Single-side power supply power distribution network current instantaneous quick-break protection override trip risk quantification method

Abstract

The invention provides a single-side power supply power distribution network current instantaneous quick-break protection override trip risk quantitative analysis method, and the method comprises the steps: building a protection range model of a protection constant value based on the topological parameters of a power distribution network and the current instantaneous quick-break protection constant value, and judging whether there is an override trip risk or not according to the protection range model; if the override trip risk exists, quantitatively evaluating the importance of the load to be cut off by mistake due to the override trip action, and obtaining the load loss severity; and combining the protection range of the override trip with the load loss severity, and constructing an override trip risk quantitative evaluation model to quantify the severity of consequences caused by the override trip. According to the method, accurate quantification of the instantaneous quick-break protection override trip risk can be realized, and a basis is provided for adaptability verification and optimization of a protection fixed value.

Description

TECHNICAL FIELD

[0001] The present application relates to a power grid tripping risk quantification method, in particular to a single-sided power supply distribution network current instantaneous speed-break protection overstep tripping risk quantification method. BACKGROUND

[0002] In the coal mine safety production system, the power supply system is the key link to ensure the safety and stability of underground operation. According to statistics, about 50% of gas explosions in coal mine accidents are caused by electric sparks, and the death rate of electric shock accidents is about 64%. Once a large-scale power failure occurs in the underground power supply system, the ventilation, drainage, signal and monitoring systems will not be able to operate normally, and the gas and other toxic and harmful gases cannot be diluted, and the accumulated water cannot be discharged, which seriously threatens the safety of underground personnel. Therefore, it is of great significance to ensure the reliability and selective protection performance of the coal mine power supply system.

[0003] At present, the relay protection of the mine power supply system has the following problems: the speed-break and overcurrent protection setting value cooperation is unreasonable; the under-voltage protection action delay setting is improper; the leakage protection selectivity is poor; the protection device function is single, and the communication and self-checking capability is insufficient. These problems often cause protection misoperation or refusal to operate when the system fails due to under-voltage, leakage, overcurrent and short circuit. Among them, the most prominent problem is "overstep tripping", which poses a serious threat to the safe and stable operation of the coal mine power supply system.

[0004] The so-called "overstep tripping" refers to the misoperation of the upper-level protection when a short-circuit fault occurs in the lower-level line or device, resulting in power failure in the non-fault interval. The line of the coal mine underground distribution network is generally short, and the system impedance is small. When a short circuit occurs at the end of the line, the difference between the end short-circuit current under the maximum operating mode and the first-stage short-circuit current under the minimum operating mode is small, making it difficult for the current speed-break protection to meet the protection range requirement of not less than 15% specified in the regulations under the minimum operating mode. Therefore, the protection setting value usually needs to be inversely set according to the end two-phase short-circuit current under the minimum operating mode not less than 1.5 times the sensitivity coefficient, resulting in a large protection range extending to the lower-level line, which easily leads to overstep tripping.

[0005] In the coal mine power supply system, once overstep tripping occurs, it will not only cause a large-scale power failure, ventilation machine stop and drainage interruption, but also may cause gas accumulation and explosion risk, bringing serious safety hazards. Therefore, how to quantitatively evaluate the overstep tripping risk of the current speed-break protection setting value and establish a protection setting value adaptability verification and optimization method for the coal mine underground distribution network has become an important direction of current coal mine power supply protection technology research. SUMMARY

[0006] In order to overcome the deficiencies in the prior art, the present application provides a single-sided power supply distribution network current instantaneous speed-break protection overstep tripping risk quantification method.

[0007] To achieve the above object, the application discloses a unilateral power distribution network current transient fast trip risk quantification method, which comprises the following steps: (S1) calculating the maximum short-circuit current at the end of each line in the maximum operating mode of the power distribution network I fj ; (S2) determining the protection setting value over coverage range according to the ratio of the line end to the existing protection setting value β j ; (S3) calculating the range α where the protection setting value will cause the over-trip (S4) constructing the load weight of the underground load of the coal mine based on the improved three-scale analytic hierarchy process W 1, the load weight of the secondary load W 2, and the load weight of the tertiary load W 3 (S5) calculating the severity of the load mis-trip after the over-trip in the coal mine S : (S6) constructing the over-trip risk quantification model: In the above, MI is the risk coefficient, MI the closer to 0, the lighter the adverse consequences caused by the over-trip, and if equal to 0, the over-trip of the setting value will not cause harm.

[0008] Preferably, the maximum short-circuit current I fj is calculated by: In the above formula, E is the phase electromotive force of the equivalent power source of the system, R min R is the system resistance in the maximum operating mode of the system, X min X is the system inductance in the maximum operating mode of the system, L j Lj is the length of the jth line, R j Rj is the unit resistance of the jth line, X j Xj is the unit inductance of the jth line.

