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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.

Partial Discharge (PD) is one of the most important factors, which causes insulation breakdown of electrical equipment. The characteristic of partial discharge (PD) occurred within the polyimide material is significantly influenced by the parameters of the defect site. The paper made a mode of polyimide material with single void in it based on Finite Element Analysis (FEA) software. In this model, the shape of the cavity and the pressure in it is constant. The characteristics of PD by different cavity diameters and different location of the cavity are analyzed. Modeling of the partial discharge activity, electric field distribution was worked out in different cavity's parameters. The mechanism of electric field distribution under the sinusoidal voltage and influence on PD of different cavity parameters within the polyimide material was worked out. The results show that with the increase of cavity diameters, the electric field has a slight decrease in the cavity, as the cavity surface is nearer to the electrode. And the electric field distortion is obvious with the cavity located out-of-Centre. This is due to the influence of the electrode. The PD activity significantly depends on the cavity's parameters within the polyimide material.

To research the influence of one of the aging product (organic acid) of cellulose on oil-paper insulation, low molecular weight of the carboxylic acid (formic, acetic) and high molecular weight of the carboxylic acid (stearic) have been added to new electric insulating oil to arrive at a neutralization value of 0.3mgKOH/g, the initial moisture content in insulation paper have been controlled at 0.5% and 2.75%. The distribution characters of organic acid in oil-paper insulation and the influence of organic acid on thermal aging of oil-paper insulation at 70°C, 90°C and 110°C have been investigated. Experimental results show that formic and acetic could be easily absorbed by insulation paper while stearic could easily dissolve in electric insulating oil. There is no significant influence of temperature and initial moisture content on the distribution characters of organic acid in oil-paper insulation. Low molecular acid would work together with moisture to accelerate the aging speed of insulation paper.

The winding hot-spot temperature is an important parameter that determines the transformer overloading capability and the aging rate of the oil paper insulation. In this paper, three simulation models based on modified IEEE model, Swift model, and Susa model are established in Matlab/Simulink. The top-oil temperature and hot-spot temperature in the models are calculated using Runge-Kutta method. Simulation results showed that Susa model and modified IEEE model are in good consistency while there is quite a difference between Swift model and modified IEEE model.

The analysis of the composition of dissolved gas composition and concentration in transformer oil is the common method for transformer to performance evaluation and schedule fault type. This paper is based on sensor technology, a vice sensor is proposed to establish bridge sensor circuit to compensate for the traditional gathering of non-linear error, so as to improve the response characteristics of the sensor and the work performance. Then putting this system into field, and the analysis of test data showed that the system can perfectly reflect the insulation performance status of transformer.

This paper used the dielectric spectrum method (Frequency Domain Spectroscopy), with laboratory equipment and facilities, built the experimental test platform for oil-paper dielectric response test. Simulated the actual operation of the transformer, and accelerated thermal aging tests by laboratory simulation of transformer oil-paper insulation aging, studied the dielectric spectra at different temperatures and different conditions of water content variation; analysis the dielectric properties of oil-paper insulation, summed up the relationship between the effect factors and the frequency dielectric spectrum, so it can supply an important basis for the correct diagnosis of transformer insulation condition, assessment of transformer's remaining life and improving power supply reliability.

As for capacitance type equipment, its dielectric loss factor test is influenced by the change of voltage on its ends when it was somewhat ageing, so when it is monitored, not only need consider the electromagnetic interference outside, but also take into account of the load change. Different from general electric power system, traction's load of traction power system often change a lot which leads to the large float of the end voltage of the transformer's casing, which seriously influence the measure of the factor. The purpose of this paper is to introduce a method to improve the measure method and algorithm to reduce the influence from the vary load.

Impulse grounding impedance cannot be described as an absolute index, because it depends on the characteristic of the impulse current waveform, soil structure type and grounding system configuration, etc. This paper presents a test system to measure the impulse grounding impedance directly in time domain, moreover, calculated and defined in frequency domain. A field test for 110kV tower footing has been performed to measure the impulse ground impedance, and compared it with the ground impedance measured by fall-of-potential method.

