问题描述
该案例涉及对发生在主要被农田和开放空间包围的农村地区的公用变压器故障的调查. 故障发生在电能质量问题很少发生的地方.
无花果. 1 显示系统的单线图. 发生故障的变压器位于中压公用设施馈线的末端. 变压器次级配置为 120/208 在, 3-阶段, 4-有线系统. 负载由三个最终用户组成: 一个小公寓大楼, 奶牛场和高尔夫球场会所.
工程师通过检查连接到同一馈线的其他变压器的问题报告开始了调查. 农村变压器故障研究没有发现任何结果, so he concluded the problem was probably related to the secondary loads. His next step was to question the end-users.
The farm owner said his milk processing equipment was running when the transformer failed. He also said nothing unusual had occurred prior to the failure, and his equipment continued to work normally after the transformer was replaced.
The apartment manager recalled that things were quiet at his facility on the evening the failure occurred. His apartment dwellers were home, cooking dinner and watching TV. Nothing unusual had occurred.
The golf course superintendent said the club had sponsored a large tournament on the day the transformer failed. The club had rented several battery powered golf carts to supplement their normal fleet. 比赛结束后，运营商将所有这些设备都插上电源进行充电. 大约一个小时之后, 俱乐部会所主服务面板的保险丝烧断.
主管更换了保险丝, 不久之后停电了——这一次, 奶牛场因变压器故障.
测量
工程师要求设置一辆高尔夫球车进行充电, 这样他就可以记录电池充电器电流的谐波频谱和波形. 结果如图. 2 和图. 3.
理论与分析
电池充电器都是非线性负载，会产生谐波电流, 由于将交流电转换为直流电的二极管或其他半导体的作用. 波形如图所示. 2 是典型的变压器耦合二极管整流器. Fluke 43B 显示总谐波失真 (总谐波失真) 高尔夫球车充电器的电流为 37 %. 以上数值 20 % 会非常危险, 给出与总变压器负载相关的充电器负载的估计大小.
当谐波电流流入变压器时, 结果是绕组和铁芯叠片中产生额外的热量. 高频涡流造成的损耗是造成这种额外热量的主要原因. 一些额外的谐波加热是由于趋肤效应造成的, 导体的有效横截面在高谐波频率下减小. 变压器可以承受的谐波发热量与总二次负载成反比. 如果大部分负载电流包含谐波，重载变压器可能会过热并发生故障.
以农村变压器为例, 三个最终用户贡献了总负载，并且所有三个用户同时经历了峰值负载. 保险丝熔断的时间和
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