| With the development of frequency control technology, pulse-width modulation (PWM) inverters are commonly used for locomotive field. Frequency control pulling motor is key equipment in alternate current drive traction locomotive. Its security and reliablility decide performance of traction locomotive. During the process of popularized frequency control system, it has been found that a number of inverter-fed motors fail prematurely. Many research reports confirm that partial discharge (PD) under PWM is one of key factors which lead to premature failure of inverter-fed motors. So research about PD under square-wave pulse helps to study failure mechanism of insulation which attributes to aging and strengthen theoretical basis for designing insulation structure of frequency control motor. Compare to PD under alternate current (AC), the measurement and analysis technology under PWM has not reached maturity and its effects needs to be approached. Research work about PD under PWM still keep initial starting step.To these questions above, some research work has been done in this paper. Firstly, PD under square-wave pulse voltage is introduced simply. According to features of square-wave pulse voltage, testing system of PD is built. The key element in this system is impulse current sensor (ICS). Secondly, based on signals from ICS, low-frequency source disturbance and high-frequency are filtered by wavelet packet and two times extremum method. PD signal is extracted clearly. Finally, the difference of PD characteristics parameters under AC and square-wave pulse voltage is discussed in the same condition. The effect of different external conditions on PD parameters under square-wave pulse voltage also is researched. Size of partial void develops quickly along electric field direction because of PD under square pulse with aging time.These conclusions could be used to further investigate properties of aging under PWM voltage and relationship between PD and insulation failure. |
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