562 / 2017-05-14 17:10:33

Study on the Transient Voltage Distribution of the Transformer Windings Caused by VFTO

14153,14170,5132

With the increasing of power system voltage level, the problem of very fast transient overvoltage (VFTO) generated by disconnector operation in gas insulated switchgear (GIS) has attracted more and more attention. VFTO has the characteristic of the steep front and high frequency oscillation and it is not only very dangerous for the parts of GIS equipment, but also harmful for the power devices connected to GIS, especially power transformer. The reasons following: Firstly, when the VFTO attacked in transformer, it has a very nonuniform voltage distribution due to its very steep front and most of it falls on a part of winding that is near the incoming wave. Secondly, when the frequency values of the VFTO oscillation is close to the intrinsic frequency of the winding, the electromagnetism oscillation in the winding may be induced and the local resonance overvoltage is higher than that of the full lighting impulse.
In this paper, VFTO at some nodes caused by disconnected operation in 800kV GIS is calculated and simulated by MATLAB, and the characteristic amplitude values of VFTO were analyzed. For the characteristic of VFTO, equivalent circuit model is used to analyze, then equivalent circuit of windings is established by MATLAB, the VFTO is applied to the transformer windings, and the transient voltage distribution of the transformer windings is analyzed, the potential gradient between the biscuits and the turns is obtained, the insulation faults of the transformer windings are found, which is in the forward end of the transformer windings.