SPD Classification by Non-linear Element Characteristics
1. Voltage switching type SPD Common nonlinear components have discharge gap, the gas discharge tube, it has chase flow capacity (nominal through-flow o current and maximum through-flow current) characteristics, which is particularly suitable for lightning over-voltage protection in the direct lightning strike vulnerable parts (ie: L PZ0A).
2. Voltage limiting type surge protection device The common used nonlinear elements zinc oxide varistors and transient suppression diodes are the commonly used over-voltage protection, generally applicable to indoor, (ie: L PZ0B, L PZ1, L PZ2 District).
3. Combined SPD Voltage switching components and pressure limiting components mix use, with the different characteristics of impulse voltage applied,cable surge protector sometimes presents switching type SPD characteristics, sometimes rendering the pressure limiting type SPD characteristics, sometimes simultaneously presents two characteristics.
SPD main technical parameter selection
1. Protected Mode SPD may be connected among the L (phase conductor), N (neutral) and PE (the protection line), such as L-2L, L 2N, L 2PE N 2PE. These connections are related to the type of the ground of the power supply system.
2. Maximum continuous operating voltage Uc The largest root square voltage or DC voltage sustained increase at both ends of SPD, and its value is equal to the rated voltage of the cable surge protector itself. The IEC6036452534 proposed, in TT systems when the SPD is located in the power supply side of the leakage current protection device (RCD), U c = 1.1U o; when the SPD is located at the load side of the leakage current protective device, U c = 1.5U o; in TN and IT systems, the U c = 1.1 U oU selection should take into account the specific circumstances of the fluctuations in the level of the local power grid and users of electricity, not blindly the greater value is good. Because if U c is large, the entire pressure-sensitive device startup voltage is large, the surge voltage will cause harm on the device. International standards have a series of preferred values, which is related to the level of the local grid.
3. Start-up voltage Uas In the past, we thought that the startup voltage was the nominal varistor voltage, actually the current through the SPD may be much greater than test current 1mA, and in this case we cannot but consider the residual pressure elevation on equipment protection. The time from voltage varistor to voltage start time is relatively long (ie, the response time of the SPD) , which is approximately 100n s. The higher the start voltage, the higher the residual pressure, the lower, the varistor is easier to aging. Its value should not be greater than the insulation level of the equipment to be protected.
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