Power transmission line single-phase adaptive reclosing method based on dynamic change of harmonic ratio

Abstract

The invention discloses a power transmission line single-phase adaptive reclosing method based on harmonic ratio dynamic change, which comprises the following steps: after a power transmission line has a single-phase earth fault, tripping off a fault phase, and obtaining the voltage of the fault phase at a preset sampling rate to obtain a sampling sequence; based on the acquired sampling sequence, selecting a sequence value after a preset sampling moment to calculate a harmonic content value of a preset number of times of the fault phase voltage; according to the calculated harmonic content value of the preset number of times, the harmonic ratio of the fault phase voltage and the harmonic content of the fault phase voltage are calculated and obtained at every sampling point; and judging the fault property of the power transmission line by using the harmonic ratio and the harmonic content of the fault phase voltage obtained by calculation, and correspondingly sending a reclosing instruction. The method ensures that reclosing succeeds in the voltage recovery stage, and reclosing under a permanent fault is effectively avoided; and a discrimination method of a fixed protection threshold value and a time fixed value is adopted, so that the method has very high adaptability.

Description

Technical Field

[0001] The invention relates to the technical field of power system transmission lines, and in particular to a single-phase adaptive reclosing method for a transmission line based on dynamic changes in harmonic ratios. Background Art

[0002] The transmission circuit has the important characteristics of high voltage level and long-distance power transmission. At the same time, because it is exposed to natural conditions and is easily affected by disasters and external forces, its single-phase grounding fault has the highest probability of occurrence in the entire power system. Single-phase automatic reclosing technology is widely used in transmission lines, which can quickly restore power transmission on instantaneous fault lines and improve the stability of system parallel operation.

[0003] The traditional automatic closing device adopts a fixed-time blind reclosing scheme, which brings a lot of economic benefits but also has many problems: when reclosing on a permanent fault, it not only fails to restore the normal power supply of the faulty line, but also causes the voltage of other healthy lines to drop again, causing more serious secondary damage to the stability of the system; when reclosing on a transient fault, the fixed reclosing time increases the non-full-phase operation time of the system.

[0004] At present, the fault nature identification method based on transmission lines is mainly based on the arc high-voltage and high-frequency components in the secondary arc stage and the voltage amplitude and phase method based on the recovery voltage stage. However, in the transmission line with parallel reactance, the secondary arc will be extinguished quickly, and the arc voltage duration is too short to have effective high-frequency components; secondly, the recovery voltage amplitude is too small and contains non-power frequency components, and the power frequency component amplitude and phase cannot be extracted in a short time, which will increase the reclosing time.

[0005] Therefore, there is an urgent need for a method that can quickly capture the instantaneous fault arc extinction moment in the parallel reactor transmission line to ensure adaptive reclosing of the transmission line during the voltage recovery stage. Summary of the invention

[0006] The present invention provides a single-phase adaptive reclosing method for a transmission line based on the dynamic change of harmonic ratio. The method is aimed at a transmission line with a shunt reactor. The method uses the dynamic change of the harmonic content ratio of the fault-tripped phase voltage and its duration to quickly capture the instantaneous fault arc extinction moment, ensure the successful reclosing in the voltage recovery stage, and effectively avoid reclosing under permanent faults. At the same time, the method uses a judgment method of fixed protection threshold and time constant, and has strong adaptability.

[0007] The present invention provides a single-phase adaptive reclosing method for a power transmission line based on dynamic changes in harmonic ratios, comprising:

[0008] S1: After a single-phase grounding fault occurs in the transmission line, the fault phase is tripped, and the voltage of the fault phase is acquired at a preset sampling rate to obtain a sampling sequence;

[0009] S2: Based on the acquired sampling sequence, the sequence value after the preset sampling time is selected to calculate the harmonic content value of the preset harmonic component order of the fault phase voltage;

[0010] S3: According to the calculated harmonic content value of the preset harmonic component order, the harmonic ratio value and the harmonic content of the fault phase voltage are calculated at every other sampling point;

[0011] S4: The harmonic ratio and harmonic content of the fault phase voltage obtained by calculation are used to determine the fault nature of the transmission line, and a reclosing instruction is issued accordingly.

