Investigation on Very Fast Transient Overvoltage Caused by Incomplete Separation of Air-Insulated Switches

The air-insulated isolation switch has the ability to interrupt small capacitive currents, but it does not have the function of extinguishing arcs. In the event of incomplete Break of Three-Phase, severe arcs can occur, and the capacitive voltage and arc current on the power side will produce a large pulse wave, which poses a great threat to the equipment insulation. Based on the actual spatial structure and electrical characteristics of the substation, each component underwent reasonable equivalence processing. Using ATP-EMTP simulation, the situation of gap discharge in the isolation switch during incomplete Break was analyzed. The transitory process of repeated breakdown of the gap was studied, and the causes of accidents caused by incomplete Break of Three-Phase were summarized. Measures and ideas for suppressing transitory overvoltage were proposed. The results indicate that incomplete Break of the isolating switch can cause a significant decrease in insulation voltage at the disconnection gap, and long-term intermittent repetitive discharge can cause high-frequency oscillations that generate rapid overvoltage with amplitudes and steepness higher than normal values. This phenomenon can easily cause damage to adjacent equipment insulation, resulting in huge hazards. In large power systems, most cases of incomplete Break of Three-Phase switch are caused by long-term overvoltage shocks that lead to equipment insulation breakdown. Appropriate line lengths and reducing residual charges can help to reduce overvoltage.