A construction method of a quasi-directional element based on a CLC tuning circuit

Abstract

This invention relates to a method for constructing directional elements based on CLC tuned circuits, belonging to the field of power system relay protection technology. The invention includes constructing π-type LC low-pass filter CLC tuned circuits on both sides of the transmission line to collect transient signals of the transmission line; based on the collected fault current information, utilizing the difference in electrical quantities collected at measurement points on the line side and bus side, extracting wavelet energy from the collected fault signals to calculate the energy of different frequency bands of the signals collected at measurement points on both sides of the CLC tuned circuit; calculating the high-frequency wavelet energy collected at measurement points on both sides of the CLC tuned circuit based on the extracted high-frequency fault components; taking the ratio of the high-frequency wavelet energy at measurement points on both sides of the CLC tuned circuit, taking the logarithm of the ratio, and establishing its sign function sgn; if this sign function satisfies log(E... m2 / E m1 If log(E) > 0, then it is judged as a positive direction fault; if log(E) > 0, then it is judged as a positive direction fault. m2 / E m1 If ) < 0, it is judged as a reverse fault; the magnitude of this sign function is used to construct the protection criterion of the protection element.

Description

Technical Field

[0001] This invention relates to a method for constructing a directional element based on a CLC tuning circuit, belonging to the field of power system relay protection technology. Background Technology

[0002] The mismatch between economic development and the distribution of electricity resources remains a major challenge for my country's future development. Against the backdrop of the "West-to-East Power Transmission" strategy, the green consumption of new energy sources, the continuous increase in installed capacity of renewable energy, and the ongoing development of long-distance, high-capacity power transmission technology, half-wavelength AC transmission technology is highly attractive. Tuned half-wavelength transmission can enable transmission lines less than 3000km in length to possess characteristics such as reactive power self-balancing throughout the entire half-wavelength AC transmission line, making it a highly advantageous option for achieving "dual-carbon" goals.

[0003] Due to objective limitations, the actual transmission distance of power lines rarely meets the half-wavelength requirement, and may even be far less. Therefore, the scheme of using tuned circuits for electrical length compensation to achieve the half-wavelength requirement has been proposed as a backup plan. Research on tuned circuits for electrical length compensation has been reported in the literature since the 1960s. However, when applied to power systems, it is necessary to consider that the power system itself is a three-phase transmission system, and that there are zero-sequence loops connected to the system when the three-phase balance is disrupted. The concept of tuned half-wavelength transmission lines transcends the traditional approach of minimizing electrical distance in transmission lines. It introduces the concept of wavelength, originally inaccessible in power frequency electrical quantities, into the power system, allowing for the exploration of various physical characteristics at the electromagnetic wave wavelength level to further develop and advance the power system. Research on tuned half-wavelength transmission lines not only contributes to the further development of long-distance, high-capacity power transmission technology but also helps future ultra-high voltage AC transmission lines reduce losses during transmission through similar or identical methods, ensuring that the power system can keep pace with the times and continuously innovate in an era of significant changes in the global energy landscape in the 21st century.

[0004] The electrical characteristics of tuned half-wavelength transmission lines after a fault differ from those of existing AC lines. Traditional AC line protection methods are insufficient to meet the protection requirements of speed and sensitivity for half-wavelength transmission lines, making the protection of tuned half-wavelength AC transmission lines a pressing problem. Tuned half-wavelength transmissions, while compensating for electrical distance, also provide new protection measurement points for half-wavelength lines. The CLC tuned circuit, essentially an LC low-pass filter, possesses unique boundary characteristics, similar to the boundary protection principle used in HVDC transmission. This invention proposes utilizing the difference in electrical quantities collected from measurement points on the line side and bus side, starting with high-frequency components, and constructing a directional protection element based on the CLC tuned circuit according to the wavelet energy ratio of the measurement points on both sides. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for constructing a quasi-directional element based on a CLC tuned circuit. By utilizing the difference in electrical quantities collected from measurement points on the line side and the bus side, starting from the high-frequency components, a quasi-directional protection element based on a CLC tuned circuit is constructed according to the wavelet energy ratio of the measurement points on both sides. It has good applicability and robustness under various fault conditions.

