Gas Insulated Switchgear Enclosure Research Articles

Numerical Study of Acoustic‐Electric Signal Conversion for GIS Discharge Detection and Structure Optimization for pMUT

With the development of microelectromechanical technology, the piezoelectric micromechanical ultrasonic transducer (pMUT) for ultrasonic detection of gas‐insulated switchgear (GIS) breakdown discharge has become possible. In this article, the ultrasonic‐solid‐pMUT coupling simulation model was established to investigate the propagation process of ultrasonic waves in GIS enclosure and the conversion between ultrasonic and electric signals through pMUT. The output electric signals for the unsimplified top electrode and simplified top electrode model were compared, and the structure of receiving pMUT was optimized according to the main ultrasonic frequency range of GIS breakdown discharge and the key performance parameters of pMUT. First, it is found that the simulation results of the ultrasonic‐solid‐pMUT coupling model are reliable, and the frequency of the output electric signal of receiving pMUT is consistent with the input signal, while the amplitude of output signal attenuates greatly. Second, simplifying the top electrode of pMUT may lead to relatively large errors in simulation results. The output response of simplified pMUT is obviously weakened, and the inherent frequency is higher. Furthermore, it is noted that the pMUT inherent frequency (f0) is inversely proportional to the radius (R) of the piezoelectric layer and directly proportional to the substrate thickness (dsi). When the coverage rate of the top electrode is between 30% and 80%, the pMUT effective electromechanical coupling coefficient () is high and has a maximum value. Finally, it is indicated that the pMUT with the optimum structure is suitable for the detection of GIS breakdown discharge ultrasonic signals, and the can be improved by 106.7%.

Simulation and Measurement of Pressure Rise in GIS 145 kV due to Internal Arcing

Internal arc testing of metal-enclosed, SF6 gas insulated switchgear (GIS) is defined by IEC 62271-203 and is not a part of mandatory type tests.
 However, due to the increasing demands on the safety of personnel, more often the implementation of this test is required in the tender documentation. According to IEC, the duration of the electric arc is related to the performance of the protective system determined by the first and second stage of protection. For the rated short-circuit current equal or higher than 40 kA, during the first stage of protection (0.1 s), no external effects on enclosure other than the operation of pressure relief device is permitted. During the second stage of protection (≤0.3 s) no fragmentation is permitted, but burn-through is acceptable. The test should be carried out on the GIS compartment with the smallest volume at nominal gas pressure. Since a newly developed GIS 145 kV is designed as a three-phase encapsulated, arc initiation is achieved by short connecting of all three phase conductors in the vicinity of a partition by means of a thin metal wire. This ensures that two electric arcs burn simultaneously commutating between the phases, so the possibility of enclosure burn-through in this type of GIS is minimized. In order to prevent the release of SF6 gas in the atmosphere during the testing, a test enclosure should be placed in a protective gastight enclosure filled with air or more often SF6 gas at pressure of 0.1 MPa. This test object configuration significantly complicates the pressure rise calculation and increases the testing cost. In order to prevent enclosure fragmentation, the pressure difference between the test enclosure and the protective enclosure during the test should always be less than the bursting pressure of test enclosure. Also, the protective enclosure should be designed to withstand the maximum pressure rise that may occur after pressure relief device opens. In order to assess the likelihood of passing the upcoming type test for newly developed GIS, a computer program for calculation of pressure and temperature in the test enclosure and protective enclosure was developed. The mathematical model is based on the paper of the working group CIGRE A3.24, published in 2014. The basic model shown in the paper is enhanced by the real properties of the SF6 gas/plasma, evaporation of the electrode material and the insulator ablation. The contribution of exothermic/endothermic reactions between the gas and the electrode material on the pressure and temperature rise was also considered. At the same time, the measurements of pressure rise in GIS enclosure and protective enclosure were carried out in Končar High Power Laboratory. The experiments performed on a copper and aluminum electrodes in SF6 gas confirmed significantly higher contribution of aluminum electrodes to the pressure and temperature rise compared to the copper electrodes. The computer program is verified by measurement results.

Investigation of GIS enclosure circulating current in UHV substation with hybrid reactive power compensation

There are typically large circulating current losses when such a current is produced in a gas-insulated switchgear (GIS). An excessive circulating current also causes a heating phenomenon and insulation aging, as well as hidden dangers and adverse effects on the normal operations of power systems. In addition, the installation of hybrid reactive power compensation (HRPC) may increase the complexity of the circulating current. Thus, a detailed investigation of GIS enclosure circulating current on an ultra-high-voltage (UHV) substation with HRPC is imperative. Here, the mechanism of the enclosure circulating current is thoroughly discussed, and models of the GIS busbar, and enclosure are established based on the partial element equivalent circuit (PEEC) method. Combined with HRPC equivalent circuit model, the equivalent calculation model for the GIS enclosure circulating current with HRPC equipment is established. The influence of the structural parameters on the circulating current, such as the inlet capacitance of the stepped controlled shunt reactor (SCSR), enclosure radius, enclosure height from the earth, and distance between earthing points, are considered in terms of the simulation model as built using transient simulation software. The factors that influence the enclosure circulating current and their associated rules are used to develop suppression measures.

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.

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.

Particle Detector for Gas Insulated Switchgear and the Effect on Environment

High voltage Gas Insulated Switchgear (GIS) is prone to metallic particles. The particle void can reduce the dielectric strength of the insulation material of SF6 gas. This paper discusses the developed particle detector for GIS using a new approach by using image processing to reduce flashover phenomena occurring on energized GIS. The particle detector consists of borescope, laptop and a detection program. The program was coded using MATLAB using image processing algorithm. The in-lab test was conducted on the simulated GIS to see the effectiveness of the particle detector to detect small particles inside the narrow GIS enclosure. In real world application, the borescope will be inserted through GIS access hole before filling the enclosure with SF6 gas. This new approach is proposed to be conducted during the erection and commissioning of new GIS. This new approach looks promising because it can reduce flashover phenomena caused by existence of metallic particle and also reduces Greenhouse gas emission to the air.