Motor efficiency is often overlooked completely when companies are addressing energy saving and the operating expenditure reductions that go hand in hand with energy saving. Even engineering companies are prone to place it somewhere beneath turning all the lights off when not in use and negotiating with their supplier to get a lower price per kilowatt hour.

Furthermore, those companies that do invest time and money in energy reduction rarely get much further than fitting inverters. However, there is a host of additional measures that can be addressed with very little capital expenditure and they all result in a long term profit as a result of reduced overheads. Here Tony Young director of CP Automation, a specialist in the service and supply of drives, controls and resistors, presents his top five tips for ensuring that the motors in your plant run as efficiently as possible.

Tip one: Consider a soft start, where appropriate 
Soft starts are increasingly common on pump applications and they dramatically reduce the energy used when starting a motor. They are also common on conveyors, where the smooth start can stop the goods being moved ending up in a pile at bottom of the belt! As an alternative to a motor starter resistor or an inverter they can be profitable, but only if the application is assessed correctly in the first instance and the device is sized appropriately.

Tip two: Make like a light switch and turn it off!
Timing devices can be a hugely underused and very cost effective way of saving energy on non-continuous use applications. Often pumps and fans run constantly, even if there are times of day when there is no demand. Furthermore, even on applications where, for instance, the movement of a conveyor is only required when another piece of automation is positioning goods on it, a timing device can be used to turn the motor of more quickly; saving energy and cash.

These devices can be extremely simple timers or quite sophisticated PLCs (Programmable Logic Controllers) and, when combined with the right sensor, can be set to respond to environmental conditions as well as just the time. Furthermore, if you have an inverter fitted on your application already then you may well have the capacity for timing in situ in the form of a built in PLC. Most inverter manufacturers now offer devices of this kind but you will need to invest in more than a basic model to get it. However, there are also plenty of other devices on the market that feature built in PLCs, from display panels to robot controllers, so you may well find the capacity for timing is already present in your application, even if you are using a basic inverter.

Tip three: 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 at only the initial capital expenditure of the application and not it’s long term running costs. This will remain true after June 2011, when all new motors will need to be high efficiency to comply with new UK regulations.

Clearly, there will then be a regulation in place that should stop end users specifying low efficiency equipment. However, similar guidelines exist at present to stop people fitting counterfeit drives and motors but it still happens. The comparison with the motorway speed limit is compelling; it’s there but not everyone drives at less than 70mph.

So my advice is stick, metaphorically speaking, to the speed limit and purchase a high efficiency motor even if you think you can get away without one.

Tip four: Choose the right motor in the first place
The first step should always be to ensure you are fitting the right size of motor for your application in the first instance. A good provider of motors, controls or inverters will always offer an audit first which will help you achieve this.  Design engineers love to over specify ‘for tomorrow’ but for plant and maintenance professionals this just means bigger energy bills. Furthermore, if you plan to add an inverter now or later as a retrofit product, ensure that the motor is inverter rated to start with. Otherwise, any retrofit project will involve replacing the motor as well.

Over specification also raises maintenance bills. I’ve seen countless motors, which are doing an easy job like driving a spindle, specified at a much higher capacity than is required. Sometimes this is to the point that the motor costs £2000 but the same job could be done by a motor costing £1000. I’ve even known motors to be sent in for an overhaul with problems on parts of the motor that just aren’t being used at all. When the situation is reported to the customer, they are completely unaware of it because it’s a problem with functionality they just didn’t need in the first place!  Remember, from a repair perspective it’s unlikely that you can solve the problem of over specification, because the motor’s housing will be designed for it to fit in place from a mechanical perspective. It can’t just be swapped out for a cheaper motor – this has to be considered at the design stage. The analogy is simple; you wouldn’t buy a mini bus for a family of four.

When you are choosing a motor for a new project, it helps to bear in mind the expected lifespan and the use that the motor is actually going to be put to. If you do this, the machine itself will ultimately have a longer and more purposeful lifetime and be less likely to eventually be scrapped due to repair costs.

