Protecting HV motors against switching overvol tages
In an industrial plant equipped with HV motors, several severe stator failures occurred in spite of the installation of MOA (metal-oxide arrester) surge arresters. All of these motors were switched with vacuum circuit breakers. The purpose of this paper is to demonstrate the necessity of complementary protection against overvoltages by adding C-R (capacitor - resistor) surge suppressors. This paper will first give an overview of the types of switching surges that can occur in this network configuration. Secondly, network simulations using EMTP/ATP software are presented. The object of these simulations is to calculate the overvoltages created during motor switching, to study the evolution of these Over voltages as a function of cable length and motor power, and to check if additional protection needs to be installed on these motors.