Circuit breakers and surge protectors: The safety guardians of photovoltaic systems

Introduction

In photovoltaic power generation systems, apart from the "star equipment" such as solar panels and inverters, there are two "unsung heroes" quietly safeguarding the system's safety - circuit breakers and surge protectors (SPDS). They are like the "fuses" and "lightning rods" of the power system, constantly protecting the entire photovoltaic system from electrical faults and lightning strikes. This article will take you through the significant roles of these two key protective devices in photovoltaic systems.

I. Circuit Breaker: The "Safety Switch" of Photovoltaic Systems

The function of a circuit breaker

Circuit breakers are the most important overcurrent protection devices in photovoltaic systems and mainly undertake three key tasks:

Overload protection: Automatically cut off the circuit when the current exceeds the design value

Short-circuit protection: Quickly disconnect in the event of a short-circuit fault

Manual disconnection: Provides a safe disconnection point for system maintenance

2. Special requirements for photovoltaic dedicated circuit breakers

Unlike ordinary AC circuit breakers, photovoltaic DC circuit breakers require special design:

Dc arc extinguishing capability: DC arcs are more difficult to extinguish and require a stronger arc extinguishing chamber design

High voltage level: The working voltage of the photovoltaic system can reach over 1000V

Weather resistance: Dust-proof and water-proof (at least IP65 grade) is required for outdoor installation

3. Typical application locations

Battery panel series output terminal

Dc input terminal of the inverter

Communication and network

Ii. Surge Protector: The defense line against "electrical surges"

The surge threat faced by photovoltaic systems

Photovoltaic systems, due to their large distribution area and exposed location, are particularly vulnerable to:

Direct lightning strike (low probability but highly destructive)

Induced lightning (the most common threat)

Switch operation overvoltage (generated internally by the system)

2. The working principle of surge protectors

SPD is like an "electrical spillway", within nanosecond time:

Detect abnormal voltage

Establish a low-impedance path

Channel dangerous energy into the earth

3. The Particularity of SPD in photovoltaic systems

Dc SPD: It needs to be specially designed for DC systems

Bipolar protection: Protects both the positive and negative circuits simultaneously

Continuous operating voltage: It must be adapted to the high voltage of the photovoltaic system

Iii. Synergistic Protection: 1+1>2 Security effect

In actual systems, circuit breakers and SPDS need to be used in conjunction:

Hierarchical protection system

First-level protection (incoming line end) : Discharge amplification current

Secondary protection (distribution end) : Further limit residual pressure

In coordination with circuit breakers: Provide backup protection when the SPD fails

Typical wiring scheme

SPD is connected in parallel to the line and protected by a series circuit breaker

Iv. Key Points for Selection and Maintenance

Circuit breaker selection

The rated voltage is greater than or equal to the maximum system voltage

The breaking capacity is greater than or equal to the expected short-circuit current

SPD selection

The maximum continuous operating voltage Uc is ≥1.2 times the system voltage

Inrush current Iimp≥12.5kA(first-class protection)

Maintenance suggestions

Check before the thunderstorm season every year

Pay attention to the SPD status indicator window

Record the number of times the circuit breaker operates

Conclusion

In photovoltaic systems, circuit breakers and surge protectors are like two well-coordinated "safety partners" : circuit breakers are responsible for handling overcurrent faults within the system, while SPDS defend against external surge attacks. Their collaborative work ensures the safe operation of the photovoltaic power station for more than 25 years. For power station owners, choosing high-quality protective devices and maintaining them regularly is an important part of ensuring a return on investment.