Flicker refers to the perceived fluctuation in light intensity that occurs when voltage fluctuations impact lighting systems. It is often caused by rapidly changing loads in the electrical network. It can be visually discomforting and can affect the performance and lifespan of sensitive equipment, especially in industries that rely heavily on precise lighting conditions or use sensitive equipment.
Flicker is characterized by voltage variation typically within the range of ±10%. These voltage fluctuations occur multiple times over a specific period, resulting in perceptible changes in light output. The variations can happen at irregular intervals and may differ in duration and intensity. The frequency of the variation, often measured in cycles per second or hertz (Hz), determines the rapidity of the flickering effect. A higher frequency of voltage fluctuations can lead to more pronounced flicker, which can be particularly noticeable in lighting systems where rapid changes in brightness can be visually disturbing.
Headaches/Visual Effects
Neurological Effects
Seizures in photosensitive epileptics
Unperceived neurological effects
Unperceived retinal effects
Visual Effects
Low frequency fluorescent
Amplitude-moderated flickering light
Various
Light-emitting diode
Various
Computer monitor
100
20-75
Various
Up to 200 Hz
76-162
70-110
Source: R. Inger el al. PLoS One, 2014
In accordance with the international electro-technical standard IEC 61000-4-15, the specifications for flicker measurement equipment are meticulously outlined. This standard establishes the framework for evaluating voltage flickering, ensuring a consistent and universally accepted method.
A flicker meter comprises multiple functional blocks designed to replicate the characteristics of a 230V/60W incandescent lamp (referred to as the reference lamp) and the intricate dynamics of the human perception system, modeled on the eye-brain interface.
The assessment of flicker involves deriving momentary values, from which Perceptibility Short Term (PST) is calculated using a statistical process over a standardized 10-minute observation interval. Simultaneously, the long-term flicker (PLT) is calculated as the cubic mean of multiple PST values over a standardized two-hour period. The calculation and scaling algorithm for the perceptibility value are intentionally crafted. A PST value of 1.0 is strategically aligned to a level at which 50% of test subjects perceive the flicker to be both noticeable and irritating. This ensures that the measurement is not only objective but also reflective of the human experience with flickering.
As seen in the equations for PLT and PST, both the voltage variation and the number of switches (denoted as “r”) have an impact on the level of flicker. Voltage Variation (V): The voltage variation, expressed as a percentage, represents the magnitude of the voltage fluctuations within a given time period. A higher voltage variation can result in more significant effects, as the changes in voltage levels have a more noticeable impact on the lighting system. Number of Switches (r): The number of switches, denoted as “r” refers to the frequency or rate at which the voltage fluctuations occur. A higher number of switches indicates that the voltage is changing more frequently, potentially leading to a more pronounced flicker effect.
The timing and duration of these switches can impact the perceived flicker characteristics. Both the voltage variation and the number of switches contribute to the overall flicker level. While the voltage variation determines the magnitude of the fluctuations, the number of switches influences the frequency and pattern of the flicker. It is important to consider both aspects when evaluating and mitigating flicker issues in lighting systems to ensure a comfortable and visually stable environment for users.
Rapid voltage changes can occur due to the switch-on phenomenon, where the voltage experiences sudden changes. In normal situations, the ΔUss (Steady State voltage variation) is limited to a maximum of 10% of the nominal voltage (Un). However, in situations without production stops, significant loads, or connections, the ΔUss is further restricted to be smaller than or equal to 3% of Un. Additionally, the ΔUmax (maximum voltage variation) is also constrained to be smaller than or equal to 5% of Un in situations without production stops, big loads, or connections. These limitations ensure stable voltage levels and minimize disruptions, providing a reliable electrical environment for operations.
Rapid voltage changes due to switch-on phenomenon.
The equation Δ𝑈=𝐼⋅𝑅⋅cos𝜙+𝐼⋅𝑋⋅sin𝜙 describes voltage variations that occur due to both active power (real power) and reactive power in an electrical system.
where,
Δ𝑈 represents the voltage variation, which is the difference between the actual voltage and the nominal voltage.
