Boxue Du - Epoxy-based Spacers for Gas Insulated Power Apparatus

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High-voltage gas-insulated apparatuses, including Gas-Insulated Substations (GIS) and Transmission Lines (GIL), play an important role in the global power transmission systems. GIS has been widely used in the transformer substation attributed to its advantages of less land occupation and superior insulation performance. GIL is an advanced medium for high-capacity and long-distance power transmission due to its advantages of large capacity, low loss, and strong environment adaptability. GIS and GIL have a similar structure with the conductor and the metal enclosed enclosure coaxially installed, using SF6 gas as the insulating medium and epoxy-based spacers for mechanical support. Because the epoxy-based spacers and SF6 gas have different electrical properties (permittivity, conductivity, etc.), the electric field distribution in GIS/GIL is extremely non-uniform, easily triggering partial discharges and even insulation breakdowns. Moreover, GIS/GIL are subjected to complex conditions during operation, the thermo-electro-structural coupled field makes the insulation failure process more complicated to be understood and suppressed.

This book is a collection of our previous researches on epoxy-based spacers for gas-insulated apparatuses. Three topics make up this book, with 79 chapters in each topic. The first topic is Electric field, Surface Charge and Discharge, consisting of nine chapters. We have paid attention to the surface charging and discharging behaviors of the epoxy-based spacers in GIS/GIL and found that the insulation breakdown of the epoxy-based spacers is closely related to the electric field distortion under variable voltage waveforms (AC, DC, impulse, etc.) and temperature gradients. The second topic is Surface Functionally Graded Materials for GIL/GIS, consisting of seven chapters. We provided an original study on the electric field relaxation of epoxy-based spacers by surface functionally graded materials (SFGM). Several optimization methods and fabrication technologies for SFGM spacers were introduced and discussed. The last topic is Electric Field Adaptive Materials for GIL/GIS, consisting of nine chapters. Nonlinear conductivity materials (NCM), such as epoxy/SiC and epoxy/ZnO composites, were applied as coatings to adaptively regulate the electric field distribution around DC-GIL/GIS spacers. Besides, the concept of the multidimensional functionally graded materials was proposed to control the electric field distribution of DC-GIL/GIS spacers under stationary and transient conditions, exhibiting great potential in the future application.

Pursuing the Research and Development of Advanced Dielectric Materials for Polymer Insulation started for me when I worked as the leader of the high voltage lab of Tianjin University, China. This book includes our recent progresses on epoxy-based insulating materials for GIL/GIS, some of which are original and quite promising. It is really a team effort to finish this book. It is my pleasure to acknowledge the numerous contributions made by my team.

Over the last few decades, the high voltage direct-current (HVDC) transmission technology have been developed to carry out long distance and high capacity power transmission []. Therefore, the surface charge accumulation and electric field distribution along the GIS/GIL spacers need to be understood. This document is the template for the preparation of a manuscript. The use of this template will ensure the professional appearance of your paper.

In order to improve the reliability of GIS/GIL, researches aiming on the surface charge measurement and simulation have been conducted worldwide. Some researchers built a scaled-down GIS/GIL and measured the surface charge distribution on the spacers []. Their measurements were conducted offline because the applied voltage on the conductor can easily cause damage to the electrostatic probe. The poor accuracy of offline measurement makes their measurements differ from each other. Besides, the accumulated surface charge at the triple junction can hardly be detected by the probe, which actually has a very significant effect on the electric field distribution.

Simulation is another way to study the surface charge distribution on spacers. Many researchers have proposed a variety of mathematical models to simulate the surface charge accumulation process []. However, few of them took the gas collision ionization and charge trapping-detrapping process into consideration. This chapter detailed the corona discharge and charge trapping-detrapping process by combining the plasma hydrodynamics and charge trapping-detrapping equations together. Under load conditions, GIS/GIL has an obvious temperature rise on the conductor. Considering there are many temperature-dependent factors in the surface charge accumulation process, the heat transfer equations are also coupled in this model to obtain the temperature distribution. Besides, the effects of shielding electrodes on the distorted electric field distribution are also studied.