| With the wide use of GIS in the power grid,the reliability of GIS is very important to the stability of the power system,in the event of failure it will cause the regional blackouts.GIS is a large enclosed composite structure system and is difficult to grasp the status.In the event of failure it will result in significant losses.It is particularly important to detect and determine operational status of the insulation before the failure in the GIS occurs.Currently,UHF partial discharge(PD)detection technology has been widely used in the area of the evaluation of the GIS insulation degradation State and it has been received more attention.Whether the insulation defects could be detected timely and diagnosed effectively is related to many factors,just like the performance of the sensor,the sensitivity of the system and the reasonability of the stationing layout scheme.(the detection system determines would greatly influence the utilization of this technology.)(the above of all are vital for detection system of UHF partial discharge.)However,the common principles of the calibration and evaluation on the performance of the UHF sensor and the detection system have not been established until now,both in China and abroad.There are two problems to be solved,the one is the system performance and its installation will have an impact on the actual detection results,the other one is how to calibrate the monitoring system performance in the field quickly.In order to solved it effectively,this paper studied the characteristics of the four different types of insulation discharge.the propagation and the attenuation characteristics of signals of UHF in the GIS,By comparing the differences between the UHF signal of the article analog pulse injection and the PD signal of the typical defect,we study the interval attenuation method based on the equivalent pulse injection method.Currently all methods about site testing is based on 5pC pulse injection by International Conference on large power grid.but we found that different injection conditions has a great impact to the amplitude of the injection pulse after a large number of experiments.Because the GIS structure of each manufacturer is inconsistent,there are some limitations that the program proposed by the International Conference on Large Power Grid is only one of the scenarios.The paper studies an interval attenuation algorithm based on equivalent pulse injection,the algorithm installs numerical sensor at the scene by calculating the attenuation value in the interval.it can effectively avoid the change of the amplitude of the injected signal caused by different injection conditions.Finally,The attenuation rules of the UHF signal and the injection simulation pulse signal in different GIS is obtained from typical simulated PD models in different GIS are experimentally studied in Taikai factory on 110 kV GIS.the paper summarizes the sensor layout scheme of typical GIS structure with different voltage levels,and measured in Xian factory on 220 kV GIS.According to the Interval attenuation algorithm,an equivalent attenuation method is proposed to realize the fast and limited sensitivity of UHF detection system under site condition,and the validity of the above method is verified by experiments. |
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