𝐼 represents the current flowing through the system.
𝑅 represents the resistance in the system.
𝑋 represents the reactance in the system.
cos𝜙 represents the power factor, which is the ratio of the real power to the apparent power.
sin𝜙 represents the reactive power factor, which is the ratio of the reactive power to the apparent power.
In simpler terms, this equation suggests that the voltage variation is influenced by the current flowing through the system, the resistance, the reactance, and the power factors (both real and reactive). By considering these factors, the equation helps in understanding and predicting voltage fluctuations that can occur in electrical systems due to both active power and reactive power components.
Understanding the quantification and perception of flicker, as outlined by the IEC 61000-3-7 standard, highlights the importance of continuous waveform recording. By recording the waveform of the electrical system continuously, we can capture and analyze the voltage variations per minute accurately. This data allows us to determine the flicker visibility borderline and assess the instantaneous flicker level. Moreover, continuous waveform recording enables us to evaluate the intensity changes (d) and the rate of changes per minute, which directly impact the perception of flicker. By having access to comprehensive waveform recordings, we can conduct statistical evaluations to understand the probability of flicker becoming irritating or hazardous. Using power quality Analyzers with continuous waveform recording is vital in ensuring accurate flicker quantification and perception assessment, providing the necessary information to address and mitigate flicker-related issues effectively.
In the context of maintaining reliable power quality, addressing flickers and voltage fluctuations becomes imperative. The equations for PLT and PST emphasize the significance of both voltage variation and the number of switches in determining the overall flicker level. This underscores the need for a comprehensive approach that considers not only the magnitude of fluctuations but also their frequency and pattern. Transitioning to reactive power compensation systems, especially those utilizing transient-free thyristor switching technology, further enhances the stability of voltage levels. These systems, by mitigating rapid voltage changes associated with active and reactive power fluctuations, contribute to a reliable electrical environment.
This article was crafted in collaboration with Christan van Dorst, HyTEPS Technical Engineering Manager.
Para abordar estos problemas, Elspec recomendó la instalación de su sistema Equalizer de 690 kVAr. El Equalizer es una solución de calidad de energía de alto rendimiento que utiliza tecnología de conmutación de tiristores para compensar la potencia reactiva, estabilizar el voltaje, filtrar armónicos y reducir las fluctuaciones de voltaje. Este sistema está diseñado
para mejorar la eficiencia energética y la confiabilidad, ofreciendo una solución en tiempo real que estabiliza el voltaje en menos de un ciclo.
Después de instalar el sistema Equalizer, los niveles de voltaje aumentaron de 447 V a 456 V y se estabilizaron en este nivel, solucionando los problemas de bajo voltaje de la planta.
La demanda de energía reactiva se redujo de un promedio de 540 kVAr a casi 186 kVAr, lo que condujo a una reducción significativa de la potencia aparente en aproximadamente 420 kVA.
Además, el factor de potencia mejoró de 0,95 (inductivo) a 0,99 (inductivo), lo que indica un uso más eficiente de la electricidad y una menor presión sobre la infraestructura.
Antes del ecualizador
Después de la ecualización
Antes del ecualizador
Después de la ecualización
Antes del ecualizador
Después de la ecualización
Antes del ecualizador
Después de la ecualización
El sistema Elspec Equalizer solucionó eficazmente los problemas de baja tensión y calidad de la energía de la planta, lo que mejoró la eficiencia energética, redujo las interrupciones operativas y ahorró costos. Al aumentar y estabilizar la tensión, reducir la potencia reactiva y mejorar el factor de potencia, el sistema optimizó el sistema eléctrico de la planta, garantizando la fiabilidad de sus equipos sensibles y evitando costosas averías. Esta solución proporcionó un importante retorno de la inversión, mejorando la eficiencia operativa y reduciendo los costos energéticos en la industria farmacéutica.
