In many cases, people complain about problems of power quality in various forms. The power distribution system now bears various loads compared with that 20 years ago, which were not considered in system design. Without obvious characteristics, they may operate in extremely high current and voltage. The cumulative effect will cause overheating, insulation overstress and resonance of electrical cabinet, and even burnout of motor, motor driver and transformer as well as the great harm to electrical components of production core. The harm of harmonic wave is potential in these systems. A small increase may destroy the transformer or other equipment early or gradually.