switch gear
"Switch gear" usually refers to switchgear, which is a complete set of devices used for **controlling, protecting, measuring, and distributing electrical energy** in the power system. It is composed of various switching appliances (such as circuit breakers, disconnectors, fuses, etc.) and auxiliary equipment. The following is a detailed analysis of it:
I. Core Definition
Switchgear is **a general term for high- and low-voltage switching appliances and their combinations**. Its main functions include:
- **Normal Operation**: Connect/disconnect the normal operating current (such as manually or automatically controlling the circuit).
- **Fault Protection**: Quickly cut off the circuit in case of faults such as short circuits, overloads, and leakage.
- **Monitoring and Control**: Integrate instruments, relays, etc. to achieve the monitoring of electrical parameters and remote control.
II. Structural Composition
Switchgear usually includes the following core components:
1. Switching Appliances
- **Circuit Breaker**
- It is the core component, used for **interrupting fault current** and has the ability to extinguish arcs (such as air circuit breakers, vacuum circuit breakers).
- Examples: Molded Case Circuit Breaker (MCCB), Air Circuit Breaker (ACB), High-voltage Circuit Breaker (such as SF6 circuit breaker).
- **Disconnector**
- It has no arc extinguishing ability and is used for **electrical isolation** (such as disconnecting the circuit during maintenance) and needs to be used in conjunction with a circuit breaker.
- Feature: There is an obvious visible disconnection point to ensure operational safety.
- **Fuse**
- It is an overcurrent protection device that cuts off the circuit by **melting the fuse element** and is often used in scenarios with high short-circuit currents.
2. Auxiliary Equipment
- **Busbar**: Conductive copper or aluminum bars are used to distribute electrical energy.
- **Protection Relay**: Monitors parameters such as current and voltage and triggers the circuit breaker to trip.
- **Operating Mechanism**: Manually or electrically operates the switch (such as a spring energy storage mechanism).
- **Instruments and Indicator Lights**: Displays current, voltage, switch status, etc.
III. Classification
1. According to Voltage Level
- **High-voltage Switchgear**: The rated voltage > 1kV (such as 10kV, 35kV switchgear), which is used in substations and power transmission and distribution lines.
- **Medium-voltage Switchgear**: 1kV ≤ rated voltage ≤ 35kV, which is commonly found in industrial power distribution.
- **Low-voltage Switchgear**: The rated voltage < 1kV (such as 400V power distribution cabinets), which is used in commercial and residential power distribution.
2. According to Installation Method
- **Fixed Type**: The switch is fixedly installed, and power needs to be cut off for maintenance (such as traditional power distribution cabinets).
- **Withdrawable (Handcart Type)**: Components such as the circuit breaker can be withdrawn, making maintenance convenient (such as middle-mounted switchgear).
3. According to Purpose
- **Power Distribution Switchgear**: Used for power distribution (such as power distribution cabinets, switchgear).
- **Motor Control Center (MCC)**: Integrates contactors and thermal relays to control the start and stop of motors.
- **Reactive Power Compensation Device**: Combines capacitors and reactors to improve the power factor.
IV. Working Principle
1. **Normal Operation**:
- The circuit breaker is closed, and the current is distributed to each branch circuit through the busbar, and the disconnector remains closed.
2. **Fault Triggering**:
- When there is a short circuit or overload in the line, the protection relay detects the abnormal current and triggers the circuit breaker to trip, cutting off the circuit.
- The arc is extinguished in the arc extinguishing chamber (such as the arc extinguishing grid of an air circuit breaker, the vacuum environment of a vacuum circuit breaker).
3. **Inspection and Maintenance**:
- After disconnecting the circuit breaker, operate the disconnector to form electrical isolation to ensure the safety of personnel.
V. Typical Application Scenarios
| Scenario | Equipment Example | Function |
| Substation | High-voltage Switchgear (such as 10kV GIS) | Control and protection of power transmission and distribution lines |
| Industrial Plant | Low-voltage Power Distribution Cabinet, Motor Control Center (MCC) | Power supply and protection of equipment such as machine tools and fans |
| Commercial Building | Floor Power Distribution Box, Small Circuit Breaker (such as C65 series) | Overload/short-circuit protection of lighting and air conditioning circuits |
| New Energy Field | Photovoltaic Combiner Box, Switchgear of Energy Storage System | Control and protection of charging and discharging of solar energy and battery packs |
VI. Difference from "Circuit Breaker"
- **Circuit Breaker**: A single device that focuses on **fault interruption**.
- **Switchgear**: A **system-level combination** that includes circuit breakers, disconnectors, busbars, etc., and realizes more complex control and protection functions.
VII. Precautions
1. **Model Selection Parameters**:
- Rated voltage, current, breaking capacity (kA), protection level (such as IP54).
2. **Standards and Certifications**:
- Follow standards such as IEC 62271 (high voltage), IEC 60439 (low voltage), and IEEE C37.
3. **Well-known Brands**:
- International: ABB, Siemens, Schneider, Eaton;
- Domestic: Chint, Delixi, Shanghai Electric.
**Conclusion**: Switchgear is the "central nervous system" of the power system. By integrating various switching appliances and protection devices, it ensures the safe distribution and reliable operation of electrical energy and is widely used in fields such as energy, industry, and construction.
