A single-phase adaptive reclosing method for power transmission lines based on dynamic change of harmonic ratio

Abstract

The application discloses a single-phase adaptive reclosing method for a power transmission line based on harmonic ratio dynamic change, which comprises the following steps: after a single-phase grounding fault occurs in a power transmission line, a fault phase is tripped, a voltage of the fault phase is acquired at a preset sampling rate, and a sampling sequence is obtained; based on the acquired sampling sequence, sequence values after preset sampling time points are selected to calculate harmonic content values of the fault phase voltage for a preset number of times; according to the calculated harmonic content values for the preset number of times, a harmonic ratio of the fault phase voltage and a harmonic content of the fault phase voltage are calculated and acquired at every other sampling point; and the calculated harmonic ratio and harmonic content of the fault phase voltage are used to distinguish the fault property of the power transmission line, and a reclosing instruction is correspondingly sent. The method ensures reclosing success in the recovery voltage stage and effectively avoids reclosing under permanent fault; and the distinguishing method adopting a fixed protection threshold and a time setting value has strong adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system transmission line, and particularly relates to a single-phase adaptive reclosing method for transmission line based on dynamic change of harmonic ratio. BACKGROUND

[0002] The transmission line has the important characteristics of high voltage level and long distance power transmission, and is easily affected by disaster weather and external force due to being exposed to natural conditions, so the single-phase grounding fault is the highest in the whole power system element. The single-phase automatic reclosing technology is widely used in the transmission line, and can quickly restore the transmission of the transient fault line and improve the stability of the system parallel operation.

[0003] The traditional automatic closing device adopts a fixed time blind reclosing scheme, which brings a large amount of economic benefits, but also has many problems: when reclosing to a permanent fault, not only the normal power supply of the fault line cannot be restored, but also the voltage of the other healthy line drops again, which causes more serious secondary damage to the system stability; when reclosing to a transient fault, the fixed reclosing time increases the non-full-phase operation time of the system.

[0004] At present, the fault property identification method based on the transmission line mainly includes the arc high-voltage high-frequency component in the secondary arc stage and the voltage amplitude and phase method in the recovery voltage stage. However, in the parallel reactor transmission line, the secondary arc will be extinguished soon, 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, so the power frequency component amplitude and phase cannot be extracted in a short time, which will increase the reclosing time.

[0005] Therefore, a method for quickly capturing the transient fault arc extinction moment in the parallel reactor transmission line and ensuring adaptive reclosing of the transmission line in the recovery voltage stage is needed. SUMMARY

[0006] The present application provides a single-phase adaptive reclosing method for transmission line based on dynamic change of harmonic ratio, which adopts the dynamic change of the harmonic content ratio of the fault opening phase voltage and its duration to quickly capture the transient fault arc extinction moment, ensures the reclosing success in the recovery voltage stage, and effectively avoids the reclosing under the permanent fault; at the same time, the method adopts the fixed protection threshold and time setting value discrimination method, and has strong adaptability.

[0007] The present application provides a single-phase adaptive reclosing method for transmission line based on dynamic change of harmonic ratio, which includes:

[0008] S1: after the single-phase grounding fault of the transmission line occurs, the fault phase is opened, the voltage of the fault phase is obtained at a preset sampling rate, and a sampling sequence is obtained;

[0009] S2: selecting a sequence value after a preset sampling moment to calculate a harmonic content value of a preset harmonic component number of the fault phase voltage based on the acquired sampling sequence;

[0010] S3: calculating a harmonic ratio value of the fault phase voltage and a harmonic content of the fault phase voltage at every other sampling point according to the calculated harmonic content value of the preset harmonic component number;

[0011] S4: using the calculated harmonic ratio value and the harmonic content of the fault phase voltage to distinguish the fault property of the power transmission line and correspondingly issuing a reclosing instruction.

