Discharge Characteristics Of Air Gap Research Articles

Intelligent computing and analysis of breakdown voltage of rod-rod long air gap

The discharge characteristics of air gap is one of the important factors to determine the insulation level which is crucial for electrical engineering construction. In order to calculate the 50% breakdown voltage of rod-rod air gap under different meteorological conditions and different gap distances, we take the positive standard switching impulse test data of rod-rod air gap under different meteorological conditions as samples. Based on training set, a breakdown voltage prediction model of rod-rod air gap under different meteorological conditions was established by cuckoo search optimized weighted support vector regression (CS-ω-SVR). The results show that the average absolute percentage error of the test set is 3.6%, which verifies the validity of this computing method. The method can provide reference for the computation of air gap breakdown voltage under different altitudes and extreme meteorological conditions.

Effect of Environmental Parameters on Streamer Discharge in Short Air Gap between Rod and Plate

Environmental meteorological parameters (temperature, humidity, air pressure, etc.) have an important impact on short gap streamer discharge. Based on the streamer theory and particle continuity equation of gas discharge, a short gap streamer discharge simulation model is established, and the influence of environmental parameters on the dynamic development process of streamer discharge is simulated and analyzed. The short gap air gap discharge characteristics were tested in a self-made gas discharge chamber. The results show that at low humidity (relative humidity <80%), with the increase of humidity, the electron density of the streamer channel increases, the field strength of the streamer head increases, the streamer development speed speeds up, and the gap breakdown voltage decrease; At higher humidity (relative humidity >80%), with the increase of humidity, the electron density of the streamer channel decreases, the field strength of the streamer head decreases, the development speed of the streamer slows down, and the gap breakdown voltage increase. With a decrease of gas pressure, the electron density of the streamer channel decreases, the field strength of the streamer head decreases, the development speed of the streamer increases, and the gap breakdown voltage decreases; The temperature change has little effect on the streamer development process.

Effect of a floating conductor on discharge characteristics of a long air gap under switching impulse

Live working is an important means for the maintenance of transmission lines. During the process of entering the equipotential, the live working lineman is a floating conductor, which affects the discharge characteristics of the air gap of the transmission line. In order to improve the safety protection of linemen, the effect of a floating conductor on discharge characteristics of a long air gap under positive switching impulse was investigated. In this paper, an experiment platform of long air gaps with floating conductors was built, and the breakdown voltage and discharge progress were studied. The experimental results showed the effect of the rod-shaped electrodes and the electrodes with rod-shaped protrusions on the breakdown voltage of the air gaps, as well as the discharge process of the air gaps when the floating electrodes were at different positions. The research conclusions can provide a theoretical basis for discharge mechanism and live working.

Influence of protrusions on the positive switching impulse breakdown voltage of sphere‐plane air gaps in high‐altitude areas

The construction of ultra-high-voltage direct-current power transmission projects in high-altitude areas calls for the research into the discharge characteristics of the air gaps in the valve hall of a power converter station in such areas. Tests on the switching impulse discharge characteristics of the sphere-plane air gap were conducted at Yangbajing test base (Tibet, China) at an altitude of 4300 m on conditions that there were burrs on the 1.3 m diameter shield balls. The discharge characteristics, under the influences of burrs with different lengths and locations, were obtained and compared with test data from low-altitude areas. The results indicate that the arrangements of burrs with different lengths and locations can significantly reduce the switching impulse discharge voltage of sphere-plane air gaps, while the voltage sag gradually decreased down with increasing burr length. Moreover, the larger the sphere-plane air gap is, the smaller the influence of such burrs have. High altitude also substantially decreased the switching impulse discharge voltage of the air gap. When the surface of shield balls was smooth, the U50 saturation of the air gap was more significant than at low altitude; however, if there were burrs on the shield balls, the saturation effect was less significant.

The Research and Engineering Practice in Air Clearance of Valve Hall and DC Field in VSC-HVDC Converter Station with High Voltage and Large Capacity

The value of air clearance is an important basis for the design of the converter station, which affects the layout and safe operation of the converter station. In this paper, the calculation method of minimum air clearance based on improved clearance shape coefficient is proposed, and the g-parameter method is used to correct the discharge characteristics of air gap under non-standard meteorological conditions. The method is applied to the valve hall and DC field air clearance design of Zhangbei ±500 kV flexible DC converter station. The Zhangbei converter station is used as a typical representative to empirically analyze the influence of temperature and humidity changes on the air gap, and we can get the temperature and humidity value when air clearance are at the maximum value, and we calculate the air clearance of different gap shape coefficients. This paper can provide method guidance and data for the selection of air clearance for other similar projects.

