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In the realm of electrical systems, power quality plays a crucial role in ensuring the efficient and reliable operation of various devices and equipment. Two significant factors that can impact power quality are flicker and voltage fluctuations. Let's delve into these phenomena, their effects, measurement techniques, and mitigation strategies.
Flicker refers to the perceived fluctuation in light intensity caused by voltage fluctuations in electrical networks. These fluctuations typically occur within a range of ±10% of the nominal voltage and can happen at irregular intervals with varying durations and intensities. The frequency of these variations, measured in hertz (Hz), determines the rapidity of the flickering effect.
Voltage fluctuations are often caused by rapidly changing loads in the electrical network. They may affect the performance and lifespan of sensitive equipment and can be visually discomforting, especially in industries that rely heavily on precise lighting conditions or use sensitive devices.
Any load exhibiting significant current variations can cause voltage fluctuations. Arc furnaces are the most common cause. Ball mills in the cement and mining industry, car shredders and rock crushers are also other examples that we have seen in the different industries so far. Below are other sources:
- Low-frequency fluorescent lights: 100 Hz
- Amplitude-modulated flickering light: 20-75 Hz
- Light-emitting diodes (LEDs): Up to 200 Hz
- Computer monitors: 70-110 Hz
The international electro-technical standard IEC 61000-4-15 outlines specifications for flicker measurement equipment. A flicker meter consists of multiple functional blocks designed to replicate the characteristics of a 230V/60W incandescent lamp (the reference lamp) and the human perception system.
Flicker assessment involves calculating two key values:
1. Perceptibility Short Term (PST): Calculated over a 10-minute observation interval
2. Long-term flicker (PLT): Calculated as the cubic mean of multiple PST values over a two-hour period
A PST value of 1.0 indicates a level at which 50% of test subjects perceive the flicker as noticeable and irritating.
Two main factors influence flicker levels:
1. Voltage Variation (V): The magnitude of voltage fluctuations within a given time period
2. Number of Switches (r): The frequency or rate at which voltage fluctuations occur
Both factors contribute to the overall flicker level, with voltage variation determining the magnitude of fluctuations and the number of switches influencing the frequency and pattern of the flicker.
Rapid voltage changes can occur due to the switch-on phenomenon, where voltage experiences sudden changes. In normal situations, the steady-state voltage variation (ΔUss) is limited to a maximum of 5% of the nominal voltage (Un)..
Voltage variations can be described by the equation:
Δ𝑈 = 𝐼 · 𝑅 · cos𝜙 + 𝐼 · 𝑋 · sin𝜙
Where:
- Δ𝑈: Voltage variation
- 𝐼: Current flowing through the system
- 𝑅: Resistance in the system
- 𝑋: Reactance in the system
- cos𝜙: Power factor (ratio of real power to apparent power)
- sin𝜙: Reactive power factor (ratio of reactive power to apparent power)
This equation helps in understanding and predicting voltage fluctuations due to both active and reactive power components.
The Importance of Continuous Waveform Power Quality Recording
Continuous waveform recording is crucial for accurately capturing and analyzing voltage variations. It allows for:
1. Determining the flicker visibility borderline
2. Assessing instantaneous flicker levels
3. Evaluating intensity changes and their rate of occurrence
4. Conducting statistical evaluations to understand the probability of flicker becoming irritating or hazardous
Power quality analyzers with continuous waveform recording capabilities are essential for accurate flicker quantification and perception assessment.
Mitigating Flickers and Voltage Fluctuations
To address flicker and voltage fluctuation issues, power conditioning systems can be employed. These systems, especially those utilizing detuned filtering technology, enhance voltage stability by mitigating rapid voltage changes associated with active and reactive power fluctuations.
By implementing these compensation systems, industries can maintain a more reliable electrical environment, reducing the impact of flicker on both equipment and human operators.
understanding and addressing power line flicker and voltage fluctuations are crucial for maintaining high power quality. By employing proper measurement techniques and implementing mitigation strategies, industries can ensure a stable and reliable electrical environment, leading to improved equipment performance and operator comfort.
Our power conditioning units can improve your operational efficiency by improving the power quality. Please feel free to contact us for further discussions on your facility’s specific needs and we will assess how we can provide you with savings and power quality enhancements.
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