Abstract: When reading a book at night, the lights suddenly flashed? It’s a flickering! So what is a flicker? Why is there a flicker? Below we first rationally understand the flicker from the theoretical aspect, and then through a practical case to emotionally feel the existence of flicker in real life.
First, the definition of flicker
Flicker is the instability of the human eye caused by the change in brightness of the light. That is, people's discomfort with changes in brightness. IEC 61000-4-15 specifies the "lamp-eye-brain" model to measure how most people are affected by flashing incandescent lamps.
figure 1
Second, the impact of flicker
Most of the flicker is caused by changes in the brightness of the grid due to grid voltage fluctuations. If the voltage amplitude changes by 0.5% and changes 6.25 times per second, it will cause obvious annoyance. Voltage fluctuations often cause many appliances to fail to function properly. Generally, incandescent lamps are much more sensitive to voltage fluctuations than fluorescent lamps, televisions, etc., and incandescent lamps are widely used early. When the fluctuation of the voltage is not enough to change the brightness of the incandescent lamp, the device such as the fluorescent lamp or the television set does not work abnormally. Therefore, the incandescent lamp operating conditions are usually used to determine whether the voltage fluctuation value can be accepted. The term flicker is a broad description of flicker, which can be understood as the perception of people's changes in the brightness of incandescent lamps, including the effects and hazards of voltage fluctuations on electrical equipment. But flicker cannot be replaced by voltage fluctuations, because flicker is the subjective perception of people's fluctuations in lighting.
High-power electrical appliances such as electric arc furnaces and rolling mills cause voltage fluctuations in the power grid during operation. When the motor starts, it will generate an inrush current. When an inrush current occurs, the impedance of the utility distribution network will increase the partial pressure, which will cause the voltage to drop. The voltage drop will cause the brightness of the incandescent lamp to drop. Even with small voltage variations, the brightness change is large because the brightness is positively correlated with the square of the voltage. as shown in picture 2. For example, if the voltage is reduced by 10%, the brightness will be reduced by 34%.
figure 2
Let's share a practical case with you.
Background: In a coffee shop, guests complain that the lights are flashing. This is a typical flicker phenomenon. You can also recall whether there have been similar phenomena around you.
Measurement: After the power supply company detected, it was found that there was a voltage fluctuation of 1~2V, and the flicker value did not exceed the standard.
Analysis: The coffee shop installed a new electric fryer in the summer of that year. At that time, the daylight was strong, no one noticed the lighting problem, the feeder to the distribution cabinet was longer, the cable was not thick enough, and the line impedance was large.
Solution: It is relatively simple to solve the problem after solving the problem. After using a single cable for the high-power load (electric fryer), the problem is solved, as shown in Figure 3 and Figure 4.
The hazards associated with flicker are widespread. The question is coming. How can we monitor the flicker to better reduce its harm? The power quality analyzer provided by Zhou Ligong Zhiyuan Electronics is a professional measurement tool for measuring, recording and analyzing power quality problems in the power grid. It can not only measure active power, reactive power, apparent power, power factor, displacement power factor, but also capture common power quality problems such as harmonics, voltage fluctuations, flicker, power and three-phase imbalance at the fault site. Performance assessment and governance decisions for power quality for smart grids, new energy, electrified railways and large industrial users.
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