Vacuum circuit breaker mechanical parameter selection method
来源: Ningbo Weige Electrical Appliances Co., Ltd. 作者: www.cn-weige.com 时间: 2012-07-24
The vacuum switch in home and abroad in various fields has been widely used, with the vacuum switch using the popularization and the enhancement, the majority of users increasingly need to understand and master the vacuum switch principle, structure, usage and maintenance of knowledge, combined with practical experience from the theoretical analysis of the mechanical reliability of the vacuum breaker and the principle of empirical data, for the majority of users better use of vacuum switch to provide some technical reference.
Vacuum circuit-breaker is in the off state, a vacuum switch tube, a static contact dynamic distance between selection and vacuum circuit breakers rated voltage, use condition, breaking current properties and contact material of vacuum gap, compressive strength and other factors, mainly depends on the rated voltage and contact materials.
As a result of the vacuum switch tube is rated torque on the insulating properties of the impact is bigger, when the rated torque from zero distance increases, the insulation level will also increase, but when the opening distance increases to a certain value, apart from the influence on insulation performance of much, if further increase the distance, will seriously affect the switch pipe mechanical life.
The vacuum circuit breaker installation, operation and maintenance of vacuum circuit breakers that rated torque range : 6kV and the following general is 4 ～ 8mm,10kV and the following general is 8 ～ 12mm,20 ～ 40mm35kV general.
Contact stroke selection must ensure contact after being worn to keep a certain pressure; in the opening so that the movable contact to obtain certain initial kinetic energy, improve the switch initial opening speed, breaking the welding point, reduce arcing time, improve the dielectric recovery rate; when closing can use contact spring get smooth buffer, reducing the bounce.
Switch contact trip is too small, cannot guarantee the contact in the burned after having contact pressure, the switch 's initial speed is too small, effects of the vacuum circuit breaker and dynamic thermal stability, at the same time have serious closing elastic vibration. Switch contact range is too big, will increase the operating mechanism of switching power, or to make closing become very unreliable. Usually vacuum circuit breaker contact stroke is generally taken rated torque20% ~40%,10kV vacuum circuit breaker contact itineraries from 3 to4mm.
The 4 contact pressure
Vacuum circuit breaker contact working pressure on the properties of vacuum circuit breaker has a great impact, the pressure is equal to a vacuum switch tube closing force and contact force of the spring and. Breaker contact pressure of work choices should meet4 requirements:1, so that the vacuum switching tube contact resistance is maintained in the specified range,2, satisfy the dynamic stability test,3, inhibition of bounce,4, reducing brake elastic vibration. As a result of vacuum circuit breaker in the closing short-circuit current, contact in to the breakdown to produce electric arc and electric repulsion, contact bounce, closing speed slowest, therefore, closing short-circuit current examination of contact pressure whether meet the requirements of the most demanding conditions.
If the contact pressure is too small, will increase the contact closing bounce time, at the same time, resulting in a loop resistance increased, directly affect the vacuum circuit breaker working temperature rise. If the contact pressure is too large, as the vacuum switch tube closing force is a constant value, then the increased work pressure, thereby increasing the contact force of the spring, causing the operating mechanism of switching power increased, increasing the vacuum tube shock and vibration.
In practical work, not only to consider the contacts of electrical power with the exception of the peak value of short-circuit current on the foreign, must also consider the switch contact structure and size, at the same time, must also consider the contact hardness, tripping speed and other factors. In short, must be in practice consideration. Vacuum switch contact pressure according to the breaking current size that empirical data for breaking current of 12.5kA, a selective pressure for the50kg. Breaking current of 16kA, a selective pressure for the70kg. Breaking current of 20kA, selection pressure is 90 ~ 120kg. Breaking current of 31.5kA, selection pressure is 140 ~ 180kg. Breaking current of 40kA, selection pressure is 230 ~ 250kg
Since the separating speed directly influences after current zero contact between the dielectric strength recovery rate, if the arc is extinguished, the contact between the dielectric strength recovery speed is less than the recovery voltage, will cause the arc reignition, in order to prevent arc reignition, and shorten the arcing time, must satisfy the opening speed. Opening speed depends on the size of the rated voltage, when the rated voltage and the contact distance is constant, the switching-off speed fluctuation range depends on breaking current size, the nature of the load, the recovery voltage and other factors, breaking current is larger, the switching-off speed should also be larger, breaking capacitive current, because the recovery high voltage, in order to reduce the reignition probability, the switching-off speed should also be larger. 10kV vacuum separate switch speed is usually taken as0.8-1.2m/s, when necessary, can be higher than 1.5m/s.
In fact, the breaking capacity of the impact is the biggest is the initial opening speed, rather than the average opening speed, therefore, some high performance of vacuum circuit breaker, and the35kV level of the vacuum circuit breaker, cross-party examination just points within a few millimeters of the switching-off speed. Seems to opening velocity of the bigger the better, but that is not the case, the switching-off speed is bigger, caused by opening the elastic vibration more calendar harm, overshoot is calendar harm, so the switch tube bellows vibration, compression is also more serious, easy to cause the bellows to damage and leakage, and at the same time, on the speed machine vibration is also greater, easy to cause damage to the parts.
As the vacuum switch tube in the rated torque of the static pressure level is relatively high, so the vacuum circuit breaker closing speed brake speed significantly lower score. In order to minimize the contact in the closing process due to the breakdown caused by wear, and avoid the occurrence of contact welding, therefore must have certain closing speed, but the high switching speed not only increases the operating mechanism of switching power, at the same time that the switch tube by closing impact increases, greatly reduce its life. Normally10kV vacuum circuit breaker speed for 0.4-0.7m/s when necessary, desirable for0.8-1.2m/s.
7contact bounce time
Vacuum circuit breaker closing time is a measure of the size of the vacuum circuit breaker, the performance is an important symbol, with the circuit breaker contact bounce pressure, closing speed, distance and vacuum switch tube contact materials, but also with the switch tube structure, circuit breaker structure and installation and commissioning about. The contact bounce time is less, the better the performance of the longer, bounce, contact wear more serious, easy generation of switching overvoltage in closing short-circuit current, or a capacitor, and action, thermal stability test will lead to contact welding. In addition, the contact bounce time is long, serious harm the switch of the corrugated tube service life. Class 10kV copper complex contact materials for vacuum circuit breaker closing bounce time does not exceed2ms, other contact materials for vacuum circuit breaker closing bounce time can be relatively large, but shall not exceed 5ms.
Vacuum circuit breaker pole synchronous said triode not closed at the same time or the extent of separation, because, of switching synchronization is relative, values of difference, so in general only the assessment of switching synchronization. Triode synchronous differential circuit breaker will seriously affect the switch breaking capacity, easy to produce a long arc time. As a result of breaker closing speed, distance is small, through the accurate debugging, achieve parameter requirements is not difficult, general rules of switching synchronization is not more than1ms.
9 dynamic, static contact of the coaxial degree
Dynamic, static contact switch tube is coaxial with a specific request to the manufacturing process to ensure that the switch tube is installed in the operating mechanism, you can ensure the coaxiality, and operation mechanism of the type and installation process of a direct relationship between, for hanging mechanism, coaxial degree depends mainly on the operating mechanism, for floor type machinery on the coaxial degree is also greatly influenced, during installation to avoid switching tubes subjected to shear and shearing stress, coaxial degree of the general requirements of not more than 2mm.