Switching equipment is generally equipped with circuit breakers, circuit breakers are one of its core components, responsible for circuit switching control and fault protection. Here's a breakdown:
1.The central role of circuit breakers in switchgear
Functional integration
Switching equipment is the "distribution hub"of power system, which combines control, protection, measurement and signaling functions. As a key component, circuit breakers function as follows:
Manual/automatic opening and closing of circuits (e.g. isolation of power supply during equipment maintenance);
Prevent overload, short circuit, underpressure, etc. (prevent equipment from burning or catching fire);
Interconnect with automation systems (e.g., by PLC remote control of circuit breakers' closing and opening).
Structural Necessity
Typical structures of switching equipment include a busbar compartment, circuit breaker compartment, cable compartment and secondary control compartment. Circuit breaker is installed independently in the circuit breaker compartment, connected to the power supply by busbar, and connected to the load by cable to form a complete power distribution circuit. If there is no circuit breakers, the switchgear can only play the role of cable branch box, lost control and protection functions. Circuit Breaker Configuration of Different Switchgear Types
Low-voltage switchgear (e.g. GCK, GCS and MNS)
Circuit breaker breaker types: ACB, MCCB, MCB.
Application scenarios:
Incoming switchgear: AC / DC cables rated 630A to 6300A are used to connect and disconnect the main power supply and provide short-circuit protection.
Outgoing switchgear: Molded case circuit breakers (MCCB, 10A to 1600A) or MCB, 1A to 125A for load-controlled branch circuits.
Capacitor compensation Switching Equipment: Special circuit breakers is used to switch reactive power compensation devices.
High-voltage switchgear (e.g. KYN28 and XGN15)
Type of Circuit breaker: Vacuum circuit breakers (VS1 and VN2) and SF6 circuit breakers (LW8). Application Scenarios:
Incoming Switchgear: Vacuum circuit breakers rated 10kV-35kV and rated 1250A-400A are responsible for switching and short-circuit protection for HV power.
Outgoing Switchgear: Vacuum circuit breakers control high-voltage loads such as transformers and motors, and their breakdown capacity must match the starting current of the load.
PT Switchgear: small vacuum circuit breakers for protection of voltage transformers.
Special-Purpose Switchgear
Box-Type Substations: high voltage side adopts Vacuum circuit breakers, lowvoltage side adopts frame circuit breaker to achieve high voltage integrated protection.
DC Switchgear (such as subway power supply): DC circuit breakers are used to quickly interrupt DC short-circuit current (DC interruptions are more difficult than AC interruptions).
3. New Energy Switchgear (such as photovoltaic (PV), wind power, etc.): circuit breakers protected by inverters are used to prevent electricity from returning to the grid. Collaboration between circuit breakers and Other Switchgear Components
Working with circuit breakers
High-voltage switchgear: circuit breaker are responsible for interrupting load current and short-circuit current, while the disconnector are responsible for isolating the power supply after the circuit breaker jumps, forming "clear breakpoints" to ensure safe maintenance.
Low-voltage switchgear: Some designs use a combination of circuit breakers and circuit breakers to achieve double isolation.
Interaction with current transformers
CTs monitor circuit currents in real time and transmit signals to circuit breaker protection devices such as overload relays and short-circuit release devices.
When current is abnormal, the protective device triggers the circuit breaker to jump and disconnect the faulty circuit.
Integration with automated systems
Modern switchgear is equipped with smart controllers that upload circuit breaker status (off and on location, fault records) to the monitoring system via communication interfaces (e.g., RS485 and Ethernet).
This enables remote operations, failure warnings and energy efficiency management.
4. A Case Study of Circuit Breaker's Missing Switching Equipment
Cable branch box
Structure: Contains busbar, cable connectors and insulator only; no circuit breakers. Function: For cable branching and connection only, no control or protection capabilities.
Limitations: If a downstream load short-circuits, it must be protected by an upstream circuit breakers, which may extend the power outage.
Simple power distribution box
Structure: Fuse + knife switches.
Question:
After the fuse has blown, it requires to be replaced to prevent a rapid power restoration.
Knife switch lacks short-circuit circuit protection and requires additional fuses.
Applicable Scenarios: Temporary electricity demand or low reliability requirements.
V. Key Considerations considerations for circuit breakers when selecting switching equipment
Load Types
Motor Loads: consider the starting current (usually 5-7 times the rated current), choose circuit breaker, circuit breaker must have sufficient breaking capacity.
Lighting Load: For stable current, standard die-press case circuit breaker may be used.
Capacitance Load: An inverseharmonic circuit breaker is required to prevent equipment damage from inrush currents.
State of the environment
High temperature environment: Select high temperature resistant circuit breaker (e.g. rated working temperature ≥ 70°C). Humid environments: Choose a circuit breakers with an IP65 protection rating or higher to prevent condensation from causing a short circuit.
Corrosive environments: choose circuit breakers with stainless steel housing or corrosion resistant coating.
System coordination
5. Matching protection levels up and down: The upper circuit breaker should work longer than the lower one to avoid over-tripping.
Short-circuit current calculation: select circuit breaker (e.g. 50kA, 65kA) according to the system's short-circuit capacity.
VI. INTRODUCTION Abstracts
Standard Configuration: Over 90% of switchboards (whether low voltage, high voltage or special purpose) are equipped with circuit breakers, which are the core of circuit control and protection.
Exceptions: Equipment without protection requirements, such as cable branch boxes and simple distribution boxes, shall not be equipped with circuit breaker. However, this type of equipment often relies on upper protective gear, limiting its applicability.
Choose the appropriate circuit breaker type and parameters according to load characteristics, environmental conditions and system requirements to ensure the safe and safe and reliable switchgear operation.
