(1) Vacuum insulation properties
The experiment shows that the vacuum gap breakdown voltage increases with the increase of vacuum degree at the initial stage. When the vacuum degree reaches 1O - 1O Torr, the breakdown voltage remains unchanged, which means that the vacuum tube vacuum degree can not be lower than 1O-1O. the reason.
(2) Characteristics of vacuum electric isolation
The main arc characteristics to determine the nature of the metal vapor. However, currents of different sizes have different characteristics of arcs. A current below several thousand amps is called a small current vacuum arc. At present, vacuum switches used in mines are generally below several thousand amps. Therefore, the phenomenon of interception is ubiquitous. The so-called interception phenomenon is a vacuum arc with a small current. When the current is small to a certain value, the arc pressure is too fast, the vapor pressure drop near the cathode shift point and the temperature drop suddenly, and the arc is difficult to maintain and suddenly extinguishes.
2. Vacuum switch equipment structure
(1) Contact of vacuum circuit breaker
(2) Material: Metal materials used as contacts can be divided into two categories: one is arc-resistant, refractory pure metal, such as tungsten, molybdenum, etc. The other is alloy material made of copper and button. The currently used oxygen-free copper is the alloy of this type. (2) Structural aspects: The main component for maintaining vacuum is the bellows. However, the volume of the vacuum tube is also as small as possible. In order to reduce the volume, only the moving and static contacts are installed in the tube without other arc extinguishing facilities, and the arc extinguishing ability is improved only by the shape design of the moving and static contacts. A common outer spiral groove contact is a typical form.
3. Circuit characteristics
(1) Set the overvoltage absorbing circuit: the operating overvoltage is generated due to the interception phenomenon; in the high voltage switch, a set of varistor is added to the f6kv1. A set of RC capacitors is added to the low-voltage vacuum switch to limit the operating overvoltage to a certain range (typically 2.5-3.5 times the phase voltage peak).
(2) A variety of protection circuits are used: è„’80A switch (generally only installed with thermal breaker). The switch above 120A is generally equipped with motor integrated protector.
4. Check before commissioning
According to my use in the field. The following checks are required before commissioning.
(1) Check that each component is complete. Is there any looseness?
(2) Check whether the standby parameters are consistent with the site requirements. (1) Check if the near and remote control switches are in the required position. (2) Whether the transformer voltage level is the same: mainly for the low-voltage switch control transformer primary tap is the same as the field voltage level. (3) Check whether the protection device settings meet the requirements: vacuum switches are generally equipped with circuits such as leakage, short circuit, overload, overvoltage protection, etc., and the leakage protection circuit and overvoltage protection circuit are generally adjusted at the factory, if there is no special Do not debug on your own. However, the short-circuit protection circuit and the overload protection circuit should be set according to the needs of the site. Firstly, the setting value is calculated through the setting calculation. At the specific timing, the switch should be adjusted accordingly. Generally used as the distribution switch, the reliability coefficient is Take the lower limit or the middle and use it as a starter, especially for starting heavy loads such as scraper conveyors, belt conveyors, etc., the reliability factor should be taken as the upper limit. This avoids frequent movements or setting due to small setting values. The value is too large to protect.
5. Check if the insulation performance is good
Due to the phenomenon of shut-off of the vacuum switch, there is an operating over-voltage phenomenon. For this reason, although the high-voltage switch is equipped with a varistor and the low-voltage switch is equipped with an over-voltage absorbing circuit, these protection circuits are only designed to limit the over-voltage to a certain value. Range f2.5 - 3.5 times the voltage peak), instead of eliminating overvoltage. Therefore, the insulation performance of the vacuum switch must meet the specified requirements, otherwise it will be easily broken down. Check the ground and phase insulation during inspection. It is worth noting that the overvoltage protection circuit and transformer must be removed from the main circuit when inspecting the phase insulation. Otherwise, accurate data cannot be measured.
6. Special inspection of vacuum switch
(1) Vacuum test: Users generally do not have special test instruments, and can only measure indirectly. There are two methods:
(a) High voltage test: For 6kv high voltage switch, generally add 2 3 kv power frequency voltage for 1 rain without flicker to pass. For 660v low voltage switch plus 1 0 kv for 1 win without flicker is qualified.
