Time–frequency analysis of lamb waves caused by partial discharges and free particles in GIS

Abstract

SUMMARYWe investigated the propagation properties of Lamb waves in a GIS tank, using time-frequency analysis to diagnose the insulation performance of GIS. We measured the acoustic signals excited by metallic particles colliding with the tank sheath, and those emitted by partial discharge in the GIS. The wavelet transform was used to decompose the wave data into its time-frequency components. As a result, it was confirmed that Lamb waves with the dispersive property of the velocity are excited and propagate in a spiral path along the tank wall due to the cylindrical structure of the tank. Taking these results into consideration, we propose a new technique for identification of defect locations in GIS based on time-frequency analysis of acoustic signals with the wavelet transform.

Development of an identification system for location of free metallic particles in GIS based on analysis of Lamb waves

“…Previous experiments with ultrasonic propagation in a 66-kV-class GIS tank demonstrated the occurrence of Lamb waves of zero-order asymmetric mode (a 0 ) [5]. We also applied the wavelet transform to time-frequency analysis of ultrasonic signals, and examined the propagation characteristics of Lamb waves in a GIS tank [6]. As a result, we confirmed the existence of roundabout (spiral) waves that occur due to the cylindrical geometry of the tank.…”

“…2 and 3, respectively. Here the Gabor function is used as the basic wavelet function, just as in the previous study [6]. The white areas in Figs (1) to deal with Lamb waves that reach the AE sensor after traveling along a straight line (direct waves).…”

“…Therefore, when calculating the position from the time difference between ultrasonic signals, merely using the speed of longitudinal and transverse waves in tank material may result in a considerable location error. We have already described the importance of velocity dispersion of Lamb waves [5,6]. Previous experiments with ultrasonic propagation in a 66-kV-class GIS tank demonstrated the occurrence of Lamb waves of zero-order asymmetric mode (a 0 ) [5].…”

“…6, in this study we examine Lamb wave propagation in higher-voltage class GIS (154-kV class), propose a method for location of free metallic particles inside a GIS using two AE sensors, and introduce a location system.…”

Influence of Sensor Location and Tank Size on Determination of Discharge Type Based on PD Electromagnetic Waves Propagation in GIS

“…in the same cross-section. Input signals are two kinds of triangle waveforms having a fixed rise time of 1 ns, and different fall time of 5 and 1 ns which simulate streamer and leader-type discharges, respectively (10) .…”