It covers five aspects: supply voltage tolerance, utility harmonic, three-phase voltage unbalance, power system frequency tolerance, voltage fluctuation and flicker.

它涵盖五个方面：供电电压允许偏差、公用电网谐波、三相电压不平衡度、电力系统频率允许偏差、电压允许波动和闪变。

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At present, our country power quality national standard was chiefly stipulated five quotas: frequency, harmonic and voltage deviation, three-phase unbalance and the voltage fluctuation and flicker.

目前我国电能质量国家标准主要规定了五个指标：频率、谐波、电压偏差、三相不平衡及电压波动与闪变。

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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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