Verification of Commutation Spark Reduction for Brushes of Large DC Motors.

Abstract

Large DC motors for driving rolling mills should have a compact motor size and tew injurious commutation spark. Good motor performance is got with a no-spark commutation of the brushes. Commutation improvements have been investigated, but problems still remain with commutation leading edge sparking and trailing edge sparking for the progress of running times of the brushes.We developed a new interpole structure to get no sparking on the leading edge. A magnetic flux adjustment winding and a leakage compensation winding is provided adjacent to the radial inner end of the interpole core to improve flux distribution under the interpoles. This approach is effective because leading edge sparking is due to unsymmetrical magnetic flux distribution under the interpoles.Further, we developed a commutation control method to maintain the best conditions on the commutation trailing edge of the brushes. The mothod adjusts the interpole flux according to the commutating conditions.We describe the circuit construction of the commutation control here. Confirmation is made of the reduction effects on the commutation leading and trailing edge sparking of the brushes when using the commutation control system for a 2, 000kW DC motor.