History Protection - Generations of Protection

Passive and Active Semiconductors, Transmitters and Transistors

Since moving parts of electromechanical relays have been an uncertainty in protection devices, the tube (see last number of PACWorld) was the choice as a solid state control element. Unfortunately the lifetime of filament was limited- semiconductors (active and passive) should be the solution. Experiments with vacuum tubes have been dismissed in 1955, separate from some exceptions. Semiconductors promised a maximum of reliability. Developing the so called “static relays” produced mature solutions, complementing electromechanical relays. The transistor was invented by the US physicist William Bradford Shockley in 1948, who later received the Nobel prize award with Bardeen and Brattain. This was a revolution for the entire world as well as for the protection devices. It took 10 years before papers described their application for protection and another 10 years for the first series production of relays with transistors inside.