Efficiency drive

Surely few engineers or managers still doubt the ability of modern electric motors and variable speed drives (VSDs) to save very significant energy costs – at source and in terms of speed control – and, indeed, to pay for themselves in short order? The case studies are far too numerous and span too many industries to leave room for deniers. But how many understand the efficiency bands, what they mandate and when? And how many worry about an apparent requirement for 'inverter-rated' motors where VSDs are recommended? Starting with the energy efficiency regulations, European Commission Regulation 640/2009 – relating to the 'eco-design' of low-voltage, three-phase electric motors and drives – requires nearly all new equipment with a rated output from 0.75 to 375kW to meet the high-efficiency IE2 specification (equivalent to the top Eff1 band under the defunct CEMEP voluntary system). That ruling came into force more than two years ago. There are still exemptions, including equipment operating at more than 1,000m above sea level, or in ambient temperatures below -15°C or above +40°C, or in potentially explosive atmospheres. However, on 1 January 2015, higher 'premium efficiency' IE3 motors and gear motors will become mandatory for all machines rated between 7.5 and 375kW. IE2 motors will no longer be permitted for sale within the EU unless used with a VSD. This ruling will then be extended to include smaller motors, down to 0.75kW, from 1 January 2017, again with the proviso that IE2 be permitted for VSD-based applications. And there's more. Some users and manufacturers are already focusing on IE4 'super premium efficiency' electric motors, which present at least 15% lower losses than IE3 – even though this standard (IEC Technical Specification IEC/TS 60034-31) has not yet been ratified. ABB and WEG were among the first to offer such machines, both in 2012: ABB's great innovation was its SynRM synchronous reluctance motor (11–315kW), while WEG's was its W22 IE4 cast iron frame induction motor (3–335kW). Indeed, WEG is among the first already to be promoting IE5 efficiency class (currently only a draft potential standard and requiring a further 15% improvement over IE4) electric motors, with its permanent-magnet machines. The firm, which is launching its new motors at this year's Hannover Fair, says mechanical and plant engineering companies can expect a rated efficiency of 96.6%. Incidentally, WEG will also be unveiling W22x explosion-proof motors at IE4, giving users non-mandated super premium energy efficiency even in notified hazardous area applications. Motor manufacturers and regulators alike now hope that growing demand for energy savings and precision speed control will lead plant and factory managers increasingly to specify IE4+ machines and, in particular, PMSMs (permanent magnet, synchronous motors). Why? Because they have the high efficiency, smoothness, accuracy and speed range credentials that induction motors don't. What about variable speed drives and any requirements they put on electric motors? As Jerry Hodek, managing director of Rotor (UK), says: "There are plenty of documented cases of motors that have given 20 or 30 years' sterling service only to fail within hours of being fitted with a VSD that was meant to save energy and protect the motor from high load on start-up." This is, to an extent, history: early adopters in the 1980s found that voltage spikes, caused by the VSD, could punch microscopic holes in the enamelled wire insulation, which could rapidly spread and cause motor burn-outs. However, while the solution then was to fit harmonic filters, specify oversize motors and/or improve the motor insulation, electric motor manufacturers have long since improved their offerings so that the problem has largely gone away. Largely, but not entirely: today, the problem only arises with retrofits and upgrade projects, when existing motors are to be reused. Hodek warns that older motors mean the same switched voltage spikes and consequent insulation holes, as well as potential problems due to inadequate ventilation at low speed, dielectric stresses on motor windings and magnetic noise. The solution: change the motor. Energy cost savings So what about those energy savings and process improvements? Look no further than Atlantic Plastics, Park Laundry and Wabtec Rail – all, as it happens, users of ABB motors and drives. Atlantic Plastics, which manufactures fittings and valves for water utilities, reports 20% energy cost savings on one of its large injection moulding machines following installation of a VSD – a result that has led the firm to seek quotes for similar systems on its remaining 35 machines. "We were trying to become greener and cut energy use, and had identified our two 400 ton injection moulding machines as energy intensive," explains Gary James, engineering manager for the Bridgend, South Wales, plant. These harness hydraulic pumps, driven by direct-on-line, fixed-speed induction motors. However, for most of the cycle, operations did not need all the oil delivered by the pump, so it was simply recirculated. ABB?partner APDS installed a trial drive to match demand and measured power drawn at 10.5kW, instead of the 25.3kW from the existing machine. That was achieved by varying flow over the on-load and off-load segments of the cycle, with the drive set up to run at two speeds selected automatically in response to torque demand. James says payback was about 12 months. Moving on to Scarborough-based Park Laundry, the firm says drive technology has improved reliability of speed control on its calender ironing machine. And Pete McHugh, joint owner of the company, adds that ABB partner Halcyon Drives also effected a very rapid repair time when its old slip-ring motor, with auxiliary servomotor speed control, suffered catastrophic failure. "It was vital that we got [the ironing machine] up and running again," says McHugh. Halcyon Drives' solution incorporated a 15kW ABB general purpose ACS550 VSD with sensors on the feeder and folder for roller speed synchronisation. It's a similar story at Doncaster-based Wabtec Rail, which also reports improvements, in terms of noise and reliability since fitting a VSD – in its case, on equipment to test railway engine and rolling stock dampers. The test facility consists of a motor connected through a gearbox to a cam, which provides the lateral movement to compress dampers at selected frequencies under operator control. The original set-up used a 15kW dc motor controlled by a frequency converter, with closed-loop speed management via a mechanical belt and drive system – until the 35-year-old dc motor failed. ABB Drives Alliance member Inverter Drive Systems (IDS) recommended replacing the existing arrangement with an 18.5kW ac motor and an ACS800 VSD. Team leader Dave Williams states that, although the majority of tests require no more than 9kW, the rating of 18.5kW ensures it can be used to test the most demanding dampers. He also says the drive was programmed and installed so that the existing controls were integrated with the VSD, with the motor speed setting selected via a drive input. Installation took one week, he says, and not only does the new system enable more accurate speed control, but it also reaches setpoint speed instantaneously, is more reliable and requires very little maintenance.