Improved Method for Acoustic Identification of Free Conductive Particle Defects in GIL

The presence of free conductive particles in gas-insulated transmission lines (GIL) is the most significant threat to their insulation. The non-invasive identification of free conductive particle defects in GILs is extremely challenging. Existing identification methods which use the acoustic amplitude-flight time (AAFT) pattern are not often adopted on site due to their faulty theory, non-robust extraction algorithm, and generally inaccurate calibration. In this study, the theory established by L. E. Lundgaard is expanded by deriving estimation equations related to the particle's moving state. A new method for extracting the state information from the raw data of acoustic signals is established and the robustness of the acoustic identification method is enhanced. A convenient calibration method is also developed by building a standard collision signal generator. The proposed methods are validated in a scale GIL model and a real GIL model. The results of this study may represent a workable reference for GIL condition monitoring.