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The history of protective relays starts with Thomas Edison. While working on his many electrical inventions, Edison needed a way to control and predict where his electrical circuits were going to fail, preventing damage to the more delicate or costly circuit elements. Edison would intentionally create weak points in the circuit and later patented the earliest protection device, the common fuse. Two years later in 1892 Thomas Edison founded GE. It's hard to believe how far GE has taken the power industry since then. The dreams of Edison to make power inexpensive and widely available to everyone would not be possible without ensuring the health of critical investments like generators, transformers and power distribution. Protection devices have always made the crucial decision during faults, which happens much too fast for human intervention. Regardless, the attention and need to innovate was slow due to a business perspective aptly described by J. Lewis Blackburn,“protective relaying is a nonprofit, nonrevenue producing item that is not necessary in the normal operation of an electric power system...” This was the perspective for years until market forces changed and demand on the grid become more complex, less of a luxury and more of a necessity. From the fuse to the induction disk type overcurrent relay introduced in the 1920's, innovation was limited to variations of overcurrent protection until the 1950's with distance protection.
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