The first thing to think about is simple; 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, there will be less to go wrong and if something does go wrong the repair will be easier and cheaper.

Of course, this isn’t always possible. Occasionally there is the need for a timing device, soft start or PLC to alter the speed, as we’ve already discussed. Equally, it may be that you need an extremely high precision motor for your application. Nevertheless, there are still some tricks of the trade you can employ to make your project cheaper and more energy efficient in the long term.

So, we know that simple is best but cheap and simple may not always be the best bedfellows when choosing a motor. A low cost and mass produced, but unreliable, motor will never be cost effective or energy efficient because of the frequency of break downs and the high likelihood that it will need to be replaced rather than repaired. There’s also a strong chance that the cheaper units will be sealed, making maintenance extremely difficult. Indeed, sealing often makes the repair process so expensive that it’s cheaper to simply replace the motor.

Inevitably one also has to address the availability of the motor at short notice in the event of a replacement being required. Of course, if spares are kept in stock this may not be necessary and so, ironically, the harder to get hold of motors are sometimes the best option. This isn’t because they are scarce, but rather because they aren’t mass produced and are normally of higher quality. So, while a replacement may not always be easy, a repair often is. In this context, when choosing someone to do the repair job, you should always go to a specialist. If you go to a company that hasn’t carved out in a niche in, say, servo motors, you will find that they will simply sub-contract your repair to a specialist; increasing your bill in the process.

Another factor to consider is the environment in which the motor is going to be used. If you are designing for a harsh environment, from the food industry right up to quarrying, go for a more complex drive that can be boxed away. The design regulations for the industry may demand this anyway, if you are dealing with pharmaceuticals for instance, but the added bonus is that the motor and drive are protected from ingress and damage.

If it’s possible to do so, choose a motor that can be swapped out and replaced 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, let’s say we are dealing with a single three phase motor with an encoder. One manufacturer might align the encoder to a particular phase (U phase to signal one for instance). Another manufacturer might decide that V phase to signal one more appropriate. So, you may end up in a situation where you can never replace your SIEMENS motor with an Indramat motor, 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 a direct replacement cannot be secured in time.  Of course, with three phase induction motors it’s little bit simpler because they are all the same. So in this context it’s simply a case of the more complex the motor the harder it is to replace.

At the specification stage you should already be anticipating the need to replace the motor and considering the potential for obsolescence. The consolidation in the drives industry means that not every supplier that’s around today will be around in the same form in five years time. As a result, there is a chance that their products may 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 were able to find six identical motors in surplus stock elsewhere, which he was able to buy. However, when these all fail, he will need to re-design his machine – with new drive cables, mechanical fittings and so on, all of which will inevitably be expensive.

Tip five: Consider a feed in tariff
It isn’t well known that users of industrial motors can get money back from the energy provider by selling 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. It can be achieved using either a combination of two inverters or, much more efficiently, by using a specialist product called RevCon, manufactured by German electro-technology specialist, Elektrotechnishe Anlagen.

RevCon will work with any AC drive and features a harmonic filter as part of the package, which ensures that the electricity returned to the network is fit for purpose and G5/4 compliant. However, the bottom line for most businesses is the commercial imperative and this is where the product really comes into its own. The cost savings can be quite extensive in a facility where there are several motors controlling manufacturing equipment, lifts, conveyors and the like.

RevCon’s global installed base is now in excess of 10,000 units and the product can be found in industries from renewable energy to packaging and handling. Amongst CP Automation’s installations in the UK are One Canada Square, the tallest elevator in Europe, and the newly re-opened Express Lift Tower in Northampton.

Just implementing a few of these tips will result in a reduced energy expenditure on running motors, and in all likelihood other associated equipment. If you do all of them, you will find it much more effective than just trying to negotiate a lower kilowatt hour price!

CP Automation is providing a free, software based, motor control audit to any reader who responds to this article quoting ‘EL’.

Call: Tony Young on 01724 851 515 quoting EL