Why is it necessary for photovoltaic power stations to be equipped with islanding protection devices?
What is an anti-islanding protection device? Why does the power grid company insist on checking this during the acceptance of Photovoltaic projects? What are the consequences of not installing it? These are some of the most common questions encountered by photovoltaic project owners and construction workers during the acceptance phase. Simply put, an anti-islanding protection device is the "last line of defense" for the safe grid connection of a photovoltaic power station. Not installing it not only prevents the power grid from passing acceptance but may also endanger the lives of power maintenance personnel. This article will explain what the islanding effect is, how serious the consequences of not configuring anti-islanding protection are, and the specific requirements of national standards.
First, let's understand one question: What is the "island effect"?
To understand why island protection is necessary, we must first understand what kind of wind it protects against.
Under normal circumstances: When a photovoltaic power station is connected to the grid, it is in a connected state with the public power grid. The power grid is like a "large pool," and the photovoltaic power station pours water into it.
Abnormal Situation (Island Effect): When the public power grid is disconnected due to faults, maintenance, or power outages, the photovoltaic power station continues to operate, supplying power to local loads and grid lines. In this situation, a distributed generation system that was originally connected to the main power grid becomes an independent and uncontrolled power supply island, detached from the main power grid.
Simply put: Even when the power grid goes out, your photovoltaic power station is still generating electricity and transmitting it to the outside world—this is the "island effect".
II. How severe are the consequences of not configuring anti-islanding protection?
This is key to understanding "why it's absolutely necessary to configure it." Not installing anti-islanding protection will lead to at least three serious consequences:
Consequence 1: Endangering the lives of maintenance personnel (the most serious consequence)
When a power grid line is shut down for maintenance, power workers assume the line is de-energized and begin repairs. However, if a nearby solar power station lacks anti-islanding protection and continues to feed power back into the grid, maintenance personnel may unknowingly touch the live lines, resulting in electric shock.
This is not a theoretical risk. Accidents involving injuries or fatalities to maintenance personnel have occurred both domestically and internationally due to islanded operation of distributed generation systems. The primary purpose of anti-islanding protection devices is to safeguard the lives of frontline power workers.
Consequence 2: Damage to power grid equipment and user equipment
When a photovoltaic inverter is operating in islanded mode, its output voltage and frequency may become uncontrolled. When the grid is reconnected, the islanded photovoltaic system may be out of sync with the grid—differences may exist in phase, voltage, and frequency. Closing the grid-connected switch at this time will generate a large inrush current, potentially causing:
Damage to switchgear and transformers on the power grid side
Photovoltaic inverter itself damaged
User-side equipment damaged due to abnormal voltage.
Consequence 3: The project cannot pass the power grid acceptance test and cannot be connected to the grid.
According to national and industry standards, photovoltaic power plants must be equipped with anti-islanding protection devices that can automatically disconnect within a specified time when the grid loses power. During grid connection acceptance, the power grid company must conduct on-site anti-islanding protection tests to verify that the device can operate within the specified time after a power outage. If the test fails, the project cannot be connected to the grid.
III. What does the national standard say? — It's mandatory, not "optional."
Anti-islanding protection devices are "essential" because they are stipulated in several national mandatory or industry standards. Here are some key standard requirements:
1. Anti-islanding protection action time limit requirements
National standards stipulate that photovoltaic (PV) systems must disconnect from the grid within 2 seconds after a power outage. This is a mandatory requirement for all grid-connected PV power plants, regardless of project size. The power grid company will test this requirement on-site during acceptance testing.
2. Requirements for Detection Accuracy and Reliability
The anti-islanding protection device needs to have two detection methods, passive and active:
Passive: Monitors abnormal changes in voltage and frequency.
Active: Injecting minute disturbance signals to detect the power grid response.
The combination of these two methods ensures reliable detection of islanded states under any operating condition, preventing false positives or false negatives. The device should also have an event logging function, recording the time, cause, and parameters of each action for easy post-event analysis.
3. Synergy with inverter anti-islanding protection
Photovoltaic inverters themselves also have a certain degree of anti-islanding protection (at the software level), while the anti-islanding protection device inside the grid-connected cabinet is an independent hardware protection. The standard requires that the two work together to form "dual protection"—if one fails, the other can still execute a trip command. During grid acceptance, not only are the anti-islanding devices in the grid-connected cabinet checked, but the inverter's anti-islanding protection function is also verified.
IV. How does the anti-islanding protection device work?
Anti-islanding protection devices continuously monitor the voltage and frequency on the grid side to determine the grid status and execute corresponding actions:
Step 1: Real-time monitoring
The device continuously collects voltage and frequency signals from the power grid and compares them with preset thresholds.
Step 2: Anomaly Detection
When a power grid loss or anomaly is detected (such as voltage <80% of rated value, frequency >50.5Hz or <49.5Hz, etc.), the device enters the "islanding determination" logic. To prevent false alarms, some devices will use multiple criteria to make a comprehensive judgment to confirm that the power grid has indeed lost power and is not just a temporary fluctuation.
Step 3: Trip the circuit breaker.
After confirming the islanded status, the device issues a trip command within a specified time (≤2s), driving the grid-connected circuit breaker to open and disconnecting the photovoltaic system from the power grid.
Step 4: Restore grid connection (automatic reclosing)
After the power grid returns to normal, the device detects stable voltage and frequency, and after a delayed confirmation, issues a closing command to automatically restore grid connection. Some devices support a no-voltage closing strategy—confirming that the line voltage has disappeared before reclosing to avoid asynchronous surges.
V. Market Brands and Selection Guide for Anti-Islanding Protection Devices
Currently, the mainstream anti-islanding protection device brands on the market include: NARI Group, NARI Technology, XJ Electric, Beijing Sifang, Shenzhen NARI, and Zhuhai Wanlida. In addition, international brands such as Schneider Electric, ABB, and Siemens also provide related protection products.
Key considerations when selecting a model:
Has it passed the type test of the National Relay Protection Testing Center?
Does it support communication protocol compatibility with the grid-connected cabinets used in the project (such as Modbus, IEC 61850, etc.)?
Does it have event logging and fault recording functions to facilitate acceptance testing and post-event analysis?
VI. Conclusion: Anti-islanding protection is not an "optional" measure, but a "veto item."
Legal Obligation: Mandatory national standard; failure to configure this constitutes illegal construction.
Safety Guarantee: Protect the lives of power maintenance personnel and prevent electric shock accidents.
Equipment protection: Prevents impact damage caused by asynchronous grid connection.
Mandatory acceptance condition: If the on-site test fails, the project cannot be connected to the grid.
Anti-islanding protection devices are the bottom-line equipment for the safe grid connection of photovoltaic power plants, and cannot be omitted, replaced, or neglected.