Calculate the measurement process: start the high voltage → leak current detection → turn off the high voltage → turn on the charge switch → the voltage reaches the specified value → start the high voltage and magnetron current → measure the leakage ionization current → deduct the leakage → the current turns into the vacuum value → display. Pull the arcing chamber moving contact away a certain distance. The pulsed high voltage is applied, the excitation coil is wound around the outdoor side of the arc extinguishing chamber, and the coil passes a large current, thereby generating a pulsed magnetic field synchronized with the high voltage in the arc extinguishing chamber. The size of the contact resistance determines the temperature rise of the switch at the rated current, and to a certain extent, it reflects the electrical contact state of the switch and the quality of assembly and maintenance. Therefore, the technical condition of the conductive circuit of the switch is determined by measuring the contact resistance.
There are many ways to measure the contact resistance, such as DC voltage drop method and double-arm bridge method. Theoretically speaking, the DC voltage drop method measures the resolution value from 0μΨ, which can reflect the contact state of the device during operation. However, this method is affected by factors such as instrument accuracy and meter reading errors, and requires more equipment and instruments. The dual-arm bridge method uses only one double-arm bridge, which has simple wiring and convenient operation, and is especially suitable for on-site measurement.
The mine uses two-arm bridges to measure the contact resistance of the vacuum tubes, which is carried out on a monthly maintenance cycle. In the case that the three-phase over-travel is adjusted to the same level, the three-phase contact resistance is basically the same and does not exceed 150 μΨ. If the three-phase contact resistance is too different (over 100μΨ), use a vacuum tube with a large difference.
The contact opening distance is the distance between the ends of the moving and stationary contacts in the opening position. The open distance should ensure that there is a reliable arc extinguishing during the opening process. It depends on the rated voltage of the vacuum switch, and also depends on the breaking properties and pressure resistance requirements under the conditions of use. The following table shows the selection range of different types of vacuum interrupter contact distances under different rated voltages.
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