EN61000-3-3:2013 Limitation of voltage changes, voltage fluctuations and flicker


What is Flicker?

The formal definition of flicker is the “impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time. Flicker can be considered as a symptom, resulting from the modulation of a load and its effect on its own terminal voltage. Whilst connected to a voltage source with finite impedance, any load modulation will cause voltage fluctuations on the supply line.

EN61000-3-3:2013 is primarily concerned with the limitation of such fluctuations and subsequent flicker upon public low-voltage systems. The Flicker standard addresses the problem where certain products may intermittently take power from the mains in such a way as to cause the voltage to dip, thus causing any lighting in the vicinity to flicker. Flicker occurring at a frequency in the range 5Hz – 15Hz is well known to be unpleasant and may cause epileptic fits in some who are susceptible. So this standard measures the current variation over time (up to 2 hours) and uses statistical techniques to derive a measure of flicker severity. The standard states that this measurement is not required ‘if the product is unlikely to cause flicker’ (which applies to most products). Note that this standard also has a requirement to measure ‘in-rush’ current…… and this does apply to all products that are connected to the mains.

The limits specified in EN61000-3-3:2013 are applicable to voltage fluctuations and flicker measured at the supply terminals of the device under test. This is an important point, as any current carrying component with measurable impedance, there will be a voltage drop across it. A current carrying cable connecting the AC Source to the equipment under test is no different and if the test equipment is placed at the output terminals it is important to remember that the overall impedance of the test circuit will include the interconnecting cabling. For voltage changes caused by manual switching, equipment is deemed to comply without further testing providing the maximum input current (including inrush current) evaluated over each 10ms window between zero crossings does not exceed 20A. Further to this, the supply current after inrush must be within 1.5A

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