Flicker (electrical engineering)
As Flicker be electric voltage fluctuations in electricity networks referred to which a visually perceptible luminance variation in unregulated electric bulbs such as fluorescent and incandescent lead. With electronically controlled light sources, such as LED light sources or compact fluorescent lamps , flicker cannot be visually perceived due to the control. Flicker is one of several criteria for assessing the voltage quality in public power supply networks and the evaluation of network perturbations from consumers in such networks.
The phenomenon of flicker was determined empirically, and as a result the flicker curve was developed and specified in the IEEE standard 519. This curve is used to determine whether flicker in incandescent lamps is not noticeable, noticeable but not disturbing or perceived as visually disturbing. The flicker curve describes the fact that not every voltage fluctuation in the power grid and the resulting change in luminance in unregulated light sources is subjectively perceived or perceived as annoying. The subjective thresholds for flicker are related, among other things, to the frequency and strength of the voltage fluctuations.
Development of flicker
The operating voltage in the public power supply network is subject to fluctuations over time, which are caused, for example, by periodic load fluctuations from larger consumers and the voltage drop on lines. Further sources are intermodulations in the area of the harmonics of the network frequency , which are triggered by the distortion reactive power of non-linear consumers.
Measurement of flicker
For the reproducible measurement of the flicker emission from devices, a measuring circuit, as shown in the adjacent figure, is necessary in order to reflect the average network impedance. Basically, according to the standard, flicker measurements require a network with a known, low and temporally constant source impedance and without variations in the open circuit voltage.
The requirements for the flicker measuring devices are specified in DIN EN 61000-4-15. The flicker meter is divided into five functional blocks. Block 1 is a voltage control loop. In blocks 2 to 4, the 230 V / 60 W incandescent lamp (reference lamp) and the human perception system (eye-brain model) are simulated. Block 5 is a statistics block for determining the strength of the flicker using the Pst method.
The instantaneous value of the measured flicker is given in "perceptibility units" P (perceptibility unit). Weighted averaging over different periods of time gives the actually important values Pst (short term) and Plt (long term).
- Limit values
For Pst and Plt, limit values are defined in DIN EN 61000-3-3 and DIN EN 61000-3-11:
- Pst of the EUT must not exceed the value of 1.0.
- Plt of the EUT must not exceed the value of 0.65.
- Pst of the source must not exceed the value of 0.4.
literature
- DIN EN 61000-3-3: 1994 + A1: 2001 + A2: 2005: Limits - Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply networks for devices with a rated current of ≤ 16 A that are not subject to any special connection requirements
- DIN EN 61000-3-11: 2000: Limit values - Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply networks - Devices and facilities with a rated current of ≤ 75 A that are subject to special connection conditions
- DIN EN 61000-4-15: 1998 + A1: 2003: Test and measurement methods - Flicker meter - Function description and design specification
- Wilhelm Mombauer: EMC measurement of voltage fluctuations and flicker with the IEC flicker meter (VDE series of publications Volume 109), ISBN 3-8007-2525-8
- Wilhelm Mombauer: Flicker in power supply networks (VDE series of publications Volume 110), ISBN 3-8007-2805-2
- Wilhelm Mombauer: Network perturbations from low-voltage devices, voltage fluctuations and flicker (VDE series of publications Volume 111), ISBN 3-8007-2806-0
Web links
Individual evidence
- ↑ IEEE519-2014 - IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems. Institute of Electrical and Electronics Engineers (IEEE), 2014, accessed on February 14, 2017 (Chapter 10.4).