A similarity coefficient protection method suitable for power automation system

Abstract

The present invention provides a similarity coefficient protection method suitable for electric power automation systems. The method comprises the following steps: firstly, collecting the pole voltage and pole current data of the transmission system; performing line mode transformation on the pole voltage and pole current signals to obtain line mode components; calculating the virtual traveling wave power and Jaccard similarity coefficient of the in-zone fault and out-of-zone fault; judging whether the fault area is an in-zone fault or an out-of-zone fault according to the comparison between the Jaccard similarity coefficient and the set Jaccard similarity coefficient threshold; calculating the ratio of the positive and negative pole virtual traveling wave power to judge the fault type. The present invention eliminates the influence of distributed capacitance, greatly reduces the delay of traditional protection schemes, and has better tolerance to noise interference and fault resistance interference.

Description

Technical Field

[0001] The invention relates to a similarity coefficient protection method suitable for an electric power automation system, belonging to the technical field of relay protection and dispatching automation. Background Art

[0002] With the advancement of the construction of new power systems, the scale of AC / DC hybrid power transmission is gradually expanding. Among them, traveling wave protection is used as the main protection in the DC transmission system, and current differential protection is used as the backup protection. The disadvantage of traditional single-ended protection is poor fault resistance. In order to improve the fault resistance of traveling wave protection, the existing DC system adopts a current differential protection scheme as backup protection. The main challenge of backup protection is the large delay caused by distributed capacitance, and its reliability is insufficient. In order to improve the reliability of backup protection, the present invention proposes a backup protection scheme based on the virtual traveling wave power Jaccard similarity coefficient.

[0003] At present, many protection schemes have been proposed at home and abroad, including overcurrent protection, traveling wave protection, and wavelet transform protection. Overcurrent protection is the most typical and common protection scheme. An invention proposes to construct a differential protection scheme using fault current. This scheme has high reliability, but long delay time. An invention proposes a DC power grid differential protection and overcurrent protection scheme. However, this invention does not consider the attenuation and delay effects of long transmission lines on signals. An invention proposes to construct a single-ended protection principle using different voltage amplitudes in a special frequency band. An invention extracts wavelet coefficients to construct a protection principle and uses an experimental platform to verify its performance. An invention analyzes the frequency difference of traveling waves in internal and external faults. The above protection schemes often require strong boundary components and cannot be directly applied to DC systems with weak or no boundary components. In addition, traveling wave longitudinal protection has attracted widespread attention because the traveling wave signal is not affected by distributed capacitance. However, traveling wave distance protection is easily affected by the busbar structure, and its threshold is difficult to set. Polarity comparison traveling wave protection separates the relationship between traveling wave amplitude and polarity and is susceptible to noise interference.

[0004] The existing DC backup principle still has the following problems to be solved:

[0005] 1) The long delay problem caused by distributed capacitance needs to be solved urgently.

[0006] 2) Many protection schemes rely on strong boundary element action, which limits their applicability.

[0007] 3) The existing polarity-based travelling wave backup protection is not reliable enough. Summary of the invention

[0008] The purpose of the present invention is to provide a similarity coefficient protection method suitable for power automation systems, which eliminates the influence of distributed capacitance, greatly reduces the delay of traditional protection schemes, and has better tolerance to noise interference and fault resistance interference.

[0009] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0010] 1) First, collect the pole voltage and pole current data of the transmission system;

[0011] 2) Performing line mode transformation on the pole voltage and pole current signals to obtain line mode components;

[0012] 3) Calculate the virtual traveling wave power and Jaccard similarity coefficient of the fault inside the area and the fault outside the area; the calculation formula of the virtual traveling wave power of the fault inside the area is as follows:

[0013]

[0014] Where: Z L1 and Z L2 Represents the equivalent impedance of the current limiting reactor, Z M and Z N Represents the equivalent impedance of the busbar system, ΔP M and ΔP N are the virtual traveling wave powers on the M and N sides respectively; ΔI M and ΔI N represent the traveling wave currents of M and N respectively;

[0015] The calculation formula of the virtual traveling wave power of the out-of-zone fault is as follows:

[0016]

[0017] Where: Z C1 and Z C2 Represents the equivalent impedance of the line;

[0018] 4) Determine whether the fault area is an internal fault or an external fault based on the comparison between the Jaccard similarity coefficient and the set Jaccard similarity coefficient threshold;

[0019] 5) Calculate the positive and negative virtual traveling wave power ratio to determine the fault type;

[0020]

[0021] W p and W n Represents the virtual traveling wave power of the positive and negative electrodes, k set1 and k set2 Represents the threshold value.

