Analysis of Arc Behavior in a Model Spark Gap After Surge Currents

The behavior of switching arcs is well known for time periods of several milliseconds. In other devices such as surge protective devices, where the operation is based on spark gap technology, the time periods are within microseconds. These devices are tested with 8-/20-μs surge currents. The behavior of the arc during this time period is rather unknown. In the event of overvoltages, the basic requirement is to establish an arc with a high conductivity between the main electrodes to conduct the surge current to the equipotential bonding. Due to the high conductivity, an additional current from the distribution grid ensues. This follow current needs to be switched OFF using the current-limiting breaking principle. In order to analyze the arc behavior, when changing from a surge current conduction to a follow current, a basic experimental setup is established. Due to the grid's alternating voltage, the influence of the synchronization angle is regarded for the two worst-case angles of 90° and 270°. The setup consists of a surge current generator for 8-/20-μs currents up to 25 kA, a distribution transformer with 130 kVA, and a modular spark gap that contains two parallel electrodes in a narrow gap. In this setup, the surge current, follow current, arc voltage, and transformer voltage are measured and discussed. In addition, a high-speed camera is used to visualize the plasma between the electrodes. The data are discussed in order to propose a simplification for the occurring arc.