[0009] Preferably, the protection setting value over coverage range β j is calculated by: In the above formula, is the protection setting value of the monitored line section, j is the line order, and the search is stopped when it is found; the last line is x , if βj If the value is less than 1, the protection setting value will not cause the over-reach tripping.

[0010] Preferably, the calculation method of the over-reach tripping range a is: In the above formula, L 1 is the length of the first level line, n and n is the number of levels of the line.

[0011] Preferably, the calculation method of the severity of the load mis-cutoff after the over-reach tripping in the coal mine is: S wherein, The present application has the following technical effects: 1. By calculating the maximum short-circuit current at the end of the line, the over-reach tripping range of the protection setting value, and the over-reach tripping range, a risk quantification model of the over-reach tripping of the instantaneous speed-break protection of the power distribution network in the coal mine is constructed. The model introduces a risk coefficient MI , the closer to 0, the lower the over-reach tripping risk, and the risk is accurately evaluated.

[0012] ‌2. The improved three-scale analytic hierarchy process is used to calculate the weights of the first, second and third levels of load (1, W 1, W 2, W 3), respectively, to ensure reasonable allocation of protection priorities of different load levels and improve the overall stability of the system.

[0013] ‌3. Through the calculation of the severity of the load mis-cutoff S , the influence of the over-reach tripping on the power supply system in the coal mine is quantified, providing a scientific basis for protection setting value optimization, reducing economic losses and safety hazards caused by mis-cutoff of the load.

[0014] 4. The calculation method of the maximum short-circuit current I fj takes into account the system equivalent power supply parameters and line characteristics, and is suitable for risk assessment under different operating modes, enhancing the universality of the model.

[0015] 5. The calculation method of the over-reach tripping range of the protection setting value β j ensures that the setting value reasonably covers the end short-circuit current, avoiding the risk of over-reach tripping, and through the calculation of the range α , the over-reach tripping boundary of the protection setting value is clear, improving the reliability of the protection device.

[0016] 6. The risk coefficient and severity index output by the model provide data support for the protection setting value adjustment and operation and maintenance of the power distribution network in the coal mine, realizing intelligent risk control. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 ​is a flow chart of a unilateral power supply power distribution network current transient fast break protection overstep tripping risk quantitative analysis method of an embodiment of the present application; Figure 2 is a schematic diagram of a coal mine underground 10kV power supply system line model. DETAILED DESCRIPTION

[0018] The principles and features of the present application are described below in conjunction with embodiments; the examples are used only to explain the present application; and are not used to limit the scope of the present application.

[0019] This embodiment takes a coal mine underground 10kV power supply system as an example, a circuit diagram of the power supply system is shown in the accompanying drawings Figure 2 The power supply system includes 3 stages of lines, which are AB segment, BC segment, and CD segment, respectively, and the parameters of the corresponding lines are shown in Table 1. Now the risk of overstep tripping of the AB segment is quantified, the protection setting value of the AB segment is 5.83kA, the total load is 25KW, the first stage load is 10.46MW, the second stage load is 6.66MW, and the third stage load is 1.9MW.

[0020] Table 1 Line parameters Line AB BC CD Length (m) 2500 800 350 Impedance (Ω) 0.146+j0.12 0.1938+j0.0768 0.0369 + j0.0305i Gamma Based on the above parameters, a unilateral power supply power distribution network current transient fast break protection overstep tripping risk quantitative method includes the following steps: (S1) calculating the maximum short-circuit current at the end of each line segment of the power distribution network under the maximum operating mode I fj The calculation method is: In the formula, E is the phase electromotive force of the system equivalent power supply, R min R is the system resistance under the maximum operating mode of the system, X min X is the system inductance under the maximum operating mode of the system, L j Lj is the length of the jth line, R j Rj is the unit resistance of the jth line, X j Xj is the unit inductance of the jth line; Z is the impedance of the line. Through calculation, the maximum protection current of the AB segment, the BC segment, and the CD segment is 7.33kA, 5.98kA, and 5.7kA, respectively.

[0021] (S2) determining the protection setting value overlap range according to the ratio of the end of the line to the existing protection setting value β j The calculation method is: In the formula, E is the phase electromotive force of the system equivalent power supply, is the protection setting value of the monitored line segment,​j For line level, find that is stop; the last line is x , if β j less than 1, the protection setting value will not occur overstep trip. Respectively define the maximum coverage of AB section, BC section and CD section is β 1, β 2 and β 3, then β 1=7.33 / 5.83, β 1>1; β 2=5.98 / 5.83, that is β 2>1; β 3=5.7 / 5.83, that is β 3<1, which shows that the protection setting value will occur overstep trip.

[0022] (S3) Calculate the range α of protection setting value that will occur overstep trip: In the formula, L 1 is the length of the first level line, n is the level number of the line. In the embodiment, all x, n are 3, so α =1.

