Running motors and drives accounts for 40% of the world’s energy, while in UK industry it accounts for 66% of the electricity consumed. What’s more, the cost of running a motor can be 10 times what it cost in the first place – the original cost, spread over its lifetime of, say, 15 years, is merely 2-10% of the running costs.
Improving the efficiency of motor operations is therefore paramount to slashing energy bills and to reducing an organisation’s carbon footprint. The Carbon Trust offers useful recommendations for reviewing motor and drive efficiency, driven by the European Commission’s core objective under its Europe 2030 strategy to reduce carbon dioxide emissions by 40%. Indeed, there is growing regulatory pressure on industry to cut back electricity consumption and boost energy efficiency.
The European Union introduced minimum legal requirements for the energy efficiency of electric motors in 2011 in the form of the EU Motor Directive. Subsequently, the EU standard series EN 50598, which came into effect at the end of 2014, shifted the focus from individual drive components to entire drive systems. EN 50598 defines the Eco Design requirements for drive systems in electrically powered machines, including energy efficiency and lifecycle analysis.
In a three-step plan, EU law prescribed improved motor efficiency in IE2 motors (0.75-375kW) by 16 June 2011; IE3 motors (7.5-375kW) or IE2 motors with speed control by 1 January 2015; and IE3 motors (0.75-375kW) by 1 January 2017. However, measures focusing exclusively on the motor are not expected to be enough to achieve the binding targets. By 2018, the directive will stipulate system efficiencies for motors and drives with an extended product approach, including mechanical power transmission and the full drivetrain system.
In a white paper on “Energy efficiency in motion”, Siemens says: “Though the new standard contributes to improving overall understanding of industrial energy efficiency, the interaction as well as application-specific know-how and the full lifecycle must be taken into account.” The company recommends establishing wider specifications for drive systems, including operation-relevant data such as load profiles to determine energy efficiency.
An efficiency strategy
Paul Huggins, associate director in the technology programme at the Carbon Trust, suggests a strategy for improving energy efficiency performance of power-hungry drives and motors.
He recommends that specifying higher-efficiency motor applications will save money. Moreover, he says: “The small additional price premium usually pays for itself in less than two years.”
If the load driven by the motor has varying demand, then a variable speed drive (VSD) could save significant energy, as even a small speed reduction can lead to substantial reductions in energy use. “Of the 100% energy put into a system, typically just under 60% is available to do practical stuff, such as running fans or pumps,” says Huggins.
For example, if you are running a 37kW motor throughout the year, you can achieve annual savings of around £28,000. So insertion of a VSD to control the motor and manage the system better, with an energy cost of about 5%, could save appreciably more than the energy it consumes.
Motor energy losses can accrue in numerous ways. Motors are often left running when not in use, so it helps to have automatic switch-off controls and manual switch-off procedures. Other ways to save energy include time switches, interlocks, sensors and intelligent controls.
Electric motors suffer heat loss, magnetic losses and frictional losses. Energy can be used more productively, for example, by using more copper or different materials. And if you reduce the speed by 20% on a variable torque application, you can achieve a 50% power saving.
“How you use your motor is an important issue to consider,” says Huggins. “If used only intermittently, the motor could be switched off from time to time. However, some motors can be switched off only so many times a day, so that has to be factored in to avoid wearing out the motor. But if a soft starter or VSD is attached, a motor can be switched on and off more regularly.”
Motor selection
There are three key factors to selecting motors for higher energy efficiency, says Huggins. First, you need to take into account how long the motor will be running. Secondly, you need to consider what the load level is. Third, you need to assess what level of energy is required, which may also dictate the level of investment required.
“If you have a process that doesn’t use the motor very often, it may be more economic to purchase a motor that is less efficient. But the more a motor is used, the more it makes sense to be efficient,” he says.
As about 97% of the cost of a motor is its lifecycle costs, only 2% is the purchase price and 1% the maintenance costs. “Therefore, small improvements in energy efficiency on a motor can actually add up to large savings in the lifecycle cost,” says Huggins.
Monitoring output
To identify where money can be saved, it’s essential to measure a motor’s output and monitor trends. Some companies simply react to motor breakdown or unexpected output changes, whereas proper monitoring will identify simple maintenance issues or serious problems.
