The pulsating current supply of the commutating machine has R notable effect on the changes in brush-commutator contact area, which is particularly obvious when determining the coefficient of friction of the brushes. These friction coefficients were measured under static and dynamic conditions using the "resistance bridge" method, and applying certain current types and other specified brush operating conditions. However, the test results themselves are not sufficient to define clearly the degree of influence that respective physical properties have on the coefficient of friction of brushes. Therefore, a mathematical model of the coefficient of friction of brushes for the test brush-commutator set has been designed. The model provides greater sureness in explaining the impact of the pulsating current supply on the static values of the coefficient of friction of brushes (the static coefficient of friction), and on the transition process when the current changes while passing between the sliding contact surfaces (the dynamic coefficient of friction).
Key Words-Eiectrographite brush, static coefficient of friction, dynamic coefficient of friction, resistance bridge, pulsating current, mathematical model of the coefficient of friction of brushes.