[0012] Furthermore, the calculation formula of the harmonic content value of the fault phase voltage is:

[0013]

[0014] Among them, U i is the i-th harmonic content value, that is, the amplitude of the i-th times power frequency of the fault phase voltage; U real is the real part of discrete Fourier transform; U imag is the imaginary component; N is the number of sampling points of one power frequency cycle; i is the number of harmonic components; j is the sequence point currently used to calculate data; u(j) is the jth sequence value in the sampling sequence.

[0015] Furthermore, the calculation formula of the harmonic ratio of the fault phase voltage is:

[0016]

[0017] Among them, HR(k) is the harmonic ratio value at the current sampling point; U i is the i-th harmonic content value, the numerator i=2a+1, representing odd harmonics; the denominator i=2a, representing even harmonics;

[0018] Furthermore, the calculation formula for the harmonic content of the fault phase voltage is:

[0019]

[0020] Among them, HRT(k) is the ratio of all harmonic content to the relative fundamental content; U i is the i-th harmonic content value, i=1, 2, 3...

[0021] Furthermore, the specific process of S4 is:

[0022] S41: Determine whether the harmonic content is greater than the preset harmonic content threshold and the duration of the harmonic ratio greater than the preset harmonic ratio threshold exceeds the preset time length: if not, determine that a permanent grounding fault occurs in the transmission line and perform locking and reclosing; if so, enter S42;

[0023] S42: Determine whether the harmonic ratio is greater than the preset harmonic ratio threshold: If so, start the counter. When the continuous counting time of the harmonic ratio exceeds the preset counting time threshold, it is determined that a transient fault has occurred in the transmission line and the arc has been extinguished, and a reclosing command is issued; if not, the counter is reset and returns to S41.

[0024] Furthermore, in order to reduce the amount of calculation and to include the influence of high-frequency components as much as possible, the preset number is 7. Too many harmonic component orders will not only increase the amount of calculation, but also cause the transmission characteristics of the high-voltage capacitive voltage transformer to decay at high frequencies.

[0025] Furthermore, the preset harmonic ratio threshold is set to 1.2.

[0026] Beneficial Effects

[0027] The present invention proposes a single-phase adaptive reclosing method for a transmission line based on the dynamic change of harmonic ratio. The method is aimed at a transmission line with a shunt reactor, and uses the dynamic change of the harmonic content ratio of the fault-tripped phase voltage and its duration to quickly capture the instantaneous fault arc extinction moment, thereby ensuring successful reclosing in the voltage recovery stage and effectively avoiding reclosing under permanent faults. At the same time, the method uses a judgment method of fixed protection threshold and time constant, and has strong adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a flow chart of a single-phase adaptive reclosing method for a transmission line based on dynamic changes in harmonic ratios provided by an embodiment of the present invention;

[0030] Figure 2 It is a two-terminal equivalent simulation model diagram of a 500kV power transmission system provided by an embodiment of the present invention;

[0031] Figure 3The following are simulation results of a transient fault in a high compensation line provided by an embodiment of the present invention: Figure (a) is the fault phase voltage under the transient fault; Figure (b) is the HR value after the fault phase is tripped under the transient fault; Figure (c) is the HRT value after the fault phase is tripped under the transient fault; Figure (d) is the arc extinction time captured by the transient fault;

[0032] Figure 4 The following are simulation results of a low compensation line provided by an embodiment of the present invention when a transient fault occurs: Figure (a) is the fault phase voltage under the transient fault; Figure (b) is the HR value after the fault phase is tripped under the transient fault; Figure (c) is the HRT value after the fault phase is tripped under the transient fault; Figure (d) is the arc extinction time captured by the transient fault;

