Surge protection of a large medium voltage motor-a case study

The raw mill motor in a cement mill had been damaged by repeated switching surges and subsequently rewound. New arresters were placed on the motor at that time. The surges coming in to the motor were measured, and the surge protection was reviewed. It was found that the original gapped silicon carbide surge arresters on the motor had insufficient protective margin, while the new zinc oxide arresters provided an adequate margin. The operation of the surge capacitors in protecting the motor was analyzed. Surge protection and insulation coordination should be reviewed in comprehensive power system studies