1 Overview The experience has proved that no matter which of the above-mentioned 50CkV power systems is used, it is rare for the surname accident to be closed due to the over-voltage of the switch. The line-closing over-voltage is the choice of the EHV power system. The factors that can determine the overvoltage of the singularity of the voltage are always limited. In the 1980s, some foreign companies found that there are two ways to close the circuit breaker. Resistor as a limiting main resistor or its operating mechanism exposes some defects such as the United States, and the arrester as a backup protection, generally referred to as the two countries Florida Power and Lighting Company (FloridaPower line of defense; the other is only used Lightning arrester to limit the over-voltage voltage LightCo, hereinafter referred to as FPL), found that the operating mechanism of the early 550kVSF gas-insulated circuit breaker closing resistor failed, and they were responsible for all 550kV faults of FPL. A large proportion of the closing resistor or its operating mechanism has defects or faulty circuit breaker manufacturers also believe that the closing resistor and its operating mechanism It is the weakest link in the circuit breaker. The damage to the power system due to the failure of the circuit breaker itself is much more serious than the transient failure of the line flashover due to the high voltage of the closing or reclosing, plus the closing time of the closing resistor. The dispersion of the three-phase action time difference of the dispersive switch makes the voltage-limiting effect of the closing resistor large, and the use of the metal oxide arrester (MetalOxideSurgeArrestei., hereinafter referred to as MOA) and its quality are continuously improved. The US FPL and the Bonneville Power Authority (BPA) began to study the elimination of the closing resistor in the EHV power system, relying solely on the arrester to limit the possible variability of the closing overvoltage. In addition, in the case of the circuit breaker, when the closing resistor is used At the time, the operating mechanism is complicated, and the cost of the closing resistor itself is relatively high, which increases the investment in the circuit breaker. Several large manufacturers in the West (such as MGABB, etc.) have actively supported the cancellation of closing resistors in recent years. They have listed 500kV circuit breakers without closing resistors as standard products in China. Traditionally, closing and reclosing voltages have been applied. The limitation is that the switch with the closing resistor is used as the first line of defense, and the silicon carbide arrester with the series gap is used as the second line of defense. With the development of the national economy, the 500kV power grid has developed rapidly. When foreign contracted projects or foreign equipment purchases, it is often found that some designs use circuit breakers without closing resistors; some manufacturers will combine the circuit breaker bodies. Brake resistors are packaged, especially in combination appliances. The closing resistors are very expensive (ABB quotes, if the closing resistors in the closed appliances are eliminated, the cost per breaker can be reduced by about $140,000-200,000). Calculated with 10 circuit breakers in a substation, each substation can save more than one million dollars in investment. Xi'an High-voltage Switchgear Factory believes that for a circuit breaker, the cost of canceling the closing resistor can be reduced by about 12% of the total cost. This makes domestic and foreign experts and scholars realize that if the cancellation is completed After the gate resistance, it can still meet the requirements of limiting the over-voltage of the closing, so the cancellation of the closing resistor can not only improve the reliability of the circuit breaker itself, the reliability of the power system, but also obtain obvious economic benefits.
From the perspective of protection: 1 closing resistor can only be used to limit some (closing, reclosing) overvoltage, while MOA can be used to limit all operating overvoltage, and can be used for traveling wave protection; The resistance voltage limiting effect is unstable, the dispersion is large, and the MOA pressure limiting effect is stable and the dispersion is small. 3 For a given system wiring, there is an optimal value for the closing resistance, that is, the “pipe†type curve, only when When it happens to be the optimal value, the pressure limiting effect is the best, but it is actually difficult to do this, and MOA does not have this problem. These indicate that MOA is obviously superior to the closing resistor in terms of protection capability. The main function of the gate resistor is to reduce the operating load of the arrester and reduce the number of actions of the arrester. After the closing resistor is cancelled, the arrester has sufficient capacity to limit the closing and reclosing voltages independently. If the operating mechanism fails or whether the closing resistor can be canceled and continues to operate, these are issues of great concern to the operating department. Due to the limitations of the conditions, the EHV power system has been closed. The pressure is still not able to carry out a large number of on-site measurements. Compared with the research methods using physical simulation (such as TNA), the numerical calculation method is not inferior in terms of the accuracy of the results, the comprehensiveness of the factors to be considered, and the flexibility of the research. The