Vacuum Circuit Breaker's Closing and Opening Vibration

Closing bouncing and opening bouncing of vacuum circuit breakers for power automation equipment Zhao Zhizhong (Department of Information Science and Engineering, Liaoning Institute of Technology, Jinzhou 121001, Liaoning, China) The greater the material hardness, the greater the closing bounce; and the higher the contact pressure, closing The smaller the bounce. Larger closing bounces increase the possibility of contact bluntness, resulting in failure of short circuit breaking. Summarizes the practical experience of commissioning vacuum switches, and gives several methods for reducing the closing bounce. At present, the vacuum switch develops in the direction of “small open distance”. When the conditions permit, the contact distance can be narrowed appropriately, increasing the speed of the sub-gate can increase the speed of the sub-gate, so it can improve the ability to open and close the short-circuit current. The analysis pointed out that: if the opening speed is too high, it will have a negative impact on the short-circuit breaking and opening and closing vibration.

Fund Project: Liaoning Provincial Education Commission Key Project which project (990831 survey) froric Publish when the Secretary after the S has reached a set speed (rigidly divided velocity static and dynamic contact closing brake is the main reason for failure of vacuum circuit breaker short-circuit breaking test 1. This point has gradually become a consensus in the vacuum switch industry.This paper attempts to analyze the closing bounce using a simple physics theory to provide a theoretical explanation for practical experience.The influence of the opening and closing failure of the opening and closing bouncing has not caused enough Pay attention to, through analysis, give the relationship between opening and closing bouncing and opening speed.

1 Closing Bounce 1.1 Causes of the closing bounce and its effects Closing bounce refers to the fact that the circuit breaker's moving contact collides with the static contact and is pushed back by the reaction force, and is then contacted and pushed open again. The severe cases are repeated 4~5 times for 2~6ms. Essentially, this is a kind of forced damped oscillation. The frequency and amplitude of the oscillation depend on the quality of the moving contact system, the speed, the spring rate, and the bumpiness of the spring. Damping situation. Analysis shows that the greater the hardness of the contact material, the longer the bounce time; when the hardness of the contact material is the same, the greater the contact pressure, the shorter the bounce time.

When the circuit breaker is charged, if there is a bouncing between the two contacts, the arc of the vacuum arc is extended. Vacuum arc is a kind of high-temperature plasma, arc temperature can reach seven or eight thousand degrees. The addition of the arcing time increases the depth and breadth of the surface of the contact. When the brake is closed, it will cause the two contacts to contact with each other. After the instant cooling, the two contacts are welded together. This kind of fusion welding cannot be opened by the opening force of a few thousand Newtons of the operating mechanism. Sometimes the welding spot is very small, and the opening force can be pulled open, but often the surface of the contact is pulled and deformed, causing a short circuit in the recovery voltage after breaking. As a result, the result of the welding may fail to open the short circuit.

1.2 Method of eliminating closing bounce When the brake is closed, the moving contact system is driven by the operating mechanism and closes relative to the static contact. The contact force F at the closing time is a key factor in determining the magnitude of the bounce generated by the circuit breaker. Let the velocity before and after the collision be V1, V2, and the action time be t. Then Newtonian mechanics will reduce F, and the bounce will also decrease. From the above formula, there are three ways to reduce the contact impact force F: reduce the mass of the movable contact system m. This can be achieved by shortening the length of the conductive rod, reducing the size of the conductive clip and the soft connection, and selecting a lightweight insulator And so on.

Reduce the absolute value of the speed difference before and after the collision. According to experience, this cannot be achieved by reducing the closing speed V1. Because when V1 is reduced to less than 0.6m/s, the closing power will be insufficient, but it will increase the extent of bouncing. Then you can only try to make V2 reduce, even toward zero. The method is: installing a compression spring on the movable contact system to compress the circuit breaker when the circuit breaker is closed to generate a pre-pressure, that is, the initial pressure of the contact, so as to offset the rebound force of the movable contact.

There are two methods to achieve the collision time t of the large dynamic and static contact: One is to ensure the coaxiality of the static and dynamic conductive rods of the switch tube when producing the switch tube, and to adjust the switch tube when the whole machine is adjusted. Make the two contacts in a plane contact, do not make line or point contact; the other is to use cushioning elements such as rubber gaskets, oil buffers, etc. at the static end to increase the impact contact time.

2 points of the gap between the opening and closing speed and the opening speed of the opening and closing distance of the two switches. At present, the opinion accepted by most people is that the vacuum switch has a strong breaking ability when the opening distance is small. As the distance increases, the limiting breaking current decreases. The reason is that after the distance is increased, the magnetic field weakens and the arc energy loss is large, which is not conducive to breaking.

The opening speed is an average speed, that is, the ratio of open distance to opening time. In the process of breaking, what really matters is the speed of just dividing, that is, the speed at which the two contacts just left. The just-separated speed is provided by the over-travel. When the splitter drive connecting rod runs beyond the required start of the separation. Practical experience shows that, under the conditions permitting, properly narrowing the contact opening distance and increasing the over-travel can improve the rigidity of the sub-speed and improve the breaking capacity.

2.2 Switching speed and opening snap-in vacuum switch In the opening process, the moving contact is not able to move to the predetermined open distance and stops completely. Because the movable contact system has kinetic energy mV2a/2 (a is the speed when the contact is opened at the open point position a), the operating system and the buffer act, and the center is set to the open position. Damping vibration, that is, the opening and closing bouncing. The displacement-time curve of the moving contact of the opening and opening vibration is as shown.

In the middle, the movable contact moves to the set open distance point at the time of opening, that is, the potential energy of the movable contact system at a point is zero. According to the law of conservation of energy, there is a marginal coefficient of the relation, and Wz is the energy converted by the buffer.

It can be seen that the displacement at point b is the maximum amplitude of the opening and closing bouncing, denoted by A. Therefore, at point b, the contact instantaneous velocity Vb = 0, so that the point b (1) becomes (2), since k, m are constant, and the maximum amplitude of the opening vibration is A with va and Wz. Changes in the changes. When the buffer performance is stable, it can be considered that the net does not change, so the larger va is, the larger the maximum amplitude of the opening and bounce vibration is. To successfully break the current, it is required that during the first half cycle (10ms) of the trip, the moving contact should be at least 50%~90% of the total open distance, that is, the range of the opening time is not large. In order to simplify the problem, it can be assumed that the opening time does not change. Therefore, it is known that the greater the va, the greater the average opening speed. Therefore, it can be concluded that when the other conditions are constant, the greater the average opening speed, the greater the opening and closing bouncing.

In recent years, due to the adoption of new contact materials, the opening distance of vacuum switches has become smaller. In the case of a small open distance, the opening and closing bounce vibrations have a particularly significant influence, and often cause the vacuum interrupter to break down due to a rebound, which should be highly valued.

3 Concluding remarks The performance parameters of the switches are mutually influential, and adjustments must be taken into consideration. In addition, some switchgear companies do not have a good understanding of the production process of some key components of the switch. For example, in the quenching and tempering of metal materials, the rigidity and toughness are not suitable, resulting in a serious deviation of the dynamic parameters of the switch from the static parameters. The success rate of the breaking test affects the service life of the switch, and the manufacturer should give sufficient attention to this.

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