(b) Measuring contact pressure (only for low-voltage switch): first close the contactor, then pull down the universal joint connected to the movable rod of the vacuum tube. Compared with other, you can get a preliminary understanding of the degree of vacuum. Because the vacuum of the vacuum tube is damaged, the negative pressure inside the tube is reduced, and the contact pressure is smaller than that of the normal tube.
(2) Three-phase contact synchronization test: Since the contact condition of the vacuum tube cannot be directly observed, it must be tested. Generally, a simple method is to string a small bulb and a dry battery on the power supply and load side. The three-phase contactor is gradually closed, and the synchronization can be judged by observing the order of the lights, and gradually adjusted.
(3) Resistor-capacitance over-voltage absorption circuit test: Disconnect the load and make the vacuum-connected device disconnected. Use a multimeter to measure the two resistors separately. Note that the measurement is in parallel with the capacitor (about 1.5 Mn1 of resistance, etc. The data can only be read after the needle is completely stable. When measuring the capacitance C (approx. O.47), if only the quality is checked, it can be determined according to whether the pointer has a swing when measuring the multimeter resistance. The accurate measurement needs to be welded and connected to measure. .
7. Downhole use and maintenance
1 Explosion-proof electrical equipment should be inspected before entering the well (product certificate, explosion-proof certificate and coal safety sign 1 are complete, otherwise it is not allowed to enter the well.
2 Due to its strong breaking current, long life and light weight, the vacuum switch should be used in the downhole working face with heavy load and inconvenient handling, such as scraper conveyor and belt conveyor.
3 After the installation is completed, carefully check the relevant settings of the protection circuit and make a record. Re-set when replacing the load.
4 After entering the well for half a year, it should be transported back to the ground for maintenance, focusing on three-phase synchronization, over-travel of each vacuum tube, protection circuit action value and other items to ensure that the switch is in good condition.
8. Difficult to check the failure analysis and handling office
1 When the overvoltage protection circuit is faulty in the field, I have conducted an investigation. It turns out that most electricians do not know the interception phenomenon, and they do not know that there is an operation overvoltage. I donâ€™t know what the resistance and protection circuit is. The electrical equipment is Breakdown does not check the protection circuit. Technical training should be greatly strengthened for this situation, especially technical training in electronic circuits.
2 vacuum tube leakage and spring rebound force is too large
The fault phenomenon is that it cannot be reliably sucked. The principle is: the intact vacuum tube is negative pressure (more than 1O "the action of the bracket 1 will attract the moving contact to the static contact, but after the spring is applied, the spring force is greater than the suction force to make the movement The contacts are separated. When the electromagnetic force is applied when the switch is closed, the final pressure of the static and dynamic contacts is: Fè›‘=F negative pressure+F magneticâ€”â€”F_elastic â‹¯ â‹¯ â‹¯â‹¯ â‹¯ â‹¯â‹¯ â‹¯ (1) Obviously, when the pipe F self-reduction during air leakage will cause a decrease in F. When it reaches a certain level, the suction table will be unstable. In this case, the pipe should be replaced in time.
3 spring rebound force is too small and there is residual magnetism armature
The fault phenomenon is that the contactor cannot be released, and it is not difficult to analyze by (1). When the F-ball falls F magnetic (this time should be F-magnetic) rises, reaching a certain level will make the contactor not release, then the electromagnetic The system is degaussed. If the pipe needs to be replaced, the three-phase pipe is also synchronized.
In short, the life of the vacuum contactor is much larger than the life of the air connector. The number of operations is from tens of thousands to hundreds of thousands of times. It is not necessary to repair the contacts during use, but only pay attention to observe the overtravel. , vacuum and other aspects. In particular, the overvoltage protection circuit should be checked frequently. The protection circuit of the high-voltage vacuum switch generally adopts a box-type structure. There are spare parts in condition. Because it is difficult to repair the electronic circuit underground, once the fault occurs, only the protection circuit can be removed to the ground for maintenance. For the low-voltage switch, Consider changing the movement. This simplifies maintenance and reduces power outages. The vacuum switch is suitable for underground coal mines. Especially when the vacuum tube is turned on and off, the spark does not leak, the load capacity is strong, the service life is long, the maintenance amount is small, and the weight is light, which meets the special requirements of coal mine production.
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