Study on Calculation of Overvoltage of Cut-off Motor in Vacuum Circuit Breaker

1 Engineering system uses calculation model 1.1 Project description The diversion project has a total of 7 pump stations. The motor adopts variable frequency starting mode. Under normal power supply conditions, it can also be used for full-voltage asynchronous direct start. The unit can be used for variable speed operation, or can be turned off The instrument is used for constant speed operation. Each pumping station is equipped with 10kV main bus and 10kV variable speed operation (inverter start) busbars. There are 10kV vacuum circuit breakers on both busbars, and the startup and variable speed (variable frequency) operation of different operation units are completed. And to switch each other, to achieve the motor, transformers and other functions to achieve operation and protection 1.2 Calculated parameters taken to explain System parameters: inductance Ls to 0. According to the system's maximum and minimum capacity conversion obtained. Resistance take 0.16 Qiu Zhicheng (1962-), male, Foshan, Guangdong, engineers, engaged in power transmission security management work ... 5 q, take the calculation to take strict cable section take 240mm2, length l = 40 ~ 270m, wave speed V = 170m /s, The wave impedance is calculated as 16.9* According to the minimum value of the motor active loss, the resistance is 0.2U. The total leakage resistance is 25% for the constant speed machine, 15% for the speed changer (provided by the manufacturer), and L=3.98~11.8mH after conversion , Motor-to-ground capacitance G = 0.24-0.36F 12A1.3 System calculation model Since the calculation model of each station has some parameters except for individual equipment, the other parameters are basically the same. Therefore, the system calculation model is established based on the system equipment parameters. Results and analysis 2.1 The most serious way to describe the operating mode is the condition of a single-bus single-unit machine. It can be divided into over-voltage cut-offs: there is a high probability of occurrence, and the hazards are more common. Therefore, the reorganization of multiple parameters should be considered when calculating. Overvoltage: The probability of occurrence is relatively small and theoretically generated. Once a three-phase current overcurrent is limited by the RC circuit and the zinc oxide arrester, a micro-probability event may occur. Generally, a low-voltage and small-capacity motor may appear. System parameters change (Ls=0.063~0.31mH), other parameters: cable cross-section 240mm2, length 1 = 270m, motor capacitance to ground 0.36MF, leakage inductance 11.8mH, calculation results show that the system parameters on the motor side of the closure of the over-voltage The influence of the value is very small, and it is not considered that there is a certain influence on the overvoltage value on the bus side. The greater the system inductive reactance, the higher the overvoltage value, but the overvoltage value does not reach a dangerous degree, and the threat to the main insulation is not significant = 0.24. 0.35F), system Ls=0.31mH, other parameters are unchanged (same as a), the calculation result shows that the overvoltage value of the cutoff current on the switch motor side and the bus side is basically unchanged (in the calculated range), which is due to the motor capacity. Large, characteristic resistance system Ls = 0.31mH, other parameters are the same as a, the calculation result shows that, Ld plus, the over-voltage value of the switch-off motor side is higher, and the influence of the voltage value on the bus-bar side is smaller = 40~270m). The frequency of power supply changes (/=35~60Hz). Other parameters are unchanged. The calculation results show that the cable length has a certain influence on the overvoltage. The cable lengthens and the overvoltage drops within the calculated range. The power frequency is on the side of the switch motor and Bus side cut Over-voltage values ​​have little effect, even negligible.

The parameters are unchanged. It can be known from the calculation results that the switch closure value has less influence on the overvoltage value on the motor side and affects the value on the bus side. The more the intercept value is for the above parameter changes, the system parameter Ls = 0.31mH, frequency 50Hz, cable Long/=40m, motor leakage inductance is 11.8mH. When the interception value is 12A, the calculated results when the short-circuit current is cut off are as shown in Table 1 to Table 1. The motor-side ground voltage is relative to the motor-side ground voltage (calculated value)/kV steady-state. Peak U2/kV* Overvoltage multiple U|U2 Phase A Phase B Phase C Phase Table 2 Motor side line voltage phase Others Motor side Relative ground voltage Steady-state peak voltage Overvoltage multiple (Calculated value)/ kV Phase A Phase B Phase C Phase Table 3 Bus Side-to-ground voltage Phase-to-phase bus side Relative ground voltage W Steady-state peak overvoltage multiple (calculated value)/kV Phase A phase B phase C re-ignition Overvoltage presence, in addition to system parameters, but also after the switch is extinguished The recovery speed of media strength and arc characteristics are related to many factors. Therefore, over-burnover over-voltage is a relatively low probability phenomenon, especially for the actual results of large-capacity motor, only the start of the motor with smaller breaking capacity of vacuum switch. Current, special Under the conditions, multiple reburn overvoltage calculations will occur, when the system parameters in the range of Ls = 31mH, when the motor parameters Cd = 0.36MF, Ld = 11.8mH, cable parameters Z = 16.S, V = 170mh When the switching medium strength recovery speed is set to 80~120VPs, re-ignition overvoltage may occur. The re-ignition overvoltage value at the motor side and the bus side is higher and the amplitude is up to 10 times higher. However, after adding RC, The re-ignition overvoltage on the motor side and the bus side greatly reduces the three-phase simultaneous cut-off overvoltage. Three-phase simultaneous cut-off overvoltage is generally caused by the high-frequency current zero-crossing after re-ignition in the first open phase, which is generated by the interphase coupling, so its probability proportion The over-voltage is even lower. Generally speaking, when the low-voltage, low-capacity motor is switched off, it can be known from the calculation results that although the three-phase simultaneous cut-off over-voltage value is higher, the probability specific gravity over-voltage is even smaller. For large-capacity motors, it may not be considered that the front has been calculated. The resistor R is connected in series with the capacitor C as a protection element and connected to the input side of the load. This type of RC protection device is also referred to as an RC overvoltage suppressor. Capacitors can both mitigate the steep rise of overvoltage and reduce the impedance of the load. Therefore, the purpose of reducing the overvoltage-reducing resistor R is: when the cut-off occurs, it consumes energy in the high-frequency oscillation of the load circuit. The overvoltage is suppressed; when the gap is reignited, it adds the attenuation coefficient of the high-frequency discharge circuit, so that the high-frequency current is rapidly attenuated and reduces the crest factor, and the number of re-ignitions can be reduced, so that multiple reburning over-voltages Can be significantly reduced, and even prevent it from happening. Therefore, the use of RC over-voltage suppressor to protect the motor and other loads, the best results.

