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This post was last edited by chenjinfeng on 2020-3-1 at 16:34. The purpose of arc flash protection is to protect nearby workers and equipment by limiting the duration of arc combustion in the event of an arc fault. Arc flash protection must first detect the fault arc before it can interrupt the fault current flowing through it. In the internal fault protection of medium and low voltage switchgear, the fault is typically eliminated by tripping the circuit breaker in order to extinguish the fault arc. When an electric arc burns, it is accompanied by radiation in the form of light, sound, and electromagnetic waves. Analysis shows that the presence of an arc can be detected through radiation in the visible light, sound wave, infrared, or radio frequency ranges; even pressure waves generated by the arc have been used to detect its presence. However, the most widely used method is still to detect visible light. The arc light protection system determines whether a fault has occurred by detecting the arc light generated when a fault takes place inside the switchgear. Arc light is the most prominent and rapidly varying characteristic physical quantity of an electric arc; therefore, arc light protection exhibits ultra-high-speed operating performance. The overall response time of this protection system can be guaranteed to be within a few milliseconds. For internal fault protection in switchgear, this over-adjustment performance is the most important. To prevent erroneous tripping of the system caused by interference from external light, an overcurrent lockout signal is often introduced in practical applications; that is, a tripping command is issued to eliminate the fault only when both an arc flash signal and an overcurrent signal are detected simultaneously, thereby further enhancing the reliability of the protection system’s operation. The main control unit of the arc flash protection system is the core component of the entire system. Its operation involves continuously monitoring the current in the electrical system, as well as analyzing and processing the information provided by the arc flash sensors; it enables the timely isolation of the fault point once a hazardous situation is detected. The main control unit is usually installed on the control panel of the incoming cable cabinet. It is able to determine its position based on the information provided by the arc sensor, and users can also select different cutting methods and signal feedback options according to various operating modes.