[0023] (S4) Construct the load weight of the first level load in the coal mine based on the improved three-scale analytic hierarchy process W 1, the load weight of the second level load W 2 and the load weight of the third level load W 3.

[0024] The principle of three-scale analytic hierarchy process is divided into the following steps: (A1) Compare each other, construct a three-scale judgment matrix, and compare any two index factors c i and c j , use a ij to represent c i and c j who is more important, a ij Use 0, 1, 2 three values to characterize, construct the judgment matrix A according to the following formula: (A2) Judgment matrix conversion Convert the judgment matrix A constructed above to construct the indirect judgment matrix B, and the factor ordering index is: The formula is the sum of the i-th row elements in the judgment matrix A, and n is the number of rows or columns of the matrix. The indirect judgment matrix B is: In the formula, wherein rmin = min r i wherein rmax = max r i wherein rmax = max max is 9.

[0025] (A3) constructing an anti-symmetric matrix C based on the above judgment matrix A; c wherein (A4) constructing an optimal transfer matrix D based on the above anti-symmetric matrix C; wherein A5) calculating a quasi-optimal consistency matrix E based on the above optimal transfer matrix D: wherein, (A6) calculating the weight of the individual index of the quasi-optimal consistency matrix E using the geometric mean method. Specifically to the present embodiment, the weight analysis of the underground primary load, secondary load and tertiary load of the coal mine is performed according to the above steps.

[0026] Firstly, a comparative judgment matrix A is established: Based on the judgment matrix A, an indirect judgment matrix B is constructed: Based on the indirect judgment matrix B, an anti-symmetric matrix C is constructed: Based on the anti-symmetric matrix C, an optimal transfer matrix D is constructed: Based on the optimal transfer matrix D, a quasi-optimal consistency matrix E is constructed: Based on the quasi-optimal consistency matrix E, the weight of the underground primary load, secondary load and tertiary load is obtained according to the geometric mean method, W = [W1, W2, W3] = [0.7073, 0.1989, 0.0939].

[0027] (S5) calculating the severity of load misoperation after the overstep trip of the coal mine underground S : wherein, Through calculation: then = 0.356.

[0028] Constructing an overstep trip risk quantification model: = 0.356 * 1 = 0.356, which indicates that the protection setting value will not only cause overstep trip but also cause certain risk after overstep trip.

[0029] The above merely provides the preferred embodiment of the present application, but not for limiting the present application; any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for quantifying the risk of cascading tripping in instantaneous overcurrent protection of a single-side power supply distribution network, characterized in that, Includes the following steps: (S1) Calculate the maximum short-circuit current at the end of each section of the distribution network under the maximum operating mode. I fj ; (S2) Determine the over-coverage range of the protection setting based on the ratio of the line end to the existing protection setting. β j ; (S3) Calculate the range α within which the protection setting will cause an out-of-level trip; (S4) Constructing load weights for the first-level load in coal mines based on an improved three-scale analytic hierarchy process. W 1. Load weight of secondary loads W Load weights for Level 2 and Level 3 loads W 3; (S5) Calculate the severity of load mis-cutting after an escalation trip occurs in a coal mine. S : (S6) Construct a quantitative model for the risk of cascading power outages: In the above, MI For risk coefficient, MI The closer the value is to 0, the less severe the adverse consequences of an over-trip. If the value is equal to 0, it means that an over-trip at this setting will not cause any harm.

2. The method for quantifying the risk of cascading tripping of instantaneous overcurrent protection in a single-side power distribution network according to claim 1, characterized in that, Maximum short-circuit current I fj The calculation method is as follows: E is the phase electromotive force of the system's equivalent power source. R min The system resistance under the system's maximum operating mode. X min The system inductive reactance under the system's maximum operating mode. L j Let j be the length of the j-th line. R j Let the unit resistance of the j-th line be . X j Let J be the unit reactance of the j-th line.

3. The method for quantifying the risk of cascading tripping after instantaneous current outage in a single-side power distribution network according to claim 1, characterized in that, Protection setting over coverage β j The calculation method is as follows:

4. In the above formula, To monitor the protection settings of the line, j The number of line segments determines the path; the search stops once a segment is found. The last segment is... x ,like β j If the value is less than 1, the protection setting will not cause an out-of-level trip.

5. The method for quantifying the risk of cascading tripping after instantaneous current outage in a single-side power distribution network according to claim 1, characterized in that, The calculation method for the range α that will result in cascading tripping is as follows: In the above formula, L 1 represents the length of the first-level line. n The number of stages in the circuit.

6. The method for quantifying the risk of cascading tripping after instantaneous current outage in a single-side power distribution network according to claim 1, characterized in that, Severity of load mis-cutting after an escalated trip in an underground coal mine S The calculation method is as follows: in, .

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