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This post was last edited by Jibao NARI – Microcomputer Protection – Islanding Prevention – Zhang on 2020-2-20 at 19:19. The hazards of the islanding effect in photovoltaic power plants: When there is a power outage on the grid side, maintenance workers need to carry out repairs. At that time, the photovoltaic system is still generating electricity and continues to supply power to the grid side, resulting in an islanding effect that poses a serious safety threat to the maintenance workers on the grid side. Similarly, when a fault occurs on the photovoltaic side and maintenance is required, and there is still electricity on the grid side, it is possible for power to flow back from the grid side to this station, which in turn poses a risk to the safety of the maintenance personnel working on the photovoltaic side. If an islanding protection device is installed, when power is lost on either the photovoltaic side or the grid side, the islanding protection microcontroller will promptly send a command to the grid connection switch to trip it, thereby effectively ensuring the safety of maintenance personnel on both sides of the photovoltaic system. The installation of islanding protection devices is primarily based on the following three considerations: 1. Stability – that is, since it is greatly affected by weather and environmental conditions, especially at night when industry and daily life still require electricity, photovoltaic power plants do not generate power during such times. It is largely determined by power supply stability, and it is also a parameter that must be taken into account when designing photovoltaic systems. 2. Considerations to ensure normal power supply operation: In modern power grids, the grid will not collapse and relevant protection mechanisms will not activate when the ratio between power supply capacity and load capacity is 25%. So even when the photovoltaic power plant is not generating electricity, the power grid can still operate. 3. From the perspective of power supply technology, photovoltaic power generation is connected to the grid through power electronics inverters, which can easily result in harmonics and unbalanced three-phase currents ； The randomness of output power can lead to voltage fluctuations and flicker in the power grid. When building photovoltaic systems are connected directly to the grid at the user side, power quality issues can directly affect the safety of the user’s electrical equipment. Power plants must be able to limit their active power output in steps of 10% (the commonly used setpoints are 100%, 60%, 30%, and 0%). When the frequency is above 50.2 Hz, the power must be reduced at a rate of 40% of the rated power per Hz; the output power may only be increased again once the frequency drops back below 50.05 Hz. It is a technical requirement designed to prevent disruptions to the operation of the power grid when the frequency is above 51.5 Hz or below 47.5 Hz. The functional features of the islanding prevention protection device are mainly applicable to distributed generation systems operating at a voltage level of 0.4 kV. Its functions are similar to those of an isolation device for faults. Its settings are based on the relevant standards and specifications for connecting distributed power sources to the grid. It integrates the switching equipment, protection systems, monitoring and control functions, as well as communication capabilities required for connecting distributed power sources to the grid, thereby meeting the requirements for detecting islanding situations, ensuring automatic and safe grid connection, providing protection, and enabling safe isolation. The device enables the integration and simplification of the equipment required at the connection point of distributed power sources, facilitating plug-and-play integration of such sources into the distribution network.