Motors and drives can be equipped with a variety of measurement equipment to monitor the condition of a system and manage output. Hours-run meters measure how long equipment has been running. A clip-on ammeter can measure a motor’s load. A portable logging device can provide an accurate picture of energy consumption over a predefined period. And large motors are often equipped with permanent kWh metering for ongoing trend analysis.
At a simple level, monthly energy bills can reveal some concerns, but manual inspection is vital. “It is important to check the condition of motors regularly, to ensure adequate ventilation, and to do an aural check to determine if the motor is running properly. Larger motors should be monitored on a continuous basis to give more accurate information on trends,” says Huggins.
Visual inspection can be accompanied by vibration analysis, to determine wear on bearings or lack of lubricant. Oil analysis is important, because presence of iron filings may indicate damage. A thermographic survey will show if some motors are running hotter than others.
Motor management policy
A structured management policy for repair and maintenance can save energy and reduce downtime. The policy should include a plan for repairing failed motors, comparing long-term repair with replacement costs, with a schedule and procedure for motor maintenance.
If a motor fails, there is always the question of ‘replace or rewind?’ Generally, the smaller the motor, the more sense it makes to replace it. “Once you get up to big motors there is an economic argument for repair and rewind, but only where the number of running hours is limited,” says Huggins. If a big motor is running constantly, it probably makes economic sense to replace it with a highly efficient motor, whereas if the motor is only used intermittently it makes more sense to get it repaired. The cost of rewinding an IE1 motor might be £350, while a new purchase might be £850 with a lifetime of 10 years.
As an example, a manufacturer in Northern Ireland produces 4,000m2 of glass each week and had total energy costs of £500,000 a year. Running old fans, it had associated energy costs of £58,000 a year. By applying a VSD, it delivered energy cost savings of £45,000 a year.
Innovation is being driven by the EU Eco Design Directive. Manufacturers of induction motors have redesigned motors for higher efficiency, with better copper and steels and improved electromagnetic properties. Permanent magnet motors are being used more regularly, as they don’t require an induction coil to create a magnetic field and have higher efficiency with a smaller footprint. Manufacturers are also introducing synchronous control motors with special electronic controls.
The way firms select induction versus permanent magnet motors or hybrids depends on the task involved. A list of suppliers is on the Energy Technology List website of the Department of Energy and Climate Change, under ‘motors and drives’.
The UK market for efficient motors is worth about £150 million to £200 million a year, the Carbon Trust estimates. Of those sales, 85% are induction motors while the remainder are permanent magnet motors and synchronous motors. The market also includes hybrid induction and permanent magnet motors, because of a shortage of rare earth elements.
Examine lifecycle costs
Companies need to consider system efficiencies in a plant in terms of “system lifecycle costs, not just to focus on motors and drives”, says Phil Banks, product manager for low-voltage drives at Siemens Digital Factory, Process Industries and Drives.
Siemens’ dynamic drives can operate in an eco-mode for partial load reduction in energy consumption, and optimise pulse rate patterns for use with its Simotics motors and bypass modes.
Siemens also offers a ‘drive technology configurator’ tool online, which enables companies to select appropriate drives and motors. “All our drives have counter-functionality built in, to monitor energy usage and savings. The drive itself will be auto-tuned to the motor, with a visual display of kilowatts consumed for trend analysis,” he says.
By defining efficiency classes, and determining losses for converters and drive systems, users can determine energy requirements and losses at defined operating points, with application-specific load profiles for their machines.
“It’s taken a long time for engineers and financial directors to comprehend that the cost of the motor is 10% or less of the running costs in an installation. You need to look at lifecycle costs and energy efficiency, as drive systems can account for one-third of total energy used,” says Banks.
What’s the load?
For a company selecting a motor, the key issue is to determine the load it will be driving – for a fan, pump or air compressor, for example, says John Guthrie, energy manager for drives at ABB. The next is to consider variable or fixed-speed drives. “We look at the load and whether to apply a VSD to control the speed and reduce the overall load chain,” he says.
“Engineers often put something in that’s a bit bigger than required, but the VSD will allow you to run the pump at exactly the right speed required, and reduces power accordingly. It’s a matter of how you control the whole system to match output required to load at all times. You also need to look at running hours,” he says.
A motor management policy is also important, he says. “A lot of customers are reactive, and only look at motors when they see a failure. So we promote a system for logging and monitoring and identifying all the motors within a plant – in particular, for motors driving critical equipment.”
Driving energy efficiency in motors and drives makes sound commercial and operational sense.