September 2020

28 n ENERGY EFFICIENCY September 2020 www.drivesncontrols.com Do IE3 motors retain their efficiency after repairs? E lectric motors place a huge demand on electrical supplies and most countries have now introduced regulations for minimum efficiency levels of new motors. With the growth in the use of high-efficiency motors, due in part to the strengthened regulations, it has become increasingly important to knowwhat effects, if any, repairing these motors will have on their efficiency. As long ago as 1998, the Association of Electrical and Mechanical Trades (AEMT) and the UK Government produced a Good Practice Guide, aimed at ensuring that motor efficiencies were maintained after they had had been repaired. The Guide, produced under the DETR’s Best Practice Programme, was based on a study of 40 motors with ratings of around 5.5kW. In 2003, the AEMT took part in a joint study with the US-headquartered electromechanical organisation Easa (Electrical Apparatus Service Association) to investigate the effects of rewinding on the performance of 23 larger motors. Considerable time was spent determining the parameters of the investigation, as well as the procedures and testing facilities. As part of this process, options such as multiple rewinds and round-robin testing were included in the study. But these were found to have no effect on the results, so they were excluded from the latest series of joint tests by the AEMT and Easa, which took place in 2019 and focused on machines with efficiency ratings up to IE3. The results of the study have been published in a report, The Effect of Repair/Rewinding on Motor Efficiency , which shows that the performance of these high-efficiency machines can be maintained after repairs. To allow comparisons to be made with the earlier studies, the latest study looked at ten premium efficiency (IE3) motors with similar characteristics to those in the 2003 tests. Their power ratings ranged from 30–75 kW (40–100 hp), with half of them having IEC frames and half being Nema designs. They had totally enclosed fan-cooled enclosures, and covered both 50 and 60Hz supplies, as well as two- and four-pole models. The repair procedures published in the 2003 Good Practice Guide were followed for each motor. This Guide has now been incorporated into the latest international repair standard (IEC 60034:23:2019) and the latest American Ansi/Easa standard (AR100). As in 2003, the IEEE 112B test standard was used. This has been harmonised with the IEC 60034-2-1 standard, so the results of the latest study comply with both standards. The efficiency tests were performed at the North Carolina Advanced Energy Corporation (Advanced Energy) using an eddy current dynamometer test stand. Advanced Energy, located in Raleigh, is the only independent motor lab in North America to hold the National Voluntary Laboratory Accreditation Program (NVLAP) accreditation for motor efficiency testing. The test results from the ten motors showed no significant change in efficiency compared to levels measured before rewinding, mirroring the results from 2003. On average, there was a drop in efficiency of just 0.1%. Because this is well within the range of the standard calibration test accuracy of ±0.2%, it effectively means that there was no efficiency change beyond that which would normally be expected during testing. The main conclusion that can be drawn from these results is that by following the latest international repair standards when repairing a motor, its efficiency will be maintained within the tolerances that it was originally manufactured to. n For more information on the effects of repairs and rewinding inmotor efficiency, download the full AEMT/Easa study from https://www.theaemt.com/technical-info The increasing use of premium efficiency (IE3) motors has brought with it renewed questions about whether these machines lose their efficiency when they are repaired. Last year, this issue was examined in an international study. Karl Metcalfe, technical support at AEMT, reports on the findings. The eddy current dynamometer test stand that US-based Advanced Energy used to measure the efficiency of ten IE3 motors before and after they had been rewound