[0006] The technical solution of this invention is: a method for constructing a quasi-directional element based on a CLC tuning circuit, the specific steps of which are as follows:

[0007] Step 1: Construct a π-type CLC tuning circuit and determine the parameters of the tuning circuit.

[0008] Step 2: Detect the transfer characteristics of the π-type CLC tuning circuit.

[0009] Step 3: Examine the effect of CT saturation on the amount of acquired current signal.

[0010] Step 4: Collect the current at the bus side and line side measuring points at both ends of the CLC tuning circuit.

[0011] Step 5: Utilize the equidistant characteristics of wavelet transform in the frequency domain to extract wavelet energy from the acquired fault signals.

[0012] Step 6: Calculate the high-frequency wavelet energy collected from the measurement points on both sides of the CLC tuning circuit.

[0013] Step 7: Take the ratio of the high-frequency wavelet energy at the measurement points on both sides of the CLC tuning circuit, and take the logarithm of the ratio of the wavelet energy at the measurement points on both sides.

[0014] Step 8: Take the sign function sgn from the logarithm of the high-frequency wavelet energy ratio at the measurement points on both sides of the tuned circuit.

[0015] Step 9: Construct a directional element based on a CLC tuning circuit.

[0016] Step 1 specifically refers to:

[0017] First, a π-type CLC tuning circuit is constructed, and then analyzed to determine the parameters of the constructed π-type CLC tuning circuit as follows:

[0018]

[0019] Simplifying equation (1), we can obtain

[0020]

[0021] In the formula, C0 is the capacitance to ground, and C1 is the capacitance between phases.

[0022] To ensure that the tuned transmission line meets the half-wavelength characteristic, the π-type tuning circuit is equivalent to a segment with a phase constant of β. k The length is l k For the transmission line, the equivalent surge impedance of the π-type tuned circuit is the same as that of the original line, β k l k It can satisfy:

[0023]

[0024] Step 2 specifically includes:

[0025] The transfer characteristics of the π-type CLC tuned circuit include the transfer voltage ratio characteristic and the transfer current ratio characteristic.

[0026] Based on the fact that the passive CLC tuned circuit is essentially a low-pass filter, and using the π-type CLC lumped circuit for analysis, its transfer voltage ratio characteristic can be obtained as follows:

[0027]

[0028] H dB =20lg[|H(s)| s＝jω (5)

[0029] Its transfer current ratio characteristic can be obtained as follows:

[0030]

[0031] H dB =20lg[|H(s)| s＝jω (7)

[0032] In the formula, H(s) is the transfer function of the π-type CLC lumped circuit, ω is the angular frequency, C is the equivalent capacitance, and L is the equivalent inductance.

[0033] Analysis of equations (4)-(7) shows that the physical boundary formed by the CLC tuning circuit on both sides of the half-wavelength transmission line has a high-frequency blocking effect. That is, when a fault occurs at different locations on the line, the characteristics of the initial voltage waveform and current waveform collected by the measuring points on both sides of the CLC tuning circuit will be significantly different, and the high-frequency components cannot pass through the CLC tuning circuit with low-pass characteristics.

[0034] Step 3 specifically refers to:

[0035] Define the transfer function of CT as follows:

[0036]

[0037] In the formula, These are the primary and secondary currents on the system side.

[0038] By establishing the equivalent circuit of CT, the transfer function of CT is derived as follows:

[0039]

[0040] In the formula, R L This represents the line resistance.

[0041] Step 4 specifically involves: when a line fault occurs, the protection devices at both ends of the π-type CLC tuned half-wavelength transmission line collect the transient signals of the transmission line and extract the required transient information of the secondary current.

