SZ11-40000/110/0.4 transformer magnetic control type tap changer

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The SZ11-40000/110/0.4 transformer usually adopts the on-load tap changer instead of the magnetic control type tap changer. However, there are some vacuum tubes with similar structures and principles that can be applied to the on-load tap changer of this transformer. The following is the relevant introduction:

### The Role of Vacuum Tubes
In the on-load tap changer, the vacuum tubes mainly play the role of connecting and disconnecting the current when switching the taps. By utilizing the high insulation performance and excellent arc extinguishing performance of the vacuum, rapid and reliable switching can be achieved, reducing the damage to the contacts caused by the electric arc, prolonging the service life of the tap changer, and ensuring that the transformer can stably adjust the output voltage under different load conditions.

### Performance Requirements for Vacuum Tubes
- **High Vacuum Degree**: Generally, the vacuum degree of the vacuum tube is required to be above 10⁻⁷ torr to ensure good insulation performance and arc extinguishing performance. A high vacuum degree can reduce the possibility of gas discharge, lower the probability of arc reignition, and improve the reliability and stability of the switch.
- **Large Current Interrupting Capacity**: It needs to be able to withstand the relatively large current generated during the tap switching process of the transformer. Generally, it is required to have an interrupting capacity of several hundred amperes or even higher to ensure that the circuit can be safely and reliably cut off under the load current.
- **Long Electrical Life**: Since the on-load tap changer needs to perform tap switching operations frequently, the vacuum tubes need to be able to withstand hundreds of thousands of or even more opening and closing operations without serious problems such as severe contact burning, adhesion, or a decrease in vacuum degree, ensuring their long-term stable operation.
- **Good Mechanical Properties**: The moving contacts of the vacuum tubes need to accurately contact and disconnect with the fixed contacts at the specified speed and trajectory, and maintain good mechanical stability during the long-term operation process, without problems such as contact loosening and deformation, to ensure the normal operation of the switch.

### Common Types of Vacuum Tubes
- **Ceramic Vacuum Tubes**: They have good insulation performance, high temperature resistance, and mechanical strength, and can work stably under high voltage and large current conditions. Their internal structures usually combine metal shielding and ceramic insulation, effectively improving the withstand voltage capacity and anti-interference ability of the vacuum tubes.
- **Glass Vacuum Tubes**: They have relatively high transparency and insulation performance, which is convenient for observing the contact state and vacuum degree inside. The manufacturing process of glass vacuum tubes is relatively simple, and the cost is relatively low. However, they are relatively weak in terms of mechanical strength and high temperature resistance, and are suitable for some on-load tap changers with medium and low voltage and small capacity.

### Maintenance and Inspection
- **Regularly Check the Appearance**: Observe whether there are abnormal conditions such as cracks, damages, or discoloration on the appearance of the vacuum tubes. If any are found, they should be replaced in time to prevent the vacuum degree inside the vacuum tubes from decreasing or discharge phenomena from occurring.
- **Measure the Vacuum Degree**: Use professional vacuum testers to regularly measure the vacuum degree of the vacuum tubes to ensure that the vacuum degree remains within the specified range. When the vacuum degree is lower than a certain value, the vacuum tubes should be replaced in time to avoid affecting the performance and reliability of the tap changer.
- **Check the Wear of Contacts**: Judge whether the contacts need to be replaced or repaired by observing the surface wear degree, burn marks, etc. of the contacts. Generally speaking, when the wear amount of the contacts exceeds the specified limit value, the contacts should be replaced in time to ensure good contact performance and interrupting capacity.