What are the main functions and components of a circuit breaker chassis vehicle?

A circuit breaker chassis trolley, also commonly known as a handcart chassis trolley or simply a handcart, is a mechanical support system installed inside a switchgear (such as the KYN28A-12 type centrally mounted switchgear). Its core function is to support vacuum circuit breakers (or other types of circuit breakers) and allow them to move inside and outside the cabinet, achieving three distinct working positions: operating position, test position, and disconnect/remove position.

Simply put, it acts like a "movable base" or "skateboard" for the circuit breaker, allowing the bulky circuit breaker to be easily pushed in and pulled out, greatly simplifying the operation, maintenance, and repair processes.

Main Functions and Three Working Positions

 

The essence of the chassis design lies in its precise positioning and interlocking functions, ensuring operational safety and correct procedures.

Working Positions

Status: The circuit breaker chassis is fully pushed into the switchgear, and the upper and lower contacts (primary circuit) of the circuit breaker are reliably connected to the stationary contacts inside the cabinet. Simultaneously, the secondary circuit plug on the chassis is also connected to the socket on the cabinet.

Function: The circuit breaker is in normal closing, opening, or automatic protection mode, capable of connecting, carrying, and disconnecting normal current and fault current.

 

Test Position

Status: The circuit breaker chassis is pulled outwards a certain distance from its working position. At this point, the upper and lower contacts of the circuit breaker are completely separated from the stationary contacts inside the cabinet, forming a clear electrical isolation break to ensure safety. However, the secondary circuit plug of the chassis remains connected.

Function:

Safe Testing: In this position, the circuit breaker can be closed and opened to test the normal operation of its control circuit and protection functions without affecting the main circuit.

Convenient Maintenance: Provides a safe space for maintenance of the main circuit or other equipment.

 

Disconnect/Remove Position

Status: The circuit breaker chassis is completely pulled out of the switchgear, or pulled to a position completely separated from the cabinet. At this time, both primary and secondary circuits are disconnected.

Function:

Complete Overhaul or Replacement of Circuit Breaker: Allows the entire circuit breaker to be removed from the cabinet for comprehensive maintenance, overhaul, or replacement.

Switchgear Cabinet Inspection: Facilitates inspection and cleaning of the switchgear interior.

 

Key Components

 

A typical circuit breaker chassis usually includes the following components:

Frame: The main steel structure used to secure the circuit breaker.

Rollers/Pulleys: Facilitate smooth movement on the switchgear rails.

Crank Handle Interface: Used to connect a dedicated operating crank, allowing precise control of the chassis's forward and backward movement. This is the most crucial operating component.

Position Indicator and Interlocking Mechanism:

Position Indicator: Clearly displays the current "operating," "test," or "disconnected" position.

Mechanical Interlock: Ensures the chassis can only be cranked when the circuit breaker is in the open position; prevents the chassis from being opened or closed under load.

Electrical Interlock: Linked with equipment such as grounding switches to prevent misoperation.

Secondary Circuit Connector: Used to connect the circuit breaker's control, measurement, and protection signal lines when the chassis is in the operating or test position.

Advance/Retract Mechanism: A gear and screw system that converts the rotary motion of the crank handle into the linear motion of the chassis.

Grounding device: Ensures that the chassis and circuit breaker are reliably grounded after the chassis is pulled out, thus ensuring personnel safety.

 

Core Advantages and Importance

 

High Safety: Clearly defined isolation points and robust interlocking effectively prevent serious operational errors such as switching on or off under load, ensuring the safety of operators and equipment.

Convenient Maintenance: Circuit breakers in individual circuits can be removed for maintenance without disconnecting the entire power distribution system busbar, significantly reducing power outage time and improving power supply reliability.

High Flexibility: Backup circuit breakers can be quickly replaced, crucial for applications requiring rapid power restoration.

Space Saving: The centrally located design results in a compact switchgear structure and a small footprint.

 

Operating Procedures (Taking Power Outage Maintenance as an Example)

 

Power Outage: Disconnect the power supply to this cabinet via the upstream switch.

Trigger Open: Press the "Trigger Open" button on the circuit breaker controller to ensure the circuit breaker is in the open position.

Roll Out: Insert the dedicated crank handle into the crank handle interface on the chassis and crank counterclockwise to move the chassis from the "Working Position" to the "Test Position." A "click" sound will be heard, indicating that it has reached the correct position.

Disconnect Secondary Connector: In the test position, the secondary circuit connector can be manually unplugged (in some designs, the connector must be unplugged before continuing to move out).

Complete Removal: Continue cranking the handle counterclockwise until the chassis is completely moved to the "Disconnect Position," then the entire circuit breaker trolley can be pulled out of the cabinet.

Maintenance/Grounding: Perform necessary maintenance work and ensure proper grounding measures are in place.

 

Summary

 

The circuit breaker chassis is one of the core components of modern medium and high voltage switchgear. Through precise mechanical design, it realizes the mechanization, proceduralization, and safety of electrical equipment operation, isolation, and maintenance, and is an important guarantee for the safe and stable operation of the power system.

Shaanxi Huadian, with years of experience in the power industry, focuses on the research and development and manufacturing of high-quality circuit breaker chassis. Our chassis series, with exquisite craftsmanship, superior performance, and absolute safety as its core, ensures smooth operation, precise positioning, and reliable interlocking for your handcart-type switchgear. Inquiries are welcome.

Email:pannie@hdswitchgear.com.

Whatsapp/Wechat:+8618789455087