Maintenance-free vacuum circuit-breaker

The introduction of vacuum switchgear represented the first step in the direction of a maintenance-free medium-voltage circuit-breaker. Switching in a vacuum was the first quenching principle to assure constant electrical and dielectric properties throughout the device´s entire service life of more than 20 years, involving for example more than 100 short-circuit clearances or 10000 to 30000 switchings of the rated normal current. These and other superlative characteristics of the vacuum interrupters mean that this quenching principle is not only one of the most reliable, but also one of the most environmentally compatible. Modern medium-voltage circuit-breakers such as those of the Siemens 3AH1 range described by the authors constitute the second step in the direction of a maintenance-free and therefore more reliable overall system. Not only the primary section with its vacuum technology is maintenance-free, the same goes for the circuit-breaker operating mechanism too. In this context maintenance-free means that throughout the circuit-breaker´s service life of more than 20 years and under normal operating conditions: no relubrication is necessary, no readjustment is necessary, and the characteristic data do not deteriorate impermissibly. The only external factor influencing the reliability of such a circuit-breaker is deterioration in the insulating capacity as a result of environmental effects. The third and final step in the direction of a completely maintenance-free overall system is integration of the maintenance-free circuit-breaker in the gas-insulated switchgear