Motoring into the IE5 era for energy efficiency

Motors convert electrical energy into mechanical energy to drive parts. Today, they are ubiquitous, with estimates of over eight billion electric motors in use in the EU alone. They come in all sizes for use in homes, offices, factories, hospital equipment and factory equipment.

They are estimated to account for over 50 per cent of global electricity consumption, and with rising fuel prices, energy-efficient operation has become an economic as well as an environmental issue. Making more energy-efficient motors available will contribute to reduced CO2 emissions and help countries achieve net-zero targets.

Industrial motors are used to control torque and speed on conveyor belts, robotic arms, automated guided vehicles and in compressors to regulate the volume of air, gas or liquid running through pipes.

They are graded in terms of International Efficiency (IE) classes, with each efficiency level generating 10 to 20 per cent less energy loss in the motor operation (see boxout below).

The IE5 class is defined for motors for variable speed operation. Richard Gee, UK sales manager, motors and generators at ABB, says IE5 motors produce up to 50 per cent lower energy losses than equivalent IE2 motors and 20 per cent lower losses compared to IE4 motors.

Synchronous motors can use permanent magnets or can create torque through magnetic reluctance. Today, there are IE5 permanent magnet (PM) motors, IE5 synchronous reluctance motors and IE5 PM-assisted synchronous reluctance motors available. There is work being done on creating an IE5 induction (or asynchronous) motor, but it is difficult to get one to such a high efficiency, says Norbert Hanigovszki, director of drives intelligence at Danfoss.

The type of magnet used affects a motor's cost and size. Rare earth materials used in permanent magnets are scarce and geo-politically sensitive because most are mined in China, explains Hanigovszki. Ferrite is a cheaper magnet but it is weaker, resulting in a larger motor.

Estimates put IE5 motors at no more than 1 per cent of the total motor market today. Part of the slow take-up may be due to the fact that governments do not require any motors above IE3. This may be dictated by the geography of motor manufacturers, observes Hanigovszki, with Danfoss, ABB and Siemens in Europe and GE and Allen-Bradley in the US but no manufacturers in China.

As a result, IE5 motors are a tool for differentiating products but viewed as a luxury upgrade rather than a necessity. Given that an IE5 motor has to be manufactured specifically, and at a premium, and bearing in mind that savings may not be realised immediately, the total cost of the project should be considered, not just the initial cost of the motor, advises Hanigovszki.

This is particularly true for municipal projects where IE5 motors can save running costs and energy use for large projects which run motors at partial load or partial speed, such as heating, ventilation and air conditioning (HVAC), pumping fresh water and wastewater treatment. The electricity used to supply water to towns and cities is usually the highest electricity charge, says Hanigovszki, so any savings will be significant.

Motors are designed to operate for at least 20 years, but total cost savings can be realised relatively quickly. ABB cites the example of a 110kW motor running at 1,500rpm. The difference in initial cost of its IE5 motor and an IE3 motor "is negligible compared to the annual savings in energy costs". The IE5 motor package will pay back the cost difference after about 13 months. In addition, it will continue to generate annual savings for the rest of its working life. Within about 10 years, the reduced energy use will cover the initial cost of the whole IE5 package, says the company.

An IE5 synchronous motor is smaller than an IE3 or IE3 induction motor, so retrofitting to the energy-efficiency model may need a redesign. The wiring and voltage balance between the motors is the same.

An IE5 synchronous reluctance motor is the same size as an IE2 induction motor, therefore no mechanical modification is needed for a retrofit. "Functionally, it operates the same way as any induction motor and so there are no specific requirements to consider, as it can be swapped like-for-like," says ABB's Gee.

It does, however, need a variable speed drive in order to reach IE5 efficiency levels. These must be a matched package, i.e. from the same manufacturer and compatible with one another, he advises.

"A variable speed drive can lead to savings which are far higher than those from the increased efficiency of the IE5 [motor] because when you adapt the speed of the motor to the speed of the application, you save a huge amount of energy," says Hanigovszki. Typically, there can be savings between 15 and 40 per cent by moving from a fixed speed motor, for example for fans, pumps and compressors.
Using an IE5 motor offers up to 30°C lower winding temperatures and up to 15°C lower bearing temperature than an IE2 motor. This increases reliability and prolongs the lifetime of the motor, says Gee. "Lower bearing temperatures are an important factor in reducing life-cycle costs, because bearing failures cause about 70 per cent of unplanned motor outages," he adds.

If a motor is used intermittently or at part load for long periods (e.g. fans and pumps), a variable speed drive can lower the input voltage and frequency to the motor, reduce the rotation speed and result in up to 30 per cent additional energy savings.

The relatively small savings when moving from an IE1 to an IE5 motor (around 5 per cent) could be one reason why retrofitting with IE5 motors is not popular. "The payback time could be five to eight years when retrofitting only the motor, whereas migrating from fixed speed to variable speed could see payback within a year," concedes Hanigovszki.

There is also a lack of awareness, adds Gee, and particularly of the potential savings that the motor can achieve over the longer term. "Steep rises in energy costs have also, inadvertently, made the case for IE5 even more compelling. The more the cost of energy increases, the faster the payback time," he says.

An example is the Südzucker sugar refinery in Belgium, which uses 3,000t/h of water in peak season to transport beet around its plant. However, analysis showed the biggest potential for energy saving came from the slicing machines. Here, six old 160kW asynchronous motors have been replaced with 134kW IE5-rated SynRM motors from ABB, paired with variable speed drives, cutting costs by 27.4 per cent for the substation, with associated lower emissions.

Undoubtedly, the energy crisis will accelerate demand for IE5 motors. Unfortunately, on top of an energy crisis, there is also a supply crisis, says Hanigovszki, with lead times of around six months for motors. The supply crisis may mean that permanent magnet motors become less popular, giving ground to synchronous reluctance motors. There may also be a hybrid motor emerging, he says. These will use smaller ferrite magnets to provide a better power factor than synchronous reluctance motors.

"If you put just enough magnet in the motor, you may be in a sweet spot... but then again, a sweet spot can be many things. For some, price is important; for others, it is power density and for still others it is efficiency no matter what it costs."