Surge Protective Devices protect electrical equipment through a set of precise, fast, and automatic physical protection mechanisms based on parallel circuit connection and nonlinear component characteristics, forming a complete overvoltage protection loop for electrical equipment.
First, the SPD is installed in parallel at the front end of all protected electrical equipment and connected to the system grounding wire, forming a standby protection loop. Under normal rated voltage operation of the equipment, the SPD is in a high-impedance insulated state. It does not shunt normal operating current, does not produce voltage drop loss, and will not interfere with the normal power supply and operation of electrical equipment.
When an abnormal voltage surge invades the circuit and acts on the electrical equipment, the SPD's internal nonlinear sensitive components immediately perceive the overvoltage signal and complete the impedance switch in microseconds. The device changes from high resistance to low resistance instantly, forming a high-speed discharge channel between the live wire and the ground wire.
Subsequently, the huge instantaneous surge current generated by the overvoltage is completely diverted to the grounding system through the SPD's low-resistance channel, instead of passing through the internal circuits, chips, and components of the electrical equipment. At the same time, the SPD clamps the abnormal surge voltage to a fixed safe low voltage value, eliminating the overvoltage impact on the equipment.
After the surge energy is completely discharged and the circuit voltage returns to the standard rated value, the SPD automatically recovers to the high-resistance standby state, cutting off the grounding discharge channel. This one-time rapid protection process avoids breakdown damage of equipment insulation, burnout of electronic components, and circuit short-circuit faults caused by overvoltage. For frequent small-amplitude voltage fluctuations and surges, the SPD can achieve continuous cyclic protection, effectively reducing equipment aging and failure risks caused by long-term voltage impact.