Water immersion testing of form-wound coil insulation

The rapid and varied growth of modern technology has created many new requirements for large industrial motors employing form-wound pre-insulated coils. In an increasing percentage of these applications a motor is required to operate with a high degree of reliability under severe environmental conditions that may adversely affect the insulation system of the machine.^1,2,15,4,5,6 Further, the trend toward less elaborate motor enclosures increases the exposure of the insulation to the degrading environmental influences. This has magnified the necessity for providing an insulation system possessing the capability of resisting the environmental influences. The type of environmental conditions referred to are found in the chemical, rubber, food, and plastics industries, where machines may be exposed to direct water spray or highly humid conditions, due to “washing down” operations with water or steam. Also, in pipe line and utility applications, essentially open motors are placed in outdoor locations that afford little, if any, protection from the elements. In still other instances, motors may even be flooded due to weather extremes. In some applications, degrading chemicals may be present in the form of solutions or suspensions. However, regardless of the type of chemical contaminant, it is of prime importance that insulation systems for motors operating in such environments be highly resistant to moisture penetration. Consequently, considerable effort has been expended by motor manufacturers in an attempt to develop insulation systems capable of providing trouble-free service under severe operational environments. The end users have recognized the problem by requiring nonstandard acceptance tests. In some cases, contractual requirements have specified that units for particular applications be capable of passing high potential tests and/or maintaining a minimum insulation resistance while submerged in water for a specified time. This is in addition to the ASA C-50 final acceptance tests.