An acoustic emission method for on-line monitoring the contamination-causing flashover of insulator
This paper presents an acoustic emission (AE) monitoring method. When a partial discharge occurs, there is an instantaneous release of energy, some of which is emitted as acoustic energy. The pollution severities of insulators in-service can be monitored and accordingly threaten to the insulation of power grid is evaluated by detecting the sound signals. To prove this AE monitoring method, artificial contaminations experiments are carried out. The essential information about the relationship of AE signal and PD are obtained in different moments of the whole process of flashover. The studied method is a new way of AE technique in monitoring and characterizing defects of electrical power equipments in-service.
Application of Data Fusion to External Insulation Strength of Contaminated-Insulator Assessment
An external insulation of contaminated-insulator assessment method is proposed based on a tri-level data fusion model of combining principal component analysis (PCA) method, artificial neural net (ANN) method and evidence theory in this paper. When contaminated-insulators partial discharge (PD) occur, much effective information obtained from the sound emitted with PD are synthesized to evaluate the external insulation strength of insulators in operation by the studied method. Firstly, nine characteristic parameters that can rapidly reflect the PD process are selected for image-level fusion of PCA to reduce dimension, which gets two new parameters. Then the new parameters are inputted to ANN for feature-level fusion. Finally, the feature-level fusion output is used as the input of decision-level fusion and fused by means of D-S evidence theory for further reducing the uncertainty of assessment. The artificial contamination experiments were explored to verify the proposed method. The result indicates that the proposed model is more precise than the ANN model under the same conditions.
Selective etching of InP in NaF solution
Abstract The crossing porous structure of InP has been obtained by electrochemical etching in NaF solutions. The behavior of the periodic oscillation occurs at different potential ranges for the different concentrations of solutions, and it will disappear with the concentration of the solution decreased. The scanning electron microscope (SEM) image shows that the pores have two directions on the surface and are perpendicular to each other. The two directions are assigned to [0 1 1] and [ 0 1 ¯ 1 ], respectively. The SEM image of the cross-section also shows that the two directions are assigned to [1 1 1]B and [ 1 1 ¯ 1 ¯ ]B. Both are due to the selective etching of F− ions. The crossing porous structure of InP is a very promising feature for the three-dimensional structure of III–V compound semiconductors for photonic band gap materials.