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Discussions on factors influencing the effective protection distance of SPD to loads

The SPD has an effective protection distance under the condition of the specific load and the specific voltage protection level of SPD. If surge protection devices (SPDs) are installed without consideration of the distance between the SPD and the protected loads, the equipment to be protected might be damaged despite of the correct energy coordination of SPDs. The IEC estimation method for effective protection distance of SPD is too rough for the guide of SPD installation. This paper reviewed our works on the effective protection distance of SPD under different voltage protection levels and different loads. The equipment characteristics, which were simulated by loads with different impedance characteristics, have strong influence on the effective protection distance of SPD. When the maximum continuous operating voltage of the SPD is determined, the higher the voltage protection level of the SPD is, the longer its effective protection distance is. Secondly, different household appliances have very different impedance characteristics, this leads the effective protection distance of different appliance to be very different. Last, there exists a worst distance between a SPD and a protected device in a low-voltage circuit. If a protected device and a SPD are separated by this worst distance, the protected device will be subject to the most severe surge voltage.