Load characteristics
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In many building power distribution systems, elevators, air conditioners and energy-saving lamps are common harmonic loads, whereas for large-scale theater / gymnasiums, there are harmonic sources in general building distribution systems In addition, there are some "unique" harmonic sources, such as: SCR dimming system, large LED equipment. SCR dimming system is the mainstream theater dimmer stage, which is actually a single-phase phase-controlled AC voltage regulator system, through the control of SCR conduction angle to achieve the purpose of control voltage. Thyristor dimming system in operation will produce a large number of third harmonic. Harmonic not only causes the inefficiency of the power equipment of the power distribution system, but also causes the light stroboscopic light to cause noise or even malfunction in the weak circuits such as communications and cable television.
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Case show
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Some big theater lights circuit SCR dimming system applied. In the actual operation process, according to the scene plot changes, the lighting will have a greater change, SCR dimming system current RMS and harmonic content will have a corresponding change. When the current is 100A, the current harmonic distortion rate is 60.5%. When the current is 440A, the total current harmonic distortion rate is 50%. At the current of 530A, the total current harmonic distortion rate is 17.9%.
◇ management measures: the application of two 90A APF harmonic control.
◇ Governance effect: APF put into use greatly improved the current waveform distortion, zero line harmonic current is greatly reduced, the filtering effect is obvious.
