Arc fault, abbreviated as AF, is an electrical phenomenon that may cause fires and significant safety incidents in electrical systems. It occurs when abnormal conduction in a circuit forms a high-temperature arc, which can ignite surrounding combustible materials. Depending on the location of the arc and its relation to the circuit, arc faults can be classified into various types, including series arc faults, parallel arc faults, ground arc faults, and combination arc faults. These faults not only threaten the safe operation of electrical systems but also directly affect personal safety and property protection.

What is the difference between DC arc and AC arc?

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The DC electric arc furnace features a single electrode, with one serving as the negative electrode and the other as the positive electrode. Its power supply system differs from that of the AC arc furnace.

In an alternating current arc furnace, arcing discharge occurs between an analysis gap using alternating current. This is categorized into high-voltage AC arcs and low-voltage AC arcs based on the voltage level.

High-voltage AC arcs, with a working voltage of 2~4kV, can be employed for direct arc ignition. However, due to the complexity of the equipment and the inherent danger in its operation, this method is seldom utilized. It is primarily utilized for qualitative and quantitative analysis of trace elements in various materials, as well as for quantitative analysis of low-content elements in metals and alloys.

In general, the voltage fluctuation and flicker generated by a DC electric arc furnace are half of those produced by an AC electric arc furnace of the same capacity. Compared to traditional AC electric arc furnaces, the key characteristics of DC electric arc furnaces are as follows:

  1. The DC arc does not pass through zero points, eliminating periodic ignition and extinguishing phenomena, thus ensuring arc stability.
  2. There is relatively less fluctuation in current and voltage, resulting in reduced impact on the power grid and prolonged cable life.
  3. Electrode loss is minimized, being 50% less than that of AC electric arc furnaces. However, its growth has been limited by the inability to obtain high power from DC power supplies, hindering its significant advancement.

Importance of Rapid Shutdown in Photovoltaic Systems

Given the severe hazards of DC arcs and the complexity and high difficulty of firefighting in PV plant fires, rapid shutdown technology has emerged as a crucial measure to ensure the safety of PV plants. This technology adheres to relevant standards of the National Electrical Code (NEC) in the United States, aiming to rapidly disconnect the connections between each PV module and adjacent modules to swiftly reduce system voltage to a safe level.

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The significance of module-level rapid shutdown includes:

Immediate response and risk reduction: It can immediately cut off the faulty circuit upon detecting abnormal or fire signals, limiting arc energy and effectively reducing the probability and spread speed of fires.

Ensuring rescue safety: Rapidly reducing voltage to a safe range, such as below 30V, greatly reduces the risk of electric shock for firefighters and other rescue personnel, ensuring their safety in emergency situations.

Adaptation to high voltage systems: With the development of PV technology, system voltages continue to rise, making the application of rapid shutdown technology more urgent. It can adapt to systems of 1000V or even 1500V, ensuring safety and controllability in high-voltage environments. Compliance with regulations: Compliance with international standards such as NEC is an important part of achieving PV system compliance, helping to improve the safety standards of the entire industry and public trust. (13)In summary, arc faults, especially DC arcs, pose significant challenges to the safety of PV plants due to their difficult-to-extinguish nature. Rapid shutdown technology, as an effective preventive and responsive measure, not only swiftly controls arc development and reduces fire risks but also demonstrates irreplaceable value in ensuring rescue operation safety, adapting to upgrades in high-voltage systems, and enhancing safety standards and public trust in the PV industry.