Simulation And Experimental Research On The Influence Of Contamination On Voltage Distribution Of Insulator Strings

Due to be affected by long-term mechanical and electrical loads and abominable natural environment,insulators in long-term operation of transmission lines gradually produce internal defects,i.e.low zero value.Pollution flashover accidents of outdoor running insulator strings are common in recent years.Research on voltage distribution of insulator strings under polluted conditions is of great significance for preventing flashover.With the development of infrared thermal imaging technology and the application of portable infrared thermal imager,fault diagnosis technology based on infrared thermal imaging technology has been widely used in fault identification of transformers,insulators and high voltage circuit breakers.However,at the present stage,there are still some problems in the infrared thermal image detection methods for insulators,such as missing and losing zero-value insulators due to imperfect diagnostic criteria and blind detection areas.The calculation of insulator voltage distribution is based on the premis e of insulator surface contamination drying,without considering the influence of contamination distribution and degree on voltage distribution under wet contamination.In order to further study the deterioration characteristics of zero-value insulators and the influencing factors of voltage distribution of insulator strings.this paper is aimed at the existing problems of infrared detection technology,and research the voltage distribution law of insulator strings under different contamination conditions by COMSOL simulation software.First,this paper establishes three-dimensional simulation models of single normal and zero-value insulator under contamination-free conditions by COMSOL(finite element simulation software).The simulation results show that the heating of single normal insulator mainly distributes in the middle of the iron foot,followed by the bond interface between the iron foot and the porcelain body;the heating of a single zero value insulator mainly concentrates at the end of the iron foot wrapped by the steel cap,followed by the bond interface between the porcelain body wrapped by the steel cap and the two layers of the cement.Then,based on the electric field calculating model of single insulator,this paper establishes a three-dimensional simulation model of 110 kV insulator strings,the voltage distribution of insulator strings with and without zero-value insulator was simulated and compared by finite element analysis under different content of pollution.The results show that the dry pollution has little effect on the voltage distribution of insulator strings;under the condition of uniform wet pollution,with the increase of equivalent salt deposit density,the string voltage distribution tends to be uniform,and the significance of negative temperature rise of zero value insulator decreases;under the condition of non-uniform wet pollution,when the lower surface of insulator string is polluted,the voltage distribution of insulator string is more uniform,and when the pollution is heavy at both ends of insulator string,the middle of insulator string has the highest voltage.At last,a series of experiments were carried out in the high-voltage artificial test room to verify the simulation results.The test data showed that under the condition of wet pollution,the zero insulator presents the characteristic of "negative temperature difference" with low temperature,and the degree of "negative temperature difference" was affected by the degree of wet pollution and the position of zero insulator in the string,the heavy pollution will affect the accuracy of infrared detection.The test results verified the simulation results.in view of false negative problems of the insulator detection in complex environment,this paper puts forward that heavy pollution will affect the reflection of infrared characteristics of zero-value insulators through simulation analysis,and finds that the uniformity of voltage distribution of insulator strings depends on the uniformity of pollution distribution.This conclusion has important significance in improving the the accuracy of infrared detection and reducing power grid accidents caused by misjudgment.