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我县某银行办公楼及家属楼共用一台自备变压器,自投运之日起,零线对地电压220Y,致使洗衣机等家用电器外壳带电。经检查发现,变压器低压侧U_(ab)、U_(bc)、U_(ca)均为380V,U_(ao)、U_(bo)、U_(co)均为220V,电压正常。用电笔测试,a相、b相及中相均亮,c相电笔不亮。该变压器中性点未装设接地线(实际接线为IT系统)。拆除低压侧四根线后测量电压及电笔测试,一切均正常。根据以上情况,判断是c相在某处接地。 查找接地点及处理办法:逐个断开办公楼及家属区的总开关检查,发现断开第二幢家属楼总开关后,电笔测试中心点不再带电。合上该开关后逐个断开该幢楼各单元的开关,发现断开第三单元总开关后,电笔测试零线不带电。合上该开关,逐个断开该单元各户开关,当断开二楼西侧用户开关后,故障现象消失。断开该单元总开关,将该用户的两根进户线对调后重新接入。送电后检查,电压测量及电笔测试均正常,家用电器外壳也不再带电。
A bank office building and family building in our county share a self-provided transformer. Since the commissioning date, the zero line voltage 220Y has caused the household appliances such as washing machines to be charged. The inspection found that the low-voltage transformer U_ (ab), U_ (bc), U_ (ca) are 380V, U_ (ao), U_ (bo), U_ (co) are 220V, the voltage is normal. Electric pen test, a phase, b phase and phase are bright, c-phase pen does not light. The transformer neutral grounding point is not installed (the actual connection for the IT system). Remove the low-voltage side of the four lines after measuring voltage and pencil test, everything is normal. According to the above situation, it is judged that the c-phase is grounded somewhere. Find the grounding point and approach: one by one off the office and their families switch the main switch and found that the second switch off the second floor of the building after the pen test center no longer charged. Close the switch one by one after the disconnect the switch of the building units and found that the first switch off the third unit, the pen test zero line is not charged. Close the switch, one by one disconnect the unit switch, when the switch off the west side of the user switch, the fault disappears. Disconnect the unit main switch, the user’s two in-line transfer after re-access. After the power transmission inspection, voltage measurement and pencil test are normal, household appliances are no longer live shell.