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As the environment deteriorates, the frequency of fog-haze weather is getting higher and higher, which greatly affects the normal life of the people and the normal operation of highspeed railway external insulation equipment. The fog-haze is a combination of fog and haze. The haze in the air will affect pollution accumulation of the roof insulator, and the fog in the air which settles on the surface of the roof insulator will make the pollution on the surface of the roof insulator humid. This kind of humid contamination greatly increases the probability of the roof insulator's flashover. The roof insulator, as an important external insulation device for electrified railways, will cause a serious impact on the stable operation of high-speed trains in the event of failure. However, there are few studies on the contamination situation under the fog-haze and airflow environment of the roof insulator. In this paper, the FQJG2-30/16 roof insulator is used as the test object, and the force of the fog-haze particles on the surface of the insulator under the highspeed air smog environment is analyzed. It is believed that the force of the fog-haze particles mainly includes gravity, airflow drag, collision force between particles and friction between the particles and the surface of the insulator, as the same time the water film formed by the water droplets in the haze environment causes the fog-haze particles to settle on the insulator. The adhesion of the surface is increased, leading to more serious surface area contamination of the roof insulator. Based on this, a simulation model of fog-haze particles deposition on the surface of insulators in a high-speed airflow for-haze environment was established. the artificial fog-haze environment was simulated under different airflow speeds by through the artificial climate chamber to study the contamination of the roof insulator. In this paper, (NH 4 ) 2 SO 4 was used to simulate the soluble salt in the haze, and the insoluble matter was simulated by diatomaceous earth. The (NH 4 ) 2 SO 4 : diatomaceous earth = 1:6 configuration haze, 0.5 g salt, 3 g ash was selected. The water mist generated by the ultrasonic water mist generator simulates the fog in the fog-haze environment, and the influence of the haze environment on the roof insulator contamination at different airflow speeds is revealed by artificially simulating the airflow haze environment roof insulator contamination test. The simulation and test results show that in the fog-haze environment, there is a difference in surface area contamination of the roof insulator under different airflow speeds. When the air velocity is less than 30m/s, the water droplets are more likely to form a water film on the surface of the roof insulator, so that the fog-haze particles are more likely to adhere to the surface of the insulator, and the insulator surface contamination is continuously reduced as the airflow speed increases, when the airflow speed is greater than 30m/s, the highspeed airflow takes away a large number of water droplets, and the surface of the roof insulator is not easy to form a water film. At this time, the effect of the water droplet adhesion force is reduced, the airflow drag force is greater than the water droplet adhesion force, and the fog-haze particles are more prone to slip on the surface of the insulator. When the airflow speed reaches 80m/s, there is almost no fog-haze particle deposition on the roof insulator surface. Therefore, the research work in this paper can provide theoretical support for the safe and stable operation of high-speed train roof insulators.

Carbon and copper materials are commonly used for pantograph and catenary system in railways, and the sliding electric contact has a prominent effect on the current-collection quality of pantograph and catenary system. This paper presents the key characteristics of sliding electric contact between couples of carbon and metal materials, where the contact resistance, the temperature rise and the micro morphology are respectively examined. Firstly, changes of contact resistance with the current, contact force and the speed were studied. Meanwhile, influence of the current on the characteristics of temperature rise of the carbon strip was discussed. Finally, the micro morphology of carbon strip was illustrated under different conditions, and discussed with the simulation results based on a magneto-hydrodynamic model.

The inverter-fed motor is a key component of environmental-friendly hybrid cars, high-speed trains, and other industrial applications. After the widespread use of inverter-fed motors, the repetitive impulse surges from inverters were found to cause new insulation problems in inverter-fed motors that were linked to premature insulation failure. The partial discharge (PD) induced by the overvoltage inner stator windings was found to be the root cause of insulation reliability problems. To mitigate this problem, PD detection and life testing at repetitive square voltages should be performed on new types of insulation models and entire motor insulation systems. The obtained partial discharge inception voltage (PDIV) and lifetime of insulation in the tests can be used to evaluate the insulation status of inverter-fed motor insulation systems and thus to improve the insulation designs. At AC voltage conditions, the voltage frequency can significantly affect PD activity. At repetitive square voltage with rapid rise time, the influence of the square voltage frequency on PD activity should be investigated (1) to suggest values for the repetitive square voltage frequency selection for the PDIV and lifetime tests, and (2) to increase the signal-to-noise ratio when extracting PD pulses from strong disturbances generated by the operating switch of impulse generators. Therefore, the main purpose of this paper was to investigate the effects of repetitive square voltage frequency on PD events. Insulation models of both Type I (low-voltage inverter-fed motor) and Type II (high-voltage inverter-fed motor) were used to obtain single-PD and multi-PD statistical features, respectively. Experimental results indicated that higher frequencies caused less PD events with lower PD magnitudes and shorter delay times in one square voltage cycle. This phenomenon was attributed to the different surface charge decay ratios and the initial electron emission probabilities resulting from different square voltage frequencies. Finally, a number of considerations for PD measurements on inverter-fed motors were provided to improve the sensitivity of the PD test system and to obtain high objective insulation lifetime test results, which are used to assess the insulation status of inverter-fed motors.

