Several issues of power quality are presented, including harmonics, reactive power, three phase unbalance, large difference between peak load and vale load, voltage disturbance and so on.

第一章简单介绍了目前电网存在的几种问题，包括谐波问题、无功问题、三相不平衡问题、用电峰谷差过大的问题以及电压异常、断电问题等；

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It is important to provide balancing compensation for shock load because of the severe voltage fluctuation and 3-phase unbalance imposed on power supply system by it.

冲击性负荷会引起供电系统严重的电压波动和三相不平衡，对其进行平衡化补偿具有重要的意义。

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