Application of vacuum switch in mine

This article mainly introduces the application of vacuum switch and puts forward solutions to the problems existing in vacuum switch application.

Vacuum Switch Application The Yangaozhuang Coal Mine is a water mining well that was trial-produced in 1997. At present, high-voltage switch low-voltage explosion-proof switches are all "vacuumized". The use of a large number of vacuum switches has brought us new topics. 1 Vacuum Switching Features Vacuum Switching is A novel power switchgear is a pair of contacts in the main circuit of the switch-off main circuit sealed in a vacuum arc-extinguishing chamber isolated from the environment. With vacuum as the insulating medium and means of arc extinguishing, when the main circuit is switched on and off, the arc and hot gas are not exposed, so it will not cause the explosion of flammable gas. In addition, the vacuum switch also has a small contact opening distance and fast action. Short arc time, short arc extinguishing, fast contact, light burn and long service life are suitable for frequent operation. During the service life of the vacuum tube, the contact part does not need maintenance and inspection. However, there are problems such as operation overvoltage and leakage of vacuum tubes in vacuum switches. 2 Operational overvoltage suppression measures Operation overvoltages are caused by abrupt changes in circuit state and energy conversion of energy storage components. When the vacuum switch is turned off, overvoltage may be caused due to the cutoff, or overvoltage may occur due to re-ignition and repeated cutoff of the high-frequency current. When the switch closes, the closure of the contact bounce or the breaking and re-ignition of the transient high-frequency current occurs. Overvoltage may also be generated. At present, the motor's factory insulation level is still 2ve+1000V. To prevent this overvoltage hazard, especially to mitigate the harm of high-frequency overvoltage on the accelerated aging of the motor insulation, the vacuum switch starter motor must be set. Over voltage protection device The measure to inhibit overvoltage in the mine is to use zinc oxide arrester and RC surge suppressor. Zinc Oxide arresters with semiconductor transistors have a very large resistance at normal operating voltages and have very low currents. When the voltage rises to a certain value, the resistance drops sharply, showing a stabilizing characteristic. Zinc Oxide arresters can limit overvoltages. However, the residual voltage of the high-frequency over-voltage still impacts the insulation of the motor. Frequent high-frequency voltage impact will accelerate the insulation aging of the motor and should be noticed.

Resistor-to-capacity over-voltage suppressor connects the resistor R and the capacitor C in series as a protection element, which is connected in parallel with the input terminal of the load and changes the impedance value of the original circuit to suppress the occurrence of various over-voltages. . Resistor-capacitor protection in the capacitor C component can slow down the rise of overvoltage, but also reduce the load of the wave impedance, thus reducing the cut-off overvoltage resistor R component role is: When the closure occurs, it is in the load circuit of high frequency The energy consumption during oscillation makes it possible to effectively suppress the overvoltage and suppress the high-frequency current during re-ignition so that it attenuates quickly, reducing the secondary voltage multiple of re-ignition to no more than 2 and using the resistance container. To mitigate the steepness of overvoltage surges and limit the amplitude with arresters, the motor protection effect is better.

3 vacuum identification vacuum tube vacuum switch, the arc chamber vacuum (vacuum pressure) is to ensure reliable operation of the vacuum switch one of the important indicators. Therefore, the vacuum tube must have a certain degree of vacuum in order to have breaking current capability. The allowable maximum value of the vacuum degree specified in the technical standards of China's Ministry of Industry (JB) is 1.33. The mine uses a high-voltage vacuum switch cabinet for nearly 10 years. Two methods were used for measurement.

The first method uses the insulation resistance method and the power frequency voltage method to determine the 6kV vacuum, ie, the 2500V rocker for measuring the vacuum tube every month, as long as the contact path of the 100 arc extinguish chamber is adjusted to its specified distance, Apply 20kV power frequency voltage between contacts and maintain for one minute. If there is no discharge phenomenon, it can be used continuously. If a glow discharge or electrical breakdown occurs in a vacuum interrupter, the vacuum degree has been seriously damaged and the vacuum tube should be replaced.

The second method uses the WT-CI vacuum tester. It is a computer-based real-time acquisition and processing system that uses advanced electronic technology and advanced magnetron discharge principles. It also utilizes single-chip microcomputer technology and is equipped with professionally designed flexible excitation coils. Realize the scene does not dismantle, the real-time acquisition processing and the microcomputer synchronous monitoring, the examination process only is about 20s, for the user masters the vacuum interrupter vacuum state, has planned the replacement vacuum interrupter to provide the reliable data.

