Research Of External Insulation Strength Of Contaminated-Insulator Monitoring Method Based On Acoustic Emission

The insulator is one of the main external insulation components in power system. As a result of long-term exposure in the atmosphere and pollution, the insulator’s external insulation level reduces, resulting in Pollution Flashover at the nominal operating voltage. Pollution flashover incidents seriously threat the security and stability of power grid operation. The power sector takes various measures to prevent the occurrence of flashover, but the achievement is not totally satisfying. A substantial amount of research work has been done on the insulator contamination monitoring at home and abroad, and a variety of insulator contamination supervisor ways are put forward. These ways promote the development of insulator contamination monitoring. However, as there are many other problems and influence, the desired results are not achieved. Therefore, it has a great theoretical and practical engineering significance for the security and stability of power grid operation.to carry out external insulation strength monitoring of polluted insulator, to find out the external insulation strength change, to timely disseminate early warning information and to take preventive measures in advance to avoid flashover accidents.Based on a large number of documents available at home and abroad, this paper analyzes the advantage and disadvantage of existing detection methods of polluted isolators and proposes a new external insulation strength monitoring method of using the acoustic emission signals generated when the polluted insulator flashover discharges.This paper analyzes the mechanism, mathematical models and the development process of polluted isolator discharge. The acoustic emission phenomenon is also analyzed in the polluted insulator discharge. This paper shows that there is a relationship between the strength of filthy discharge and acoustic emission signals, so a new external insulation strength monitoring method of using the acoustic emission signals generated when the polluted insulator flashover discharges is proposed.This paper designs a focused sound sensor and monitoring device with high sensitivity and high Signal to Noise Ratio. The focused sound sensor consists of a piezoelectric sensor and a focusing paraboloid, which is used to receive weak acoustic emission signal generated by the long-distance discharge of polluted insulators. The monitoring device consists of the pre-amplifier, two-stage amplifier, compensation amplifier, filter circuit, AD, MCU, communication interface and host computer. The designed model machine is used in the polluted experiment and has a good performance. This paper does the research on the mathematical morphology and explores its application in the filthy noise signal processing of acoustic emission. The peak/valley filtering method and the edge detection filtering method are compared, and the result is that the edge detection filtering method has a better effect in the noise reduction of filthy discharge acoustic emission signal.This paper does the research on the principal component analysis and its application in the feature extraction of filthy discharge acoustic emission signal. The principal component analysis is used to remove redundant information in filthy discharge acoustic emission signal, extract the features that can reflect the real external insulation strength of polluted insulator, overcome the impact of redundant information in classification efficiency and accuracy of polluted insulator discharge stage and improve the classification efficiency and accuracy of polluted insulator discharge stage.This paper does the research on the least squares support vector machine classification and information fusion classification, and uses these two methods in the classification and identification of different external insulation strength stage. After analysis and comparison, the information fusion classification has a higher accuracy in the classification of different external insulation strength stage.Based on the theoretical study and research project, this paper does the artificial contamination experiments on one-chip insulator, two-chip insulator and multi-chip insulator with different materials. The main content of the experience is as follows:1. Observe the relationship between polluted insulator discharge intensity and acoustic emission signal strength.2. Acquire the acoustic emission signals of different contamination degree’s insulator in the stage from filthy discharge to flashover when the insulator gradually damps in the operating voltage and analyze the relationship between acoustic emission signal features and filthy discharge intensity in the stage from filthy discharge to flashover.3. Acquire the acoustic emission signals generated in insulator contamination discharge, precondition them, extract the signal features and classify the external insulation strength of insulators.4. Test the results of repeated measure of the same insulator in the same condition, and the classification consistency of the external insulation strength.5. Analyze the features of corona discharge acoustic emission signal and polluted Insulator discharge acoustic emission signal in amplitude, phase, etc. Distinct these two forms of discharge based on the features and eliminate the influence of corona discharge on the monitoring of insulator discharge. Through a large number of artificial contamination experiments, the feasibility, accuracy and practicality of the external insulation strength monitoring method of polluted insulators based on acoustic emission technology, which is proposed in this paper, are tested.This paper proposes a new external insulation strength monitoring method of polluted insulators based on acoustic emission technology, and hopes to explore a new approach to online monitoring of polluted insulator’s external insulation strength, with the aim to reduce the occurrence of flashover accident in transmission line and improve the security and stability of power system.