Transient Enclosure Voltage Research Articles

Dispersion characteristics of switching transients from large‐scale experiments in a 1100 kV gas insulated switchgear circuit

AbstractThe switching operation of gas insulated switchgear (GIS) disconnector will produce multiple random spark discharges between the gas gaps of the disconnector. Each spark discharge can be affected by various random factors, such as trapped charge on the load side, the initial operating phase, gap distance and operating speed of the disconnector, leading to dispersion characteristics. At present, some studies have mentioned this dispersion, but its impact is still unclear due to the lack of experimental data, resulting in a deviation between the simulation results and the measured results. In this study, thousands of switching operations were carried out based on the 1100 kV full‐scale GIS circuit in Wuhan ultra‐high voltage alternating current Test Base. The maximal information coefficient analysis, linear regression fitting and other statistical methods were used to discuss the dispersion characteristics of very fast transient overvoltage (VFTO) and transient enclosure voltage (TEV) from large‐scale experimental data. The results show that the dispersion of VFTO and TEV in amplitude aspects both increase gradually as the breakdown voltage increases, with the maximum difference of five times of TEV amplitude at normalised breakdown voltage. In terms of frequency characteristics, the dispersion of different frequency components in TEV is always greater than that of VFTO, especially for the high‐frequency components. Moreover, by comparing the frequency characteristics of TEV at different positions, we notice that the dispersion is almost independent of the spatial position but only determined by the randomness of spark discharges. These discoveries reveal the importance of the dispersion in switching transients and make up for the lack of theoretical understanding of the correlation among them.

Numerical simulation and analytical calculation of the GIS transient enclosure voltage interaction with grounding system

Gas-insulated substations (GISs) are widely used in power systems due to high reliability, convenient maintenance, and small area occupation. Transient enclosure voltage (TEV) is a consequent effect of very fast transient overvoltage (VFTO) during the switching operations in GISs. It can lead to insulation degradation, damage to the secondary equipment connected with the shell of GIS, and harm to the working staff. This paper presents a correlation between a lumped-circuit model based on transmission line theory (TLT) for purpose of the simulation and an analytical approach based on the scattering matrix for the evaluation of TEVs. Furthermore, a frequency-dependent model is proposed to quantify the transient grounding impedance (TGIM) against the waves with high-frequency content such as TEVs. The interaction between the TEV and the grounding system has been investigated analytically, and experimentally based on the field measurements in other efforts. The comparisons indicate that the modified wide-band TGIM results in an improvement in comparison with the other works to track both the front and tail of a measured voltage-wave within acceptable accuracy. Furthermore, the role of the ground strap as a damping structure using a modified model on TEV profile has been scrutinized regarding the grounding system model and the rising rate of TEVs. It is indicated that considering frequency-dependent TGIM could lead to a 25% variation in the estimation of amplitude of TEVs.

Analysis of Discharge Faults Between Flanges Caused by Transient Enclosure Voltage

An increase in transient enclosure voltage can threaten the personal safety of workers and the normal operation of secondary equipment and may cause discharge between the flanges of gas insulated switchgear (GIS) enclosures. This study considered the spark–discharge fault between GIS enclosure flanges of a 500-kV nuclear power plant in China when the disconnect switch is operated in the background. The dynamic arc model during the operation of the disconnect switch was improved in this study, and the equivalent calculation model of transient enclosure voltage (TEV) caused by very fast transient overvoltage generated during the operation of the disconnect switch was established using the electromagnetic transient program ATP-EMTP. Suppression measures of the discharge phenomena were also discussed. The results demonstrated that the transient enclosure voltage caused by the operation of the disconnect switch can reach 75 kV in the most severe case, which causes discharge between the flanges. Reducing the residual charge on the island side of the disconnect switch, installing a metal oxide arrester, and reducing the inductance of the ground wire have different inhibitory effects on this discharge phenomenon, but they all have their limitations. The most simple and effective control measure is to use a short joint between two flanges. The study conclusions can be used as reference for preventing such discharge phenomena.

An Approximate Calculation Method of Broadband Impedance of GIS Pipe Brackets

In Gas Insulated Switchgear (GIS) substation, the grounding bracket of GIS pipe is used to support GIS pipe, meanwhile, it’s a part of grounding system connecting GIS pipe to grounding grid. The frequency of transient enclosure voltage(TEV) generated during switching operation of disconnector in gas insulated switchgear (GIS) with no-load short busbar can be up to tens or even hundreds of megahertz(MHz). Because of the impact of skin effect and proximity effect, the impedance of bracket will vary considerably with frequency. A simple and effective method of broadband impedance modeling was proposed based on electromagnetic field numerical calculation method and the physical structure of the grounding bracket in this paper. At last, the validity of the method was verified through calculating and analyzing some typical grounding bracket.

The electromagnetic effect study of GIS enclosure under high‐frequency electromagnetic pulse

In gas insulated switchgear (GIS) substation, due to the operation of disconnect switch and circuit breaker, as well as short-circuit fault, SF6 will break down very rapidly. The superposition of refraction and reflection of high-frequency travelling waves will cause the very fast transient electromagnetic pulse (EMP). High-frequency EMP propagating along GIS core wire will couple to GIS enclosure which forms transient enclosure voltage (TEV). Through the study of new GIS enclosure coupling model which can be verified by site test and frequency effect on the enclosure coupling under high-frequency EMP, results indicate the generation of TEV is closely related to GIS structures and the electromagnetic wave propagation characteristics on its core wire and enclosure. Electromagnetic coupling model must consider the entire propagating and coupling process of EMP in GIS. Paper also shows that TEV is mainly formed by high frequency >0.1 MHz EMP coupling and the difference on coupling extent when frequency is >1 MHz is small.

