Apply Ray Tracing to Back Track Partial Discharge in Transformer Based on Combined Array Sensor

To locate partial discharge (PD) in power transformer, a combined array sensor is manufactured which consists of a cross-shaped ultrasonic array with 25 elements and an ultra-high frequency (UHF) array with 2*2 elements. Algorithms for PD location are studied based on the sensor arrangement, and a total of 193 ultrasonic and 13 UHF virtual elements are achieved via virtual expansion. At first, two-sided correlation transformation based on the UHF virtual expanded array is employed to pre-estimate the PD's direction, and then rotated signal sub-space based on the ultrasonic array is used to direct accurately. To enhance the accuracy and success rate of an array, ray tracing technique which consists of geometrical optics and uniform geometric theory of diffraction is studied to backtrace the wave emitted by PD, considering the UHF signal as an example. The PD location experiments in a transformer model indicate that the location algorithms based on the proposed combined array sensor adapt the PD's broadband signal well, and ray tracing of the electromagnetic wave emitted by PD makes the location much accurate and successful than that of a single array. The PD location based the proposed combined array takes the advantages of the high sensitivity of UHF array and the high accuracy of the ultrasonic array.