Electric arc furnaces are among the most significant sources of voltage fluctuations in power systems, particularly due to their dynamic and unpredictable load characteristics. A key feature of their operation is the frequent occurrence of short circuits between the electrode and metal scrap, followed by the extinction of the arc when molten material falls from the electrode. This random transition between short-circuit and open-circuit conditions leads to severe current variations, which in turn cause voltage fluctuations at the point of common coupling (PCC). Measured data shows that these voltage fluctuations take the form of amplitude-modulated waves with a carrier frequency equal to the power system frequency, typically around 50 Hz. The modulation frequency is approximately 215 Hz, resulting in noticeable flicker in lighting systems.
Medium and large electric arc furnaces have a more pronounced impact on the grid, prompting careful attention to electrical design and reactive power compensation. However, small-capacity electric arc furnaces are often overlooked, especially when they lack reactive power compensation equipment. In such cases, if the power supply system is weak, these furnaces can cause significant voltage fluctuations and flicker at the PCC, potentially disrupting the operation of other connected loads. For example, in a mechanical factory, an electric arc furnace with a capacity of only 1.5 T was found to generate a flicker level of 3.04%, far exceeding the national standard of 0.6% for general lighting. This has led to serious issues, including lighting flickering and intermittent operation of plant loads during the melting phase.
To address this problem, the paper presents a case study of the factory's electric arc furnace and proposes practical measures to mitigate voltage fluctuations and flicker. One of the primary methods used to assess the severity of voltage fluctuations is the short-circuit voltage drop method, which involves analyzing the voltage levels at the PCC under three operating conditions: open circuit, short circuit, and rated operation. Based on these measurements, it is possible to determine whether the furnace can be safely connected to the grid.
In terms of mitigation strategies, several approaches can be taken. First, improving the power supply system by isolating the electric arc furnace from other loads, using dedicated lines or transformers, and increasing the voltage level can help reduce the impact on the grid. Second, within the furnace workshop, installing series reactors can stabilize the arc and reduce voltage fluctuations, although this may slightly lower the furnace's efficiency. Additionally, reactive power compensation devices such as static var compensators (SVCs) or thyristor-controlled capacitors (TSCs) can be employed to manage the rapid changes in reactive power caused by the furnace’s operation.
For smaller installations, static capacitors or self-saturated reactor-based compensators are viable options, though they come with limitations in terms of flexibility and cost. More advanced solutions like thyristor-controlled reactors (TCRs) or active filters are also available but may not be economically feasible for small-scale operations.
In conclusion, the voltage fluctuations and flicker caused by small electric arc furnaces should not be ignored, especially when improper wiring and no reactive power compensation are present. These issues can significantly affect the stability of the power grid and the performance of other connected loads. Therefore, companies utilizing small electric arc furnaces must implement appropriate mitigation measures to ensure safe and efficient operation.
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