Simplified Method for the measurement of loss angle of a high voltage transformer

Measurement of loss angle of a transformer insulating material and its winding capacitance between primary and secondary windings or between windings and ground by bridge technique may suffer from errors due to the effect of stray capacitance between the bridge output lead wires as well as between the lead wires and ground. The conventional Wagner-earth technique may be used to minimise this effect. But one disadvantage of this technique may be the requirement of several repetitions of bridge balance and Wagner earth balance in each observation. In the present paper a modified operational amplifier based Schering bridge network has been proposed, where the effect of stray capacitance may be assumed to be negligible. Moreover, the bridge sensitivity may be adjusted by a linear potentiometer. The experimental work was performed with 33/3.3 kV transformers in the field at 33 kV substation. The dissipation factor for the adjustable value of the bridge sensitivity factor potentiometer with the change of high voltage at power frequency were obtained and reported. These experimental results appear to reveal the satisfactory performance of the bridge network.