Introduction to the History of Selective Protection

Author: Walter Schossig, Germany

100 Years Selective Protection

Developments in PAC equipment were not linear or consistent throughout the years. Some ideas and proposals were rejected initially (perhaps the market conditions were not right or there was not a full appreciation for the proposal's capability or there was no apparent need for the solution). Some ideas were discarded only to be rediscovered by others who recycled them, improved them and exploited them to their full potential driven perhaps by different market conditions or technical challenges facing power system engineers.

The beginning of relay development goes back into the first half of the 19th century. In a paper for the French Academy of Sciences, the Frenchman Breguet noted the physical appearance of thin conductors near a telegraph station after a lightning strike. He had observed that the thin conductors had disintegrated after the lightning strike leaving only traces of what had existed beforehand.

His paper, dated the 3rd of May 1847, stated that " protect the devices and especially to protect the employees in the station I recommend the use of electricity conductors, 3-4mm in diameter, made of iron and to be located 5-6m from the device." The report continued, "We connect larger diameter wires of equal metallic behavior to the thinner wire conductors. This approach allows only the amount of electricity that can be carried through the thin wire to be conducted to the stations. In the case of a fault discharge the wire fuses and interrupts the current outside the building, not inside." The Breguet paper is considered the birth of the fusible link.

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