[0022] Preferably, the Jaccard similarity coefficient calculation formula is as follows:

[0023]

[0024] Where J represents the Jaccard similarity coefficient; A and B represent two discrete data sets and; x i and i Respectively represent the data in group A and group B. In the present invention, A and B represent the virtual traveling wave power on both sides of the line respectively.

[0025] Preferably, the Jaccard similarity coefficient threshold is 0.9.

[0026] Preferably, the threshold k set1 is 1.5, k set2 It is 0.67.

[0027] The advantages of the present invention are as follows: the protection scheme of the present invention eliminates the influence of distributed capacitance and greatly reduces the delay of the traditional protection scheme; at the same time, it has better ability to tolerate noise interference and resist fault resistance interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0029] Figure 1 It is a schematic diagram of the process structure of the present invention.

[0030] Figure 2 It is a schematic diagram of the structure of the four-terminal DC transmission engineering model of the present invention.

[0031] Figure 3 This is a schematic diagram of the fault equivalent circuit in the area of ​​the present invention.

[0032] Figure 4 This is the schematic diagram of the equivalent circuit of the out-of-area fault of the present invention DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example

[0035] 1) First, collect the pole voltage and pole current data of the transmission system;

[0036] 2) Performing line mode transformation on the pole voltage and pole current signals to obtain line mode components;

[0037] 3) Calculate the virtual traveling wave power and Jaccard similarity coefficient of the fault inside and outside the area; Figure 1Taking the DC transmission engineering model shown in the figure as an example, the fault characteristic formula of virtual traveling wave power is analyzed.

[0038] When an internal fault f1 occurs, the fault equivalent circuit can be obtained according to Peterson's law as follows: Figure 3 As shown. Among them, Z L1,L2 ,Z C1,C2 , and Z M,N Represent the equivalent impedance of the current limiting reactor, line and busbar system respectively. Define ΔP as the virtual traveling wave power, according to Figure 3 It can be obtained that when there is a fault in the area, the calculation formula for the virtual traveling wave power at the measuring points M and N is:

[0039]

[0040] Among them, ΔP M and ΔP N are the virtual traveling wave powers on the M and N sides respectively; ΔI M and ΔI N Represent the traveling wave currents of M and N respectively.

[0041] Out-of-area fault

[0042] When the backside faults f2 and f3 occur, the equivalent circuits on the M and N sides are as follows: Figure 4 shown.

[0043] in accordance with Figure 4 It can be obtained that when there is a fault outside the back area, the calculation formula for the virtual traveling wave power at the measuring points M and N is:

[0044]

[0045] because Figure 1 The transmission line in the example uses the same current limiting inductor and the same busbar system on both sides. The equivalent impedance on both sides of the line has the following relationship: Z M =Z N ,Z L1 =Z L2 Therefore, when there are faults inside and outside the zone, the ratio formulas of the virtual traveling wave power are:

[0046]

[0047] Obviously, the difference in virtual traveling wave power between the two sides when there is a fault inside or outside the zone is expressed as Therefore, it is necessary to analyze the values ​​of the equivalent impedances of each part.

[0048] 1) Z C1 and Z C2Equivalent impedance: First, use the detailed parameters of the actual project to calculate the line wave impedance, and you can get the amplitude-frequency characteristics of the line wave impedance, as shown in Table 1. It can be found that the impedance of the line mode wave stabilizes at 255Ω after the frequency is greater than 100Hz. C1 and Z C2 The equivalent impedance is about several hundred ohms.

[0049] Table 1 Amplitude-frequency characteristics of line wave impedance

[0050]

[0051]

[0052] 2) Z N and Z L2 Amplitude: The busbar system includes various components such as transmission lines, voltage transformers, current transformers, and traps. The stray capacitance of the busbar system to the ground ranges from 6000pF to 0.1μF. The commonly used current limiting inductor value in the flexible DC system is 100mH to 150mH. Calculate Z N and Z L2 The amplitude-frequency characteristics are shown in Table 2.