[0033] Figure 5 It is a simulation result diagram under permanent fault provided by an embodiment of the present invention: Figure (a) is the fault phase voltage under instantaneous fault; Figure (b) is the HR value after the fault phase is tripped under instantaneous fault; Figure (c) is the HRT value after the fault phase is tripped under instantaneous fault; Figure (d) is the arc extinction time captured by instantaneous fault. DETAILED DESCRIPTION

[0034] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0035] Example 1

[0036] This embodiment provides a single-phase adaptive reclosing method for a transmission line based on dynamic changes in harmonic ratios, including:

[0037] S1: After a single-phase grounding fault occurs in the transmission line, the fault phase is tripped, and the voltage of the fault phase is acquired at a preset sampling rate to obtain a sampling sequence. The sampling rate can be adjusted according to the actual situation of the specific implementation. In this embodiment, the voltage of the fault phase is acquired at a sampling rate of 6400 Hz to obtain a sampling sequence u(k), where k is the current sampling sequence value, k=1, 2, 3...

[0038] S2: Based on the acquired sampling sequence, the fault phase voltage after the preset sampling moment is selected to calculate the harmonic content value of the preset harmonic component order of the fault phase voltage. The preset sampling moment and the preset harmonic component order can be adjusted according to the actual situation of the specific implementation. In this embodiment, the fault phase voltage after the sampling time exceeds one power frequency is selected for harmonic content value calculation, that is, the fault phase voltage after the sequence value k=128; the preset harmonic component order is set to 7, and then the harmonic content values ​​of the 1st to 7th order of the fault phase voltage are calculated. Too many harmonic component orders will not only increase the amount of calculation, but also cause the transmission characteristics of the high-voltage capacitive voltage transformer to attenuate at high frequencies.

[0039] Among them, the calculation formula of the harmonic content value of the fault phase voltage is:

[0040]

[0041] Among them, U i is the i-th harmonic content value, that is, the amplitude of the i-th times power frequency of the fault phase voltage; U real is the real part of discrete Fourier transform; U imag is the imaginary component; N is the number of sampling points of one power frequency cycle; i is the number of harmonic components; j is the sequence point currently used to calculate data; u(j) is the jth sequence value in the sampling sequence.

[0042] S3: According to the calculated 7th harmonic content value, the harmonic ratio HR of the fault phase voltage and the harmonic content HRT of the fault phase voltage are calculated at every other sampling point.

[0043] Among them, the calculation formula of the harmonic ratio HR of the fault phase voltage is:

[0044]

[0045] Among them, HR(k) is the harmonic ratio value at the current sampling point; U i is the i-th harmonic content value, the numerator i=2a+1, representing odd harmonics; the denominator i=2a, representing even harmonics;

[0046] Furthermore, the calculation formula of the harmonic content HRT of the fault phase voltage is:

[0047]

[0048] Among them, HRT(k) is the ratio of all harmonic content to the relative fundamental content; U i is the i-th harmonic content value, i=1, 2, 3...7.

[0049] S4: The harmonic ratio and harmonic content of the fault phase voltage obtained by calculation are used to determine the fault nature of the transmission line, and a reclosing instruction is issued accordingly.

[0050] S41: Determine whether the harmonic content is greater than a preset harmonic content threshold (set to 0.1 in this embodiment) and the harmonic ratio is greater than a preset harmonic ratio threshold (set to 1.2 in this embodiment, that is, the critical value of the harmonic ratio before and after arc extinction under instantaneous fault is 1, multiplied by the reliability coefficient 1.2, to ensure the margin of the instantaneous fault judgment after arc extinction) and the duration exceeds a preset time (set to one quarter cycle in this embodiment): If not, it is determined that a permanent grounding fault has occurred in the transmission line, and the reclosing is locked; if so, enter S42.

