Some people in the installation of photovoltaic system, will hold a "even if the power grid power failure, if there is the sun, their home can also be used for electricity" mentality, the reality is that when the power grid power failure, their home photovoltaic system will only bask in the sun, will also stop running, the same can not be used for electricity.
The reason for this phenomenon is that the grid-connected inverter must be equipped with anti-island device. When the grid voltage is zero, the inverter will stop working. Anti-island device is a necessary device for all photovoltaic grid-connected inverters. The reason for doing so is mainly for the safety of the power grid. When the power grid fails, maintenance personnel are ready to overhaul the circuit. Therefore, the national standard provides that the photovoltaic grid-connected inverter must have the detection and control function of island effect.
The detection methods of island effect include passive detection and active detection. The passive detection method detects the amplitude of voltage and current at the output end of the grid-connected inverter. The inverter does not add interference signals to the power grid.
This way does not cause power grid pollution, and there will be no energy loss; And active detection refers to the grid inverter, timing, actively exert some disturbance signal of power grids, such as frequency and phase movement, due to the power grid can be as an infinity of voltage source, a power grid when the interfering signal will be absorbed by power grid, power grid in the event of power failure, the jamming signal will form a positive feedback, will eventually form frequency or voltage levels, This can be used to determine whether the island effect has occurred.
At present, the anti-islanding function technology of grid-connected inverter is fully mature, so there is no need to purchase anti-islanding device in household grid-connected projects. Because in some places, not only photovoltaic grid-connected inverter is connected to the grid, but also distributed power supply such as wind power generation, biomass power generation and energy storage system, etc.
According to the regulations of State Grid Corporation of China, when the power grid access capacity exceeds 25% of the rated capacity of the substation, the low-voltage side knife fusion main switch of the substation shall be transformed into the low-voltage main switch, and an anti-island device shall be installed at the low-voltage bus of the substation; The low-voltage master switch shall have the function of operating latching between it and the anti-island device, and the contact switch shall also have the function of operating latching between it and the anti-island device when there is contact between busbars.
