How to Design Tripping Mechanism of Vacuum Circuit Breaker?

For the design of the tripping mechanism of the outdoor VCB vacuum circuit breaker, the first step is to choose the type of mechanism, and then determine the size of the buckling surface, calculate tripping power and tripping torque of the mechanism to design the tripping drive device.

1. Mechanism type of the outdoor VCB automatic recloser

It is mainly determined by the overall layout of the whole outdoor VCB breaker mechanism and the allowable space size, and the tripping mechanism should be placed in the link with less force as much as possible. When choosing the mechanism, the stability of the buckle and the size of the tripping force, as well as the tripping work must also be considered. Based on the comparison of several tripping mechanisms, the toggle tripping mechanism is suitable for occasions with large buckling force, high buckling stability and strong tripping device.

The two buckle structure parts of the hook-type tripping mechanism are separated. Therefore, the position of the impact point should be paid attention to in the design, especially for the tripping mechanism and the hook mechanism of the flat buckle. If the force acting in the direction of buckling is in the direction of tripping the ballast, the buckle will fail and unstable factors will be generated. Therefore, the manufacturing error has a greater impact on the stability of the buckle.

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2. The buckle surface size of the outdoor VCB automatic recloser

For the hook mechanism, the stability of the buckle also affects the tripping work. In terms of the stability of the buckle, the acting torque on the buckle node should be the torque to prevent tripping, and it is better if it is larger. However, power line recloser increases the tripping work. In terms of reducing the tripping work, the tripping stroke should be reduced. The smaller the length of the buckle surface, the better. The manufacturing error is the main factor affecting the size.

3. Calculation of tripping drive device of the outdoor VCB automatic recloser

Based on the calculated dynamic characteristics and the required trip time, the output characteristics of the needed drive device can be estimated by using the functional relationship. In addition, the set driving device design output tripping time and principle that the output torque of the static characteristics of the driving device is greater than the tripping torque can be used for calculation. The output torque has an impact on the tripping member of the outdoor VCB, so this calculation is relatively safe.

However, the tripping drive sometimes has additional requirements. For example, the high-voltage circuit breaker must operate without error at 65% of the rated voltage, and must not operate at 30% of the rated voltage. In this case, in addition to calculations, experimental verification is needed to ensure the pole mounted auto recloser reliability of the work.

4. Failure control of the buckle surface of the pole mounted recloser

The buckle of the locked door (or latches) and the locked hook is in line or small area contact. The contact point has to withstand high-impact stress. Also, the surface of the buckle has relative movement under higher pressure stress. Therefore, the surface strength, hardness and wear resistance of the material should be fully considered. Otherwise, plastic deformation, brittle peeling and pits will appear on the buckle surface. In a long term, the surface will be rough with the increase of tripping relay and wear, the geometric shape and size of the buckle part will be destroyed, and the stability and reliability of the tripping mechanism of the outdoor VCB will be affected.

Therefore, appropriate materials and surface treatment methods should be selected to make the surface of the automatic circuit recloser buckle has an appropriate hardness, and the internal components have sufficient strength and toughness. The purpose is to resist impact and prevent plastic deformation and brittle spalling on the surface. For example, using carbon steel quenching or surface carburizing quenching method can make the surface hardness reach a bonding state of about RC60. The transition part of the joint surface should be properly rounded corners to avoid bad contact and damage in the early stage.

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