[0051] S42: Determine whether the harmonic ratio is greater than the preset harmonic ratio threshold: If so, start the counter. When the continuous counting time of the harmonic ratio exceeds the preset counting time threshold (set to 5ms in this embodiment), it is determined that a transient fault has occurred in the transmission line and the arc has been extinguished, and a reclosing signal is issued.

[0052] In specific implementation, when the value of the harmonic content HRT(k) is greater than 0.1, and the duration of the harmonic ratio HR(k)>1.2 exceeds one quarter of a cycle: when the harmonic ratio HR(k) is greater than 1.2, the counter is started, and if the harmonic ratio HR(k)<1.2, the counter is reset; if the harmonic ratio HR(k) is counted continuously for more than 5ms, it can be considered that a transient fault has occurred in the transmission line and the arc has been extinguished, and a reclosing command is issued. The conditions for judging the nature of the transmission line fault are as follows:

[0053]

[0054] If no conditions satisfying the fault nature judgment of the transmission line are detected within the inherent reclosing time (in this embodiment, the inherent reclosing time ranges from 800ms to 1.2s), it can be considered that a permanent grounding fault has occurred in the transmission line, and the reclosing switch is locked at this time.

[0055] In order to further verify the technical solution of this application, Figure 2 The two-terminal equivalent simulation model of the 500 kV transmission system shown in the figure is used as an example to explain in detail. The equivalent impedance at both ends of the system is: Z A1 =(2+j40.2)Ω, Z A0 =(1+j20)Ω, Z B1 =(1+j20)Ω, Z B0=(0.5+j10)Ω. The line is 240km long, and the total line parameters are: Z1=(4.5717+j68.262)Ω, Z0=(43.692+j159.58)Ω, Y1=(1.7889+j993.79)uS, Y0=(-2.505+j767.22)uS. The parallel reactor compensation is adopted, and the parallel reactance X is changed. L and neutral point reactance X N The value of can change the compensation degree of the line.

[0056] When a transient fault occurs in the high compensation line, the simulation settings are as follows: the transient fault occurrence time is set at 0.1s, the tripping time is 0.2s, and the arc extinguishing time is set at 0.4s. It can be seen from the simulation results that Figure 3 As shown in (a), after the instantaneous fault extinguishes the arc, the recovery voltage exhibits a beat frequency characteristic because it contains a non-periodic oscillation component close to the power frequency. Figure 3 As shown in (c), when Fourier analysis is used, a higher harmonic content appears, which is greater than 10%; and the 2nd, 4th, and 6th harmonic contents are higher than the 3rd, 5th, and 7th harmonic contents, and the ratio between the two is stable above 1.4, as shown in Figure 3 As shown in (b), a constant of 1.2 is used. Figure 3 As shown in (d), the final captured arc extinction time is about 0.414s, which is about 15ms slower than the actual arc extinction time, and can quickly detect arc extinction.

[0057] When a transient fault occurs in the low compensation line, the simulation settings are the same as above. From the simulation results Figure 4 It can be seen that the beat frequency phenomenon of the recovery voltage under low compensation degree is weakened, but the harmonic content ratio and the size and dynamic change trend of the harmonic content value remain basically unchanged. Finally, the arc extinction time is detected to be 0.4159s. The arc extinction time can also be detected when it is less than one power frequency cycle.

[0058] The simulation results under permanent fault are as follows: Figure 5 As shown, Figure 5 After the permanent fault in (a) is tripped, the fault phase voltage only has the electromagnetic coupling voltage, which shows a sinusoidal component characteristic. Figure 5 (d) It can be seen that the harmonic content HRT is extremely low. Therefore, although the dynamic change trend of the harmonic content ratio HR is not much different from the instantaneous nature, the distribution of HRT can be used to determine that this is a permanent fault.

[0059] It should be understood that in the embodiments of the present invention, the processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the type of device.

