Economics, Evaluation, and Trends of High-Temperature Motors

The enormous strides which have been made in the development and processing of high-temperature insulations over the past 15 years has caused a reevaluation of their use in rotating machines. This reappraisal is resulting in furnishing more and more electric machines to industry on a Class B or higher temperature basis. Less than 5 years ago, 95% of induction machines in 150-5,000-horsepower sizes were furnished with Class A insulation (rated for 105 C [degrees centigrade] total temperature). Today it is estimated that 40% of all units falling in this category are Class B (rated for 130 C total tempera-ture) or higher. The conversion to higher temperature machines is continuing rapidly and it is reasonable to expect that 75% of all units falling in this horsepower range will be furnished on a Class B basis within several years. How will higher temperature machines differ from the older Class A motor designs? What basic improvements in high-temperature insulations have been made which make an industry transition appropriate? It is the purpose of this paper to answer these questions and to set in focus the reasons for the trend to higher temperature machines.