Robert Boyce, US Division Manager for IEC Low Voltage Motors at ABB, makes the case for synchronous reluctance motor (SynRM) technology
A new class of motor can save biogas plants hundreds of thousands of dollars in operating costs, and the upgrade can pay for itself in around eight months.
The International Electrotechnical Commission (IEC) recently added a new energy efficiency class, IE5 (Ultra-Premium Efficiency), to its standard (IEC 60034-30-1:2025). But some motor manufacturers are already developing motors that meet the anticipated definition of IE6 ‘Hyper-Efficiency’. These motors are already on the market in power ratings from 110 to 450 kilowatts (150 to 600HP).
Robert Boyce
For now, IE3 (Premium Efficiency) and some IE4 (Super Premium Efficiency) motors are still the standard in US industrial specifications.
But on a 110 kW (150HP) application running at 75% average load for 8,760 hours per year, specifying an IE6 motor vs the traditional IE3 version is estimated to deliver more than $100,100 in energy cost savings over a 20-year operational life, and to reduce CO2 emissions by 157,540 kilos over the same period.
Multiply those anticipated savings across the 20-40 motor-driven loads typical of a mid-size agricultural biogas plant. As the scale of the installation increases, so does the financial imperative to consider hyper-efficient motors.
The hyper-efficiency difference
A conventional induction motor uses electromagnetism to induce current in the rotor, generating torque. The new generation of motors achieve hyper-efficiency using a fundamentally different principle: synchronous reluctance (SynRM) rotor technology.
SynRM motors have no current running through the rotor. SynRM rotors are precisely engineered laminated steel components with alternating flux barriers and flux guides. The design means the rotor tends to align itself with the rotating magnetic field produced by the stator, and it is this tendency that produces the necessary torque.
With no current flowing through it, a SynRM rotor does not heat up like a conventional rotor. ABB’s IE6 SynRM motors run up to 30°C cooler in the rotor and 15°C cooler in the bearings than a comparable induction motor.
Cooler operating temperatures mean the motor’s bearings can last up to twice as long, cutting down on unexpected outages, maintenance time and costs. When they do eventually reach the end of their operating lifetimes, SynRM motors are as easy to replace as induction motors. They require no special tools or processes. Because SynRM motors contain no permanent magnets or rare earth metals, supplies are less likely to fall victim to geopolitical instability.
SynRM motors require variable frequency drives (VFDs), which adjust motor speed in real time to match the fluctuating requirements of biogas processes. Motors’ electricity consumption varies with the cube of speed, so when a VFD adjusts a pump or compressor motor to 70% of its rated speed, its power consumption drops to about 34% of maximum. Direct on line (DOL) motors operate at a fixed speed and usually use more power than needed to fulfil their function. By using just the right amount at all times, SynRM motors provide a clear efficiency advantage.
Clear priorities
Few people outside the sector appreciate how motor-intensive a biogas plant is. Converting raw biogas to renewable natural gas (RNG) requires a network of motor-driven compressors, pumps and blowers.
The total cost of ownership of a motor is 97% electricity costs. Over the lifecycle of a biogas-to-RNG plant, the up front cost of motors is comparatively insignificant: only 2% of total cost of ownership, with maintenance making up the other 1%.
When outfitting a new plant, or replacing motors at the end of their lives, the decision-making process is simple. To optimise total cost of ownership, don’t prioritise purchase price; prioritise efficiency.
To learn more about IE6 SynRM, click
