In 2006, a power supply bureau in Guangdong carried out maintenance work in a substation. When switching 10kV outgoing line, due to illegal operation and failure of interlocking function in the switch cabinet, arc short circuit fault occurred when the line knife switch of the live line was opened with load. The arc effect caused by the fault led to the burn of maintenance staff.

Arc light is usually caused by air breakdown due to over-voltage and poor insulation coordination in the operation of electrical equipment, and the high temperature caused by arc light phenomenon causes combustion and explosive pressure.

There are many reasons for arc light, such as insulation aging and mechanical wear; man-made operation error; many outgoing lines, frequent operation, large operating current and high fault overvoltage; one-time breakdown of voltage transformer; artificial operation error; gap between equipment safety distance and high-voltage equipment; rodent hazard.

The harm of electric arc light is also relatively large, and the harm to power distribution equipment is: strong vibration leads to looseness of fixed parts; rapid expansion of gas leads to explosion of switch cabinet; high temperature leads to burning of cables and copper bars. Harm to human body: toxic gas damages respiratory system; damages muscles and nerves; stabs eyes and burns skin.

In the arc withstand time, the arc light protection can be used to remove the arc short circuit fault in the existing standard electrical switch cabinet, so as to protect the safety of personnel and equipment, and reduce the equipment maintenance cost and maintenance time. The main action basis of arc protection device is two different factors of fault: arc light and current increment. When arc and current increment are detected at the same time, the trip command is issued.