[0042] Step 5 specifically includes:

[0043] When a fault occurs in a transmission line, the frequency characteristics of the fault signal are time-varying. Wavelet transform, due to its equidistant frequency domain characteristics, can well reflect the original fault signal and ensure the consistency of energy. That is, the energy of the fault signal can remain consistent in both the time scale and the wavelet scale. By performing wavelet energy extraction on the signals collected by the measurement points on the bus side and the line side respectively, it is possible to calculate the energy of different frequency bands of the signals collected by the measurement points on both sides of the CLC tuning circuit.

[0044] The wavelet energy expression is defined as follows:

[0045]

[0046] In the formula, E k Let W be the wavelet energy of the k-th layer signal, m be the data width of the time window, and W be the wavelet energy of the k-th layer signal. k (m) represents the wavelet transform coefficients of the k-th layer. The wavelet energy spectrum sequence of the discrete wavelet transform is:

[0047] E = [E1, E2, E3, ..., E k [,…] (11)

[0048] The energy spectrum at eight scales of wavelet transform is selected for calculation, and the time-frequency eigenvector matrix is ​​defined as follows:

[0049]

[0050] In the formula, ω T and ω F These are the lengths of the time window and the frequency window, respectively. Using the time-frequency matrix L... TF By combining the characteristics of a signal in the time and frequency domains, its time-frequency characteristics can be fully reflected.

[0051] Step 6 specifically refers to:

[0052] The measuring point on the M-terminal bus side is designated as m1, and its corresponding voltage and current are U and U, respectively.m1 I m1 The line-side measuring point is m2, and its corresponding voltage and current are U and U, respectively. m2 I m2 .

[0053] Define the wavelet high-frequency energies of measurement points m1 and m2 as E, respectively. m1 E m2 ,but:

[0054]

[0055]

[0056] In the formula, The wavelet high-frequency energy of the k-th layer signal at the M-end bus side measurement point. The high-frequency energy of the wavelet signal at the k-th layer of the line-side measurement point at terminal M is given.

[0057] Step 7 specifically refers to:

[0058] The ratio of the high-frequency wavelet energies at the measurement points on both sides of the CLC tuning circuit is taken as E. m2 / E m1 And take the logarithm of the ratio of wavelet energies at both measuring points: log(E m2 / E m1 ).

[0059] Step 9 specifically refers to:

[0060] The value of the sign function sgn is used as a fault direction criterion for constructing directional elements in CLC tuned circuits.

[0061] When the logarithm of the wavelet energy ratio is greater than 0, sgn[δ] = 1.

[0062] When the logarithm of the wavelet energy ratio is less than 0, sgn[δ] = -1.

[0063] The positive direction of the current is defined as the direction from the busbar to the line.

[0064] If log(E) m2 / E m1 If ) > 0, then it is judged as a positive direction fault.

[0065] If log(E) m2 / E m1 If ) < 0, then it is judged as a reverse direction fault.

[0066] When a fault occurs in the forward direction of the line, the high-frequency components of the fault current collected by the line-side measuring point at the connection between the tuning circuit and the line are abundant. However, when a fault occurs in the reverse direction of the line, the high-frequency components of the current collected by the line-side measuring point are relatively small. By utilizing the difference in electrical quantities collected by the line-side and bus-side measuring points, starting from the high-frequency components, and based on the ratio of wavelet energy at the measuring points on both sides, a quasi-directional protection element based on the CLC tuning circuit is constructed.

[0067] The beneficial effects of this invention are:

[0068] 1. This invention is applicable to half-wavelength transmission lines with tuning. It utilizes the difference in electrical quantities collected from measurement points on the line side and the bus side, starting from high-frequency components, and constructs a quasi-directional protection element based on CLC tuning circuit according to the wavelet energy ratio of the measurement points on both sides. It can accurately distinguish between forward and reverse faults under any position, fault angle, and transition resistance. The AD acquisition module does not require high precision and has good robustness.