[0053] Table 2 Amplitude-frequency characteristics of busbar system and current-limiting reactor

[0054]

[0055] It can be seen from Table 1 and Table 2 that the equivalent impedance of the busbar system and the current-limiting inductor is much larger than the line wave impedance. The fault characteristics of the virtual traveling wave power of the DC system are as follows: when the fault occurs within the area, the virtual traveling wave powers on both sides of the line are almost the same, and the ratio is about 1; when the fault occurs outside the area, the virtual traveling wave powers on both sides of the line differ greatly, and the ratio is very large. If the virtual traveling wave power ratio is used as the criterion alone, the system parameter change may cause the criterion to fail. The present invention uses the Jaccard similarity coefficient to express the relationship between virtual traveling wave powers.

[0056] 4) According to the comparison between the Jaccard similarity coefficient and the set Jaccard similarity coefficient threshold, it is determined whether the fault area is an internal fault or an external fault; the definition of the generalized Jaccard similarity coefficient is:

[0057]

[0058] Where J represents the Jaccard similarity coefficient; A and B represent two discrete data sets and; x i and iRepresent the data in groups A and B respectively. In the present invention, A and B represent the virtual traveling wave powers on both sides of the line respectively. The Jaccard similarity coefficient is an indicator to measure the similarity of two groups of data. The larger the Jaccard similarity coefficient, the higher the similarity. When there is an in-zone fault, the virtual traveling wave powers on both sides of the line are almost the same; when there is an out-of-zone fault, the virtual traveling wave powers on both sides of the line differ greatly. When there is an in-zone fault, the Jaccard similarity coefficient of the virtual traveling wave powers on both sides is very large; when there is an out-of-zone fault, the Jaccard similarity coefficient of the virtual traveling wave powers on both sides is very small. Therefore, the criterion for the fault identification element is:

[0059] Fault within the zone: J ≥ J set (5)

[0060] Among them, J set Represents the threshold value of the Jaccard similarity coefficient. Its value should be determined according to system parameters, and is set to 0.9 in the present invention.

[0061] 5) Calculate the positive and negative virtual traveling wave power ratio to determine the fault type;

[0062] When a bipolar short circuit fault occurs, both the positive and negative poles can obtain the same virtual traveling wave power; when a unipolar fault occurs, only the fault pole can obtain the virtual traveling wave power, and the virtual traveling wave power of the non-fault pole is almost zero. Therefore, the present invention proposes a fault pole selection scheme based on the virtual traveling wave power ratio as follows:

[0063]

[0064] Among them, W p and W n Represents the virtual traveling wave power of the positive and negative electrodes, k set1 and k set2 represent thresholds, which are defined by the present invention as 1.5 and 0.67 respectively.

Claims

1. A similarity coefficient protection method suitable for power automation system, characterized in that: The following steps are involved: 1) First, collect the pole voltage and pole current data of the transmission system; 2) Perform line mode transformation on the pole voltage and pole current signals to obtain line mode components; 3) Calculate the virtual traveling wave power and Jaccard similarity coefficient of the fault inside the area and the fault outside the area; the calculation formula of the virtual traveling wave power of the fault inside the area is as follows: Where: and represents the equivalent impedance of the current limiting reactor, and represents the equivalent impedance of the busbar system, and are the virtual traveling wave powers on the M and N sides respectively; and represent the traveling wave currents of M and N respectively; The calculation formula of the virtual traveling wave power of the out-of-zone fault is as follows: Where: and Represents the equivalent impedance of the line; 4) Determine whether the fault area is an internal fault or an external fault based on the comparison between the Jaccard similarity coefficient and the set Jaccard similarity coefficient threshold; 5) Calculate the positive and negative virtual traveling wave power ratio to determine the fault type; and represents the virtual traveling wave power of the positive and negative poles, and represents the threshold value; The Jaccard similarity coefficient calculation formula is as follows: in, represents the Jaccard similarity coefficient; and represents two discrete data groups and; and Respectively represent and The data in the group, and Represent the virtual traveling wave power on both sides of the line respectively.

2. The similarity coefficient protection method applicable to the electric power automation system according to claim 1, characterized in that: The Jaccard similarity coefficient threshold is 0.

9.

3. The similarity coefficient protection method applicable to the electric power automation system according to claim 1, characterized in that: The threshold is 1.5, It is 0.67.

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