Investigations on Transformer Oil Temperature Sensing using CuAlNi/Polyimide Shape Memory Alloy composite film

Power transformer is the one of the largely important as well as one of the costly elements in the electricity grid. Any malfunction of this element may affect the reliability of the entire network and could have considerable economic impact on the system. For several reasons, overloading of power transformers beyond their rating has been reported frequently. The primary issue leading to the failure of transformer is contamination of transformer oil by the working components due to prolonged high temperature exposure. Transformer oil temperature can be utilized as a primary parameter in monitoring the life of the transformer. At present, electrical approach are vulnerable to electromagnetic interference and are limited by sensors lifetime. Other non-contact techniques are ineffective due to difficulties in processing the output signal. In this work a CuAlNi/Polyimide shape memory alloy composite has been applied to act as a temperature sensor in mineral oils. The composite film has been developed through thermal evaporation which exhibited two-way displacement without and post-processing and training. The developed films are employed in a custom made oil rig and the suitability of using it as a circuit breaker in temperature sensing application has been probed. The circuit breaker can be triggered by measuring the displacement of the bimorph using laser displacement sensor. The measurement is of non-contact type and the temperature can be monitored at regular intervals. For comparison a procure Nickel-Titanium spring with transformation temperature less than 100 degrees C is also used for the studies. The results show that the developed bimorphs has good sensitivity of 0.2 mm/degrees C and the output displacement is significant. Further the effect of contamination in the mineral oils is also probed by adding known amounts of impurities and the ageing effect has been studied. A higher resolution measuring system using interferometry has been proposed.