Mathematical modelling of commutator DC motor in failure conditions

The commutator of dc motor is approximated by equivalent resistance circuit. Extremely different values are assigned to circuit parameters depending on the angular position of the rotor. Created for diagnostics purposes mathematical model of commutator dc motor with loop rotor winding is a set of stiff nonlinear differential equations. The characteristics of dc motor were investigated in failure conditions. The shorting of rotor coils causes the considerable deformations of currents, voltages, electromagnetic torque and velocity in motor. From the calculations it can be seen that this mathematical model is particularly advantageous for diagnostics of dc motor. Measurement investigations have been carried out for commutator dc motor with loop rotor winding specially designed for diagnostic aims. Construction of this motor enables to realize the breaking of one rotor coil and shorting of two groups of rotor coils. Each group contains three rotor coils. In investigations these defects have been realized separately and simultaneously. In paper are presented simulation and measurement results. The results have been compared. The basis of this comparisons were transients: current and voltage of excitation circuit, current and voltage of armature circuit, shorted coil currents and velocity of rotor.