| Very fast transient overvoltage (VFTO) and transient enclosure voltage (TEV) generated during switching of disconnector in AC ultra high voltage (UHV) gas insulated switchgear (GIS), have high amplitude, steep wave, wide bandwidth, and they constitute a serious threat to the normal operation of monitoring equipment and internal insulation in GIS. Research on the characteristics of electromagnetic transient generated during switching of disconnector in AC UHV GIS have important academic value and application significance to reliable design and safe operation of AC UHV GIS.This paper supported by the National Basic Research Program of China of "Mechanism and Control of Electromagnetic Transient Overvoltage in UHV Substation" (Grant No.2011CB209405) and Science and Technology Project of State Grid Corporation of "Simulation Research on GIS Internal Transient Electromagnetic Field and Enclosure Transient Ground Potential Overvoltage" (Grant No. SGKJJSKF[2009]776), etc.. TEV measurement device was developed, by experimental measurement and modeling and simulation, characteristics of electromagnetic transient, influencing factors and suppression measures of 1000kV AC UHV GIS were further researched. The main research works of this paper are as follows:(1) The definition of TEV and standardized measurement method of arrangement and shielding of measurement wire were presented, technical requirements of TEV measurement device were given. TEV measurement device which developed, had characteristics of strong anti-electromagnetic interference, independent power supply, synchronous trigger, optical fiber communication and remote monitoring, etc., tests of various performance, electromagnetic compatibility and insulation withstanding were passed, the length of measurement wire was normalized. Measurement device met field measurement requirements of TEV in AC UHV GIS, it provide a reliable measurement device to TEV measurement in the future.(2) TEV waveform and distribution characteristics were obtained, tests researched on TEV characteristics under different connection modes which cost three years were developed in two test circuits of 1000kV AC UHV GIS, statistical characteristics of TEV waveform parameters on different locations in test circuits were analyzed, including full waveform characters of TEV, pulse numbers, full waveform durations, single pulse waveform characters, frequency components, single pulse waveform durations, amplitude rising and TEV amplitude characters influence in pre-charge or no pre-charge DC voltage, different branch bus lengths, replacement disconnector connection directions. Amplitude relationships of breakdown voltage, VFTO and TEV which met to linear function of direct proportion were obtained, correlations of breakdown voltage, VFTO and TEV were studied. Typical waveform and parameter definition of TEV were proposed, statistical values of each waveform parameter were extracted, transient characteristics of TEV on 1000kV AC UHV GIS were revealed.(3) Wideband equivalent circuit models of ground pillar, ground grid and elements of casing, disconnector, branch bus, bus and insulating flange in 1000kV AC UHV GIS were established, simulation model combined VFTO and TEV which coupled with multi-conductor transmission line and broadband lumped element was proposed. Simulation and measurement results of TEV and VFTO measurement points in test circuits of UHV GIS were compared, the validity of modeling method and simulation model was verified, a new simulation model was provided to modeling and simulation of TEV and VFTO.(4) Influencing factors of TEV and VFTO in GIS were studied, including electromagnetic leakage of insulating flange, electromagnetic leakage of casing, damping resistor of disconnector, different lengths of branch bus, wave impedances of bus, ground pillar and heights of GIS, etc., suppression measures of TEV and VFTO were proposed, and they were applied in practical engineering. |
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