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Digital relays also can provide protection strategies impossible to implement with electromechanical relays. This is particularly so in long-distance high voltage or multi-terminal circuits or in lines that are series or shunt compensated [24]: 3 They also offer benefits in self-testing and communication to supervisory control systems.
Distance protection detects both voltage and current. A fault on a circuit will generally create a sag in the voltage level. If the ratio of voltage to current measured at the relay terminals, which equates to an impedance, lands within a predetermined level the circuit breaker will operate.
In 1971 M. Ramamoorty was the first to describe [8] 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.
21 - Distance Relay; 21G - Ground Distance; 21P - Phase Distance; 22 – Equalizer Circuit Breaker; 23 – Temperature control device, Heater; 24 – Volts per Hertz Relay (in some old analog applications, a 59 and an 81 device would be chained together as a 59/81 to implement the equivalent of V/Hz protection) 25 – Synchronizing or ...
The circuit diagram is part of an issued patent for an electronic power contact arc suppressor intended to protect the contacts of electrical relays or contactors. It suppresses arcs by providing an alternate path around contacts as they open or close.
Surge Protection Device (SPD) for installation in a low-voltage distribution board. A surge protector (or spike suppressor, surge suppressor, surge diverter, [1] surge protection device (SPD), transient voltage suppressor (TVS) or transient voltage surge suppressor (TVSS)) is an appliance or device intended to protect electrical devices in alternating current (AC) circuits from voltage spikes ...
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This type of protection will not fully protect against the hazards of GPR where the danger is from a remote ground on the same circuit.) Telecommunication standards define a "zone of influence" around a substation, inside of which, equipment and circuits must be protected from the effect of ground potential rise.