new legislation addresses this by measuring the efficiency level 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.

Thus engineers, who are used to over-specifying motors, will need to adjust their thinking, change company policies and update design procedures. Existing installations are exempt from MEPS, but it may be worth modernising equipment anyway to get the energy saving benefits. It is also notable that a drive may make a significant contribution to overall efficiency by allowing a smaller motor to be specified. The motor would be sized for ‘normal’ duty, but the drive can push through a bit more power when required for short-lived unusual circumstances. The net result could be a significant energy saving, with a payback period of just a few months, leading to a positive contribution to the overall bottom line within the first financial year.

Variable speed drives can also be effective in fixed speed applications, as it is probably the most efficient way to set a precise system output speed. But is it worth exchanging old motors for new more efficient ones? Each case needs to be considered on its own, but as a general rule new motors are so much more efficient that those that are 5-10 years old that swapping them out is worthwhile. This is particularly true with larger motors, where the energy savings quickly mount up.

All engineers understand the theories of energy and cost efficiency, and now more than ever they need to apply them rigorously to make sure that they are not burning money that could be put too much better use.

Stuart Harvey of Soft Start UK – guest blogger for March 2013


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