[0069] 2. The fault signal acquisition of this invention is not affected by CT saturation. Before CT saturation, the secondary current waveform exhibits an unsaturated state in the CT during the first 1 / 4 cycle (5ms time), during which the CT can accurately transmit the primary current. Therefore, by using data within 3ms after startup, the same variation pattern as the primary current can be completely obtained, demonstrating good anti-CT saturation performance.

[0070] 3. Due to its equidistant frequency domain characteristics, wavelet transform can well reflect the original fault signal and ensure the consistency of energy. That is, the energy of the fault signal can remain consistent in both the time scale and the wavelet scale. When extracting wavelet energy from the signals collected by the measurement points on the bus side and the line side, it is possible to calculate the energy of different frequency bands of the signals collected by the measurement points on both sides of the CLC tuning circuit.

[0071] 4. The fault information acquisition required by this invention has a low sampling rate, only requires the acquisition of the initial fault current signal, requires a small amount of data, and has flexible system configuration. It can achieve accurate identification of faults in both directions under low sampling rate and has strong engineering applicability. Attached Figure Description

[0072] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0073] Figure 1 This is a simulation model diagram of a tuned half-wavelength transmission line according to the present invention;

[0074] Figure 2 This is a diagram of the π-type CLC tuning circuit containing zero-sequence compensation of the present invention;

[0075] Figure 3 This is the lumped circuit diagram of the π-type CLC of the present invention;

[0076] Figure 4 This is a characteristic diagram of the transfer voltage ratio of the π-type CLC tuning circuit of the present invention;

[0077] Figure 5 This is a current ratio characteristic diagram of the π-type CLC tuning circuit of the present invention;

[0078] Figure 6 This is a voltage and current waveform diagram on both sides of the CLC tuning circuit of the present invention;

[0079] Figure 7 This is a fault voltage and current waveform diagram on both sides of the CLC tuning circuit of the present invention;

[0080] Figure 8 This is the CT equivalent circuit diagram of the present invention;

[0081] Figure 9 This is the CT spectrum diagram of the present invention;

[0082] Figure 10 This is the CT transient flux map of the present invention;

[0083] Figure 11 This is a schematic diagram of the RTDS simulation system of the present invention;

[0084] Figure 12 This is the additional fault circuit and grid diagram within the line area of ​​Embodiment 2 of the present invention;

[0085] Figure 13 This is a logarithmic graph of the wavelet energy ratio when a fault occurs every 400km along the entire length of the line in Embodiment 2 of the present invention;

[0086] Figure 14 This is a fault diagram of four types of faults occurring in the reverse direction at end 3M of the present invention: AG, AB, ABG, and ABCG. Detailed Implementation

[0087] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0088] Example 1: As Figure 1As shown, a method for constructing a directional element based on a CLC tuning circuit includes the following steps:

[0089] Construct a simulation model of a half-wavelength transmission line containing a CLC tuning circuit, as follows: Figure 1 As shown, the line is 2560km long. The CLC tuning circuit is installed at both ends of the line, with a total compensated electrical length of 440km. The CLC tuning circuit at each end compensates for 220km.

[0090] Step 1: Construct as follows Figure 2 The π-type CLC tuning circuit with zero-sequence compensation shown is used for electrical distance compensation.

[0091] like Figure 2 As shown, C0 is the capacitance to ground, L1 is the inductance per unit length of the line, C1 is the inter-line capacitance, and M1 is the inter-line mutual inductance. After analysis, the calculation formulas for each parameter can be obtained as follows:

[0092]

[0093] Simplifying equation (1), we can obtain

[0094]

[0095] To ensure that the tuned transmission line meets the half-wavelength characteristic, the π-type CLC tuning circuit is equivalent to a segment with a phase constant of β. k The length is l k For transmission lines, the equivalent surge impedance of the π-type CLC tuned circuit should be the same as that of the original line, β k l k It can satisfy:

[0096]

[0097] Step 2: Based on the characteristic that the passive CLC tuning circuit is essentially a low-pass filter, utilize, for example... Figure 3 By analyzing the π-type CLC lumped circuit shown, its transfer voltage ratio characteristic can be obtained.

