Electromagnetic Radiation Characteristics of Partial Discharge in Inverter-Fed Motor Turn-Turn Insulation

Insulation degradation and flaws can be identified using the partial discharge (PD) test. Ultra-high-frequency (UHF) antenna sensors are commonly used for the detection of PD signals which are helpful to diagnose the insulation performance of inverter-fed motor. The electromagnetic signal generated by the PD contains a large amount of helpful information. The frequency content of the collected PD is closely related to the type of PD, the type of sensor antenna and the signal receiving device, but it is unclear whether the collected signal is the characteristic of the PD or the characteristic of the tested sample as the transmitting antenna. The turn-turn insulation sample of the motor and its simplified insulation sample (such as single-point cross-insulated sample) have the physical form of a typical dipole antenna. Theoretically, PD is a radiation source. The creation of PD is a normal electromagnetic radiation process, and the insulating sample can be utilized as a transmitting antenna for electromagnetic radiation. Therefore, this paper investigates the electromagnetic radiation characteristics of the turn-turn insulation sample as the transmitting antenna. Then, a PD detection platform for the turn-turn sample was built using a wide-band antenna (0.5～2 GHz Archimedes spirl antenna) to analyse the PD signals in the frequency spectrum. First, the dipole antenna is modeled using a single point cross polyimide sample. Using high-frequency electromagnetic simulation software, the antenna resonance frequency is calculated, and the radiation characteristics of the test antenna under various lengths and cross-angles are simulated. Then, an experimental platform for PD detection of turn-turn insulation is built by using a repetitive impulse voltage source. Experimental research the impacts of insulation sample length, environment, and impulse voltage parameters on the frequency domain characteristics of PD signal. The outcomes are as follows: firstly, as insulation sample length is increased, the resonant frequency of the sample antenna and the frequency domain of the PD signal shift to low frequency. The resonant frequency of the 10 cm sample antenna is 2.15 GHz, and the PD information discovered by the experiment with this insulation sample is substantially missing in the frequency domain and has a much reduced amplitude in the time domain. Second, the distribution of PD frequency domain is unaffected by the cross Angle of a single-point cross-insulated sample, changes in atmospheric pressure, changes in impulse voltage rise time, or changes in duty cycle. Finally, the turn-turn insulation sample from the flat wire motor exhibits multi-band characteristics as a transmitting antenna, and its effective working bandwidth completely covers the PD frequency domain distribution of the turn-turn insulation. Additionally, the properties of the sample antenna's multi-resonant band are unaffected by the change in the feed point. The PD frequency domain distribution produced by the turn-turn insulation of the same structure is consistent and is unaffected by changes in PD position. According to the aforementioned findings, the PD characteristic of the turn-turn insulation is related to its radiation characteristic as a transmitting antenna. In other words, while partial discharge is happening, the insulating sample as a transmitting antenna is actively involved in radiating the electromagnetic wave signal. © 2023 Chinese Machine Press. All rights reserved.