Enhance Your Motors’ Efficiency

Consider more than just using variable frequency drives

By Tony Young, CP Automation

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Chemical companies often completely overlook motor efficiency when seeking energy savings and the associated operating expenditure reductions. That’s a serious mistake.

When you consider that electric motor systems account for about 60% of global industrial electricity use, the potential savings become clear. A Siemens’ 2014 white paper “Turn Down the Power” includes estimates (termed highly conservative, by the way) of industrial electrical overspending in the five following years directly attributable to non-implementation of variable frequency drives (VFDs). The United States led with $20.9 billion, followed by China with $10.9 billion, Russia with $9.0 billion, and Germany with $8.1 billion.

Electricity costs are rising as global demand continues to grow, ramping up the need for industrial companies to contain electrical consumption. Those firms that do invest time and money in energy reduction rarely get much further than fitting VFDs or haggling on price per kilowatt hour. However, a host of additional measures that require very little capital expenditure all can result in substantial savings that can bolster long-term profitability.

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Here are some ideas you should consider to ensure the motors in your plant run as efficiently as possible.

Opt for a soft starter where appropriate. Soft starters are increasingly common on pump applications; they dramatically reduce the energy used when activating a motor. They also are seeing greater use on conveyors, where the smooth start prevents objects from falling. A soft starter may provide a more-profitable alternative to a motor starter resistor or a VFD — but only if the application is assessed correctly in the first instance and the device is sized appropriately.

Time it. The chemical industry hugely under uses timing devices; they are a very cost-effective way to save energy on non-continuous services. For instance, often pumps and ventilators run constantly even though no demand exists during certain times of the day.

Not running a motor unnecessarily not only saves energy but also extends the life of your systems. For example, the hydraulic pumping efficiency of a cooling systems will degrade less over time and remain optimally efficient for longer.

Don’t be tempted by cheaper alternatives. Choosing a high-efficiency motor isn’t always a given in every application — particularly if someone in the buying chain is looking only at the initial capital expenditure and not long-term running costs.

Mandates in place such as the European Union’s Ecodesign Directive should cut down on end users specifying low-efficiency equipment. Similar guidelines exist at present to stop people fitting counterfeit drives and motors but that still happens. A comparison with a highway speed limit is compelling: it’s posted but not every driver adheres to it.

So, metaphorically speaking, I advise sticking to the speed limit and purchasing a high-efficiency motor even if you think you can get away without one.

Choose the right motor in the first place. Your initial step always should be to ensure the proper motor is fitted for the application, whether this is for pumps, fans or compressors. A good provider of motors, controls or VFDs usually will offer an audit first to help you achieve this.

If you plan to retrofit a VFD now or later, make sure the motor is VFD-rated. Otherwise, any retrofit project will involve replacing the motor as well.

Design engineers love to over-specify “for tomorrow” but this incurs bigger energy bills. Over-specification also raises maintenance bills. I’ve seen countless motors for easy jobs like water pumping that are specified at a much higher capacity than required. Sometimes, this leads to spending, say, $2,500 on a motor for a job for which a $1,250 one would suffice.

I’ve even known of motors sent in for an overhaul with problems on parts that aren’t being used at all. Yet, when this situation is reported back, the customer is completely unaware of it because the problem is with functionality not needed in the first place!

Consider another car analogy: you wouldn’t buy a minivan for a family of four.

Keep it simple if you can. Always remember the less complex the motor the better. From a repair perspective, if you can use a standard energy-efficient motor, which you can switch on and have spin at the right speed with no bells or whistles, then use it. It will be cheaper to install and have less to go wrong. Moreover, if something amiss does occur, the repair will be easier and less costly.

Of course, this isn’t always possible. Occasionally, as we’ve already discussed, a timing device or soft starter is needed to alter the speed. Or perhaps you require an extremely high-precision motor for your application. Nevertheless, you still can employ some tricks of the trade to make your project cheaper and more energy efficient in the long term.

While simple is best, cheap and simple certainly may not be when choosing a motor. A low-cost mass-produced but unreliable motor never will be cost effective or energy efficient because of the frequency of breakdowns and the high likelihood that you will have to resort to replacement rather than repair. There’s also a strong chance the cheaper unit will be sealed, severely impeding maintenance. Indeed, sealing often makes the repair process so expensive that it’s cheaper just to replace the motor.

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