Electric arc furnaces (EAFs) are among the most significant sources of voltage fluctuations in power systems due to their dynamic and unpredictable load characteristics. One of the defining features of EAF operation is the frequent occurrence of short circuits between the electrode and the metal scrap, followed by an arc extinction when molten material falls from the electrode. This random transition between short-circuit and open-circuit conditions results in severe current variations. As the fluctuating current flows through the power network, it causes corresponding voltage fluctuations at the Point of Common Coupling (PCC), which can lead to noticeable light flicker.
Large and medium-sized EAFs typically have a more pronounced impact on the grid, prompting careful consideration of electrical wiring and reactive power compensation. However, small-capacity EAFs often receive less attention. Without proper reactive power compensation, especially when the power supply system is weak, these devices can cause significant voltage fluctuations and flicker at the PCC, potentially disrupting the operation of other connected loads. In one case involving a mechanical plant with a 1.5-ton EAF, the voltage flicker was found to exceed acceptable limits, leading to operational challenges and reduced productivity.
To address this issue, the paper investigates the voltage fluctuations and flicker caused by a small EAF and proposes practical mitigation strategies. The short-circuit voltage drop method is used to assess the severity of the flicker, based on three typical operating conditions: open circuit, short circuit, and rated operation. By analyzing the voltage levels at the PCC, it is possible to determine whether the EAF can be safely connected to the grid.
In the specific case studied, the EAF was directly connected to the factory bus without any reactive power compensation. The reactor on the high-voltage side was damaged, further exacerbating the problem. As a result, the flicker level reached 3.04%, far exceeding the national standard of 0.6% for general lighting. This situation forced the factory to schedule EAF operations during off-peak hours, negatively affecting both staff schedules and production efficiency.
To mitigate these issues, several measures can be implemented. On the power supply side, isolating the EAF from other loads and using dedicated transformers or lines can increase the short-circuit capacity, thereby reducing voltage fluctuations. In the EAF workshop, installing reactors can help stabilize the arc and reduce voltage variation, although care must be taken to avoid excessive voltage drops that could lower efficiency. Additionally, static var compensators (SVCs), such as Thyristor Switched Capacitors (TSCs) or Self-Saturated Reactors (SRs), can be used to compensate for rapid reactive power changes.
For small EAFs, while advanced solutions like thyristor-controlled reactors or active filters are available, they may not be cost-effective. Instead, simple and economical options such as reactors and static capacitors can provide sufficient improvement. Based on the analysis, it is recommended that the reactor be repaired and reinstalled, and that a static compensator be considered if the power system is insufficiently strong.
In conclusion, voltage fluctuations and flicker from small EAFs can significantly affect the stability of the power grid if not properly managed. Enterprises utilizing such equipment should implement appropriate measures to ensure reliable and efficient operation.
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