Dynamic brush placement of large dc machines in mining industry : a feasibility study

Abstract—Large direct current machines have been used in the mining industry for many years due to their practicality and simplicity. The operational nature of DC machines causes a shift of the electrical neutral axis in the armature of the machine, changing the ideal position of the commutating brushes and possibly causing sparking. Direct current machine technology has been well developed to contain compensating windings and interpoles, which counteract armature reaction. However, there has never been a system designed to compensate for the rotation of the electrical neutral axis due to armature reaction. This paper outlines four alternate options, which could be used to design a device, which rotates the brushes of the machine with the changing electrical neutral axis. The paper also presents a comprehensive analysis of the benefits of such a device. The technical details of each option are identified along with a discussion of the designs. These four designs are then comparedusing an unbiased decision making tool resulting in the selection of most practical and effective design.