What is AFCI?
AFCI (Arc-Fault Circuit-Interrupter) is an important protective device used in photovoltaic inverters. Photovoltaic inverters are devices that convert the direct current generated by solar panels into alternating current. AFCI plays a crucial role in preventing arc faults in the circuit, ensuring the safety of individuals and electrical equipment.
AFCI is an electrical safety device designed to detect arc faults in a circuit. Arc faults can generate high temperatures and sparks, potentially leading to fires. In photovoltaic inverters, arc faults are typically caused by factors such as wire wear, poor connections, and overheating.
The working principle of AFCI involves detecting arc fault signals in the circuit. When an arc fault signal is detected, the AFCI immediately interrupts the circuit to prevent fire hazards caused by arc faults. AFCI can detect different types of arc faults, including series arc faults and parallel arc faults.
In photovoltaic inverters, AFCI is usually integrated into the inverter itself, providing protection for the entire circuit. The use of AFCI significantly enhances the safety performance of electrical equipment and reduces the occurrence of fire accidents.
Background: Fire hazards pose significant risks to the economic viability of photovoltaic (PV) power plants, and when installed on rooftops of buildings or residences, they can also endanger personal safety. In conventional centralized PV systems, there are high-voltage direct current lines, ranging from 600V to 1000V, extending several tens of meters between PV module arrays and inverters, which can be considered as safety hazards to both individuals and the PV infrastructure. Among the various factors contributing to fire accidents in PV power plants, statistics show that over 80% of these incidents are caused by faults on the direct current side, with arcing being a primary reason.
Reasons: In the entire PV system, the direct current side typically operates at voltages as high as 600-1000V. Loose connections, moisture affecting wires, insulation breakdown, and other factors easily lead to direct current arcing. Direct current arcing can result in a rapid increase in temperature at the contact points. The sustained arcing generates temperatures of 3000-7000°C, causing surrounding components to carbonize. In severe cases, it can lead to the melting of fuses and cables or even the destruction of modules and equipment, ultimately causing fires. Currently, UL and NEC safety regulations mandate the inclusion of arc-fault detection in all direct current systems above 80V. Since water cannot be used to extinguish fires in PV systems, early warning and prevention become crucial. This is especially challenging for maintenance personnel inspecting faults and hazards on roofs with corrugated steel sheets, highlighting the necessity of installing inverters with arc-fault detection capabilities.
Solution: Apart from the inherent fire risks associated with high-voltage direct current, extinguishing fires in PV systems is also challenging. For residential rooftop PV systems, it is recommended to opt for system configurations where the direct current voltage does not exceed 120V. For PV systems with direct current voltages exceeding 120V, it is advisable to install protective devices such as AFCIs (Arc-Fault Circuit-Interrupters) and direct current switches. When the DC cable length between PV modules and inverters exceeds 1.5 meters, the installation of rapid shutdown devices or the utilization of optimizers to promptly disconnect high-voltage direct current during fire incidents is recommended. AFCI is a protection device that detects arc-fault characteristic signals in the circuit and interrupts the power supply circuit before arc faults escalate into fires or short circuits.
- AFCI, as a circuit protection device, plays a crucial role in preventing fires caused by arc faults and effectively detects loose screws and poor contacts in DC loops. Additionally, it has the ability to differentiate between normal arcs generated during inverter startup, shutdown, or switching operations and fault arcs. Once a fault arc is detected, the circuit is promptly disconnected. Other notable features of AFCI include:
- Effective DC arc detection capability, allowing a maximum DC current of up to 60A.
- User-friendly interfaces for remote control of circuit breakers or connectors.
- RS232 to RS485 communication capability for real-time monitoring of module status.
- LED indicators and audible alarms for quick identification of module operation status.
- Modular design for easy integration into various product series.
In terms of arc-fault protection in photovoltaic (PV) systems, there is a significant focus on harnessing the role of PV as a clean energy source. Specialized AFCI solutions have been developed specifically for PV DC systems, addressing the arc-fault protection needs of PV inverters, combiner boxes, and series-connected PV module arrays. These solutions aim to meet the new requirements of smart grids for switchgear, enabling AFCI to be communicable, networked, and intelligent. The utilization of bus technologies and communication networks in AFCI implementation will maximize its effectiveness.
Standardization and product line development are also key aspects in the field of AFCI. The standardization and modularization of AFCI, along with its accessory modules, will greatly enhance its application scope in terminal distribution systems. By standardizing AFCI products and developing accessory modules, the integration of AFCI into various PV system configurations will be streamlined, leading to improved efficiency and wider adoption in the field of PV system arc-fault protection.