[0060] The readable storage medium is a computer-readable storage medium, which may be an internal storage unit of the controller described in any of the foregoing embodiments, such as a hard disk or memory of the controller. The readable storage medium may also be an external storage device of the controller, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the controller. Furthermore, the readable storage medium may also include both an internal storage unit of the controller and an external storage device. The readable storage medium is used to store the computer program and other programs and data required by the controller. The readable storage medium may also be used to temporarily store data that has been output or is to be output.

[0061] Based on this understanding, the technical solution of the present invention, in essence or in other words, the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned readable storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., various media that can store program codes.

[0062] It can be understood that the same or similar parts of the above embodiments can be referenced to each other, and the contents not described in detail in some embodiments can refer to the same or similar contents in other embodiments.

[0063] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A single-phase adaptive reclosing method for a transmission line based on dynamic changes in harmonic ratios, characterized in that: include: S1: After a single-phase grounding fault occurs in the transmission line, the fault phase is tripped, and the voltage of the fault phase is acquired at a preset sampling rate to obtain a sampling sequence; S2: Based on the acquired sampling sequence, the sequence value after the preset sampling time is selected to calculate the harmonic content value of the preset harmonic component order of the fault phase voltage; S3: According to the calculated harmonic content value of the preset harmonic component order, the harmonic ratio value and the harmonic content of the fault phase voltage are calculated at every other sampling point; S4: The harmonic ratio and harmonic content of the fault phase voltage obtained by calculation are used to determine the fault nature of the transmission line, and a reclosing instruction is issued accordingly.

2. The single-phase adaptive reclosing method for a power transmission line based on dynamic changes in harmonic ratio according to claim 1 is characterized in that: The calculation formula for the harmonic content value of the fault phase voltage is: Among them, U i is the i-th harmonic content value, that is, the amplitude of the i-th times power frequency of the fault phase voltage; U real is the real part of discrete Fourier transform; U imag is the imaginary component; N is the number of sampling points of one power frequency cycle; i is the number of harmonic components; j is the sequence point currently used to calculate data; u(j) is the jth sequence value in the sampling sequence.

3. The single-phase adaptive reclosing method for a power transmission line based on dynamic changes in harmonic ratio according to claim 1 is characterized in that: The calculation formula of the harmonic ratio of the fault phase voltage is: Among them, HR(k) is the harmonic ratio value at the current sampling point; U i is the i-th harmonic content value, the numerator i=2a+1, representing odd harmonics; the denominator i=2a, representing even harmonics.

4. The single-phase adaptive reclosing method for transmission lines based on dynamic changes in harmonic ratios according to claim 1 is characterized in that: The calculation formula for the harmonic content of the fault phase voltage is: Among them, HRT(k) is the ratio of all harmonic content to the relative fundamental content; U i is the value of the ith harmonic content.

5. The single-phase adaptive reclosing method for power transmission lines based on dynamic changes in harmonic ratios according to claim 1, characterized in that: The specific process of S4 is: S41: Determine whether the harmonic content is greater than the preset harmonic content threshold and the duration of the harmonic ratio greater than the preset harmonic ratio threshold exceeds the preset time length: if not, determine that a permanent grounding fault occurs in the transmission line and perform locking and reclosing; if so, enter S42; S42: Determine whether the harmonic ratio is greater than the preset harmonic ratio threshold: If so, start the counter. When the continuous counting time of the harmonic ratio exceeds the preset counting time threshold, it is determined that a transient fault has occurred in the transmission line and the arc has been extinguished, and a reclosing command is issued; if not, the counter is reset and returns to S41.

6. The single-phase adaptive reclosing method for power transmission lines based on dynamic changes in harmonic ratios according to claim 1, characterized in that: It is characterized in that The harmonic component order is preset to 7 in S2.

7. The single-phase adaptive reclosing method for transmission lines based on dynamic changes in harmonic ratios according to claim 5, characterized in that: It is characterized in that The default harmonic ratio threshold is set to 1.2.

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