In an industrial plant equipped with HV motors, suppressors. several severe stator failures occurred in spite of the The paper will first give an overview of the types of switching installation of MOA (metal-oxide arrester) surge arresters. All surges that can occur in this network configuration i.e. current of these motors were switched with vacuum circuit breakers.chopping and voltage escalation at de-energization and pre-The purpose of this paper is to demonstrate the necessity of ignition at energization. complementary protection against overvoltages by adding C-R Secondly, network simulations using EMTP/ATP (capacitorresistor) surge suppressors.(ElectroMagnetic Transients Program / Alternative Transients This paper will first give an overview of the types of switching Program) software are presented, including a complete surges that can occur in this network configuration. Secondly, simulation of the vacuum circuit breaker. This model takes into network simulations using EMTP/ATP software are presented. account the chopping current, the slope of recovery strength The object of these simulations is to calculate the overvoltages and the current slope that the vacuum switch is able to created during motor switching, to study the evolution of these interrupt. The object of these simulations is to calculate the overvoltages as a function of cable length and motor power, overvoltages created during motor switching, to study the and to check if additional protection needs to be installed on evolution of these overvoltages as a function of cable length these motors. and motor power, and to check if some additional protection The comparison is made between the simulated voltages and needs to be installed on these motors. the motors withstand voltage capability defined in the IEC The maximum overvoltages obtained in the simulations 60034-15.often exceeds the withstand level of the motor insulation, the It can be concluded that even with two MOA surge arresters, comparison is done not only with magnitude criteria but also the protection of the motor is not guaranteed.with time rise. A full motor protection is provided by installing C-R surge It can be concluded that even with two MOA surge arresters, suppressors thus eliminating multiple reignitions. one located at the load terminals of the vacuum circuit breaker This paper will give installation recommendations for both the and the other located at the motor terminals, the protection of C-R surge suppressors and the MOA surge arresters. the motor is not guaranteed. Full motor protection can be provided by installing C-R surge Index Terms -Switching overvoltage, Vacuum circuit suppressors and by keeping the MOA surge arresters on all breaker, MOA surge arrester, C-R surge suppressor, Motor. the motors.
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