Factors Affecting the Discharge Characteristics of Rod-Rod Long Air Gaps at Different Altitudes

The impulsive discharge characteristics of the air gap is one of the main bases for the design of the external insulation of high-voltage electrical equipment; meanwhile, air gap discharge characteristics at different altitudes have been of concern for a long time. In this paper, the impact discharge tests of rod-rod gaps at different altitudes were carried out to study the influences of elements such as electrode shape, voltage polarity, altitude and temperature. It can be found that, with the increase of the gap distance, the 50% impulse voltage of the switching impulse tends to be saturated, and the discharge characteristic curve can be fitted by exponential function. The 50% impulse voltage of the lightning impact and the gap distance shows a good linear relationship which can be fitted by the linear function. This is no direct relationship with temperature and altitude. The saturation tendency of switching impulse’s 50% discharge voltage decreased with the decrease of temperature. With the increase of the altitude and the decrease of the 50% impulse discharge voltage, the polar effect of the air gap between the rod-rod and the rod-plate decreases. The results are of great reference value for Insulation configuration of electrical equipment in high altitude.

낙뢰 리더의 대지부착과정에 대한 기초적 연구

This paper presents the results of model tests for the attachment process of lightning leader to ground which is one of poorly understood processes of cloud-to-ground lightning discharges. In order to simulate the attachment process of lightning leader to ground, we investigated the discharge characteristics of air gap between the tip of needle-shaped electrode and the soil surface as a parameter of moisture content in soils when the positive and negative 1.2/50㎲ lightning impulse voltages are applied. The breakdown voltage and the discharge light were observed. As a result, the attachment processes of lightning leader to ground are strongly dependent on the grain size and the moisture content of soils. The time to breakdown was shortened with increasing the magnitude of incident impulse voltages. The delay time from application of the highest voltage to breakdown in sand is shortened with increasing the moisture content. The delay time from application of the voltage to breakdown in gravel varied from about 0.5㎲ to several ㎲. As the moisture content in soil increases, the breakdown voltages are decreased and the breakdown voltage versus time to breakdown curves are shifted toward the lower side. The results obtained in this work are similar to those for non-uniform air gap stressed by lightning impulse voltages.

Test Research on Phase-to-Ground Air-Gap Discharge Characteristics of UHV Substation

In order to optimize the design of UHV substation and reduce its construction investment, it is necessary to take further research of UHV substation air-gap discharge characteristics. In this paper, by using sub-conductor and tower to simulate UHV substation air-gap, lightning and switching impulse discharge characteristics tests of UHV substation are taken in the UHV AC test base of SGCC. The results show that, when the distance of conductor between tower is in range of 4m to 7m, the 50% lightning impulse and switching impulse discharge voltage rise along with the rise of air gap distance. As the air-gap increases, the switching impulse discharge voltage presents the trend of saturation. According to the analysis of test results, we can draw a conclusion that the gap factor of switching impulse discharge can be 1.22 when the minimum distance between conductors and tower is 5~8m.

Effects of Dynamic Air Gap on Air Gap Breakdown Discharge in Sand/Dust Environment

AbstractEffects of vibration frequency and amplitude on air gap discharge characteristics were studied by simulation experiments through a special model. The results show that in clean air environment the air gap discharge characteristics are mainly affected by the minimum air gap distance, while in the sand/dust–air environment the air gap discharge characteristics are affected by the swing amplitude and frequency as well as by the minimum air gap distance. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Improved method of calculating lightning stroke rate to large-sized transmission lines based on electric geometry model

The characteristics of the lightning shielding of large-sized transmission lines have been calculated based on an electric geometry model (EGM) proposed by Armstrong and Whitehead. However, the characteristics of lightning strokes to large-sized transmission lines observed in recent years differed from calculation results, hence the present study was conducted to improve the conventional calculation method. First, the relationship between the striking distance and the lightning current was reviewed. Specifically, the air gap discharge characteristics based on test data with complementing the large gap region were applied. In addition, the return stroke velocity distribution obtained by actual measurement was newly applied. Second, the distribution of lightning waveforms was reviewed; the distribution of peak values of lightning current with the distribution of front duration was used in this study. With these improvements, the calculated lightning stroke rate to power lines and ground wires differs less from actual observations than that calculated by the conventional method.

Air-Gap Discharge Characteristics in Foggy Conditions Relevant to Lightning Shielding of Transmission Lines

The features of lightning shielding of transmission lines have been calculated using the electrogeometric model (EGM) proposed by Armstrong and Whitehead. Discrepancies, however, have been found in the case of ultra-high voltage (UHV)-designed transmission lines. UHV-designed transmission lines often pass through high-altitude mountain areas, where foggy or rainy conditions are common when there is lightning. While the electrogeometric model determines the striking distance based on the lightning stroke current, environmental conditions, and how they might affect lightning discharge paths, they are not considered. It is possible, therefore, that foggy conditions may cause differences in the performance of transmission-line lightning shielding. This study used scale models of transmission lines for discharge tests with a 1-m air gap and analyzed differences in discharge paths and locations in dry and foggy conditions. The results showed that the polarity of the discharge had a significant influence, but differences in dry and foggy tests were negligible.