1 Introduction At present, vacuum switches have been widely used in various fields at home and abroad. With the popularization and improvement of the use of vacuum switches, users are increasingly in need of understanding and mastering the knowledge of the principles, structure, use and maintenance of vacuum switches. The practical experience theoretically analyzes the selection principle and empirical data of the mechanical parameters of the vacuum circuit breaker, and provides some technical references for the users to use the vacuum switch better. 2 rated opening distance When the vacuum circuit breaker is in the open state, the distance between the vacuum switch tube and the static contact is selected and the rated voltage of the vacuum circuit breaker, the use condition, the nature of the breaking current, the contact material, the compressive strength of the vacuum gap, etc. The factors depend on the rated voltage and the contact material. Since the rated opening distance of the vacuum switch tube has a great influence on the insulation performance, when the rated opening distance increases from the zero opening distance, the insulation level will also increase, but when the opening distance increases to a certain value, the opening distance is insulated. The effect of performance is not great. If the opening distance is further increased, the mechanical life of the switch tube will be seriously affected. Through the installation, operation and maintenance of the vacuum circuit breaker, the rated opening range of the vacuum circuit breaker is generally selected as follows: 6kV and below is generally 4 to 8mm, 10kV and below is generally 8 to 12mm, and 35kV is generally 20 to 40mm. 3 contact contact stroke The contact contact stroke must be selected to ensure that the contact maintains a certain pressure after wear; when the brake is opened, the movable contact obtains a certain initial kinetic energy, increases the initial opening speed of the switch, breaks the fusion joint, and reduces The arcing time increases the recovery speed of the medium; when the switch is closed, the contact spring can be used to obtain a smooth buffer and reduce the bounce. The contact stroke of the switch is too small to ensure the contact pressure of the contact after the burnout. The initial speed of the switch is too small, which affects the breaking and dynamic thermal stability of the vacuum circuit breaker, and at the same time generates a serious closing spring. If the contact stroke of the switch is too large, the closing work of the operating mechanism will be increased, or the closing of the switch will be extremely unreliable. Generally, the contact stroke of the vacuum circuit breaker generally takes 20% to 40% of the rated opening distance, and the contact stroke of the 10kV vacuum circuit breaker generally takes 3 to 4 mm. 4 contact working pressure The working pressure of the vacuum circuit breaker contact has a great influence on the performance of the vacuum circuit breaker. The pressure is equal to the sum of the self-closing force of the vacuum switch tube and the contact spring force. The working pressure selection of the circuit breaker contacts should meet the requirements of 4: 1. Keep the contact resistance of the vacuum switch tube within the specified range, 2. Meet the requirements of the dynamic stability test, 3. Suppress the closing bounce, 4 Reduce the opening and closing vibration. Since the vacuum circuit breaker closes the short-circuit current, the contact generates arc and electric repulsion after the pre-breakdown, the contact bounces, and the mechanism closing speed is also the slowest. Therefore, closing the short-circuit current is to check the working pressure of the contact. Whether the most demanding conditions are met. If the working pressure of the contact is too small, the bounce time when the contact is closed will be increased, and at the same time, the resistance of the primary circuit will increase, which directly affects the long-term working temperature rise of the vacuum circuit breaker. If the working pressure of the contact is too large, since the self-closing force of the vacuum switch tube is a constant value, the working pressure is increased, thereby increasing the spring force of the contact, resulting in an increase in the closing work of the operating mechanism, increasing the vacuum tube. Shock and vibration. In actual work, it is necessary to consider not only the electric power between the contacts but also the peak value of the short-circuit current. It is also necessary to consider the contact structure and size of the switch. At the same time, factors such as the hardness of the contact and the opening speed must be considered. In short, comprehensive consideration must be made in practice. The contact contact pressure of the vacuum switch is based on the magnitude of the breaking current to obtain empirical data. When the breaking current is 12.5 kA, the selection pressure is 50 kg. When the breaking current is 16kA, the selection pressure is 70kg. When the breaking current is 20kA, the selection pressure is 90-120kg. When the breaking current is 31.5 kA, the selection pressure is 140 to 180 kg. The breaking current is 40kA and the selection pressure