Experimental investigation of high frequency voltage oscillation in transformer windings

ery Fast Transient Overvoltage (VFTO) comprising oscillating waveform generates a voltage oscillation in a transformer winding. The behavior of the voltage oscillation in the winding i s investigated experimentally on 500kV class transformers using a pulse and a sinusoidal voltage. The interturn voltages are directly measured using an optical fiber transmission system. In the case of a pulse application, i t is found that an interturn traveling wave is generated at either end of coil and i t propagates along the winding. In the case of a sinusoidal voltage application, a resonance phenomenon, probably due to the superposition of the traveling waves, is found in the interturn voltage, which could reach 0.25 times of the applied voltage. In the tested transformers the estimated interturn voltage level a t incoming of VFTO can be 3 times higher than that in the lightening impulse voltage t e s t .