Calculate the measurement process: Start high voltage - Measure leakage current * Turn off high voltage - Turn on charge switch - Voltage up to specified value - Start high voltage and magnetron current - Measure leakage + ionization current - Subtract leakage - Current into vacuum value - Display will be off The arc chamber movable contact pulls a certain distance to apply a pulsed high voltage, and the excitation coil is wound on the outdoor side of the arc extinguishing chamber. The coil passes a large current, thereby generating a pulsed magnetic field synchronized with the high voltage in the arc extinguishing chamber. In this way, under the action of the pulsed magnetic field, the electrons in the arc extinguishing chamber make a spiral movement and collide with the residual gas molecules to form an ion current, and the generated ion current is approximately proportional to the residual gas density, that is, the degree of vacuum, for different diameters. Vacuum tubes, in the same degree of vacuum conditions, the size of the ion current is also different through the experiment can be calibrated a variety of tube vacuum and ion current curve corresponding to the measured ion current, you can query the ion of the tube type The current-vacuum curve obtains the degree of vacuum of the tube. This process is automatically performed by the computer. 4 The problems in the practical application of the vacuum switch and the processing methods There are various problems in the practical application of the vacuum switch. Discussion of electrical problems 4.1 Contact resistance The size of the contact resistance determines the temperature rise of the switch at the rated current, and to a certain extent, it reflects the electrical contact state of the switch and the quality of the assembly repair. Therefore, the contact resistance is used to measure the conduction of the switch. The technical state of the circuit has many ways to measure the contact resistance, such as the DC voltage. Decline, dual-arm bridge method, etc. Theoretically speaking, the direct voltage drop method is used to measure the resolution value from 0n, which can reflect the contact state of the device during operation. However, this method is affected by factors such as instrument accuracy and meter reading errors, and requires more equipment and instruments. The dual-arm bridge method uses only one double-arm bridge, which has simple wiring and convenient operation, and is especially suitable for on-site measurement.

The mine uses two-arm bridges to measure the contact resistance of the vacuum tubes, which is carried out on a monthly maintenance cycle. In the case that the three-phase over-travel is adjusted to the same level, the three-phase contact resistance is basically the same, not> 150 tons, if the three-phase contact resistance is too different (more than 100(4)), the vacuum tube with a large difference must be replaced with 4.2 contacts. And the adjustment of the overtravel stroke distance is the distance between the ends of the moving and stationary contacts in the opening position. The open distance should ensure reliable arc extinguishing during the opening process. It depends on the rated voltage of the vacuum switch and also depends on the fan and mine ventilation network matching under the conditions of use (turning to page 22). Before the test, drain the wind to collect stagnant water so as not to obstruct the static pressure tube and the full pressure tube due to stagnant water. Before the error test, fix the full pressure tube and the static pressure tube in the meter pressure field to avoid the full pressure tube and the static pressure tube. Damage, causing errors.

Due to the determination of the spare ventilator, the organization of the measurement should be strict, the identification time should be shortened as much as possible, and the corresponding safety technical measures should be taken. The pressure production field should be selected in the stable location of the wind within the wind, so that the measured data is highly accurate. At one operating point, there must be enough time to ensure that the air volume is stable before reading.

The use of regression analysis to draw curves, to a certain extent, can eliminate the instability caused by hand drawing.

Zhang Ruijiang (1971-), male, Ventilation Area Engineer of Kailuan Group Co., Ltd., Tangshan Mining Branch. He graduated from China Mining Ventilation Specialties in 1994. He had broken the nature and pressure requirements in the following table (on page 19). The selection range of different types of vacuum interrupter contact distances under different rated voltages.

The overtravel of the contact is the distance from the beginning of the contact of the movable contactor to the end of closing, that is, the stroke of the direct contact of the moving contactor. Its role is: to ensure that the contact can still wear after the rated voltage (kV) rated distance (mm) vacuum contactor vacuum circuit breaker to maintain a certain contact pressure and reliable contact; in the opening, the moving contact Acquiring a certain initial acceleration and welding points that break the contacts. When the brakes are closed, the impact of the movable contacts on the static contacts can be reduced. Normally, the overtravel of the vacuum switch only takes about 15-40% of the contact distance. For example: The contact distance of the ZNK-3/630~100 mining high voltage vacuum circuit breaker is 9t 1mm. Overtravel is the two important indicators of the vacuum switch. Special attention should be paid to the on-site maintenance. In particular, large-capacity (with the motor 1250kW) as the coal water pump is frequently started (20 times per day, or 30 times per day). Motors should be adjusted according to the prescribed distance and overtravel. The mine is adjusted according to a maintenance cycle every month. If the distance and the overtravel of the contact and the contact resistance are carefully measured and measured according to the specified inspection cycle, the motor damage rate can be greatly reduced.

5 Conclusions According to the experience of using vacuum switch, for high-voltage motors such as coal-water pumps, which are frequently started with large capacity, the use of vacuum switches has the characteristics of low maintenance, low consumption of accessories, and safety and reliability. However, only vacuum circuit breakers are provided in high-voltage vacuum switchgears. The manufacturer's electrical life is 10,000 times, and the actual electrical life is far less than 10,000 times. In order to improve the electrical life, vacuum circuit breakers and vacuum are provided in high-voltage vacuum switchgears. One set of contactors, used in series. The vacuum circuit breaker can be used as a protection and the accidental current vacuum contactor (electricity life 100,000 times) can be used for frequent start-up. In this way, the goal is to achieve complete protection and improve the electrical life.

Guo Wei (1968-, male, graduated from Shandong University of Science and Technology in 2000, an electrical and mechanical engineer, and now works in the Electrical and Mechanical Department of the Gaozhuang Coal Mine of Zaozhuang Mining (Group).

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