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

[0013]

[0014] wherein, Ui is the i-th harmonic content value, i.e. the amplitude of the i-th multiple of the power frequency of the fault phase voltage; U is the discrete Fourier transform real component; U is the imaginary component; N is the number of sampling points of one power frequency cycle; i is the harmonic component number; j is the sequence point currently used for calculation data; and u(j) is the j-th sequence value in the sampling sequence. i real imag

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

[0016]

[0017] wherein, HR(k) is the harmonic ratio value at the current sampling point; Ui is the i-th harmonic content value; the numerator i=2a+1 represents the odd harmonic; and the denominator i=2a represents the even harmonic. i

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

[0019]

[0020] wherein, HRT(k) is the ratio of all harmonic contents to the fundamental content; Ui is the i-th harmonic content value; and i=1, 2, 3, …. i

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

[0022] ​​​​​S41: judge whether the duration that the harmonic content is greater than the preset harmonic content threshold and the harmonic ratio is greater than the preset harmonic ratio threshold meets a preset time length: if not, it is determined that the power transmission line has a permanent grounding fault, and a reclosing is blocked; if yes, S42 is entered;

[0023] S42: judge whether the harmonic ratio meets a preset harmonic ratio threshold: if yes, a counter is started, and when the time of the continuous counting of the harmonic ratio exceeds a preset counting time threshold, it is determined that the power transmission line has a transient fault, and the arc has been extinguished, and a reclosing instruction is sent; if not, the counter is cleared, and S41 is returned.

[0024] Further, in order to reduce the calculation amount and as much as possible to include the influence of the high-frequency component, the preset number of times is 7 times. Too many harmonic component numbers not only cause the calculation amount to increase, but also cause the transmission characteristic of the high-voltage capacitor voltage transformer to attenuate at high frequencies.

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

[0026] Beneficial effects

[0027] The application provides a single-phase adaptive reclosing method for a power transmission line based on dynamic changes of a harmonic ratio, which is used for a power transmission line with a shunt reactor, adopts dynamic changes of a harmonic content ratio of a fault tripped phase voltage and a duration thereof to quickly capture a transient fault arc extinguishing moment, ensures reclosing success in a recovery voltage stage, and effectively avoids reclosing under a permanent fault; meanwhile, the method adopts a fixed protection threshold and a time setting value discrimination method, and has strong adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0029] Figure 1 is a flow chart of a single-phase adaptive reclosing method for a power transmission line based on dynamic changes of a harmonic ratio provided by the embodiment of the application;

[0030] Figure 2 is a double-end equivalent simulation model diagram of a 500kV power transmission system provided by the embodiment of the application;

[0031] Figure 3is a simulation result diagram of the high compensation line when a transient fault occurs, provided by the embodiment of the present application: Fig. (a) is the fault phase voltage under the transient fault; Fig. (b) is the HR value after the fault phase is tripped under the transient fault; Fig. (c) is the HRT value after the fault phase is tripped under the transient fault; and Fig. (d) is the arc extinguishing time captured under the transient fault.

[0032] Figure 4 is a simulation result diagram of the low compensation line when a transient fault occurs, provided by the embodiment of the present application: Fig. (a) is the fault phase voltage under the transient fault; Fig. (b) is the HR value after the fault phase is tripped under the transient fault; Fig. (c) is the HRT value after the fault phase is tripped under the transient fault; and Fig. (d) is the arc extinguishing time captured under the transient fault.

[0033] Figure 5 is a simulation result diagram under the permanent fault, provided by the embodiment of the present application: Fig. (a) is the fault phase voltage under the transient fault; Fig. (b) is the HR value after the fault phase is tripped under the transient fault; Fig. (c) is the HRT value after the fault phase is tripped under the transient fault; and Fig. (d) is the arc extinguishing time captured under the transient fault. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0035] Embodiment 1

[0036] The embodiment provides a power transmission line single-phase adaptive reclosing method based on dynamic change of harmonic ratio, comprising the following steps.

[0037] S1: after a single-phase grounding fault occurs in the power 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 specific implementation. In the embodiment, the voltage of the fault phase is collected at a sampling rate of 6400 Hz to obtain a sampling sequence u(k), wherein k is a current sampling sequence value, k=1, 2, 3…….

