the AC waveform. An op-amp and comparator is used to create a DC that rises when a trip point is reached. Then a relatively simple microprocessor does a slow speed A/D conversion of the DC signal, integrates the results to create the time-overcurrent curve response, and trips when the integration rises above a set-point. Though this relay has a microprocessor, it lacks the attributes of a digital/numeric relay, and hence the term "microprocessor relay" is not a clear term. History The digital/numeric relay was invented by George Rockefeller. George conceived of it in his Master's Thesis in 1967–68 at Newark College of Engineering. He published his seminal paper Fault Protection with a Digital Computer in 1969. Westinghouse developed the first digital relay with the Prodar 70 being developed between 1969 and 1971. It was commissioned in service on a 230kV transmission line at PG&E's Tesla substation in February 1971 and was in service for six years. In 2017, George received the IEEE Halperin Electric Transmission and Distribution Award. The award was for "pioneering development and practical demonstration of protective relaying of electric power systems with real-time digital computer techniques." George was chairman of the IEEE Power System Relaying and Control (PSRC) committee (1981-1982) as well as a member of the "Computer Relaying Subcommittee" which was created by the PSRC in 1971 and disbanded in 1978. He wrote the foreword for the PSRC tutorial on Computer Relaying produced in 1979. In 1971 M. Ramamoorty was the first to describe calculation of impedance for distance protection using discrete Fourier analysis. The first practical commercially available microprocessor based digital/numeric relay was made by Edmund O. Schweitzer, III in the early 1980s. SEL, AREVA, and ABB Group's were early forerunners making some of the early market advances in the arena, but the arena has become crowded today with many manufacturers. In transmission line and generator protection, by the mid-1990s the digital relay had nearly replaced the solid state and electro-mechanical relay in new construction. In distribution applications, the replacement by the digital relay proceeded a bit more slowly. While the great majority of feeder relays in new applications today are digital, the solid state relay still sees some use where simplicity of the application allows for simpler relays, which allows one to avoid the complexity of digital relays. Protective element types Protective elements refer to the overall logic surrounding the electrical condition that is