[0098]

[0099] H dB =20lg[|H(s)| s＝jω (5)

[0100] In the formula, H(s) is the transfer function of the π-type CLC lumped circuit, ω is the angular frequency, C is the equivalent capacitance, and L is the equivalent inductance.

[0101] Transfer voltage ratio characteristics such as Figure 4 As shown.

[0102] Its transfer current ratio characteristic can be obtained:

[0103]

[0104] H dB =20lg[|H(s)| s＝jω (7)

[0105] Transfer current ratio characteristics such as Figure 5 As shown.

[0106] Depend on Figure 4 , 5 It is known that the physical boundary formed by the CLC tuning circuit on both sides of a half-wavelength transmission line has a high-frequency blocking effect. That is, when a fault occurs at different locations on the line, the characteristics of the initial voltage waveform and current waveform collected by the measuring points on both sides of the CLC tuning circuit will be significantly different, and the high-frequency components cannot pass through the CLC tuning circuit with low-pass characteristics.

[0107] When operating without faults, such as Figure 6 The voltage and current waveforms of phase A on both sides of the CLC tuning circuit at the beginning of the line are shown, among which... These are the phase voltage and phase current measured at the busbar side. These are the phase voltage and phase current measured at the line side. It can be seen that the CLC tuning circuit will cause a slight phase shift in the voltage and current passing through it, while the amplitude remains basically unchanged.

[0108] from Figure 6 As can be seen from the transfer characteristic analysis above, the connection of the CLC tuning circuit essentially changes the electrical distance of the transmission line. During normal operation of a half-wavelength transmission line, the tuning circuit does not alter the transmission line characteristics. However, when a fault occurs on the line, the connection of the CLC tuning circuit will affect the transient process of the transmission line, and the voltage and current waveforms before and after the CLC tuning circuit will change.

[0109] In actual transmission lines, faults are mainly single-phase grounding faults. Suppose that a phase A grounding fault occurs on a half-wavelength line with tuning, and the fault is located 400km from the starting point.

[0110] The waveform of the faulty phase measured at the first end is as follows Figure 7 As shown, due to the influence of the boundary characteristics of the CLC tuning circuit, the high-frequency information of electrical quantities on the line side is richer, while the high-frequency information of electrical quantities on the bus side will be filtered by the CLC tuning circuit. Similarly, when a fault occurs outside the line area, the high-frequency information of electrical quantities on the bus side is richer, while the high-frequency information of electrical quantities on the line side will be filtered by the CLC tuning circuit.

[0111] Step 3: Define the transfer function of CT as follows

[0112]

[0113] In the formula For the primary and secondary currents on the system side, adopt as follows Figure 8 The CT equivalent circuit shown is analyzed for its passband.

[0114] In the diagram above, C3 and C4 represent the primary and secondary inter-electrode capacitances, respectively; R3 and R4 represent the primary winding resistance and secondary winding resistance, respectively; L3 and L4 represent the primary winding leakage reactance and secondary winding leakage reactance, respectively; Z m =R m +jωL m This represents the excitation impedance.

[0115] From this equivalent circuit, the transfer function of the CT can be derived as follows:

[0116]

[0117] In the formula R L This represents the line resistance.

[0118] Depend on Figure 9 It can be seen that for high-frequency 20kHz sampling rate conditions, the transmission signal can be transmitted without distortion, that is, saturation has almost no effect on the ratio of high-frequency wavelets.

