A new measurement technique for the investigation of arcing processes of sliding contacts

The current leakage between the brushes and commutators of electrical motors generates arcs causing high-frequency pulses in the commutating current. Pulse amplitude and intensity depends on the material pairs, wear-in conditions, and mechanical tolerances of the brush-commutator system. To investigate the brush sparking of electric motors the high-frequency part of the motor current between 1 MKz and 50 MHz was considered. By use of a spectrum analyzer and advanced evaluation methods the quality of commutation can be determined. The high-frequency part of the motor current is an equivalent criterion of the intensity and arc rate of the brush sparking for quality assessment. The applicability of this method was tested using 25 AC motors rated at 230 V and 1.2 kW. In a first coarse evaluation of the measurement, good correlation between the new electronic and the conventional subjective-optical method was found. The information volume contained in the electrical spectrum, however, is considerably greater than that obtainable by the optical method.<>