Impact of the Initial Transient Interruption Voltage (ITIV) on the Design and Operation of Hybrid Current-Injection DC Circuit Breakers

In hybrid DC circuit breakers with current-injection, the arc in the mechanical switch is extinguished with a current pulse. After the arc extinction, the voltage increase across the mechanical switch must be limited in order to avoid an arc reignition. The voltage across the MS is usually assumed to be equal to the voltage across the capacitor $C_{CI}$ in the current-injection circuit, which increases slowly due to slow charging of the capacitor by the fault current. However, in reality the voltage across capacitor $C_{CI}$ is usually not zero at the point in time of the arc extinction. This results in high transient voltages across the mechanical switch, the so called so-called initial transient interruption voltage (ITIV) after the arc extinguishes. However, a fast increasing ITIV can lead to a thermal reignition of the arc. Therefore, it is crucial for the design of a DC-CB to understand, which effects contribute to a high ITIV. In this paper, these causes and the influence of the ITIV are investigated. Furthermore, the beneficial influence of grading capacitors parallel to the MS is investigated. Finally, an optimization of a DC-CB including the ITIV and its results are presented for a typical implementation of a current-injection DC-CB.