First IE4 synchronous reluctance motor and driveinstallation is game changer09 January 2013

The world's first IE4 synchronous reluctance motor and drive package (SynRM) from ABB has replaced an induction motor-based variable-speed drive (VSD) package at South Staffs Water in the UK – and made waves in the industry.

According to Keith Marshall, supply director at South Staffs Water, it has led to a 6% energy saving (on an already efficient system), with the potential for that to rise to 10—15% where SynRM technology replaces older motor packages.

Marshall explains that the company needed to replace a 20-year old, 115kW induction motor used to control a single vertical shaft-driven borehole pump, which abstracts 2.5 million litres of water per day.

This IE2 motor was already controlled by an ABB ACS800 VSD, so had maximised the process energy saving opportunities from flux optimisation.

The utility, says Marshall, was interested in trialling the SynRM motor to verify its claimed benefits, in terms of higher efficiency and reliability, lower heat loss, less noise and reduced maintenance.

"The biggest benefit is the 6% reduction in energy," comments Marshall. "While being one of the most efficient companies in the industry, our electricity bill is more than £9 million per year.

"Pumping water accounts for some 90% of this spend, as we have one of the highest pumping heads of any UK water utility. So a 6% reduction on one pump in a system that was already very efficient is massive news for us."

"Including the UK government's Enhanced Capital Allowances (ECAs), we estimate the return on investment to be between five to six years. Given that the existing drive and motor were already fairly efficient and therefore squeezing more savings was always going to be difficult, then this is a very acceptable return."

Marshall also points to the fact that this first SynRM motro has resulted in 58% reduction in frame temperature, compared to the induction motor. "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 says.

"As the rotor has effectively no losses this lowers the bearing temperature. So we can either extend the period between greasing or increase the bearing life expectancy," he adds.

Other key findings: SynRM has resulted in a 75% reduction in noise (down to 72.3 dBA at 1,450 rpm); but, more importantly, significantly greater energy saving potential elsewhere.

"We chose to trial the SynRM on an application already using leading-edge drive technology, although controlling a 20-year old high efficiency induction motor," explains Glen Hickman, from Sentridge Control, which installed and commissioned the equipment.

"We could have reduced the size of the motor but, for the purpose of a like-for-like comparison, we retained the same frame size. Also, if we choose [to replace] an older motor and drive combination elsewhere on the plant we believe the energy savings could easily reach 10—15%."

And Hickman adds: "The 6% energy saving is incredible, given that the application was already deemed to be extremely energy efficient... We are now looking at applications using really old drive technology or where a motor-drive combination is deemed suitable."

"This is such a sizable leap forward in technology over traditional induction motors that we are now considering other applications across our sites," confirms Marshall. "Suddenly, other applications that might have had low priority become easy targets within our investment programme.

A SynRM rotor has neither a conducting short circuit cage (as with induction motors), nor permanent magnets, nor a field excitation winding.

Instead, it relies on the magnetic principle of reluctance, so the streamlined rotor structure eliminates rotor cage losses, hence increasing efficiency and compactness.

Achieving standard power and torque levels at a lower temperature also improves the lifetime of the motor insulation and extends bearing lifetime or greasing intervals.

Brian Tinham

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