Valsala Kurusingal
Ctr. for Mater. Technol., Univ. of Technol., P.O. Box 123, Broadway, NSW 2007, Australia
Ultrasonic techniques alone or in combination with electrical methods are increasingly being used for the detection and/or location of partial discharge (PD) in high-voltage transformers and other electrical plants. Ultrasonic transducers used for fault location are traditionally coupled externally on to the transformer wall. Mounting transducers inside the transformer steel tank has certain definite advantages like better noise immunity, increased sensitivity due to better acoustic matching to oil, and less complicated signals (only longitudinal waves). Transformers are filled with mineral oil whose temperature could rise up to 110 (degrees)C during normal operation. Also, there are large electric and magnetic fields and strong mechanical vibrations as well inside the transformer. The authors has developed 1--3 piezopolymer composite transducers which are capable of operating in this adverse environment. These transducers were life tested in mineral oil at 130 (degrees)C for over 500 days and their k[sub t] values monitored as a function of time. Life test and vibration test data for several transducers as well as sensitivity, frequency response, pulse width, and constructional details are presented.