Measurement method of transient overvoltage distribution in transformer windings

This paper presents a new method for measuring the very fast transient overvoltage (VFTO) distribution in the windings of transformers. Classical methods usually have direct electrical connections with the windings, which can influence the transient process. The method here is based on the coupling capacitive sensor, and wide frequency band measurement of transient overvoltage can be realized. The transformer winding used in this experiment is the low voltage winding of a 1000kV grade UHV power transformer. Three kinds of coils (sandwich-interleaved coil, interleaved coil and continuous coil) are used in the winding. Thirty-six sensors are distributed by equivalent distance from the first to last disc, and a mathematical conversion is used to get the corresponding disc transient overvoltage. The voltage and voltage gradient distributions of different discs are mapped and studied. The effects of rise time and fall time on the distributions are studied. By analyzing the experiment result, several conclusions can be drawn: the longer the rise time, the more homogeneous the voltage distribution, but the fall time has little effect. The voltage gradient is large in the first several discs and the interface of the two different structures of the windings.