The quality of the electric energy is the quality of the electric energy in the power system. The ideal electric energy should be a perfectly symmetrical sine wave. Some factors cause the waveform to deviate from the symmetrical sinusoid, resulting in power quality problems. Power quality problems can be defined as deviations of voltages, currents, or frequencies that cause electrical equipment failure or normal operation, including frequency deviations, voltage deviations, voltage fluctuations and flickers, three-phase unbalance, transient or transient overvoltages, waveform distortions (harmonics), voltage sags, interrupts, and sags. Power supply continuity and so on.
In modern power systems, voltage sag, temporary rise and short-time interruption, harmonic distortion caused by harmonics have become the most important power quality problems.
Improvement measures
（1） Improve the power factor and make the reactive power balance on the spot.
（2） Reasonable selection of power supply radius.
（3） The cross section of the wire of the power supply system is selected reasonably.
（4） Reasonable distribution of transformer and distribution equipment to prevent overload operation.
（5） Appropriate voltage regulation measures should be adopted, such as series compensation, transformer installed with on load voltage regulating device, installing synchronous phase adjusting camera or electrostatic capacitor.
