Identification of Acoustic Signals of Internal Electric Discharges on Glass Insulator under Variable Applied Voltage

Abstract

A Partial Discharge (PD) is an unwanted phenomenon in electrical equipment. Therefore it is of great importance to identify different types of PD and assess their severity. This paper investigates the acoustic emissions associated with Internal Discharge (ID) from different types of sources in the time-domain. An experimental setup was arranged in the high voltage laboratory, a chamber with an electrode configuration attached to it was connected to a high voltage transformer for generating various types of PD. A laboratory experiment was done by making the models of these discharges. The test equipment including antennas as a means of detection and digital processing techniques for signal analysis were used. Wavelet signal processing was used to recover the internal discharge acoustic signal by eliminating the noises of many natures. Keyword:Acoustic INTRODUCTIONOutdoor insulation represents an important component of electric power transmission and distribution systems, given that a single insulator failure can result in an excessive outage of the power system. Different insulator designs and materials are employed by power corporations and their behaviours are investigated and tested in laboratories and field tests as well as during service conditions. Specimens (rods and plates) are also tested when researchers focus on investigating certain phenomena of surface activity or material performance without being influenced by the insulator design [1]. The performance of insulators is strongly linked to local conditions, especially to the accumulation of pollutants and the wetting mechanisms present.The weak parts of the insulation are the cavities, since the gas breakdown strength is lower than that of the solid insulation. On the other hand, the electric field in the cavities is much stronger than in the big insulation parts due to lower gas permittivity [2]. Hence, the PD is limited inside the cavities and does not penetrate through the solid material to reach the electrodes. Initiation of a PD in a cavity needs two major conditions; essentially the cavity electric field should be more than that of the gas, a condition called the inception voltage level. To start an electron avalanche, a free electron must be present in the cavity [3]. The extinction voltage level may depend on the actual voltage at which a discharge starts, since presumably a higher inception voltage yields a higher initial temperature in the streamer channel. In this study, the adaptability of the Daubechies wavelets of orders 2 has been evaluated, and results have shown the superiority. It is befitting to select a suitable number of breakup levels based on the nature of the signal.

Classification of common discharges in outdoor insulation using acoustic signals and artificial neural network

“…Alternatively, ultrasound AE sensors have been used to measure both PD and DBA [10, 11]. Measuring both PD and DBA simultaneously is a cost‐effective option for power utility companies.…”