Study On The Methodology Of Monitoring Insulation Defects Of High-voltage Bushing

High-voltage bushing is key electric accessory,(such as main transformer bushing etc.) for the insulation of lead-to-metal casing in transformers, reactors and other high-voltage electrical equipment. High-voltage bushing is one of the most important parts of the power system. Its insulation performance directly affects the security, stability and economic operation of the power grid. There are still some problems on the existing methods of monitoring bushing insulation defects in the reliability and practicability. Therefore, the study on the more effective methodology of monitoring insulation defects of high-voltage bushing has important practical significance.A new methodology of monitoring insulation defects of high-voltage bushing is put forward in this paper. The methodology uses the bushing transient voltage and current (from normal operating system or other faults caused) as information source, acquires the monitoring and diagnostic discriminant function of bushing insulation defects, and diagnoses the bushing insulation defects according to the maximum of the discriminant function. The equivalent network model of bushing is built in this paper. In the case of transformer bushing, the electric field distribution of high-voltage bushing is simplified, and the proportion of equivalent horizontal, vertical capacitance of the bushing is determined by the relative size of axial and radial field strength, then the equivalent network parameters is also determined according to the dielectric loss test data of the bushing. The monitoring methodology proposed in this paper is verified through simulation and test verification. Lots of ATP simulation results confirmed the effectiveness and feasibility of the methodology. The model is built by the110kV capacitor oil-filled bushing; three conditions of different insulation defects levels are set to verify the methodology of diagnosing the bushing failure. The three diagnostic results of the test are basically correct, the accurate diagnosis can be made to judge bushing working state that is normal or not. The results of laboratory tests initially confirmed the feasibility and effectiveness of the methodology.In this paper, the transient voltage and current of the bushing shared with related equipment are only required to achieve the monitoring and diagnosis of the location and severity degree of the high-voltage bushing insulation defects. The methodology does not require large or complex additional equipment; it is economical and practical, and has strong operability.