[0119] In the case of a non-ideal CT, considering the "cropping" effect of the transient waveform after CT on this method, according to the relevant transformer calculation methods, we can obtain:

[0120]

[0121] In the formula, u and Φ are the per-unit values ​​of the rated voltage and magnetic flux of the CT under rated operating conditions. Assuming a fault occurs at time zero, the voltage on the primary side of the CT is u = U. m sin(ωt+α), where α is the voltage phase at the fault point at the fault time. Substituting u into equation (10) yields:

[0122] Φ=-Φ m cos(ωt+α)+Φ0 (11)

[0123] In the formula, Φ m This is the extreme value of the magnetic flux under power frequency conditions, at which point Φ m =U m / ω;Φ0 is the initial value of the magnetic flux linkage in the steady state. Since the magnetic flux linkage cannot change abruptly, at time zero, we can obtain:

[0124] Φ0=Φ m cosα+Φ s (12)

[0125] In the formula Φ sFor the remanence of the CT, the calculated Φ0 is greater than the critical value Φ for magnetic flux saturation. b A CT state will occur. When the fault occurs at the voltage zero crossing point, the aperiodic component of the fault signal attenuation is large, and the maximum flux linkage will far exceed the critical value Φ. b like Figure 10 As shown.

[0126] When CT saturates, according to equation (11), there are two moments within one cycle when the magnetic flux equals the saturation value. Let the variable γ = ωt + α, then in the first cycle, both points γ1 and 2π-γ1 are saturation points, and Φ b =-Φ m cosγ1+Φ0. When γ is between the two saturation points and the period boundary point, the CT is unsaturated. At this time, the excitation current is approximately zero. In the first 1 / 4 of the period, the CT will not saturate, and the flux linkage and excitation current satisfy Φ-Φ. b =i μ *L μ The excitation current during the (0, 2π) period can be expressed as:

[0127]

[0128] In the formula, i μ For the excitation current, L μ Let be the slope of the magnetization curve after saturation. Using the Fourier function to represent the excitation current, we have:

[0129]

[0130] In the formula, a n b n Let the amplitudes of the sine and cosine terms of each component satisfy:

[0131]

[0132] From equations (14) and (15), it can be seen that the content of each component is only related to the discontinuity angle. The secondary current can be obtained by dividing the difference between the primary current and the excitation current by the turns ratio, i.e. Substituting into equation (14) and considering periodicity, we can obtain the secondary current:

[0133]

[0134] In the formula, Let n be the primary and secondary currents of the CT. CTLet be the transformation ratio of the CT. From the above formula, it can be seen that when the CT is saturated, the secondary current waveform exhibits an unsaturated state in the CT during the first 1 / 4 cycle (5ms time). At this time, the CT can accurately transmit the primary current. Therefore, by using data within 3ms after startup, the same variation pattern as the primary current can be completely obtained, and this invention will not be affected by CT saturation.

[0135] Step 4: When a line fault occurs, the protection devices at both ends of the π-type CLC tuned half-wavelength transmission line are used to collect the transient signals of the transmission line and extract the required transient information of the secondary current.

[0136] Step 5: When a fault occurs in a transmission line, the frequency characteristics of the fault signal are time-varying. Wavelet transform, due to its equidistant frequency domain characteristics, can well reflect the original fault signal and ensure the consistency of energy. That is, the energy of the fault signal can remain consistent in both the time scale and the wavelet scale. By performing wavelet energy extraction on the signals collected by the measurement points on the bus side and the line side respectively, the energy of different frequency bands of the signals collected by the measurement points on both sides of the CLC tuning circuit can be calculated.

[0137] The wavelet energy expression is defined as follows:

[0138]

[0139] In the formula, E k W represents the wavelet energy of the k-th layer signal; m represents the data width of the time window; W k (m) represents the wavelet transform coefficients of the k-th layer. Then the wavelet energy spectrum sequence of the discrete wavelet transform is:

[0140] E = [E1, E2, E3, ..., E k [,…] (18)

[0141] The energy spectrum at eight scales of wavelet transform is selected for calculation, and the time-frequency eigenvector matrix is ​​defined as follows:

[0142]

[0143] In equation (19), ω T and ω F These are the lengths of the time window and the frequency window, respectively. Using the time-frequency matrix L... TF By combining the characteristics of a signal in the time and frequency domains, its time-frequency characteristics can be fully reflected.

