high-voltage switchgear with withdrawable circuit breakers

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The following is a detailed introduction to the contacts of high-voltage switchgear with withdrawable circuit breakers.

### Types and Structural Features
- **Bellows Contact**: It is a common type of contact, which is composed of rectangular sheet-shaped contact pieces in cross-section, a loop frame with a supporting function, and an outer annular spring. Two contact pieces form a group and are sleeved on the loop frame to form a circular shape. Generally, its contact pieces are made of T2 copper plate through precision punching, with a thick silver plating on the surface. They have the characteristics of remaining unchanged in color for a long time after anti-tarnish treatment and having an attractive appearance. Moreover, they are bound by non-magnetic stainless steel annular tension springs, and the pressure of the annular springs is uniform, which can avoid eddy currents.
- **Stationary Contact**: It usually has a hollow cylindrical structure. There are a first mounting hole and a second mounting hole at the bottom. The first mounting hole is located at the center of the bottom surface of the stationary contact, and the second mounting hole is located on the strengthening convex surface at the bottom of the stationary contact. This structure can improve the stability of the connection with the busbar and the contact box as well as the current-carrying capacity, thereby reducing the temperature rise.

### Working Principle
- **Moving Contact**: When the circuit breaker is closed, the moving contact moves towards the stationary contact under the action of the operating mechanism, contacts the stationary contact and applies a certain pressure to ensure good electrical conductivity. When the circuit breaker is opened, the moving contact is quickly separated from the stationary contact under the drive of the operating mechanism to cut off the circuit.
- **Stationary Contact**: It mainly plays the roles of fixing and cooperating with the moving contact, providing a path for current, and transmitting current from the busbar to the moving contact or from the moving contact to the busbar.

### Technical Parameters
- **Rated Current**: Common ones are 630A, 1250A, 1600A, 2000A, etc. Appropriate contacts with the rated current need to be selected according to the actual usage requirements and load conditions of the switchgear.
- **Rated Voltage**: Generally, it matches the rated voltage of the high-voltage switchgear with withdrawable circuit breakers, such as 10kV, 35kV, etc.
- **Contact Resistance**: It is required that the contact resistance between the contacts be as small as possible to reduce energy loss and heat generation during the current-carrying process, and it is generally at the micro-ohm level.

### Maintenance and Inspection
- **Daily Maintenance**: Regularly check the appearance of the contacts to see if there are burn marks, discharge marks, oxidation and discoloration, etc. If there are any, they should be dealt with in a timely manner. Clean the dirt and dust on the surface of the contacts. You can use a clean cloth dipped in a small amount of alcohol to wipe them. Check whether the connecting bolts of the contacts are loose. If they are loose, they should be tightened in time.
- **Regular Overhaul**: Every certain period of time, such as 1 to 3 years, conduct a comprehensive inspection and maintenance of the contacts, measure the contact resistance of the contacts to ensure that it is within the specified range, check the wear condition of the contacts, such as the thickness of the contact pieces and the elasticity of the springs. When the wear exceeds the specified value, they should be replaced in time. Lubricate the contacts. You can apply an appropriate amount of conductive paste on the surface of the contacts to reduce the contact resistance and prevent oxidation.
- **Fault Maintenance**: When the contacts have faults such as overheating, arcing, and poor contact, they should be repaired in time. Analyze the causes of the faults and take corresponding measures to repair or replace them. For example, if the poor contact is caused by the oxidation of the contact surface, you can gently polish the contact surface with sandpaper, remove the oxide layer and then apply conductive paste.

### Common Faults and Treatment Methods
- **Overheating**: It may be caused by reasons such as excessive contact resistance, current overload, and poor heat dissipation. Treatment methods include checking the contact condition of the contacts, cleaning the dirt and oxide layer on the contact surface, tightening the connecting bolts to ensure good contact, checking the load condition to avoid overload operation, and checking the ventilation system of the switchgear to ensure good heat dissipation.
- **Poor Contact**: It may be caused by reasons such as oxidation of the contact surface, wear, and weakened elasticity of the springs. You can polish and clean the contact surface, replace the severely worn contact pieces or springs, and adjust the pressure of the contacts to make them meet the specified requirements.
- **Arcing**: Generally, it is caused by the generation of electric arcs during the opening and closing process of the contacts. It may be caused by reasons such as inappropriate opening distance and overtravel of the contacts, or uneven contact surface and burrs. It is necessary to adjust the opening distance and overtravel of the contacts to make them meet the specified values. Check the quality of the contact surface, polish and buff it to remove burrs and unevenness.