Background Fire risk: Fire is the biggest economic loss of photovoltaic power plants. If it is installed on the roof of a factory or residential building, it can easily endanger personal safety. In general centralized photovoltaic systems, there are tens of meters of high-voltage DC lines between 600V and 1000V between the photovoltaic module array and the inverter, which can be regarded as a potential safety hazard for people and buildings. There are many factors causing fire accidents in photovoltaic power stations. According to statistics, more than 80% of fire accidents in photovoltaic power stations are caused by DC side faults, and DC arcing is the main reason.
2. Reasons In the entire photovoltaic system, the DC side voltage is usually as high as 600-1000V. DC arcing can easily occur due to loose joints of photovoltaic module joints, poor contact, moisture in the wires, ruptured insulation, etc. DC arcing will cause the temperature of the contact part to rise sharply. Continuous arcing will produce a high temperature of 3000-7000℃, accompanied by high temperature carbonization of surrounding devices. In the least case, fuses and cables will be blown. In the worst case, components and equipment will be burned and cause fires. Currently, UL and NEC safety regulations have mandatory requirements for arc detection functions for DC systems above 80V. Since a fire in a photovoltaic system cannot be extinguished directly with water, early warning and prevention are very important. Especially for color steel tile roofs, it is difficult for maintenance personnel to check fault points and hidden dangers, so it is necessary to install an inverter with arc detection function. Very necessary.
3. Solutions In addition to high-voltage direct current easily causing fires, it is also difficult to put out fires when a fire occurs. According to the national standard GB/T18379 DC voltage specification for building electrical equipment, for home rooftop photovoltaic systems, system solutions with a DC side voltage not exceeding 120V are preferred. For photovoltaic systems with a DC side voltage exceeding 120V, it is recommended to install protection devices such as arc fault interrupters (AFCI) and DC switches; if the DC cable from the photovoltaic module to the inverter exceeds 1.5 meters, it is recommended to add a quick shutdown device, or use Optimizer, so that when a fire occurs, the high-voltage direct current can be cut off in time to extinguish the fire. AFCI: (Arc-Fault Circuit-Interrupter) is a protection device that disconnects the power circuit before the arc fault develops into a fire or a short circuit occurs by identifying the arc fault characteristic signal in the circuit. As a circuit protection device, AFCI's main function is to prevent fires caused by fault arcs and can effectively detect loose screws and poor contacts in the DC loop. At the same time, it has the ability to detect and distinguish between normal arcs and fault arcs generated by the inverter when starting, stopping or switching, and promptly cuts off the circuit after detecting fault arcs.
In addition, AFCI has the following characteristics: 1. It has effective DC arc identification capability, allowing the maximum DC current to reach 60A; 2. It has a friendly interface and can be remotely connected to control circuit breakers or connectors; 3. It has RS232 to 485 communication function and can monitor the module status in real time; 4. LED and buzzer can be used to quickly identify the working status of the module and provide sound and light alarms; 5. Functional modularization, easy to transplant to various series of products
In terms of arc fault protection of photovoltaic systems, we give full play to the role of photovoltaic clean energy and develop special AFCI for photovoltaic DC systems, involving series DC arc fault protection of photovoltaic inverters, combiner boxes, and photovoltaic battery modules. To meet the new requirements of smart grid for switching appliances and realize the communication and networking of AFCI, intelligence and related bus technology, communication and networking and other technologies will play a greater role. In terms of AFCI product serialization and standardization, AFCI's serialization, standardization, and accessory modularization will greatly increase its application scope in terminal power distribution.
