ACOUSTIC WAVEGUIDES FOR SENSING AND LOCATING ELECTRICAL DISCHARGES IN HIGH-VOLTAGE POWER TRANSFORMERS AND OTHER APPARATUS

For safety and convenience, ultrasonic corona sensors are mounted on the outer surface of power transformer tanks, and consequently, can only receive ultrasound from internal electrical discharges after attenuation through the oil and tank wall. In order to reduce this attenuation and maximize the detected signal, it was thought that low-loss acoustic waveguides would be helpful as a means to transmit the ultrasonic emissions from internal discharges to an external sensor. To assess the feasibility of this idea, the attenuation and frequency characteristics of several forms of guides were determined by measuring the acoustic emissions from sparks in air and oil. It was found that Pyrex glass and epoxy-fiberglass rods, as well as fiberglass optical guides function as low-loss ultrasonic waveguides. Also, these can be bent around corners in both oil and air, and pass from oil to air without additional loss of the transmitted signal. It is believed that the use of these guides would increase the sensitivity of transformer ultrasonic corona sensors by an order of magnitude. Also, during the study, it was discovered that a single continuous waveguide with acoustic sensors at each terminal, has the property of receiving acoustic waves at any point along its surface and transmitting a response to the sensors. Consequently, a discharge location can be estimated from the difference in arrival time of the terminal signals, and it is believed that a system of this nature permanently installed within a power transformer, would yield as much information as numerous internal sensors. Copyright © 1979 by the Institute of Electrical and Electronics Engineers, Inc.