The Conducted EMI of the Single-Phase Series Commutator Motors : On the Mechanism of Generation and Propagation

Generally, the noise of the single-phase series commutator motors occurs due to a spark discharge, its frequency spectrum contains high-frequency componets (-VHF range), and generate interference to many other electronic equipments (for example Radio, Television Receivers, etc.). As mean for protection to the conducted EMI (electro magnetic interfernce), generally, 0.1μF capacitor are installed between the conductors in a power cord and 0.003μF capacitor between the each conductor of a power cord and the metallic part of the instrument. However, the interference exist in many areas, and this tendency will become more pronounced. Hence, we made an experiment to clarify the mechanism of generation and propagation of the conducted EMI, which is necessary in order to establish the preventative method. We measured the spectrum of the noise current which propagate on the line, the voltage waveform between brushes (noise source), under various conditions (brush pressure, length of the line, revolutions per minute of the armature, etc.). The spectrum is measured by a spectrum analyzer, and the voltage waveform is measured by a cathode-ray oscilloscope (CRO). The results written in this paper are as follow, 1) the noise occuring at regular intervals, the magnitude of the noise is influenced of spark discharged voltage and of the stability of contact between brush and commutator, 2) the noise current generated by spark discharge at the brushes, propagates to the power line and is reduced by passing through the field winding (include the core), 3) the envelope and level of the spectrum of the noise current which propagate on the line are influenced by the line constants, the length of the line, and the magnitude of the sparking voltage which is proportional to the revolutions per minute. We consider that result 2) is an important fact to prevent the noise current and it seem to suggest that the field winding has a specific characteristic.

Generally, the noise of the single-phase series commutator motors occurs due to a spark discharge, its frequency spectrum contains high-frequency componets (-VHF range), and generate interference to many other electronic equipments (for example Radio, Television Receivers, etc.). As mean for protection to the conducted EMI (electro magnetic interfernce), generally, 0.1μF capacitor are installed between the conductors in a power cord and 0.003μF capacitor between the each conductor of a power cord and the metallic part of the instrument. However, the interference exist in many areas, and this tendency will become more pronounced. Hence, we made an experiment to clarify the mechanism of generation and propagation of the conducted EMI, which is necessary in order to establish the preventative method. We measured the spectrum of the noise current which propagate on the line, the voltage waveform between brushes (noise source), under various conditions (brush pressure, length of the line, revolutions per minute of the armature, etc.). The spectrum is measured by a spectrum analyzer, and the voltage waveform is measured by a cathode-ray oscilloscope (CRO). The results written in this paper are as follow, 1) the noise occuring at regular intervals, the magnitude of the noise is influenced of spark discharged voltage and of the stability of contact between brush and commutator, 2) the noise current generated by spark discharge at the brushes, propagates to the power line and is reduced by passing through the field winding (include the core), 3) the envelope and level of the spectrum of the noise current which propagate on the line are influenced by the line constants, the length of the line, and the magnitude of the sparking voltage which is proportional to the revolutions per minute. We consider that result 2) is an important fact to prevent the noise current and it seem to suggest that the field winding has a specific characteristic.