Fluid Handling / Motors & Drives

Enhance Your Motors’ Efficiency

Consider more than just using variable frequency drives

By Tony Young, CP Automation

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.

Top Tips

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.

Move away from mass production. If swapping out eventually is required, you must grapple with whether a replacement motor is available at short notice. Of course, keeping a spare in stock can avoid the problem. Ironically, a harder-to-obtain motor sometimes is the best option — because it isn’t mass produced and normally is of higher quality. So, while procuring a replacement for it may not always be easy, getting a repair often is.

When choosing a company to do a repair, you always should select a specialist. If you go to a firm that hasn’t carved a niche in, say, servo motors, it likely simply will sub-contract your repair to a specialist — increasing your bill in the process.

Another factor to consider is the environment in which the motor will operate. In a harsh environment such as often found in chemical processing, opt for a more-complex drive that can be boxed away. Regulations may demand this anyway but the added bonus is that the motor and drive are protected from ingress and damage.

Stay flexible. If it’s possible to do so, choose a motor that can be swapped out with one from a different manufacturer. However, this isn’t always an option; for instance, with servos every manufacturer has its own set up. As an example, one maker of a three-phase motor with encoder might align the encoder to a particular phase, say, U phase to signal one, while another manufacturer might decide that V phase to signal one is more appropriate. So, you may end up in a situation where you can never replace your Siemens motor with an Indramat one, to pick two major manufacturers at random.

When this happens, the design guidelines I’ve laid out in this article will come to the fore — because your maintenance partner will be attempting to repair the motor or looking for easily sourced equivalent parts if it can’t secure a direct replacement in time.

With three-phase induction motors it’s little bit simpler because they all are the same. So, in this context, it’s simply a case of the more complex the motor, the harder it is to replace.

Right at the specification stage, you should think about the eventual need to replace the motor and consider the potential for obsolescence. The consolidation in the drives industry means that not every supplier around today will exist in the same form in five years’ time. As a result, there’s a chance that a vendor’s products will have been absorbed into other product lines or discontinued. This is another reason to adopt the maxim simple is best.

For instance, we recently had a customer whose motor was beyond repair but no longer in production. Fortunately, we found six identical motors in surplus stock elsewhere. The customer bought them but, when they all fail, it will need to re-design its machine — with new drive cables, mechanical fittings and so on, all of which inevitably will be expensive.

Consider a feed-in tariff. It isn’t well known that users of industrial motors can get money back from their energy provider by sending excess energy produced during braking back to the grid. This is done using a feed-in tariff, exactly as it is with wind turbines and solar panels.

A plant can recover the excess energy using either a combination of two inverters or, much more efficiently, via a specialized regenerative unit. Such a unit will work with any AC drive, ensuring that excess energy returns to the power grid efficiently rather than being dissipated as heat in a resistor. A facility with several motors controlling manufacturing equipment, lifts, conveyors and the like can achieve extensive cost savings.

Implementing only a few of these tips will result in a reduced energy expenditure on running motors and, in all likelihood, other associated equipment. You will find that taking advantage of all of them is much more effective than just trying to negotiate a lower kilowatt hour price.


TONY YOUNG is director of CP Automation, Scunthorpe, U.K. Email him at tony.young@cpaltd.net.