In order to reveal the mechanism of the contamination depositing on the surface of the roof insulator under the high speed flow, the particle collision number was used to describe the contamination depositing characteristic in this paper, and the effect of particle size and wind speed on contamination depositing was analyzed. In sandy area, asymmetry of friction makes the particles charged, and the trajectories of charged particles under the electric field were carried out. The results show that the faster air velocity, the greater particles diameter, the more serious contamination depositing; when the contamination particles are charged, the contamination depositing characteristic on the surface of the insulator changes little. As for this result, a hypothesis was proposed after the analysis and calculation, and finally this hypothesis was proved to be right through the simulation.

Surge voltage on the carriage which transports along high speed train occurs frequently in the process of pantograph rising, the surge voltage is likely to cause electromagnetic interference or logical confusion to vehicle control and communication system, and even damage the vehicle-mounted components. That maybe a potential threaten for normal operation of high speed train. And the amplitude of surge voltage varies with the change of the grounding mode. In order to study the surge voltage systematically, an equivalent circuit model was built in the process of pantograph rising based on the grounding mode of a certain-type high speed train. The mechanism and propagating characteristics of surge voltage were studied and the influence of different grounding modes on the surge voltage was analyzed in the process of pantograph rising. The results show that the grounding mode affects the carriage surge voltage significantly. The maximum amplitude of surge voltage reaches 4.85kV and rapidly decays in 15 μs in the original grounding mode, while it decreases to 2.4kV in direct grounding mode. However, the transient impulse voltage that the weak current system can withstand should not exceed 2kV. The surge voltage value can be effectively decreased by parallel connecting a capacitor with a grounding resistor. The amplitude of surge voltage relates to the value of the parallel capacitance, and the value of surge voltage will be reduced below 2kV when the value of capacitance is 10μF. The conclusions provide theoretical basis for studying the influence of grounding mode on surge voltage in the process of pantograph rising for high speed train.

In order to assess the moisture content of insulating pressboard in oil-immersed transformer, and thus providing reliable guidance for insulation condition and life estimation of oil-immersed transformer, in this paper, we made four groups of oil-paper insulation samples with different moisture content under laboratory conditions and studied the relationship between pressboard and moisture content by using polarization and depolarization current (PDC) technique. The experiment result shows that PDC curve is very sensitive to the change of moisture content, and the change of moisture content mainly affects the tail of depolarization current curve; the extended Debye model parameters can be obtained from depolarization current curve, and as the moisture content increases the number of branches in Debye model increases, the largest time constant becomes large; the peak of time domain spectroscopy turn up at 1000s., the time constant branch which is longer than 1000s presents the pressboard branches of Debye model; the feature quantity Q paper can show the internal polarization of insulating paper and has a linear fitting relationship with moisture content, so Q paper can be used to assess the moisture content of insulating pressboard.

To study the feasibility of applying frequency domain dielectric spectroscopy method to the diagnosis of generator insulation aging state. Dielectric spectrum of motor stator bar sample was measured using frequency domain dielectric spectroscopy method under different aging degree and different temperature. Then the relationship of dielectric loss factor and complex dielectric constant with aging state was researched. The influence of temperature on the frequency domain dielectric characteristic was also analyzed. Results show that dielectric spectrum at low frequencies are sensitive to the aging state of bar sample, which can assess the aging state. Temperature had a great influence on the measured results. Spectrum curves increase with the rising of temperature and moves to higher frequency. The influence of the temperature should be considered.

Due to overvoltage produced by inverter output, inverter-fed motor insulation systems often experience fast electrical aging process, especially when partial discharge (PD) is incepted. Before putting into use, the PD detection should be performed on inverter-fed motors at repetitive square voltages to avoid the PD caused insulation deterioration when the motors are collected to inverters having specific characteristics. However, unlike PD tests at AC/DC voltages proposed in IEC 60270, the PD detection at repetitive square voltages is much more complex because of serious interference generated by impulse generator. To solve the problem, ultra-high frequency (UHF) method seems recommendable for its preferable signal-to-noise ratio (SNR). The chief aim of this study is to investigate PD pulse and statistical characteristics of turn-to-turn insulation for inverter-fed traction motors. A square-shaped Archimedes antenna, specially designed for the PD detection at repetitive square voltages of fast rise times, was used to perform PD tests on turn-to-turn insulation models. Time and frequency analysis results indicate that energy component of generator disturbance and PD pulses are mainly distributed in the 0–0.5 GHz and 0.6–1.5 GHz range, respectively. Based on the results, suitable filter was designed for power disturbance suppression. Additionally, resorting to the sensor unit (i.e. antenna and filter) and the PD test system, the PD statistical features at square voltages of different frequencies were obtained. Experimental results show that higher frequency will give rise, statistically, to PD of lower magnitudes distributing at smaller phases. A reasonable interpretation of this phenomenon was presented. Lastly, according to the PD statistical features, some suggestions for the PD detection system design, generator parameter optimization and the PD pulse extracting were given. The results of this work would be beneficial to the increase of the sensitivity when performing the PD detection on insulation systems for inverter-fed motors at repetitive square voltages and thus, improving the reliability of inverter-fed motors.

Voltage distribution in windings is important for inverter-fed traction motors. The analysis on voltage distribution characteristics is significant to the study of insulation failure mechanisms and structure design. First, a distribution parameter model has been developed according to the winding structure of an inverter-fed traction motor. Based on the model, finite element differential method was employed to determine voltage distribution characteristics. Simulation results were compared with actual voltage distribution. Moreover, the influence of pulse rise time and cable was discussed. The results show that the shorter the pulse rise time is, the more uneven the voltage distribution is. In addition, cable length has little influence on voltage distribution characteristics. However, the amplitude of voltage would also increase by 40% in coils and turns.