numerical simulation of the numerical simulation is used to study the closing overvoltage of the EHV power system. In particular, it is an ideal method to study the closing overvoltage after the closing of the closing resistor. Because the closing operation is canceled, the closing operation is over the voltage. The distribution is very different from that before the cancellation. It shows the shape of the line at both ends low and the middle is high. Therefore, the characteristic difference method is a good choice for the overvoltage calculation part. The biggest feature is that it can easily calculate the line. The statistical rule and regression analysis of the overvoltage distribution along the line. After the closing resistor is cancelled, the closing overvoltage on the line and the dissipated energy of the MOA are regular. They are related to the line length, power supply capacity, and circuit breaker closing phase. Angles, etc. all have a close relationship, but this relationship is not a definite relationship, but a statistical correlation. For this correlation, we can use Monte Carlo method is used to study. The specific idea is that when the probability of a random event needs to be obtained, it can be realized by some kind of random sampling test. When the number of trials is enough, the statistical result obtained by the experiment can be regarded as a problem. The approximate solution to the problem we have studied has many random factors that affect it, such as the dispersion of switch closing time. Strictly speaking, to study such a problem, all these influencing factors should be regarded as random variables. And to find their distribution law, constitute a complete but very complex model, and then carry out random sampling and a large number of calculations on this basis, and finally get the results. Obviously, such a model is too complicated and difficult to implement. Even if it is implemented, because there are too many unresearched factors, the results may not reflect the actual situation correctly. Therefore, in the research, we establish a fixed network structure and parameters. In the probability model, some minor factors are neglected, and the switch closing time that has the greatest influence on overvoltage and MOA dissipated energy is taken as the random variable. 21 Closing overvoltage and MOA dissipative energy statistical law 21.1 Distribution of overvoltage along the line The influence of the probability distribution with the closing time of the switch When there is no pressure limiting measure or the use of the closing resistor as the pressure limiting measure, the distribution along the line of the no-load line closing or reclosing voltage is gradually increased from the head end to the end. Therefore, in general, when designing the insulation, only the overvoltage of the line receiving end is not more than 2.OPU. However, the situation is different after the closing of the closing resistor. Let us take the distribution of overvoltage along the line of the closing voltage of a system with a length of 301km as an example. As shown in the figure, the curve 1 23 indicates that there is no pressure limiting measure, only when there are MOA at both ends, and there are two closing resistors. The distribution of overvoltage along the line with MOA is obvious from the figure. After the closing of the closing resistor, the overvoltage is limited by the MOA at both ends of the line. The distribution of the overvoltage is low at both ends and high in the middle. MOA is installed at both ends of the line, the overvoltage is limited to the operating wave protection level of the MOA, and in the middle of the line away from the MOA, since the protection range of the MOA may be exceeded, the overvoltage is often cancelled. After that, the design of the line insulation must take into account the law of the distribution of this overvoltage along the line, and can not only be based on the overvoltage of the receiving end not exceeding 2. OPU. In addition, it can also be seen that the overvoltage is limited. The angle analysis has the best effect when both the closing resistor and the MOA, but we can also see that the overvoltage can be limited to the allowable range only by relying on the MOA voltage limiting.
For the distribution of three-phase switch closing time, there have been two different opinions at home and abroad: one is that the distribution of the switching closing phase angle and the pre-breakdown between the switching contacts are related to the actual Soviet 330kV air circuit breaker. The study of the closing phase shows that the switch closing time is normally distributed during the power supply period. Another type of modern circuit breaker is considered to have a high closing speed, and the pre-breakdown between the contacts during closing can be ignored, so that it is subject to uniform distribution within one week. The field test in China shows that the actual average closing phase of the 330kV air circuit breaker is relatively close according to our statistics. Whether it is the phase-to-phase or phase-to-phase failure rate, the closing time is evenly distributed when it is higher than the normal distribution. Whether the maximum dissipated energy of the head end or the end MOA is also high when the closing time is evenly distributed. Because it is the result of statistical calculation, it can be considered that there is a certain universality, that is, from the perspective of overvoltage and MOA dissipated energy, the switch closing time is more uniform than the normal distribution.
