Intelligent specification of drivetrain components can lead to improved integration

Depending on the industry, environment and requirements of any given application, there are many different methods of transferring power from mains supply to machines. But no matter what the layout of the drivetrain, there will always be some solutions that offer smoother integration and better efficiency than others.

The recent introduction of IE3 has seen many more energy-efficient motors come to market. In reality, however, an efficient motor only plays a small part in the potential energy savings available to the system as a whole. Indeed, many industry experts are encouraging engineers to hand-pick components to maximise the energy efficiency during integration, as each stage of the drivetrain can offer efficiency savings. Markus Kutny, permanent magnet synchronous motor (PMSM) product specialist for Bauer Gear Motor, says: "Energy efficiency is a hot topic across every industry at the moment, but without fully understanding all the components within the drivetrain, only a fraction of the potential savings can be realised." Throughout the drivetrain, the potential energy savings available are approximately, 10% from improved motor efficiency, 30% via electronic speed regulation, and as much as 60% from the optimisation of the mechanical system. "This highlights the fact that, while the current focus on energy-efficient motors is important, it's even more important that engineers don't lose sight of the other areas where improvements can be made," says Kutny. "Maximising the savings potential across each of the fields listed above is possible through smart specification of parts that focus on a combination of long-term reliability, low maintenance costs and the best energy efficiency possible." Recent technological advances in motor design have allowed manufacturers to deliver radical improvements in energy efficiency. Added to the recent IE2 and IE3 regulation (and the future IE4 regulations) this means that most applications are already benefitting from improved electrical efficiency. A recent comparison test carried out on a Huber disc thickener at a water treatment works in Germany between a standard IE2 asynchronous motor and a Bauer IE4 super premium efficiency motor showed energy savings of over 40% is possible with the newest technologies. Driving efficiency With a great deal of attention being focused on improving motor efficiency and further IE classification rumoured to be on the way, most leading motor manufacturers are able to offer IE4 performance where required. Bauer, for example, has developed a range of stainless steel IE4 motors for easy 'washdown' and even an ex-rated (flame- and spark-proof) solutions. With the increasing choice available, engineers are also having to consider purchase price, running costs and reliability as factors when selecting and sourcing motors, as well as integration with other components. "While motor efficiency and speed control currently enjoy the majority of media coverage, the fact is that mechanical optimisation accounts for the majority of potential savings in most existing drivetrain solutions," says Kutny. "In fact, the opportunities are so vast that we split it into two further sub-categories: Gear Technologies and Drivetrain Optimisation." Other factors to consider for an efficient system include using a speed control device to monitor the output of the motor and regulate its energy use accordingly. This is well known to be a quick and simple way of increasing the efficiency of a system. Depending on the requirements of the application, there are many different control and monitoring concepts which may offer the best combination of cost and efficiency. "Most leading manufacturers are able to offer products with varying degrees of control and performance, all of which are extremely reliable," says Kutny. "However, it's always worth speaking to an expert to source a solution which will integrate best with the motor and other components, that you have specified." Clearly, specifying the right gearbox design with optimised ratios to maximise efficiency is crucial. A well-specified gearbox can help to ease the load on the rest of the drivetrain simply by delivering better reduction ratio between the motor and the drivetrain. For applications which require accurate speeds, or high torque transfer, a bespoke design is always preferable as good quality manufacturers should be able to work with design team to develop bespoke solutions. "Drivetrain optimisation is the last piece of the puzzle, but no less important than the considerations that have come before it," says Kutny. "Once each aspect of the drivetrain has been specified, it must then be integrated into a machine with as much efficiency as possible. This requires an indepth understanding of the drivetrain as well as the specific demands of the given industry." Bauer is working on a number of methods that can help further the efficiency improvement during the integration stage. An example is where it is using gearing to take over the bearing function. This helps to reduce the overall number of components, can offer improvements in efficiency equivalent to the step-up from an IE1 motor to an IE4 in the same drivetrain. So the potential is very significant. With such dramatic performance increases possible, end-users are increasingly seeking out manufacturers and suppliers that are able to offer integration support. Modern day technology means that engineering as a whole is quickly moving towards new levels of efficiency that were previously thought to be impossible. "Not only does this help to cut end-users' running costs, it is making a real difference to the environment," says Kutny. "While individual technological advances are exciting, it's important not to lose focus on the energy-saving possibilities of the entire drivetrain." IE3 and specifying energy-efficient motors IE3 motors are gaining significance as components for energy saving machines because from January 1, 2015, motors with a rated output between 7.5 kW and 375 kW shall comply either with efficiency class IE3 or IE2 if they are equipped with a variable speed drive. Many companies are already able to offer motors with premium efficiency IE3 and they may even be beginning to supply super premium efficiency IE4. The exceptionally high energy efficiency of these motor-drive packages derives from the virtually complete elimination of rotor losses and the optimised rotor design of the synchronous reluctance motors and optimised drive control. Improvements in motor efficiency have been made possible thanks to new materials, better design and better manufacturing. Through the innovative design requiring no cage (and no permanent magnets) the rotor of the synchronous reluctance motor has virtually no losses and the rotor temperature is lower than that of conventional rotors with all the advantages. A higher efficiency motor typically costs more than the motor it is replacing. However, the higher purchase cost is recouped by the power savings it makes during its operational life. For example when working near full load a typical 11kW IE3 motor will be around 1.6% more efficient than an IE2 equivalent and might cost up to £200 more to buy. If the IE3 motor was running continuously, you'd save around 1,290kWh a year compared to the IE2 equivalent. With electricity costing 8p/kWh (including Climate Challenge Levy), this gives a £100 saving each year, paying back the additional investment cost in 24 months.