1250A Circuit Breaker in KYN28a-12 Cabinet

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# Model and Applicable Scenarios - **Common Models**: Common models include VS1-12/1250A, VD4-12/1250A, etc.

- **Application Scenarios**: It is applicable to three-phase AC 50Hz power grids with a rated voltage ranging from 3.6kV to 12kV and a rated current of 1250A. It is widely used in scenarios such as power transmission in power plants, power receiving, power distribution in power systems and substations of industrial and mining enterprises, and starting of high-voltage motors. It can realize functions of circuit control, protection and detection.

### Working Principle - **Normal Operation**: When the circuit is working normally, the contacts of the circuit breaker are in a closed state, allowing current to pass freely. The operating mechanism keeps the contacts closed, and the circuit operates normally.

- **Fault Protection**: When faults such as overload or short circuit occur in the circuit and the current exceeds the set value, the tripping device will detect the change in current in a timely manner and act accordingly. In the case of overload, the thermal-sensitive elements in the thermal tripping device generate heat due to the current, and when the temperature rises to a certain level, the contacts will open to cut off the circuit. In the case of a short circuit, the electromagnetic tripping device will generate a powerful electromagnetic force, quickly triggering the circuit breaker to open the circuit.

- **Arc Extinction Process**: When the contacts are opened, an arc will be generated. The arc extinguishing devices in the arc extinguishing chamber quickly extinguish the arc through various methods, such as using vacuum, arc extinguishing plates, etc., to prevent the arc from causing damage to the contacts and surrounding equipment.

### Characteristics - **Structural Characteristics**: It adopts a center-mounted structure, with the circuit breaker located in the middle of the front cabinet of the switchgear, saving the lower space and allowing for the expansion of other schemes such as the cable room.

- **Protection Performance**: The enclosure protection level of the switchgear is IP4X, and when the doors of the circuit breaker compartments in each compartment are opened, the protection level is IP2X, which can effectively prevent debris and pests from entering and provides good protection.

- **Interlocking Function**: It has a complete mechanical interlocking device to prevent misoperation. For example, the handcart can only be moved when the circuit breaker and the earthing switch are in the open position; the circuit breaker can only be closed when the handcart is in the test or operating position. This can effectively prevent electrical misoperation accidents.

- **Convenient Maintenance**: The handcart has good interchangeability, and it is simple to replace the circuit breaker. Moreover, the switchgear can be installed and debugged from the front, facilitating the operation and maintenance by maintenance personnel. What is the working principle of the 1250A circuit breaker in the KYN28a-12 cabinet? The working principle of the 1250A circuit breaker in the KYN28a-12 cabinet is as follows:

### Normal Working State When the circuit is operating normally, the contacts of the circuit breaker are in a closed state, allowing current to pass freely. The operating mechanism keeps the contacts closed, and the circuit operates normally.

Fault Protection - **Overload Protection**: When the current in the circuit exceeds the set safety value but has not reached the short-circuit level, the thermal-sensitive elements in the thermal tripping device generate heat due to the current, and when the temperature rises to a certain level, the contacts will open to cut off the circuit.

- **Short Circuit Protection**: When a short circuit occurs in the circuit and the current increases sharply beyond the safety limit, the electromagnetic tripping device will generate a powerful electromagnetic force, quickly triggering the circuit breaker to open the circuit.

### Arc Extinction Process When the contacts are opened, an arc will be generated. The arc extinguishing devices in the arc extinguishing chamber quickly extinguish the arc through various methods, such as using vacuum, arc extinguishing plates, etc., to prevent the arc from causing damage to the contacts and surrounding equipment.

### Circuit Restoration Once the fault is eliminated or the current returns to normal, the operator can manually or automatically reset the circuit breaker to close the contacts and restore the normal operation of the circuit.