With the rapid development of renewable energy technologies, photovoltaic (PV) and energy storage systems play an increasingly prominent role in power supply structures. However, these systems may encounter islanding effects during operation, posing significant challenges to grid safety and stability. This article delves into the working principles, functions, and indispensable role of anti-islanding protection devices in ensuring the safe and stable operation of power systems.

1. What Are the Definition and Risks of Islanding Effects?

The islanding effect refers to a scenario where distributed generation equipment, such as PV power plants and energy storage systems, continues to supply power to local loads after the main grid loses voltage or is disconnected, forming an isolated power supply area independent of the main grid. Islanding effects can be categorized as:

• Planned Islanding: Predefined and controllable isolated areas that can maintain stable operation after disconnection from the main grid.
• Unplanned Islanding: Caused by grid faults, where energy storage systems continue to supply power, forming self-sufficient islands outside the control of the main grid.

Unplanned islanding poses the following safety risks and equipment damage issues:

• Personnel Safety Risks: During grid power outages for maintenance, repair personnel may face electrocution risks due to unawareness of the island's existence.
• Equipment Damage: Voltage and frequency become uncontrollable during islanding, leading to degraded power quality and potential damage to electrical equipment.
• Impact on Power Systems: Continued power generation by inverters can cause phase misalignment between grid voltage and inverter output. Upon grid restoration, surge currents may occur, resulting in tripping, equipment damage, or compromised grid stability.

2. Why Is Anti-Islanding Protection Necessary?

To address these risks, anti-islanding protection devices were developed. These devices accurately monitor grid conditions, intelligently detect grid anomalies, and swiftly disconnect energy storage systems from the grid upon detecting faults to prevent islanding.

Anti-islanding protection devices monitor key grid parameters in real-time, including voltage, frequency, active power, reactive power, and phase. When an anomaly is detected (e.g., voltage dips or frequency deviations), the device promptly activates protection mechanisms, disconnecting the energy storage system from the grid. Modern devices are equipped with self-learning and adaptive functions, optimizing detection algorithms based on historical grid data and real-time feedback to reduce false alarms and enhance reliability.

Core Functions of Anti-Islanding Protection Devices Include:

• Protecting the safety of power maintenance personnel.
• Ensuring proper operation of distribution system protective switches.
• Maintaining voltage and frequency stability within islanding areas.
• Preventing surge currents caused by phase misalignment during power restoration.
• Addressing single-phase power supply issues that result in under-phase conditions for three-phase loads.

3. How Do Anti-Islanding Protection Devices Function?

The key function of anti-islanding protection devices is detecting grid disconnections. Typically, they employ passive or active detection methods. Upon confirming grid disconnection, they must switch the grid-tied inverter to off-grid mode within two seconds to ensure personnel and equipment safety. These devices are not limited to disconnection protection but also integrate various protective functions, forming a comprehensive safety framework:

• Overvoltage/Undervoltage Protection: Monitors grid voltage fluctuations and triggers protection when values exceed preset thresholds.
• Overfrequency/Underfrequency Protection: Ensures grid frequency remains within safe limits, preventing adverse effects of frequency fluctuations.
• Reverse Power Protection: Prevents reverse power flow, safeguarding the grid and associated equipment.
• Residual Current Protection: Detects circuit leakage and takes timely measures to prevent electrical fires and related accidents.

Conclusion

In summary, anti-islanding protection devices are essential for ensuring the safe and stable operation of PV and energy storage systems. Megarevo's full range of energy storage inverters is equipped with anti-islanding protection features, effectively preventing islanding phenomena and enhancing overall system safety and reliability.

Looking ahead, with the widespread adoption of smart grid technologies, anti-islanding protection devices will play a pivotal role in building greener, more efficient, and stable energy systems.

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