Permanent Magnet Synchronous Motors Maximise Efficiency

In any industry, securing efficiency is important. For critical infrastructure such as wastewater treatment plants, where duty requirements are continuous, it is even more so. Therefore, selecting an optimum geared motor to efficiently meet these duty requirements can deliver a winning combination of cost-effectiveness and increased environmental protection. This is exactly what Bauer Gear Motor, a leading brand of Altra Industrial Motion Corp., has enabled for an eccentric screw pump at Bayreuth sewage treatment plant in Germany.

Bear Gear Motor is a world leader in technology for geared motors - always ahead of the curve in terms of delivering high performance and efficiency drives. Since the founding of the business in 1927, it has focused on providing optimum motor and gearbox solutions - allowing operators to access application reliability while safeguarding return on investment (ROI) and overall energy consumption.

This is of pertinence for the water treatment sector. At Bayreuth, the eccentric screw pumps are required to operate almost continuously 365 days of the year. Over such duty requirements, an improper motor can generate excessive costs for operators. Specifying an oversized motor, matching it to incorrect components, missing the operating point or improper gear selections can have a debilitating effect on long term energy efficiency. Specifying an optimum drive solution for this application, in conjunction with the pump manufacturer, what the challenge presented to Bauer by plant operators.

As is to be expected of a global technology leader, Bauer had a solution. Working with the pump manufacturer, Bauer discovered that the installed 15kW IE3 asynchronous motor (ASM) could be downsized to a 5.5 Kw IE3 drive with PMSM technology.

A downsized motor obviously provides improved energy efficiency, but the design of Bauer PMSM drives home the advantage. An exceptionally efficient rotor design features specialized permanent magnets, which provides power savings and improved environmental credentials compared to traditional motors. Heat losses from the rotor are eliminated and total losses reduced by 25 percent, which results in consistent motor efficiency improvements of over 10 percent compared to competitor drives. These characteristics ensure high efficiency even across varied duty requirements.

Other eccentric screw pumps at the plant were still operating ASM variants, which allowed Bauer and operators to conduct a direct comparison. Operating both ASM and PMSM variants at a constant speed of 25Hz, the PMSM was found to deliver continuous energy efficiency across the curve, especially at low load. When speed was varied, the PMSM was still more efficient under partial load. At low speed and load, the PMSM achieves 85 percent efficiency compared to 65 percent for the ASM. This illustrates the wide partial load operation and speed range offered by the inherently efficient PMSM.

Benefits to the application are many. Eccentric screw pumps operate at different speeds and operating points depending on requirement, which suits the wide partial load operation and speed range offered by the PMSM. Furthermore, this range offers a higher overload capability, which is advantageous if another pump fails on-site and the same duty requirements are spread across fewer pumps. If installed motors provide greater overload capability, this requirement is easily met, protecting uptime. A high starting torque is another inherent feature, which is important when pumping fluids. Downsizing the motor also eases future maintenance, as the smaller motor can be easily replaced if the need arises. Connecting cables were also half the thickness of the ASM equivalents, also reducing costs while ensuring easier handling and maintenance.

However, the principle benefits to operators was increased efficiency across all duty requirements. A minimum 10 percent overall efficiency improvement extending over yearly operating cycles delivered considerable cost savings of up to € 9,000 per pump per year and environmental advantages on top. As well as reducing energy bills, operators could easily meet targets for CO2 emissions, which are tightening in all aspects of industry. This matched with the inherent performance and reliability of the PMSM, means the operators reached the goldilocks zone of efficiency created by an optimum motor designed for varied duty requirements.