Maintenance testing of rotating machine insulation

Rotating electric machines contain conductors, a magnetic circuit and insulation in both the stationary and rotating elements. These elements, along with the mechanical supporting structure form the essential design components of the machine. The electrical insulation is one of the most important factors in determining the reliability of a machine. Much of the uncertainty in connection with machine maintenance concerns the proper evaluation of the insulation condition and the detection and correction of conditions which may have an adverse affect on insulation life. This paper deals with the testing techniques involved in a well planned preventive maintenance program and outlines some of the fundamental principles.