低压电涌保护器的有效性分析

采用标准的6kV/3kA的混合波发生器作为冲击源,采用单相低压配电系统作简单仿真模型,研究了不同长度的电缆与不同负载产生的反射与振荡现象,分析了不同类型负载和不同电缆长度对低压电源电涌保护器(SPD)保护效果的影响。仿真结果表明:对于纯电阻负载,负载阻抗增加到300Ω时,电缆长度应低于5m;增加到500Ω以上时,电缆长度应低于1m。对于纯电容负载,建议直接将负载与SPD连接,电容大于10μF时,可考虑采用50 m以上的电缆。对于阻容性负载,电阻值低于电缆的特性阻抗且电容不大于0.1μF,电缆的长度不受限制,被保护的设备上不会出现过电压;若电阻值大于电缆的特性阻抗且电容不大于0.1μF,电缆长度应限制在1m以内;若电容大于10μF,可考虑采用长度大于50m电缆。无法确定负载特性时,可采用零距离连接,即中间无连接电缆;若距离太远而无法直连,可以在15m左右的电缆后增加一级SPD,再直连负载,这时要求两级SPD能量匹配。

Analysis on Protection Effectiveness of Low-Voltage SPD

Surge reflection and oscillation on cables of different length at different loads were studied with simple simulation on single phase LV distribution system,using normal 6 kV / 3 kA composite surge generator as the surge source,and the effect of different loads and cable of different length on protection of LV SPD.Simulation shows that for pure resistive load the cable length shall be less than 5 m at load resistance increased to 300 Ω,or less than 1m at load resistance increased to higher than 500 Ω.For pure capacitive load it is recommended to directly connect the load with SPD,or use cable of above 50 m in length when the capacitance is higher than 10 μF.In case of resistive-capacitive load with resistance lower than impedance of cable and capacitance more than 10 μF,a cable of more than 50 m in length may be used.In case of unknown load property,direct connection without cable can be applied.If it is not possible,direct connection with a cable of 15 m in length with additional SPD shall be applied,with proper coordination of capacity between two SPD.