2 MOA absorption energy capacity problem after canceling the closing resistance The function of the closing resistance is not only to reduce the over-voltage of the closing operation, but also to greatly reduce the operating load of the arrester at both ends of the line and reduce the number of actions, then after canceling the closing resistance Does MOA have sufficient capacity to limit the overvoltage of the closing operation without being damaged? For the MOA used in 500kV, GE has a specific energy of 13k/kV, and the specific energy of China's western porcelain is 10.28k/kV. According to the manufacturer, “In each operation, the energy absorbed by the MOA does not exceed 85% of the above specified value, and the MOA can be reused when the time interval between the two operations is greater than one minute.†The 1440 line lengths we performed were from In the statistical calculation of the closing operation of the closing switch of more than 50 kilometers to more than 400 kilometers, the results of the MOA dissipated energy are shown in Table 1. Table 1 1440 times of the unclosed resistance closing operation statistical calculation results Rate ROF (%.) phase-to-phase insulation head-end MOA head-end phase-to-phase insulation maximum dissipation MOA2% failure rate) energy dissipation energy maximum dissipation MOA% consumption can be seen from the table, the largest of the 1440 times MOA dissipation The energy is 2931k. In addition, according to the related article, the maximum energy absorbed by MOA is 2600k in 300 operations of 500kV system with a length of about 330km, and the maximum energy absorbed by MOA in 300 operations of 500kV system with a length of about 240km. Only 1400k is visible. The maximum value of 2931k in our calculation is a value that has a very low probability of occurrence. This value is compared with the data given by Nishio, and there is: even in the case of such a heavy burden, MOA The absorption capacity still has a certain margin, and the probability of such a large energy is extremely small during random operation. Therefore, we believe that the MOA load is aggravated after the closing of the closing resistor, but this The burden MOA is a fully affordable 3 line insulation failure rate and the statistical correlation between the MOA dissipated energy and various influencing factors has a large impact on the overvoltage, generally: line length, power supply capacity, line compensation and so on. For the control of overvoltage along the line, we believe that after canceling the closing resistor, it is not appropriate to use the end of the line or the whole line does not exceed 20 PU as the standard, not only because of the change in the distribution characteristics of the overvoltage, but also because of the current number of insulators of the 500kV tower. The air gap size is often not determined by the operating overvoltage, so the operating overvoltage that they can withstand is not only 20 PU. For example, the calculations in the article indicate that for an area below 1000 m above sea level, the linear rod uses 28 insulators and air gap. For 3m, it can withstand the statistical operation overvoltage of 1PU. Therefore, we recommend using the full-line insulation failure rate as the standard for limiting overvoltage. 3.1 The statistical correlation between line length and line length L is obviously one of the factors affecting the overvoltage condition. Our calculation results show the relationship between the phase-to-phase insulation failure rate of the whole-line insulation failure rate and the maximum dissipation energy of the MOA at the head end of the line and the line length. It can be seen from the figure that as the line length increases , the insulation failure rate of the whole line will increase, and will increase rapidly after 300km, the energy absorbed by MOA Increasingly, this is because after the line length increases, the power frequency overvoltage rises severely, the number of full-line insulation increases, and the protection of MOA has a certain range, resulting in an increase in overvoltage and an increase in MOA absorption energy. Reflected in the insulation is the increase of the failure rate 2 and the statistical correlation between the first self-oscillation angle frequency (standard value) of the system. It is considered that the change of the power supply capacity has little effect on the medium-length line closing overvoltage. For short lines, the power supply capacity increases, and the closing overvoltage increases. For long lines, the power supply capacity increases, and the closing overvoltage decreases. These studies are correct in their respective research areas. Because the power supply capacity increases, the power frequency voltage rise caused by the first effect of the standard will decrease, and the overvoltage will decrease, but the increase of the power supply capacity will lead to the first role in the free oscillation component of the overvoltage. The increase of the vibration angle frequency makes the overvoltage maximum appear earlier and the amplitude attenuation is smaller, resulting in an increase in overvoltage. It can be seen that the influence of the power supply capacity is two-sided, as a general The judgment basis in the law is not appropriate. We think it is reasonable to reflect the situation of the research system with the value of the first self-oscillation angle of the system, because it not only reflects the power supply capacity, line length, line parameters, but also reflects the line. The compensation situation is a relatively "comprehensive" parameter to explore its correlation with overvoltage and MOA dissipated energy. It is possible to draw general rules. According to our calculation results, the full-line insulation failure rate and the maximum dissipation energy of the MOA at the first end are respectively reduced and monotonously reduced. The maximum dissipated energy of the MOA