The photovoltaic (PV) power generation industry has developed rapidly in China, promoting the development of many other sectors. Anti-islanding and anti-peaking devices are explicitly required by the State Grid Corporation of China for distributed PV power generation. Therefore, to meet the requirements of the local power supply bureau when constructing a PV power station, grid connection conditions must be considered, including anti-islanding and anti-peaking devices. So, which of these two is more suitable for a PV power station?
In photovoltaic (PV) power plants, there's a phenomenon called "islanding operation," which means the PV power plant operates independently of the grid. This is generally not permitted. For larger PV power plants with grid connection voltage levels of 10kV or higher, these types of power plants often use anti-islanding protection devices, which are secondary equipment of microprocessor-based protection devices. Anti-islanding, on the other hand, is a distribution cabinet, and its operating principle is completely different from anti-islanding. For users building PV power plants, several grid connection issues they consider include: how many PV units can be connected to each substation? What technical requirements must the PV connection meet? The State Grid has clear regulations on these. For PV connection, without anti-islanding devices, the PV power plant is only allowed to connect up to 25% of its PV capacity. If anti-islanding cabinets are installed, then the PV capacity can be 50% or 80%, the specific amount determined by the local power supply department. To illustrate simply, if a transformer has a capacity of 100kW, then 80% of its capacity would be 80kW. This transformer is a public transformer. If each household has a 5kW photovoltaic power station connected to it, that would be 16 households. Each household can then connect to the grid independently via a grid-connection cabinet. Generally, grid-connection cabinets require isolating switches, circuit breakers, etc. Some areas require anti-islanding protection, meaning each household would need an anti-islanding protection device. For 5kW photovoltaic power generation, the capacity is relatively small. Installing anti-islanding protection devices on every grid-connection cabinet would significantly increase costs and maintenance. Adding an anti-islanding device solves the grid connection problem for all 16 households, making anti-islanding control cabinets quite useful for small rooftop photovoltaic systems. Its protection principle is not based on detecting a fault and tripping before islanding operation. Instead, when islanding has already occurred, the RCX-9390K load controller and anti-islanding switch are used to control the input of disturbing loads, thereby forcing the inverter to stop working.
Inverters inherently possess anti-islanding protection, automatically tripping and stopping operation when grid anomalies occur, provided the inverter is fault-free and properly commissioned. Power supply departments require grid-connected switches to have anti-islanding protection as an additional layer of protection. Anti-islanding, on the other hand, involves measures taken when grid isolation occurs; although a low-probability event, its impact can be significant if it does occur.
