公寓开发商无法获得必要的运营许可证，因为两部大楼电梯无法使用大楼的紧急备用发电机运行. 初步诊断为地下室主服务入口与十楼电机房之间电压降过大. 相关技术人员花费了大量时间和金钱试图解决这个被错误诊断的假定问题. 尝试过的解决方案包括: 变压器抽头的调整 +5 百分之, 将变压器更换为阻抗较低的型号, 以及电子分接开关调节器的安装. 一 450 甚至还引入了千瓦应急发电机进行测试，看看是否有必要更换现有的 175 千瓦单位.
All of these attempts had some limited success, but none offered an acceptable solution.
A consultant used a power monitor to evaluate the quality of the voltage and current supplied to the elevator motor. 图 1 shows the current swell during motor startup, 而 图 2 reveals the effect of the current demand on the voltage.
Using the power monitor was essential to uncover the real problem. Two factors became evident: 第一, the true RMS voltage reported by the monitor showed that the values measured by the less accurate average reading DVM’s were misleading. The actual voltage drop was not as severe as first indicated. 第二, analysis of the current and voltage waveforms (both visually and using harmonic analysis) showed that harmonic distortion, not low voltage, was the real source of the problem. 电压波形中的第五次和第七次谐波的水平是由于发电机绕组响应电梯电机控制器的非线性电流需求而产生的电抗造成的. 电机控制器中的电路对这些频率下的谐波失真很敏感, 将它们误认为是相位旋转误差. 该解决方案是通过花费几美元更换该电路来实现的.
源:
Dranetz
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