Implementation Aspects of DC Hybrid Opening Switch

A DC opening switch based on hybrid technology which uses a mechanical vacuum breaker and solid-state devices is presented. The vacuum breaker provides a low-loss high-current charging path and serves as a first stage for the opening sequence. The solid-state devices are built from fast integrated gate-controlled thyristors (IGCTs) and serve for the second stage of the opening sequence. The IGCTs are turned-on after opening the vacuum breaker, thereby transferring all the current to the IGCTs. For safe shut-down of the IGCTs, a pre-charged capacitor is discharged to counter the high-current, i.e. to temporarily create current zero in the IGCTs. Since the IGCTs are asymmetric, free-wheeling diodes are connected in parallel to the IGCTs. However, due to a finite recovery time these diodes cause an abnormally high voltage across the IGCTs. Two methods are presented to minimize this voltage by transferring the energy directly to the load. The DC opening switch was tested up to a current of 47 kA at the load.