593 / 2017-05-15 09:51:50

Fundamental investigation on DC arc formation and extinction in separation process of brush and commutator segment

DC arc,Brush wear,DC motor,Breaking voltage,Electrode fall voltage

DC motors have been widely used in industry and transportation fields. When a commutator segment separates from a brush in DC motors, an arc discharge can be formed between them. The arc discharge formation causes brush wear, resulting in the decrease in brush lifetime.
However, few researches have been undertaken to reveal characteristics of DC arc between brush and commutator segment in DC motors. In this research, an experimental equipment was constructed to simulate a brush and a commutator segment. The equipment consisted of a fixed electrode (main component: graphite) simulating the brush and a movable electrode (copper) simulating the commutator segment, and they were arranged in atmosphere. After the terminals of the equipment were connected to a voltage source (output voltage of 12.6 V) through a resistor to supply a direct-current of 10 A, the movable electrode moved downward. When the movable electrode separated from the fixed electrode, an arc discharge was established between electrodes. In the separation process, we measured the time variations in the voltage between the electrodes and an instantaneous current flowing between the electrodes. As a result, the voltage proved to generate in the following two stages. (i) The voltage gradually rises to about 4 V just before the electrodes separation, and results in the reduction in the instantaneous current from 10 to 9 A. This voltage is considered to be a breaking voltage. (ii) After the electrodes separation, the voltage of about 14 V is generated between electrodes during arc formation. This voltage contributes to decrease in the instantaneous current from 9 to 0 A. This voltage is considered to be an electrode fall voltage. It is therefore pointed out that the breaking voltage and the electrode fall voltage are important factors for affecting the current decreasing process.