Breaking Overvoltage of Dry-Type Air-Core Shunt Reactors and its Cumulative Effect on the Interturn Insulation

The mechanism of overvoltage formation in the breaking process of a dry-type air-core shunt reactor (DTACSR) is studied in this paper. In addition, the effect of the overvoltage on the interturn insulation characteristics of the DTACSR is also discussed. Based on the actual working condition of a 66 kV DTACSR used in the Chinese power system, a three-phase simulation model and an equivalent circuit are proposed. The maximum chopping overvoltage and reignition overvoltage are obtained through the combination of theoretical analysis, simulation, and data fitting. An overvoltage accumulation test of the interturn insulation specimens is carried out with our established test platform, and the characteristic parameters of the interturn insulation specimens of the DTACSR in different stages of aging are measured. The results show that the combined method is very effective in evaluating the switching overvoltage of the DTACSR. Compared with the traditional single-phase circuit model, the proposed three-phase circuit model obtains a more accurate overvoltage equation. During the breaking process of a DTACSR, a chopping overvoltage with an amplitude greater than 5 p.u. and a reignition overvoltage with an amplitude greater than 8 p.u. may form. The cumulative effect of the overvoltage causes aging of the interturn insulation, and the degree of aging becomes more serious as the amplitude of the overvoltage increases.