According to the theoretical calculations and verification results, it can be confirmed that the parameters of the RC protection device can be selected as follows: 0 - the equivalent inductance of the connection line.

Combined with our calculations, the parameters of the RC overvoltage suppressor are taken as R 1MF, and the RC wiring position should be between the cable and the motor. (6) The arrester arrester can limit the magnitude of the overvoltage, but it cannot slow down the rise of the overvoltage. . Therefore, it is generally used to protect the voltage cut-off overvoltage of the transformer. It cannot be used alone to protect the motor when repeated re-ignition overvoltage occurs. If the arrester is connected in parallel with the RC suppressor to protect the motor, it is more complete. Therefore, it is recommended to use an RC suppressor and a zinc oxide surge arrester (rotary motor type) in parallel to protect the motor. It is recommended to use a zinc oxide surge arrester (power station type) to protect the transformer on the line side. 3. Conclusion From the above analysis and calculation results, we can see that: The most severe operating mode should be that only one motor on a bus runs and the overvoltage occurs when the motor is switched off. The system parameter has little effect on the motor-side shut-off overvoltage value, and it may not consider the bus-side overvoltage The higher the system inductive reactance, the higher the over-voltage value, but the over-voltage amplitude does not reach a dangerous level. The threat to the main insulation is not within the calculation parameters of this paper, and the motor port capacitance and power supply frequency change (/=35- 50Hz) has little effect on the overvoltage value of the shutoff, respectively, and can be ignored.

It is necessary to install a RC absorber. The RC absorber shall be installed on the motor side of the switch and shall be installed in series. Its insulation requirements are the same as those for general 10kV equipment.

A rotary motor metal oxide surge arrester is installed on the motor side of the switch, and a metal oxide arrester is installed on the busbar for routine protection.

(Continued from page 37) Learning criteria and the basis for the review, did not engage in what to check, how to check, blindly into battle, hastily completed the review work. In order to ensure the quality of self-examination and avoid self-inspection, it is necessary to conduct random inspections, multiple inspections, and major inspections of the self-examination of each unit, especially the self-inspection of branch and station stations, and to provide self-inspection in the assessment report. The evaluation can effectively promote self-examination through these measures, so as to win the initiative and pertinence of the rectification work.

(7) It is necessary to maximize the sharing of the results of the assessment of the safety of transmission grids. Therefore, it is important to implement and strengthen adjustments to improve the safety evaluation of transmission grids. The first step is to clarify the status quo of the transmission grid. The next step is to take measures to actively eliminate these problems and risk factors. This is the purpose of the evaluation work. When carrying out transmission network safety assessment, it is first necessary to focus on deep investigation and evaluation, identify hidden problems, then identify problems, and arrange rectification plans in a unified manner to implement safety measures and centralize the problem. Doing so will help overcome the "headaches and foot pains" approach, which is conducive to the in-depth development of evaluation work. (8) The work of evaluating the safety of transmission grids is a systematic project. Therefore, strengthening the participation of all leaders is to improve the evaluation of the Internet. The key to effectiveness is due to the long time, extensive investment, and wide range of safety assessment of the transmission grid. All employees need to participate, and some problems involve multiple departments and units, which need to be comprehensively coordinated. The main leaders need to be personally involved and the leadership in charge of individual orphans The evaluation work must not only conduct general mobilization and overall coordination, but also must be careful in organizing evaluations when investing in rectification of key problems identified in the investigation. It is also necessary to constantly supervise and inspect the rectification situation in order to improve the safety evaluation of the transmission network. Effectiveness 4 Conclusions The assessment of transmission grid safety is a long-term task and an important aspect of safety management. To carry out this task requires constant exploration during the course of study. Continuous deepening in practice will enable safety assessment. Work has been continuously improved and improved.

Automatic Fireworks Machine

Fireworks Production Equipment,Automated Electro-Optical Flower Machine,Automatic Electro-Optical Flower Production Line,Automatic Fireworks Machine

Dongguan City Li you machinery and Equipment Co., Ltd. , https://www.gdliyou.com