[0144] Step 6: Taking terminal M as an example, the measuring point on the bus side of terminal M is defined as m1, and its corresponding voltage and current are U and U, respectively. m1 I m1 The line-side measuring point is m2, and its corresponding voltage and current are U and U, respectively. m2 I m2 .

[0145] Define the wavelet high-frequency energies of measurement points m1 and m2 as follows: E m1 E m2 This invention utilizes the db6 wavelet to extract wavelet energy at the second, third, and fourth scales within 3ms after a fault, resulting in:

[0146]

[0147]

[0148] In the formula, The wavelet high-frequency energy of the k-th layer signal at the M-end bus side measurement point. The high-frequency energy of the wavelet signal at the k-th layer of the line-side measurement point at terminal M is given.

[0149] Step 7: Take the ratio of the high-frequency wavelet energies at the measurement points on both sides of the CLC tuning circuit: E m2 / E m1 And take the logarithm of the ratio of wavelet energies at both measuring points: log(E m2 / E m1 ).

[0150] Step 8: Take the sign function sgn by taking the logarithm of the high-frequency wavelet energy ratio at the measurement points on both sides of the CLC tuning circuit.

[0151] Step 9: Calculate the value of the symbol function sgn established above, and use it as the fault direction criterion for constructing directional elements of CLC tuned circuits; stipulate that when the logarithm of the wavelet energy ratio is greater than 0, sgn[δ] = 1; stipulate that when the logarithm of the wavelet energy ratio is less than 0, sgn[δ] = -1; stipulate that the positive direction of the current is the direction from the busbar to the line.

[0152] If log(E) m2 / E m1 If log(E) > 0, then it is judged as a positive direction fault; if log(E) > 0, then it is judged as a positive direction fault. m2 / E m1 If ) < 0, then it is judged as a reverse direction fault;

[0153] When a fault occurs in the forward direction of the line, the high-frequency components of the fault current collected by the line-side measuring point at the connection between the tuning circuit and the line are abundant. However, when a fault occurs in the reverse direction of the line, the high-frequency components of the current collected by the line-side measuring point are relatively small. By utilizing the difference in electrical quantities collected by the line-side and bus-side measuring points, starting from the high-frequency components, and based on the ratio of wavelet energy at the measuring points on both sides, a quasi-directional protection element based on the CLC tuning circuit is constructed.

[0154] A half-wavelength 1000kV transmission line simulation model was built on the Real-Time Digital Simulator (RTDS). The model is as follows: Figure 1As shown, the simulation sampling rate is 20kHz, and the simulation platform is as follows. Figure 11 As shown, a model of a half-wavelength transmission line with tuning is constructed based on the triangular arrangement of line parameters and line type of the "Southeast Shanxi-Nanyang-Jingmen" 1000kV UHV test demonstration project that has been put into operation in my country. At this sampling rate, the A / D acquisition module only needs to use 14 bits to meet the minimum requirements.

[0155] Example 2: Traverse faults within the line protection zone in steps of 400km, with the specific steps as shown in Example 1.

[0156] like Figure 1 As shown, the positive direction of the current is defined as the direction from the busbar to the line. Since the CLC tuned circuit is a strong boundary, high-frequency signals will be reflected. To better understand the transient process, we analyze it from the perspective of traveling wave theory. According to the superposition principle, the fault-addition circuit is as follows: Figure 12 As shown in (a), the traveling wave grid diagram is as follows: Figure 12 As shown in (b).

