The effects of impulse voltages on transformer windings

Abstract

TABLE OF CONTENTS-continued. SUMMARYThe effects of the application of impulse voltages of varied wave-shapes to transformers are analysed theoretically and experimentally. Single and multiple transients have been considered, and oscillographic tests have been made on model transformers of different winding characteristics, and on both single-phase and 3-phase transformers. The constants of the transformers important for determining the voltage distribution within the windings due to Ihe impact of a surge have been calculated and measured, and the effect of altering these constants has been examined. In general, good agreement has been obtained between theory and experiment. The transference of surges from one winding to another has been briefly considered, and the testing of transformers with impulse voltages has been discussed in the light of the foregoing analytical study. TABLE OF CONTENTS(1) Introduction.(2) Theoretical Treatment. (3) Technique of Measurement. (a) Description of experimental transformers. (b) Measurement of constants of winding. (c) Impulse-generator circuit for voltage-distribution tests. (d) Initial voltage distribution. (e) Check on the oscillographic technique. (4) Applications of Impulses to a Model Transformer. (a) Initial voltage distribution. (6) Subsequent voltage distribution. (c) Effect of wave-front of applied impulse. (d) Effect of wave-tail of applied impulse. (e) Effect of winding resistance. (/) Effect of removing transformer from its tank. (g) Effect of addition of series capacitance.(h) Effect of earthing the transformer through an impedance not equal to zero. Effect of isolating the neutral point, and of applying impulses to both ends of the winding. Effect of a discontinuity in the winding such as occurs at a tap-changing point. Effect of reinforced coils, (m) Effect of static end ring.

Generalized analytical formulae to compute electrical characteristics of a homogenous ladder network of the transformer winding

“…The theories based on standing [28][29][30][31] and travelling waves 32,33 have been applied to determine the internal voltage distribution or surge phenomena in the transformer. These theories are based on the concept that under surge condition, voltage stresses are developed due to the interaction of electric and magnetic fields and are defined as the function of time and location.…”