| Very fast transient overvoltage?VFTO?with contain complex frequency components with high frequency and large amplitude will be generated during the operation of switchgear in power system,which will seriously interfere the equipment in the adjacent secondary side.Gas insulated substation?GIS?is the curial switchgear apparatus in ultra and extra high voltage power system,with the rapid development of smart grid in China in recent years,higher frequency and amplitude VFTO would appear as the consequence of frequently operation of GIS disconnector.The miniaturization design of GIS requires the compact design of the main architecture and the integrated installation of primary and secondary equipment.It reveals the electromagnetic compatibility in GIS leading to the wide attention on the low signal-to-noise ratio of secondary devices,distortion of combined unit signals,relay protection misoperation,easy interference and even damage of signal acquisition devices.Thus this dissertation studied the generation mechanism and inhibition measurement of VFTO and the propagation characteristics of VFTO electromagnetic interference sources in GIS,investigated the influence of the sources on the electromagnetic compatibility of secondary devices,designed a secondary side signal acquisition device and further improved the shielding box structure.The main works show as follows:?1?VFTO simulation system and test detection system were built with high voltage equipment such as impulse voltage generator,weakly damped capacitor voltage divider and steeping gap etc.The influence of distance and air pressure on VFTO in steeping gap was obtained with the insulation gases of air,N2,SF6 respectively in the steeping gap.The method was present to suppress VFTO oscillation amplitude by changing pressure.Combined with the experimental results,the generation mechanism of VFTO were revealed.By analyzing the time spectrum characteristics of VFTO simulation experimental waveform,the frequency of VFTO simulation experimental waveform mainly includes 5,10,27,45 and 79 MHz etc.?2?Straight conductor electromagnetic radiation mathematical model was used,method was put forward based on hilbert huang transform?HHT?,electromagnetic field intensity distribution of complex frequency components electromagnetic interference sources was calculated in the space and the electromagnetic field intensity and the changing rule of electromagnetic field intensity distribution with observation distance and time were studied.GIS simulation models were built with and without shells,oscillation frequency at the end of GIS equipment and the electromagnetic field distribution in GIS under VFTO interference source were calculated,the influence of GIS shell on the energy,oscillation frequency and the electromagnetic field intensity of GIS space were analyzed and the propagation characteristics of VFTO electromagnetic interference sources were obtained.The calculation results showed that the shell structure layout can create a weak electromagnetic field intensity area and determine the placement position of sensitive equipment in GIS.?3?Secondary side signal acquisition device integrating control module,signal acquisition module,AD conversion module,signal processing module,communication module and upper computer system was designed,the simulation model of GIS and signal acquisition device was established,the distribution of the electromagnetic field in the signal acquisition device and the current of the core circuit board circuit in the signal acquisition device were calculated under the action of different VFTO electromagnetic interference sources,the influence law of electromagnetic interference source on electric field and circuit current of core circuit board was analyzed in signal acquisition device and the relation between the line length and the disturbed current in the core circuit board of the signal acquisition device was studied.?4?The conductor through the hole joint of the shielding box was equivalent to the suspended metal placed at the hole joint,further four pore structure,the structure of the eight hole,hole seam adding suspended metal plate structure,the structure of the volume amplification,double layer structure of signal acquisition device shielding box model were set up respectively,and internal and external structure of electromagnetic field distribution of shielding box were simulated,the influence of different structures on the shielding effectiveness was obtained.Through the analysis of the electromagnetic field distribution in the shielding box under different schemes,it was found that the shielding box of the double layer structure signal acquisition device showed the best shielding effect.GIS and double layer structure shielding box are connected by connecting terminals.The influence of the radius and length of the connecting terminal on the electric field intensity inside the shielding box was studied,shield box structure of secondary side signal acquisition device was optimized and designed in GIS,double layer shielding box structure in GIS was put forward with the connection terminals radius and length of 20 mm and 80 mm respectively,and the radius of the signal conductor in connection terminal and the inner conductor shielding layer hole joints respectively was 15 mm,18 mm.The electric field intensity inside the shielding box was 28.4V/m.The shielding effectiveness curve reaches 80dB,which is much higher than the level 3 of the national military standard. |
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