Flickering light and voltage fluctuations Importance, effects and measurement »»Do you have symptoms of dizziness in areas illuminated by artificial light? »»Your electrical and electronic devices turn off or do not work correctly?
Fliker and voltage fluctuations Flicker, otherwise known as the flickering light parameter, is directly related to fluctuations in the supply voltage. This parameter determines the degree of voltage fluctuations in power grids and allows to assess the impact on the human body. Where there are exceeded levels of the flicker specified in the standards, it is required to use mitigation techniques to limit the effects of voltage fluctuations. Voltage fluctuations have the greatest effect on incandescent lighting. Therefore, the importance of the flicker is lower at present because of the more common use of LED lighting, which is more stable and less sensitive to voltage fluctuations. In many countries, the measurement of a flicker is important for energy suppliers who have to meet the power supply parameters specified by the standards. Exceeding the parameters of standards is also related to the application of penalties, which makes flicker control more common.
What are voltage fluctuations and what causes them? Voltage fluctuations can be described as repetitive (periodic) or accidental changes in voltage envelope due to sudden load changes. In Figure 1, the shape of the voltage waveform shows changes, which is evident in the periodic envelope changes (here a sinusoid). In practice, the voltage envelope profile will depend on the type and duration of the load.
Figure 1. Voltage waveform with envelope. There are clear voltage fluctuations.
Loads that can cause voltage fluctuations include: 1. Installations with frequent engine starts 2. Motor drives with cyclical operation 3. Arc welding machines 4. Arc furnaces
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The effects of voltage fluctuations 1. Neurological symptoms in humans under the influence of a flicker. The flickering of light is the result of voltage fluctuations. The influence of flickering of light on the human body is always unfavorable and can cause the appearance of such symptoms as dizziness and even cause an epileptic attack in photosensitive people.
Figure 2. Under the influence of voltage fluctuations, street lighting flickered. One of the passersby, sensitive to flickering light suffers an epileptic seizure. Physician intervention is required.
2. Electronic devices do not work properly Voltage fluctuations can also affect sensitive electronic devices, such as TVs and computers, or affect industrial processes that rely on stable voltage supply.
Figure 3. Under the influence of voltage fluctuations, the picture on the television flickered.
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Figure 4. Under the influence of voltage fluctuations and flickering of lighting. An employee operating a lathe, suffers dizziness while working
3. The spread of voltage fluctuations in the network. Typically, voltage variations caused by loads are not isolated. Distortions in the form of voltage fluctuations will propagate in a weakened form throughout the entire distribution system, which can have an adverse effect on many connected consumers.
Flickering parameters (Flicker) There are two main indicators used to assess flicker in power systems. Short-term flicker, Pst, and long-term flicker, Plt. The IEC 61000-3-3 standard specifies the observation intervals and limit values for Pst and Plt. For low voltage networks, the limit values of these parameters are 1 and 0.65 respectively.
Devices for measuring the flickering of light In connection with the proven harmful effect of voltage fluctuations in power grids and the formation of flickering, standards have been created for measuring devices, allowing the measurement and assessment of the impact on the human body. The requirements for flicker measurement equipment are specified in the international electrotechnical standard IEC 61000-4-15. All Sonel PQM series analyzers have the ability to measure Plt and Pst parameters according to the above-mentioned standard.
Figure 5. Flicker parameters, Pst and Plt chart made in the Sonel Analysis program. The data comes from measurements made with the Sonel PQM meter. The levels of Pst and Plt parameters exceed the limits specified in IEC 61000-3-3.
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A few simple steps to perform the measurement and diagnosis of a flicker: 1. Connect any PQM Sonel analyzer according to the manufacturer’s instructions and set the Pst and Plt measurement mode. 2. After the appropriate measurement time, read the measured values for the Pst and Plt parameters and compare with the limit values. 3. If the level of a parameter exceeds the threshold of IEC 61000-3-3 or other standards, take action to mitigate the fliker.
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