air circuit breaker

Air Circuit Breaker (ACB) is an important electrical protection device that is widely used in medium and low voltage power distribution systems. The following will introduce it from multiple aspects:

# I. Basic Definition and Working Principle

# 1. Definition

An air circuit breaker is a circuit breaker that uses air as the arc extinguishing medium and insulating medium. It is mainly used to protect electrical equipment from faults such as overload, short circuit, and undervoltage. At the same time, it can also be used for circuit switching under normal conditions.

# 2. Working Principle

 - **Overload Protection**: When the current in the circuit exceeds the rated current for a certain period of time, the bimetallic strip in the thermal release bends due to heat, pushing the tripping mechanism to act, causing the circuit breaker to trip.

 - **Short Circuit Protection**: When a short circuit occurs in the circuit, the short-circuit current will make the electromagnetic release generate a large enough electromagnetic force to push the tripping mechanism to act, achieving rapid tripping.

 - **Undervoltage Protection**: When the power supply voltage drops to a certain value, the electromagnetic force of the undervoltage release is not enough to overcome the pulling force of the spring, the tripping mechanism acts, and the circuit breaker trips.

# II. Product Structure and Characteristics

# 1. Product Structure

 - **Contact System**: It includes moving contacts and stationary contacts, which are key components for the opening and closing of the circuit. Materials such as silver alloys are usually used to improve electrical conductivity and arc resistance performance.

 - **Arc Extinguishing System**: The arc is elongated and cooled through the arc extinguishing chamber to extinguish the arc. Common arc extinguishing methods include longitudinal slot arc extinguishing and grid arc extinguishing.

 - **Release**: It includes thermal release, electromagnetic release, and undervoltage release, etc., which are used to achieve different types of protection functions.

 - **Operating Mechanism**: It is used to achieve the closing and opening operations of the circuit breaker and can be divided into manual operating mechanism and electric operating mechanism.

# 2. Characteristics

 - **Strong Breaking Capacity**: It can quickly cut off the circuit in case of faults such as short circuits, and the breaking capacity can reach dozens of kiloamperes or even higher.

 - **Complete Protection Functions**: It has a variety of protection functions such as overload, short circuit, and undervoltage, and can be adjusted according to different application scenarios.

 - **High Degree of Intelligence**: Modern air circuit breakers are usually equipped with intelligent releases, which can realize functions such as remote monitoring, fault diagnosis, and parameter setting.

 - **High Reliability**: After strict design and testing, it can operate reliably under harsh environmental conditions.

# III. Main Parameters and Selection Key Points

# 1. Main Parameters

 - **Rated Voltage**: It refers to the voltage level at which the circuit breaker works normally. Common ones are 230V, 400V, 690V, etc.

 - **Rated Current**: It refers to the maximum current that the circuit breaker is allowed to pass through for a long time. Common ones are 630A, 1000A, 1600A, 2500A, 4000A, 6300A, etc.

 - **Breaking Capacity**: It refers to the maximum current that the circuit breaker can safely cut off the circuit in case of faults such as short circuits, usually expressed in kA.

 - **Tripping Characteristics**: It includes tripping characteristics such as overload long-time delay, short circuit short-time delay, and short circuit instantaneous, which can be selected according to the nature and requirements of the load.

# 2. Selection Key Points

 - **Voltage Level**: Select the appropriate rated voltage according to the actual power supply voltage used.

 - **Current Size**: Select the appropriate rated current according to factors such as the rated current and starting current of the load.

 - **Breaking Capacity**: Select a circuit breaker with sufficient breaking capacity according to the magnitude of the short-circuit current at the installation site.

 - **Protection Functions**: Select a circuit breaker with corresponding protection functions according to the characteristics and requirements of the load.

 - **Brand and Quality**: Select products from well-known brands and with reliable quality to ensure the safety and reliability of use.

# IV. Application Scenarios

# 1. Industrial Field

 - Factory Power Distribution System: It is used to protect equipment such as motors and transformers and prevent damage to the equipment caused by faults such as overload and short circuit.

 - Large Mechanical Equipment: Such as cranes, steel rolling mills, etc., to provide reliable electrical protection for the equipment.

# 2. Commercial Field

 - Power Distribution Systems in Shopping Malls, Hotels and other Places: To ensure the safety and stability of power supply and prevent the occurrence of accidents such as electrical fires.

## 3. Power System

 - The Low Voltage Side of Substations: It is used to control and protect circuits such as busbars and feeders to ensure the normal operation of the power system.

# V. Maintenance and Fault Handling

# 1. Maintenance Key Points

 - **Regular Inspection**: Regularly inspect the appearance, contacts, releases and other components of the circuit breaker to ensure its normal operation.

 - **Cleaning and Maintenance**: Regularly clean the surface and interior of the circuit breaker to prevent dust, dirt, etc. from affecting its performance.

 - **Lubrication of the Operating Mechanism**: Regularly lubricate the operating mechanism to ensure its flexible movement.

 - **Testing of Tripping Characteristics**: Regularly test the tripping characteristics of the release to ensure that its protection function is normal.

# 2. Common Faults and Handling Methods

 - **Closing Failure**: It may be caused by reasons such as a malfunction of the operating mechanism and poor contact of the contacts. It is necessary to check the operating mechanism and contacts and carry out corresponding repairs or replacements.

 - **Opening Failure**: It may be caused by reasons such as a malfunction of the release and the jamming of the operating mechanism. It is necessary to check the release and operating mechanism and carry out corresponding repairs or replacements.

 - **Frequent Operation of Overload Protection**: It may be caused by reasons such as excessive load and improper parameter setting of the release. It is necessary to check the load situation and adjust the parameters of the release.

 - **Failure of Short Circuit Protection to Act**: It may be caused by reasons such as a malfunction of the release and poor contact of the contacts. It is necessary to check the release and contacts and carry out corresponding repairs or replacements.

# VI. Example of Siemens Air Circuit Breaker

Take the Siemens 3WL series air circuit breaker as an example:

 - **Technical Parameters**: The rated current range is 630A - 6300A, the maximum breaking capacity can reach 150kA, and the rated voltage is 400V - 690V.

 - **Characteristics**: Equipped with an intelligent release (such as the EASY control unit), it supports electrical energy monitoring and remote communication (Profibus/Modbus), and can realize real-time monitoring and remote control of the circuit breaker; advanced arc extinguishing technology and contact materials are adopted, which improves the breaking efficiency and reliability; it has a high protection level and is suitable for harsh environments.

 - **Application Cases**: It is widely used in scenarios such as the low voltage side of substations and the power inlets of large industrial equipment. In the power distribution system of a certain large factory, the 3WL series air circuit breaker provides reliable protection for the factory's motors, transformers and other equipment, ensuring the normal production of the factory.