Detection of low-level electromagnetic signal of partial discharge by means of disturbed acquisition discrimination

conference paper

English

The proposed article will present a new approach to detection of very weak electromagnetic signal, which is generated by partial discharge (PD). This approach is a part of radiofrequency method, known as ultra-high frequency (UHF) method. The UHF method is utilized for detection, activity quantization and localization of PD in high-voltage power transformers. The UHF method is the most advancing method for this type of transformer diagnostic. The state of the art in instrument technology allows real-time acquisition and processing of pulsed broad band signals together with 3D localization of PD occurrence. The UHF method is based on measurements of electromagnetic waves in UHF spectrum produced by PD. Typical spectrum of the PD UHF signal ranges from hundreds of MHz to units of GHz. The UHF signal is detected by sensing heads that enter the transformer through its casing. Sensing heads, which were developed at Brno University of Technology (BUT), contains antennas and a set of high-frequency components, which adapt the signals from the antennas. The signals from the sensing heads are processed by a digitizer and real-time evaluated by a custom-made software developed at BUT also. The measurement of PD activity has been made on eight power transformers in the Dukovany nuclear power plant in the Czech Republic. The initial experimental measurement, which was under full working arrangements, has been accompanied by some issues. The recorded signals contained strong interference. It has been estimated that the source of the interference is probably situated in the high voltage bushings, which feed the transformer from a turbo-generator. The interfering signal in form of electromagnetic waves has propagated through the air vicinity and it has coupled to the sensing heads. It has been found that the proper shielding is a crucial factor, while the PD signal level is far below the level of the interference. An improved shielding has been developed and it has significantly reduced the level of interference. However, the signal level of expected PD activity was still below the level of the interference. Therefore, a new method for weak PD signal detection has been proposed, developed and verified. The method is based on the discrimination of signal acquisitions, which are disturbed by the interference, while the acquisitions of the desired weak signal are passing to further processing. The method was verified within an experiment, when very short electrical pulses were injected in the transformer vessel by antenna. The pulses closely simulated the spectral composition, time characteristic and the magnitude of real weak PD. The weak pulse signals were successfully detected in the presence of high level interference.

partial discharge, UHF method, source localization

DREXLER, P.; ČÁP, M.; STEINBAUER, M.; FIALA, P.; KAŠKA, M.; KOČIŠ, L.

2014

25. 8. 2014

978-1-934142-28-8

Progress in Electromagnetics Research Symposium 2014, Guangzhou

1559-9450

Progress In Electromagnetics

United States of America

213

216

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