Study of Transient Enclosure Voltage Coupling to Secondary Cables in a Gas-Insulated Substation

Transient enclosure voltage (TEV) induces a relative potential difference between grounding conductors and then couples to secondary cables and may cause malfunction and even damage to secondary equipment. This study investigates the coupling mechanism of TEV to secondary cables from an experimental point of view and presents a cable model suitable for calculation. Experiments are carried out on test platforms established in a laboratory. The experimental results indicate that the magnitudes of port voltages are roughly 1.5‰ of TEV magnitudes, and the waveform of the start port voltage has the same profile but in antiphase with that of the end port voltage. Moreover, only common-mode voltage with no differential-mode voltage exists for the twin core cable. Based on these results, an equivalent circuit for a secondary cable is proposed. This circuit can generate similar waveforms as those measured in the experiment. The experimental and theoretical results presented in this paper should prove helpful for evaluating the interference severity of secondary cables resulting from TEV for the electromagnetic protection of secondary ports.

Statistical characteristics of transient enclosure voltage in ultra-high-voltage gas-insulated switchgear

Transient enclosure voltage (TEV), which is a phenomenon induced by the inner dielectric breakdown of SF6 during disconnector operations in a gas-insulated switchgear (GIS), may cause issues relating to shock hazard and electromagnetic interference to secondary equipment. This is a critical factor regarding the electromagnetic compatibility of ultra-high-voltage (UHV) substations. In this paper, the statistical characteristics of TEV at UHV level are collected from field experiments, and are analyzed and compared to those from a repeated strike process. The TEV waveforms during disconnector operations are recorded by a self-developed measurement system first. Then, statistical characteristics, such as the pulse number, duration of pulses, frequency components, magnitude and single pulse duration, are extracted. The transmission line theory is introduced to analyze the TEV and is validated by the experimental results. Finally, the relationship between the TEV and the repeated strike process is analyzed. This proves that the pulse voltage of the TEV is proportional to the corresponding breakdown voltage. The results contribute to the definition of the standard testing waveform of the TEV, and can aid the protection of electronic devices in substations by minimizing the threat of this phenomenon.

Calculate Very Fast Transient Current by the Inverse Operation of the Transient Electromagnetic Near Field due to Switch Operation in Gas Insulated Switchgear

For the direct measurement of very fast transient current (VFTC) due to switch operation in gas insulated switchgear (GIS), usually it will interfere the original operation or change the structure of switch. In this paper a method for calculation of transient current caused by the disconnect operation in GIS by the inverse operation of the electromagnetic (EM) near field is presented. A GIS is modeled by the finite integration technique (FIT), and all the media between the excitation source and the observation position are considered as a black box whose input is VFTC and output is EM field. A coefficient matrix is established to reflect the connection between the input and output in frequency domain, and the VFTC in frequency domain will be the result of multiplying the inverse matrix by the measurement result minus the EM field caused by transient grounding potential rise (TGPR) or transient enclosure voltage (TEV) in the observation position. Finally the time domain form of VFTC can be obtained by the interpolation and IFFT. Comparison between the result and simulation shows the validation of this method.

ANALYSIS OF TRANSIENT ENCLOSURE VOLTAGES IN GIS (EMTP SIMULATION STUDIES)

Abstract Transient Enclosure voltage is special case of very fast transient overvoltages which occurs due to disconnect switch operation or earth ground. Transient Enclosure Voltage appears on external of earthed enclosure of Gas Insulated Systems. Despite of proper grounding, this phenomenon indicates presence of high potentials on Gas Insulted System enclosures so the grounding system impedance is thoroughly examined and designed. In this study EMTP Software is used for analysis. Simulation was done by varying the different parameters. Variations of waveforms of the Transient Enclosure Voltage with various parameters have been studied. Index Terms: Transient Enclosure Voltage (TEV), Gas Insulated System (GIS), Very Fast Transient Overvoltages (VFTO) Transient Ground Potential Rise (TGPR), Disconnector Switch ----------------------------------------------------------------------***------------------------------------------------------------------------ 1. INTRODUCTION

Line constant measurements and loading current test in long-distance 275 kV GIL

This paper reports on the results of a loading current test and measurements of the line constants of a long-distance gas-insulated transmission line (GIL) in a tunnel. The loading current test was carried out at 80% rated current, to verify the soundness of the thermal expansion and contraction of the GIL. As a result, the performance of the GIL was confirmed to be appropriate in terms of the thermal expansion and contraction. With respect to the line constants and transient enclosure voltage, each of the measured values was found to be at an appropriate level presenting no problem for the service operation of this line.

Very fast transients in GIS

Different types of very fast transients (VFTs) are classified and their characteristic parameters are summarized based on measurements in a 800 kV SF/sub 6/ gas-insulated pilot installation and 420 kV GIS (gas-insulated switchgear) in service. The electromagnetic field between the enclosure and earth results in a transient enclosure voltage of up to some 10 kV and at the same time in a radiated electromagnetic field from the enclosure with amplitude of some 10 kV/m. The electromagnetic wave guided by the overhead line results in an overvoltage with a multifrequent oscillation of some 10 to 100 kHz, depending on the parameters of the overhead line and the adjacent equipment, e.g. the transformer. The transient enclosure voltage and measures to reduce it are analyzed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>