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

[0039] The calculation formula of the harmonic content value of the fault phase voltage is:

[0040]

[0041] The calculation formula of the harmonic content value of the fault phase voltage is: i The calculation formula of the harmonic content value of the fault phase voltage is: real The calculation formula of the harmonic content value of the fault phase voltage is: imag The calculation formula of the harmonic content value of the fault phase voltage is:

[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] The calculation formula of the harmonic content value of the fault phase voltage is:

[0044]

[0045] The calculation formula of the harmonic content value of the fault phase voltage is: i The calculation formula of the harmonic content value of the fault phase voltage is:

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

[0047]

[0048] The calculation formula of the harmonic content value of the fault phase voltage is: i The calculation formula of the harmonic content value of the fault phase voltage is:

[0049] S4: The nature of the fault in the transmission line is determined by the calculated harmonic ratio and harmonic content of the fault phase voltage, and a reclosing command is issued accordingly.

[0050] S41: Determine whether the duration of harmonic content being greater than the preset harmonic content threshold (set to 0.1 in this embodiment) and harmonic ratio being greater than the preset harmonic ratio threshold (set to 1.2 in this embodiment, i.e., the critical value of the harmonic ratio before and after arc extinction under transient fault is 1, multiplied by the reliability coefficient 1.2 to ensure the margin of the criterion after arc extinction of transient fault) exceeds the preset duration (set to one-quarter cycle in this embodiment): If not, determine that a permanent grounding fault has occurred in the transmission line and block reclosing; if yes, proceed to S42.

[0051] S42: Determine whether the harmonic ratio is greater than the preset harmonic ratio threshold: If yes, 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 the transmission line has experienced a transient fault and the arc has been extinguished, and a reclosing signal is issued.

[0052] In specific implementation, when 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, a counter is started; if the harmonic ratio HR(k) < 1.2, the counter is reset to zero; if the harmonic ratio HR(k) counts continuously for more than 5 ms, 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 fault nature of the transmission line are as follows:

[0053]

[0054] If no conditions for determining the nature of a transmission line fault 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 reclosing will be blocked.

[0055] To further verify the technical solution of this application, Figure 2 Taking the double-ended equivalent simulation model of the 500kV transmission system shown below as an example, 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 length is 240 km, 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. With shunt reactor compensation, by changing the value of shunt reactor X L and neutral point reactor X N , the compensation degree of the line can be changed.

[0056] The simulation settings when the transient fault occurs in the high compensation line are as follows: the transient fault occurs at 0.1 s, the tripping time is 0.2 s, and the arc extinguishing time is set at 0.4 s. As can be seen from the simulation results, as shown in Figure 3 (a), after the arc extinguishing of the transient fault, the recovery voltage presents the beat frequency characteristics due to the non-periodic oscillation components close to the power frequency. As shown in Figure 3 (c), when Fourier analysis is used, a higher harmonic content greater than 10% appears; and the 2nd, 4th, and 6th harmonic contents are higher than the 3rd, 5th, and 7th harmonic contents, and the ratio of the two is stable at 1.4 or more, as shown in Figure 3 (b), the fixed value of 1.2 is used. As shown in Figure 3 (d), the final capture arc extinguishing time is about 0.414 s, which is about 15 ms slower than the real arc extinguishing time, and the arc extinguishing can be quickly detected.

[0057] The simulation settings when the transient fault occurs in the low compensation line are the same as above, and 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, the harmonic content value, and the dynamic change trend are basically unchanged, and the final detected arc extinguishing time is 0.4159 s, which is also less than one power frequency cycle to detect the arc extinguishing time.

[0058] The simulation results under permanent fault are shown in Figure 5 , as shown in Figure 5 (a), after the permanent fault is tripped, the fault phase voltage only remains the electromagnetic coupling voltage, and thus presents the sine component characteristics. From Figure 5 (d), it can be seen that the harmonic content HRT is extremely low, so although the dynamic change trend of the harmonic content ratio HR is not much different from that of the transient fault, combined with the distribution of HRT, it can be determined that this is a permanent fault.

