Best of both worlds

The world's first IE4 super-premium efficiency synchronous reluctance electric motor-drive package (SynRM) from ABB, which recently replaced a conventional induction motor-based, variable-speed drive (VSD) package at South Staffs Water, is making waves in industry. According to Keith Marshall, supply director at South Staffs Water, it led to a 6% energy saving – and that was on a system already thought to be efficient. Indeed, he now believes it has the potential to offer 10-15% efficiency improvements, certainly where it replaces older motor packages. Marshall explains that the water supply company needed to replace a 20-year old, 115kW IE2 (formerly EFF1) high-efficiency induction motor, used to control a single vertical shaft-driven borehole pump that abstracts 2.5m litres of water per day. While clearly old, the motor was controlled by an ABB ACS800 VSD, so engineers had already maximised the energy-saving that derives from voltage-reducing flux optimisation. The company trialled the new SynRM motor to assess its claimed benefits – higher efficiency and reliability, lower losses, less noise and reduced maintenance. It worked. As Marshall puts it: "Our electricity bill is more than £9m per year [and] pumping water accounts for 90% of that, as we have one of the highest pumping heads of any utility. So a 6% reduction on one pump in a system that was already classed as efficient is massive news." How massive? "Including the government's ECA [Enhanced Capital Allowance], we estimate the return on investment to be five to six years." Given the challenge to squeeze more savings out of this particular drive and motor combination, Marshall says this is very acceptable. And there are other benefits:?this first SynRM motor has resulted in 58% reduction in frame temperature, compared to its induction motor predecessor. "In the summer, lots of sites run hot, so using SynRM across more sites means we can dramatically reduce the need for forced ventilation," he adds. "Also, as the rotor effectively has no losses, this lowers the bearing temperature. So we can either extend the period between greasing or increase the bearing life expectancy," he says. Other key findings: SynRM has resulted in a 75% reduction in noise (down to 72.3 dBA at 1,450 rpm). Glen Hickman, from Sentridge Control, which installed and commissioned the equipment, says the future is bright. "We chose to trial the SynRM motor on an application already using leading-edge drive technology. We could have reduced the size of the motor but, for the purposes of a like-for-like comparison, we retained the same frame size. "If we replace an older motor and drive combination, we believe energy savings could reach 10-15%." For Marshall, the new electric motor technology is a step change. "This is such a sizeable leap forward over induction motors that we are now considering other applications across our sites," he confirms. "Suddenly, low priority projects become easy targets." Under the covers A SynRM rotor has neither an induction motor's conducting short-circuit squirrel cage, nor permanent magnets. Unlike traditional synchronous designs, there is also no field excitation winding. Instead, it relies on the magnetic reluctance in combination with a conventional laminated stator and motor frame. Most importantly, the streamlined rotor structure eliminates rotor cage losses, and that, in turn, increases efficiency, while also ensuring that the motor runs cool. That means lower bearing temperatures and hence better reliability and reduced maintenance. It also means extended motor insulation lifetimes. What's more, like-for-like motor output can be delivered in a smaller footprint. ABB describes its award-winning technology as 'delivering the performance of a permanent magnet motor but as easy to service and cost-efficient as an induction motor'. Although the legislative framework does not yet concern itself with IE4 – instead making IE3 premium efficiency mandatory by 1 January 2015 for electric motors between 7.5 and 375kW (IE2 only in combination with a variable speed drive) – it is only a matter of time. ABB's development exceeds regulatory requirements, and offers significant energy, cost and maintenance savings immediately.