What role does photovoltaic reclosing play in the power grid?

Inside the distribution box of a Photovoltaic power station, there is a seemingly inconspicuous yet crucial device—the photovoltaic reclosing switch. It can "close automatically" after a brief power outage and "trip decisively" in the event of a grid anomaly. What role does this "close-and-open" device play in the power grid? This article will break down the core role of the photovoltaic reclosing switch in the power grid from four dimensions: fault recovery, safety protection, power quality, and system coordination.

First, let's understand: What is reclosing?

Reclosing, also known as automatic reclosing device, is a device that automatically recloses a circuit breaker after it has tripped due to a fault.

Why is this function needed? Because most faults in power grid lines are transient—such as lightning strikes causing insulator flashover, or strong winds causing tree branches to briefly touch the line. After the circuit breaker trips, the arc extinguishes and the fault point disappears, and the line itself remains intact. If someone were to manually close the circuit breaker for every transient fault, not only would power restoration be slow, but maintenance costs would also be extremely high. The purpose of reclosing is to automatically "test close," allowing the line to quickly restore power after a transient fault.

II. Function 1: Automatic power restoration – reducing power outage time and improving power supply reliability

This is the most basic and direct function of reclosing.

When a transient fault occurs in a power grid line, the line protection device will first trip the circuit breaker to interrupt the fault current. If manual intervention is required to close the circuit breaker after each trip, the power outage could last for several hours. Reclosing automatically performs the closing operation after a trip. If the fault has disappeared (transient fault), the line returns to normal power supply; if the fault persists (permanent fault), the reclosing device will trip again, either without reclosing or awaiting manual intervention.

This function is particularly important for photovoltaic power plants. Photovoltaic power plants are mostly located on rooftops or in remote areas, and if manual switching is required for every grid fluctuation, the operation and maintenance costs will be prohibitive.

Third, function two: Anti-islanding protection – ensuring the safety of power grid maintenance personnel (core function)

This is the most critical grid-level safety function of photovoltaic reclosing.

What is the island effect? ​​When the public power grid is shut down due to maintenance or a fault, the photovoltaic system continues to operate and supply power to the grid lines, forming an independent "power island".

Why is it dangerous? When power workers are inspecting power lines, they assume the lines are already de-energized. However, if the photovoltaic system is still feeding power back into the lines, the workers may unknowingly come into contact with live wires, resulting in electric shock or injury.

How does the reclosing switch function? The photovoltaic reclosing switch is equipped with a voltage detection module that continuously monitors the grid voltage. When a grid power outage or voltage anomaly is detected, the reclosing switch automatically trips, disconnecting the photovoltaic system from the grid. The national standard GB/T 29319 clearly requires that the photovoltaic system must be disconnected within a specified time after a grid power outage.

Simply put, anti-islanding protection is the "bottom-line function" for photovoltaic reclosing to ensure grid security.

IV. Function Three: Power Quality Assurance – Ensuring that Photovoltaic “Green Electricity” Meets Standards

The alternating current output from a photovoltaic inverter may contain harmonics, and its voltage may fluctuate with sunlight. If this "unclean" electricity is fed into the power grid, it may affect the power quality of the grid and even damage other users' equipment.

Photovoltaic reclosing switches play a "gatekeeper" role in this regard:

- Voltage monitoring: Continuously monitors the voltage on the power grid and photovoltaic side, and automatically trips the circuit breaker when overvoltage (e.g., ≥270V) or undervoltage (e.g., ≤165V) occurs.

- Leakage current monitoring: Detects leakage current in the circuit; if the leakage current exceeds the standard, it will promptly cut off the circuit to protect personal safety.

- Phase sequence and phase loss monitoring: Detects whether the phase sequence of the three-phase power supply is correct and whether there are any missing or disconnected phases.

Some intelligent reclosing circuit breakers can also upload monitoring data to the backend via RS485 communication, enabling remote monitoring and parameter setting.

Fifth, Function Four: Coordination and Cooperation with Power Grid Relay Protection

In power grid systems, reclosing does not work independently, but rather in coordination with line protection devices.

When other electrical loads are simultaneously connected to the grid-connected line of a photovoltaic power station, the national standard requires that the anti-islanding protection action time of the photovoltaic power station should be shorter than the reclosing time of the grid-side line protection. The logic behind this is that when a grid fault occurs, the line protection trips first and then attempts to reclose to restore power supply. If the photovoltaic system is still "islanding" before the reclosing is successful, it may affect the success rate of reclosing and even damage the equipment.

Therefore, the timing of photovoltaic reclosing must be precisely coordinated with the grid-side protection to prevent islanding operation from endangering safety and to avoid affecting the success rate of grid reclosing due to excessively rapid tripping.

VI. Special characteristics of photovoltaic scenarios: Why do photovoltaic systems require "dedicated" reclosing devices?

Photovoltaic systems have several special requirements for reclosing, which are difficult for ordinary circuit breakers to meet:

1. Wide voltage adaptability

Photovoltaic systems experience significant voltage fluctuations, and the voltage withstand limit of ordinary circuit breakers is typically 1.1 times their rated voltage. Photovoltaic-specific reclosing circuit breakers, however, can withstand operating voltages up to 400V (single-phase), making them better suited to the voltage fluctuations of photovoltaic systems.

2. Low-voltage delayed trip

Ordinary reclosing circuit breakers trip immediately when the voltage drops below a threshold. However, photovoltaic power generation is affected by weather conditions—brief cloud cover can cause a temporary voltage drop, and immediate tripping could lead to unnecessary outages. Photovoltaic-specific reclosing circuit breakers incorporate a low-voltage delayed tripping function, allowing for a maximum delay of 10 seconds before tripping, preventing accidental tripping due to brief periods of shading.

3. Intelligent spatial background electromagnetic field detection

Some intelligent photovoltaic (PV) reclosing systems employ spatial background electromagnetic field detection technology. This technology detects the phase and frequency of a 50Hz power frequency electromagnetic field in space and compares this information with the output voltage of the PV inverter to determine whether the PV system is truly disconnected from the grid. This technology can more accurately identify islanded states and reduce false alarms.

VII. Summary: The Role of Photovoltaic Reclosing in the Power Grid

In summary, photovoltaic reclosing switches play a four-fold role in the power grid: "automatic restorer + safety gatekeeper + quality supervisor + system coordinator."

| Role | core role |

| Automatic Restore | Automatic reclosing after a momentary fault reduces power outage time and lowers maintenance costs. |

| Safety Goalkeeper | Automatic disconnection in the event of a power grid failure to prevent islanded operation from endangering the safety of maintenance personnel. |

| Quality supervisor | Monitor parameters such as voltage and leakage current to ensure that the power quality supplied to the grid meets standards. |

| System Coordinator | In coordination with line protection, it operates according to a set timing sequence to ensure the overall stability of the power grid. |