Stator insulation of inverter-fed motors experiences continuous impulses with significant harmonics and transients, which may result in early failure. There are many differences in insulation aging mechanism between under continuous impulses and sine waves. In order to test insulation properties under continuous impulses, a new insulation aging test system is used to simulate the aging effect of converter on the winding insulation in the inverter-fed motors. The influences of multi-stress including impulse amplitudetemperature, impulse frequency-temperature and impulse frequency-amplitude on insulation lifetime are investigated. And the test data under different conditions are analyzed by the statistic analysis method of Weibull distribution. Finally, insulation life models for multi-stress is developed based on the above test results, which is helpful for the insulation design of inverter-fed motor.

Lightning is the main reason that endangers the safety and reliability of transmission line, but the existing models of estimating shielding failure flashover rate can not be in agreement with field experience at present. This paper deals with shielding failure flashover rate of the EHV transmission lines with many parameters by the improved electric-geometry model. The parameters consist of phase wires, shield wires, and the ground angle. In the improved model, "strike distance" is calculated with the expression recommended by IEEE, "the striking distance factor" is introduced to describe the difference of electric intensity between lightning stroke on the transmission line and the ground, and the "uncovered distance" is adopted to calculate shielding failure flashover rate for ultra high voltage transmission line. Taking 500 kV transmission line as example, the improved electric-geometry model gets the result in agreement with field experience. Compared with the order of the method, it is more accurately. At the same time, the paper analyzes the influence of the shielding angle, the height of wire, the grounding obliquity on shielding failure flashover rate. The results of studies show that the shielding failure flashover rate is a function of the shielding angle, ground angle and the height of tower. It will increase with the increase of the grounding obliquity, protection angle and the height of tower. The simulation calculation shows that when the shielding angle is -6.24 degrees, the shielding failure flashover rate reduces from 0.2135 to 0 in this paper. It will help designers in making the correct economic judgment.

High voltage square impulses from converter can make stator insulation of inverter-fed motors damaged much earlier. There are many differences in insulation aging mechanism between under continuous impulses and under sine waves. In order to test insulation properties under continuous impulses, a new insulation aging test system is used to simulate the aging effect of converter on the winding insulation in the inverter-fed motors. The influences of impulse amplitude, frequency, on insulation lifetime are investigated by using polyimide film. Finally, an insulation electrical aging lifetime model is developed based on the test results.

The pulse capacitor, as the important energy storage device, its stability will directly influence the dependability of the pulse power system that capacitor located in. Life-span of the capacitor has strong relationship with its working dependability, In this paper, by charging and discharging to the pulse capacitor and testing direct current partial discharge to the capacitors at different stage of life-span, the three curves of relation between life-span and maximal discharge magnitude, mean discharge magnitude, mean discharge frequency were obtained. Observing the surface topography of capacitor film at different stage of life-span by the scanning electron microscopy, analyzing the influence of charge and discharge aging test to its surface topography. Finally referring to the actual situation of capacitor breakdown and summarizing the factors that caused the variation of pulse capacitor partial discharge performance, pointing out that some insulating defect existed in the edge area of electrodes was the main reason that caused the capacitor breakdown.

PD (partial discharge) measurement is one of the most important parts in HV (high voltage) diagnostics. There are a lot of measuring methods of PD, such as impulse current, ultra-high frequency, super sonic method, and so on. The impulse current method is the earliest used in PD detection and is the most basic. Further the balance method is one of the impulse current methods. This method has higher inference rejected ability than others. But, the input circuits of traditional balanced PD measurement methods are composed of two parallel circuits of resistance and capacitance. There are many disadvantages with using this measuring circuit such as utilizing its application in HV and UHV (ultra-high voltage) measurements. A new selective frequency balance measurement theory for PD was put forward by the authors in 1988. The device, which was based on this theory, was also determined. Now, it will be verified in the HV field. The noise signal can be rejected more than 1000 times by this device. Furthermore, the device is very easy and cheap to produce using the new theory. The system structure of the selective frequency balance measurement circuit is dissertated. The design method is also explained and measuring results are illustrated.

In the traditional transformer fault monitoring system, the LPU (Local Process Unit) usually sends the data to the MMC (Main Monitoring Computer), which completes the complicated fault diagnosis and is the process center. In this paper, a novel transformer monitoring system is presented. The LPUs, the embedded systems, are designed to possess of the approximately functions to MMC such as monitoring, diagnosing and alarm. The TCP/IP and the Pub/Sub (Publish/Subscribe) technology are used to realize the design of LPU. The TCP/IP protocol and the network chip make the LPU with high transmission speed. The complicated diagnosis task is dealt with by a computer with strong data treatment capacity. The LPU and MMC can subscribe some fault diagnosis subjects.