is 230~250kg. Since the opening speed directly affects the speed at which the dielectric strength between the contacts recovers after the current crosses zero, if the arc strength is restored, the medium strength recovery speed between the contacts is less than the recovery voltage, which will cause the arc to reignite, to prevent the arc from reigniting, and to shorten the combustion. The arc time must meet the opening speed. The speed of the opening speed mainly depends on the rated voltage. When the rated voltage and the contact opening distance are fixed, the fluctuation range of the opening speed depends on the magnitude of the breaking current, the load property, the recovery voltage, etc., when the breaking current is large. The opening speed should also be large. When the capacitor current is broken, because the recovery voltage is high, in order to reduce the chance of reignition, the opening speed should also be large. The opening speed of the 10kV vacuum switch is usually 0.8-1.2m/s, and can be higher than 1.5m/s if necessary. In fact, the biggest impact on the breaking capacity is the initial opening speed, not the average opening speed. Therefore, some high-performance vacuum circuit breakers and 35kv-class vacuum circuit breakers are only within a few millimeters of the party’s assessment. Opening speed. It seems that the greater the speed of opening, the better, but this is not the case. The greater the speed of opening, the more the damage caused by the opening of the brake, the more the overshoot is, so the vibration and compression of the bellows of the switch tube Severe, it is easy to cause the bellows to leak early and leak air. At the same time, the vibration of the speed machine is also larger, which is easy to cause damage to parts. Since the static withstand voltage level of the vacuum switch tube at the rated opening distance is relatively high, the closing speed of the vacuum circuit breaker is significantly lower than the opening speed. In order to minimize the electrical wear caused by the pre-breakdown of the contact during the closing process, and to avoid contact welding, it is necessary to have a certain closing speed, but the excessive closing speed not only increases the cooperation of the operating mechanism. The brake work increases the closing impact of the switch tube and greatly reduces its service life. In general, the closing speed of a 10kV class vacuum circuit breaker is 0.4-0.7m/s and may be 0.8-1.2m/s if necessary. 7 contact closing bounce time The closing time of the vacuum circuit breaker is an important indicator to measure the performance of the vacuum circuit breaker. It is related to the contact bounce pressure, closing speed, opening distance of the circuit breaker and the contact material of the vacuum switch tube. It is also related to the structure of the switch tube, the structure of the circuit breaker and the installation and debugging. The smaller the contact bounce time, the better the performance, the longer the bounce time, the more serious the electrical wear of the contact, the easy to generate the closing overvoltage, when closing the short circuit current or capacitor, and the action and thermal stability test. Will cause the contacts to be welded. In addition, the longer the contact closing bounce time, the serious damage to the service life of the bellows of the switch tube. The vacuum circuit breaker closing time of 10kV copper contact material does not exceed 2ms. The closing time of the vacuum circuit breaker closing of other contact materials can be relatively large, but it must not exceed 5ms. 8 tripolar synchronicity The three-pole synchronism of the vacuum circuit breaker indicates the degree of closure or separation of the three poles at different times. Since the phase-synchronization and closing-up are relative, the values ​​are not much different, so in general, only the three-pole closing synchronism is evaluated. Circuit breakers with poor three-phase synchronization will seriously affect the breaking capacity of the switch, and it is easy to generate excessive arcing time. Since the opening and closing speed of the circuit breaker is faster and the opening distance is smaller, it is not difficult to achieve the parameter requirement through accurate debugging. Generally, the closing synchronization time is not more than 1 ms. 9 coaxiality of moving and static contacts The coaxiality of the moving and stationary contacts has specific requirements for the true switching tube and can be guaranteed by the manufacturing process. Whether the switching tube is mounted on the operating mechanism can ensure its coaxiality, and the type and installation process of the operating mechanism are Direct relationship, for the hanging mechanism, the coaxiality mainly depends on the operating mechanism, and the influence of the floor-standing machine on the coaxiality is also great. During the installation process, the switching tube must be protected from shear and shear forces. Function, coaxiality is generally required to be no more than 2mm. Absolute Linear Encoders,Custom Absolute Encoder,Rotary Encoder Magnetic,Miniature Absolute Encoder Yuheng Optics Co., Ltd.(Changchun) , https://www.yhencoder.com
5 opening speed
6 closing speed 