Hainan transformer
? In recent years, many substations of Electric Power Industry Bureau have increased the rod gap on the neutral point of 110kV classified insulation transformer, which is prone to misoperation in the gap of multi-minefield. This paper will analyze this.
The original intention of installing the parallel gap is to prevent the lightning arrester from exploding when it acts under internal overvoltage, which will damage the main transformer and nearby equipment. Therefore, the matching characteristics of the gap are required as follows: when lightning overvoltage acts, the lightning arrester acts and the gap does not act; When the internal overvoltage acts, the lightning arrester does not act, but acts intermittently. The division of labor between the two is clear. The gap should meet the conditions of action value and non-action value, which is easy for the neutral point of 220 kV transformer, but difficult for the neutral point of 110 kV transformer. In the past, it was only assembled according to the gap size provided by the electric power test unit, and no more tests were required. However, the data provided by the laboratory were measured under the conditions of processing frequency voltage and lightning wave respectively, which was quite different from the actual operating conditions.
In the multi-minefield, when the line near the substation is grounded in single phase, the atmospheric overvoltage and internal overvoltage often appear at the same time, and then are transmitted to the neutral point with gaps. At this time, the overvoltage is neither pure power frequency overvoltage nor standard lightning wave, and the two independent data obtained in the laboratory are difficult to represent the real situation encountered. In addition, the air gap is affected by meteorological conditions, electrode shape and the discreteness of its own discharge voltage, and its reliability is poor, which is confirmed by at least operating experience.
It should also be emphasized here that in the past, gaps were also added to the neutral points of some transformers that did not need to be equipped with bar gaps. It was mistakenly believed that adding gaps would always be beneficial, and the relay protection configuration would not cut off power. According to statistics, during the lightning period from 1994 to 1997, when the 110 kV line in Zhuhai was grounded in single phase, the gap acted 11 times, with a misoperation rate of 100%, but the one without gap was safe. Hainan distribution cabinet?