at the first end also decreases monotonously with the increase of the first self-oscillation frequency. They all show a significant negative correlation. Since the first self-oscillation angle frequency reflects many factors in the system, and these factors are mutually influential, our preliminary analysis believes that the first self-oscillation angle frequency is small, indicating that the system capacity is small and the line is long, which inevitably leads to the failure rate. The increase of the MOA burden and the aggravation of the MOA burden. From the plotted figure, it can be seen that the line insulation failure rate has a significant correlation with the line length and the first self-oscillation angle frequency value, and presents a power function curve. Characteristics; the maximum dissipated energy of the MOA at the first end is also significantly correlated with the line length and the first self-oscillation angle frequency, and exhibits the characteristics of the exponential function and the inverse exponential function curve respectively. To further explore the law, we Using 1440 closing operation statistical calculation results, the line insulation failure rate is used for the line long work and the first self-oscillation angle frequency value and the first end MOA maximum dissipated energy versus the line length and the first self-oscillation angle frequency value. The correlation diagram of the self-oscillation angle frequency value is shown in the figure. The process of regression bifurcation regression analysis is shown in Table 2 and Table 3. The full-line insulation failure rate follows the first self-oscillation angle frequency. Increase Table 2 Regression Analysis Process Number Line Length Log Value V=bgL Angle Frequency Logarithmic Value U Phase One Ground Insulation Failure Rate Log Value R=logROF Interphase Insulation Failure Rate Log Value p=logPROF Line Length L Angle Frequency Reciprocal W=1/ 01 MOA end MOA maximum dissipation maximum dissipative energy logarithm energy logarithm WS-n2 Then the regression coefficients of four regression equations are obtained by the following two regression coefficient formulas: regression significance test numerical characteristics are shown in Table 4 Whether the regression is established or not, the following three test formulas can be used to obtain the numerical characteristics of the regression significance test, the regression coefficient and the regression coefficient of Table 4 and the regression significance test digital feature 2.1788. Obviously, the T in Table 4 is greater than 2. The significant level a. = 5%, can accept the above significant regression hypothesis, so that the regression equation of the whole line insulation failure rate to the line length and the first self-oscillation angle frequency value and the maximum dissipation energy of the first end MOA to the line length and the first The regression equation of the self-oscillation angle frequency is as follows: 5 Conclusion 5.1 After the closing of the closing resistor, the distribution of the over-voltage of the closing operation presents a bow with a low end and a high middle at both ends.
5.2 Due to the extensive use of MOA and the continuous improvement of its performance, in the past, in order to reduce the overvoltage of closing (reclosing) operation, it is not reasonable to use the circuit breaker with shunting parallel resistance for 500kV line. It is recommended to use MOA as a limit. The only means of operating overvoltage for 500kV line closing (reclosing) 5.3 After the closing of the closing resistor, the absolute value of the overvoltage is higher than the normal distribution when the switch closing time is evenly distributed, and the insulation failure rate of the whole line is large, the burden of MOA It is also important that although the closing resistance is cancelled, the MOA's action load is increased to a different extent. However, due to the good energy absorption capacity of the MOA, the increase of this burden does not cause damage to the MOA or reduce its normal operating life.
When the first end of the 5.4 uses the MOA with rated voltage of 420kV, the line insulation failure rate shows a significant positive correlation and negative correlation between the line length and the first self-oscillation angle frequency (the value of the standard). It also shows a significant positive correlation and negative correlation between the line length and the first self-oscillation angle frequency (the value of the standard value). The regression equation reflecting this correlation is shown in the following equation. The result can be used as the relevant engineering design: bimonthly, publication The number is for the call for papers. The journal is under the jurisdiction of the State Machinery Industry Administration, and the Shenyang Electric Drive Research Institute sponsors the publication of “Reviewâ€, “Design and Calculationâ€, “Practice and Applicationâ€, “Process and Standardsâ€, mainly reporting high and low voltage electrical appliances. Explosion-proof electrical appliances, complete sets of electronic control devices and special electrical control equipment, etc. Requirements for the manuscript: 1. Please use the standard fonts to be neatly arranged, and the measurement unit shall adopt the national legal measurement standard unit and the symbol of about 5,000. The special draft may be around 8,000. The manuscript will be echoed within the month, regardless of whether it is adopted or not. Please keep the manuscript from the manuscript. The journal is not retired. Please attach the resume (name, age, If you want to order a 2001 magazine, you can contact the local post office, the postal code is 8-65, or you can directly subscribe to the address: No. 64, Xinggong North Street, Tiexi District, Shenyang, China. Magazine Zip: 110025 Contact: Zhang Liming Telephone
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