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Edmund O. Schweitzer III

Digital Protective Relay

US Patent No. 4,300,182
Inducted in 2019
Born October 31, 1947

Edmund O. Schweitzer III brought the first microprocessor-based digital protective relay to market, revolutionizing the performance of electric power systems with computer-based protection and control equipment, and making a major impact in the electric power utility industry. Previously, utilities relied on bulky relays made of springs, magnets and coils. Schweitzer’s more precise, more reliable digital relay was one-eighth the size, one-tenth the weight and one-third the price.

Schweitzer became intrigued with electric power system protection and protective relays as an electrical engineering student, earning his bachelor’s and master’s degrees at Purdue University and, in 1977, his doctorate at Washington State University. In 1982, he started Schweitzer Engineering Laboratories (SEL) in Pullman, Washington, today an employee-owned company, to develop and manufacture digital protective relays, which exist to make electric power safer, more reliable and more economical.

Schweitzer’s multifunctional digital relay, the SEL 21, not only protected power systems; it recorded data, helped locate faults and provided additional innovations that have since become standard features of protective relays. The SEL-PRTU, a later device, was the first to enable communication to multiple relays.

Schweitzer’s digital technology led to reduced design work in protection and control systems, flexible operation options and increased reliability, resulting in reduced cost. SEL equipment is in service worldwide at voltages from 120 volts through 765 kilovolts, protecting feeders, motors, transformers, capacitor banks, transmission lines and other power apparatus for customers including utility companies, and operations using large amounts of power, like mines, factories, hospitals, universities and data centers. SEL products can be found in 163 countries around the world.

A member of the National Academy of Engineering and an IEEE Fellow, Schweitzer received the IEEE Medal in Power Engineering in 2012.

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