Photo from power switching component book by Kaveh Niayesh , Magne Runde
Compared to medium voltage circuit breakers, load break switches are inexpensive, and are extensively used in distribution systems at medium voltage level(typically 6–36 kV); often in series with fuses. An example of a load break switch with air as an interrupting medium is shown in the figure(in the close and open position).
The nozzle is made of a material, which produces gas with a high H2 content when exposed to an arc. hydrogen is a very good interruption medium making the interruption easier than if the arc burns in pure air.
The switchgear has two pairs of contacts, and the driving mechanism is constructed in such a way that the main contacts are the last to mate when closing and the first to separate when opening. The nozzle is narrow causing heat from the arc to generate a certain pressure rise and gas flow as the arcing contact opens. The piston
is mechanically linked with the driving rod and generates an airflow onto the arc during the interruption.
This and similar circuit breaker designs are very popular in medium voltage distribution systems of the medium or low current rating.
The Hardgas principle is only used in load break switches for distribution system voltages.