• Zhejiang Zhilu Transmission and Distribution Equipment Co., Ltd

Technical Analysis of Core Components in Photovoltaic Grid - Connection Cabinets: Circuit Breakers, Inverters, and Relays

Technical Analysis of Core Components in Photovoltaic Grid - Connection Cabinets: Circuit Breakers, Inverters, and Relays

Abstract

1. Introduction

2. Circuit Breakers in PV Grid - Connection Cabinets

2.1 Working Principle

2.2 Technical Characteristics

• Rated Current and Voltage: Circuit breakers must be rated to handle the maximum current and voltage levels expected in the PV system. For a typical 10kV PV grid - connection system, the circuit breaker should have a rated voltage of at least 10kV and a rated current determined by the system's power capacity (e.g., 630A for a 10MW PV plant).

• Short - Circuit Breaking Capacity: This parameter indicates the maximum short - circuit current that the circuit breaker can safely interrupt. In PV applications, where high - current faults can occur due to array interconnections or equipment failures, a circuit breaker with a sufficient short - circuit breaking capacity (e.g., 25kA or higher) is required.

• Tripping Characteristics: Circuit breakers have different tripping curves (e.g., instantaneous, short - time delay, long - time delay) to respond appropriately to various fault conditions. Instantaneous tripping is used for severe short - circuits, while time - delayed tripping can prevent unnecessary interruptions during transient overcurrents.

2.3 Key Performance Indicators

• Mechanical and Electrical Life: The number of times a circuit breaker can operate (both open and close) without losing its performance. High - quality circuit breakers can have a mechanical life of over 10,000 operations and an electrical life of several hundred operations under rated current conditions.

• Arc - Extinguishing Efficiency: Efficient arc - extinguishing reduces the duration of arcing, minimizing damage to the circuit breaker contacts and preventing secondary electrical failures.

3. Inverters in PV Grid - Connection Cabinets

3.1 Working Principle

3.2 Technical Characteristics

• Conversion Efficiency: Inverters with high conversion efficiency (e.g., over 98%) minimize power losses during the DC - to - AC conversion process. Efficiency is typically measured under standard test conditions (STC) and real - world conditions (e.g., low irradiance or high temperature).

• Power Rating: Inverters are rated based on their maximum output power capacity, which should match the size of the PV array. For example, a 50kW inverter is suitable for a PV system with a peak power of around 50kW.

• Grid - Connection Compatibility: Inverters must comply with grid - code requirements, including voltage and frequency tolerance, power factor control, and anti - islanding protection. Anti - islanding protection ensures that the inverter disconnects from the grid during a power outage to prevent electrical hazards.

3.3 Key Performance Indicators

• Total Harmonic Distortion (THD): THD measures the quality of the AC output by quantifying the amount of harmonic content. A low THD value (e.g., less than 5%) indicates a high - quality sinusoidal output, reducing the impact on the electrical grid.

• Dynamic Response: The ability of the inverter to quickly adapt to changes in PV power output (e.g., due to cloud cover) while maintaining stable grid connection. A fast - responding inverter can minimize power fluctuations and improve grid stability.

4. Relays in PV Grid - Connection Cabinets

4.1 Working Principle

4.2 Technical Characteristics

• Contact Rating: Relays are rated based on the maximum current and voltage they can handle. For PV applications, relays with high - current - carrying capacity (e.g., 100A) and suitable voltage ratings (e.g., 1000V DC) are required.

• Switching Speed: Electromechanical relays have relatively slower switching speeds compared to solid - state relays. In applications requiring fast response times (e.g., anti - islanding protection), solid - state relays are preferred due to their microsecond - level switching capabilities.

• Isolation Resistance: High isolation resistance between the control circuit and the power circuit ensures electrical safety and prevents interference.

4.3 Key Performance Indicators

• Contact Life: The number of times a relay can switch before its contacts degrade. Proper selection and maintenance can extend the contact life, reducing the need for frequent replacements.

• Leakage Current: In solid - state relays, low leakage current is crucial to prevent unnecessary power consumption and ensure reliable operation.

5. Interaction and Coordination of Core Components

6. Conclusion