Selection of power cables for PWM AC adjustable-speed drives

This paper identifies and discusses the reliability issues associated with three-phase electric motors controlled by constantly improving, fast-switching pulse-width modulated AC adjustable-speed drives and the selection of the power supply cable. The fast switching rates of PWM drives generate high frequency currents and induced potentials on the motor, drive and interconnected equipment. This leads to premature motor bearing failure and electrical interference to the drive and nearby equipment. Research shows solutions related to the power cable dictate a construction that must provide an effective electrostatic shielding for isolation of the high frequency currents and potentials, and an effective low impedance path to ground for draining canceling ground currents. This paper presents an overview of the benefits and drawbacks of typical National Electrical Code power cable constructions that help reduce or eliminate the problems associated with PWM AC adjustable-speed drives.