[0059] It should be understood that in the embodiments of the present application, the processor can be a central processing unit (CPU), and the processor can 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, and the like. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor. The memory can include a read-only memory and a random access memory, and provide instructions and data for the processor. A portion of the memory can also include a non-volatile random access memory. For example, the memory can also store device type information.

[0060] The readable storage medium is a computer readable storage medium, which can be an internal storage unit of the controller, such as a hard disk or a memory of the controller. The readable storage medium can also be an external storage device of the controller, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, and the like. Further, the readable storage medium can include both the internal storage unit and the external storage device of the controller. The readable storage medium is used to store the computer program and other programs and data required by the controller. The readable storage medium can also be used to temporarily store data that has been output or will be output.

[0061] Based on such understanding, the technical solutions of the present application, essentially or in the contribution to the prior art, or all or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned readable storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0062] It can be understood that the same or similar parts in the above-mentioned embodiments can be mutually referenced, 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 application have been shown and described above, it can be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application, and the ordinary skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A method for single-phase adaptive reclosing of a power transmission line based on dynamic variation of harmonic ratio, characterized in that, The method comprises: S1: after a single-phase grounding fault of a power transmission line occurs, the fault phase is tripped, and a voltage of the fault phase is obtained at a preset sampling rate to obtain a sampling sequence; S2: based on the obtained sampling sequence, a sequence value after a preset sampling time is selected to calculate a harmonic content value of a preset harmonic component number of the fault phase voltage; S3: according to the calculated harmonic content value of the preset harmonic component number, a harmonic ratio of the fault phase voltage and a harmonic content of the fault phase voltage are calculated at every other sampling point; S4: the calculated harmonic ratio and harmonic content of the fault phase voltage are used to determine the fault property of the power transmission line, and a reclosing instruction is issued accordingly; wherein the calculation formula of the harmonic content value of the fault phase voltage is: ； ； wherein, is the i-th harmonic content value, i.e. the amplitude of the i-th multiple of the fundamental frequency of the fault phase voltage; is the real part of the discrete Fourier transform; is the imaginary part; is the number of sampling points per fundamental cycle; is the number of harmonic components; is the current sequence point used for the calculation of the data; is the j-th sequence value in the sampling sequence; the calculation formula of the harmonic ratio of the fault phase voltage is: ； wherein, is the harmonic ratio value at the current sampling point; is the i-th harmonic content value, the numerator i = 2a + 1 represents the odd harmonics and the denominator i = 2a represents the even harmonics; the calculation formula of the harmonic content of the fault phase voltage is: ； wherein is the ratio of all harmonic content and relative fundamental content; is is the i-th harmonic content value.

2. The method for single-phase adaptive reclosing of transmission lines based on dynamic variation of harmonic ratio according to claim 1, characterized in that, the specific process of S4 is: S41: whether the duration that the harmonic content is greater than a preset harmonic content threshold and the harmonic ratio is greater than a preset harmonic ratio threshold exceeds a preset time length is determined: if not, it is determined that the power transmission line has a permanent grounding fault, and the reclosing is blocked; if yes, S42 is entered; S42: whether the harmonic ratio is greater than the preset harmonic ratio threshold is determined: if yes, a counter is started, and when the continuously counted time of the harmonic ratio exceeds a preset counting time threshold, it is determined that the power transmission line has a transient fault and has been arc extinguished, and a reclosing instruction is issued; if not, the counter is cleared, and S41 is returned.

3. The method for single-phase adaptive reclosing of transmission line based on dynamic variation of harmonic ratio according to claim 1, characterized in that, The preset harmonic component number in S2 is 7.

4. The method for single-phase adaptive reclosing of transmission line based on dynamic variation of harmonic ratio according to claim 2, characterized in that, The preset harmonic ratio threshold is set to 1.2.

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