Definition of High Voltage Circuit Breaker

A high-voltage circuit breaker is a switching device that can close, carry, and interrupt normal operating currents, and also interrupt specified abnormal currents (such as short-circuit currents and overload currents) within a specified time, with a rated voltage of 3kV and above.

Functions and Roles of High Voltage Circuit Breakers

High voltage circuit breakers are essential control and protection equipment in electrical power systems. They serve two primary functions:

1.Control Function: Based on the operation requirements of the power grid, they control the operation of certain electrical equipment and lines, putting them into or out of operation, and switching them to standby or maintenance states.

2.Protection Function: In the event of faults in electrical equipment or lines, the circuit breaker acts through relay protection and automatic devices to quickly isolate the fault section from the power grid, preventing the accident from spreading, and ensuring the normal operation of the fault-free sections of the grid.
The working characteristics of high-voltage circuit breakers are that they instantaneously change from a conducting state to an insulating state, or from an insulating state to a conducting state. Therefore, the breaker must have the following capabilities:

(1)Conduction: In the closed state, it must be a good conductor, capable of withstanding not only normal currents but also the heating and electrodynamic effects of specified short-circuit currents, while maintaining reliable  contact.

(2)Insulation: There must be good insulation between phases, between phase and ground, and across the contacts, withstanding the maximum operating voltage and transient overvoltage and operation-induced overvoltage.

(3)Interrupting: Under any condition in the closed state, it should be able to interrupt the specified short-circuit current in the shortest possible time without causing hazardous overvoltages.

(4)Closing: Under any condition in the open state, it should be able to safely close the specified short-circuit current in a short time without causing contact welding.

Basic Structure of High Voltage Circuit Breakers

1.Switching Elements: These perform the task of opening or closing the circuit. The core part is the contacts, and the presence and effectiveness of arc extinguishing devices or their capabilities determine the breaker's interrupting capacity.

2.Operating Mechanism: Provides the energy required to open or close the switching elements and ensures various specified sequence operations while maintaining the closed state of the breaker.

3.Transmission Mechanism: Transmits the operating energy and commands from the operating mechanism to the switching elements.

4.Insulating Supporting Elements: Support and fix the switching elements, ensuring insulation between various structural parts.

5.Base: Supports, fixes, and installs all parts of the circuit breaker to form an integrated system.

Types of High Voltage Circuit Breakers

High voltage circuit breakers are classified into several types based on their arc extinguishing media and principles:

1.Oil Circuit Breaker: A circuit breaker that uses insulating oil as the arc extinguishing medium.

2.Compressed Air Circuit Breaker: A circuit breaker that uses compressed air as the arc extinguishing medium and operating energy source.

3.Vacuum Circuit Breaker: A circuit breaker that interrupts the current in a vacuum, utilizing the high insulating strength of vacuum to extinguish the arc.

4.Sulfur Hexafluoride (SF6) Circuit Breaker: A circuit breaker that uses SF6 gas, which has excellent arc-extinguishing properties, as the arc extinguishing medium.

Technical Parameters of High Voltage Circuit Breakers

1.Rated Voltage (kV): The voltage level that the circuit breaker can handle for long-term operation (line voltage). Considering different voltages at the start and end of lines and voltage regulation requirements, the breaker may operate at a voltage higher than its rated voltage for extended periods. The maximum working voltage is 1.15 times the rated voltage for equipment rated up to 220kV, and 1.1 times the rated voltage for equipment rated at 330kV or above. Common rated voltage levels include 3kV, 6kV, 10kV, 35kV, 60kV, 110kV, 220kV, 330kV, 500kV, 750kV, and 1000kV. Rated voltage not only determines the insulation level of the breaker but also significantly affects its size and arc-extinguishing conditions.

2.Rated Current (A): The maximum working current that the breaker can carry continuously under specified ambient conditions without exceeding the maximum allowed temperature. Rated currents commonly used are 200A, 400A, 630A, 1000A, 1250A, 1600A, 2000A, 2500A, 3150A, 4000A, 5000A, 6300A, 8000A, 10000A, 12500A, 16000A, and 20000A. Rated current determines the size and structure of current-carrying parts like conductors and contacts.

3.Rated Short-Circuit Breaking Current (kA): The maximum short-circuit current the circuit breaker can reliably interrupt under the rated voltage. It reflects the breaker’s ability to interrupt the circuit. For voltages lower than the rated voltage, the breaker can interrupt higher currents, known as the "limit breaking current."

4.Rated Closing Current (kA): The maximum short-circuit current peak value the breaker can reliably close under the rated voltage. This reflects the breaker’s ability to close during a short-circuit fault and depends on the arc-extinguishing device performance, contact structure, and operating mechanism.

5.Rated Thermal Stability Current (kA): The maximum short-circuit current the breaker can sustain for a specified time (usually 4 seconds) without exceeding temperature limits due to thermal effects. It is equal to the rated short-circuit breaking current.

6.Rated Dynamic Stability Current (kA): The maximum short-circuit current peak value the breaker can withstand while closed, reflecting the breaker’s ability to endure the electrodynamic effects of the short-circuit current. It depends on the mechanical strength of the conductor and insulation. This value equals the rated closing current and is 2.55 times the rated thermal stability current.

7.Closing Time (s): The time interval from when the breaker receives the closing command to when the contacts just close.

8.Total Opening Time (s): The time interval from when the breaker receives the opening command to when the contacts fully separate, extinguishing the arc. It includes:

 1)Inherent Opening Time: Time from receiving the opening command to the moment when the contacts just separate.

 2)Arc Extinguishing Time: Time taken for the arc to be completely extinguished after the contacts separate. Typical total opening times range from 0.06 to 0.12 seconds. Breakers with opening times less than 0.06 seconds are considered "fast breakers."

9.Rated Operating Sequence: A set of standard operations defined based on actual operating needs to assess the breaker’s ability to interrupt. It is divided into two types:

 (1)Non-Automatic Reclosing Breaker: Includes situations such as "open—180s—close—open—180s—close" for permanent faults, or "close—open—15s—close—open" for cases where the breaker re-closes after a fault.

 (2)Automatic Reclosing Breaker: The operation sequence is "open—0.3s—close—open—180s—close."