When a voltage surge invades an electrical circuit, the SPD completes the whole protection process of response, conduction, discharge, voltage clamping, and reset in microseconds, with the specific working process as follows:​

First, real-time surge sensing. When a transient voltage surge occurs in the circuit, the circuit voltage instantly rises far beyond the rated operating voltage. The SPD's internal nonlinear components continuously monitor the circuit voltage in real time and immediately capture the overvoltage abnormal signal at the moment the surge arrives.​

JDZ-3Q Voltage Transformer

Second, rapid impedance conversion. Driven by the overvoltage, the core components of the SPD (varistors, discharge tubes) undergo instantaneous physical characteristic changes. The device rapidly switches from the high-resistance insulated state during normal operation to an ultra-low-resistance conductive state, forming a stable low-impedance discharge channel between the circuit live line and the grounding system.​

Third, surge current diversion and energy release. The high-energy instantaneous surge current generated by the voltage surge will preferentially flow through the low-resistance channel of the SPD. All abnormal surge energy is quickly diverted to the ground and released, avoiding the surge current passing through the protected electrical equipment.​

Fourth, voltage clamping stabilization. While discharging the surge current, the SPD limits the peak voltage of the circuit to a fixed safe residual voltage value. This eliminates the overvoltage impact on electrical equipment, keeps the terminal voltage of the equipment within the safe withstand range, and prevents insulation breakdown and component damage.​

Fifth, automatic reset and standby recovery. After the surge energy is completely released, the circuit voltage quickly returns to the normal rated level. The SPD's internal components automatically restore their original high-resistance characteristics, cut off the grounding discharge channel, and return to the normal standby protection state, ready to respond to the next voltage surge impact.