Opportunities to improve reliability and efficiency of medium-voltage electric motors

While there is a great deal of emphasis on replacement of NEMA frame motors with EPAct/Premium Efficient^™ motors, the vast majority of medium-voltage motors in use today fall outside the scope of EPAct. Many of these machines offer considerable opportunities to enhance performance during future rewinds. This paper focuses on practical measures to improve the performance (reliability and efficiency) of existing form-wound motors. Some of these opportunities can be capitalized on during the course of a repair, by optimizing the winding design, with little additional effort beyond the routine rewind. Others can be applied to in-service machines with no requirement to remove the machine from service. This study evaluated 94 sets of form coil winding data, comparing wire and slot dimensions, to assess the opportunity for magnet wire slot fill improvement. Motor ratings ranged from 200 to 5,000 hp (149 to 3730 kW), from 2 to 32 poles, 2.3 to 13.2 kV. The preponderance of data (43 motors) was for 2- and 4-pole machines, since those are most common in the petrochemical industry.