Rosemount罗斯蒙特3051GP2A2B21AB4HR5
1中性线断路的危害
在供电系统运行过程中，中性线由于热效应、机械力、接头氧化或外力影响等因素，均可发生断路故障。中性线一旦断路，由于没有中性线导通不平衡电流，负荷中性点将产生严重位移，造成三相供电电压严重不平衡。在三相四线不平衡供电系统中，中性线断线，负荷中性点将向负荷大的那相位移，负荷大的那相电压降低了，而负荷小的相电压升高了，三相负荷不平衡程度愈严重，负荷中性点位移量就越大。负荷端相电压对称性被破坏，出现了不同程度的不平衡。我们所遇到的中性线断路事故中，负荷大的那相电压可降低30～60V，使灯泡发红，日光灯和家用电器起动不起来;而负荷小的那相则相电压可升高到300V左右，大大超过了家用电器的额定电压，此时若熔断器熔体没有熔断，将使家用电器被烧毁，造成不应有的损失。
若在中性线断线时发生了相线对地短路，则中性点位移会更大。在低压接中性线保护系统中若发生中性线断路事故，就等于电器设备失去了保安措施，电器设备一旦漏电，人体触及家用电器外壳将会造成人身触电，起不到应有的保护作用。由此可见在低压供电系统中中性线断路危害是十分严重的，应该引起人们足够的重视。
2中性线连接注意事项
(1)不同金属、不同规格、不同绞向导线，严禁在档距内连接。
(2)在一个档距内，每根中性线不应超过一个接头。铝绞线连接应采用压接法。
(3)铝绞线弓子线连接或弓子线与主导线连接应用并沟线夹，线夹规格应与导线截面积相对应。
(4)铜、铝导线连接应用铜铝线夹，线夹规格应与导线截面积相符。
(5)入配电箱的主线路需要分支时，不宜将多根分支中性线捆成一体，应采用端子排进行分接。端子排应与中性线所用材料相同，不同时，应采用铜铝过渡措施。
3防止中性线断路的技术措施
为了防止中性线断路并保证中性线可靠运行，应在技术采用多种措施使中性线安全可靠。
(1)在三相四线低压供电系统中，应将三相用电负荷调整得尽可能平衡，不致在正常运行时，中性线中有较大的不平衡电流通过。
(2)三相四线低压供电系统中的中性线截面积应为相线的截面积一半以上;单相供电回路，中性线截面积应与相线截面积相同。在低压供电系统中性线的载流能力不得小于供电回路中单相最大用电设备的额定电流，在室外架空线铝质中性线不得小于16mm2，铜线不得小于10mm2，并应采用多股导线。
(3)中性线应重复接地。为了确保接中性线保护的安全可靠和减少中性线断路后的负荷中性点位移量，低压配电线路在干线或分支终端处以及沿线每隔1km处，中性线应重复接地。低压进户线在进入大型建筑处，应将中性线重复接地，每一重复接地装置的接地电阻不应大于10Ω。
(4)加强低压供电端的巡视与维护。每次巡视应注意沿线有无危及线路安全运行的树木、天线、施工机械等;线路上有无搭落的树枝、风筝、铁丝等，导线上有无断股、烧伤，接头是否变色;进户线和配电箱中性线接头是否有过热现象，是否有断线：如发现有上述情况应采取有效措施加以修理。供电线路停电检修时，就中性线而言，应把重点放在接头处。
(5)在三相四线低压供电系统中中性线严禁装设熔断器或单独的开关装置，以防中性线在此处断路。中性线的重复接地不是可有可无，而是保证安全运行非常重要的技术措施。
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