[0157] Figure 12 In (b), the solid line represents the high-frequency part of the transient component, and the dashed line represents the low-frequency part. The transient components at m2 are as follows:

[0158]

[0159]

[0160] I m =F m -B m =β i H x (ω)S0 (24)

[0161] In the formula, S0 is the initial traveling wave of the fault; F m Forward traveling wave; B m For reverse traveling wave; I m For current; A x (ω)=e -γx ,β M，f β F，f The reflection coefficients of bus M and fault point F1 are respectively; β i =(β) M,f -1) represents the current coefficient; The same applies to the N-end.

[0162] Taking terminal M as an example, the measuring point on the bus side of terminal M is specified as m1, and its corresponding voltage and current are U and U, respectively. m1 I m1 The line-side measuring point is m2, and its corresponding voltage and current are U and U, respectively. m2 I m2.

[0163] Define the wavelet high-frequency energies of measurement points m1 and m2 as follows: E m1 E m2 This invention utilizes the db6 wavelet to extract wavelet energy at the second, third, and fourth scales within 3ms after a fault, resulting in:

[0164]

[0165]

[0166] In the formula, The wavelet high-frequency energy of the k-th layer signal at the M-end bus side measurement point. The high-frequency energy of the wavelet signal at the k-th layer of the line-side measurement point at terminal M is given.

[0167] Take the ratio of the high-frequency wavelet energies at the measurement points on both sides of the CLC tuning circuit: E m2 / E m1 And take the logarithm of the ratio of wavelet energies at both measuring points: log(E m2 / E m1 ), and establish its symbolic function sgn.

[0168] Calculate the magnitude of the established symbol function sgn, and stipulate that when the logarithm of the wavelet energy ratio is greater than 0, sgn[δ] = 1; stipulate that when the logarithm of the wavelet energy ratio is less than 0, sgn[δ] = -1; construct the fault direction criterion for CLC tuned circuit type directional elements;

[0169] If log(E) m2 / E m1 If log(E) > 0, then it is judged as a positive direction fault; if log(E) > 0, then it is judged as a positive direction fault. m2 / E m1 If ) < 0, then it is judged as a reverse direction fault;

[0170] To verify the applicability of directional elements based on CLC tuned circuits under different operating conditions, fault simulations were performed across the entire line length in 400km increments, simulating a phase A metallic ground fault. For example... Figure 13 The figure shows the simulation results of the fault-type directional element calculation obtained after traversing the faults along the entire line at a step size of 400km, following the steps described above. As can be seen from the figure, the logarithm of the wavelet energy ratio is greater than 0 when the fault occurs at a step size of 400km along the entire line, i.e.: log(E m2 / E m1 )>0; According to the judgment result, it meets the positive direction fault criterion and can reliably identify positive direction faults.

[0171] Example 3: A fault occurs in the reverse direction of the line. The specific steps are as shown in Example 1.

[0172] To verify the applicability of the directional element based on the CLC tuning circuit under different operating conditions, simulations were performed outside the reverse direction region at the M end using four fault types: AG, AB, ABG, and ABCG at F2. For example... Figure 14 As shown, F2 represents the simulation results of the fault-type direction element calculation obtained according to the steps of Example 1 after four types of faults (AG, AB, ABG, and ABCG) occur in the reverse direction at the M end. The figure shows that the logarithm of the wavelet energy ratio is less than 0 when the four different types of faults (AG, AB, ABG, and ABCG) occur in the reverse direction at the M end, i.e.: log(E m2 / E m1 The result of the simulation is less than 0. As can be seen from the simulation results, it meets the fault criteria for the reverse direction and can reliably identify faults in the reverse direction.

[0173] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for constructing a quasi-directional element based on a CLC tuning circuit, characterized in that: Step 1: Construct a π-type CLC tuning circuit and determine the parameters of the tuning circuit; Step 2: Detect the transfer characteristics of the π-type CLC tuning circuit; Step 3: Examine the effect of CT saturation on the amount of acquired current signal; Step 4: Collect the current at the bus side and line side measuring points at both ends of the CLC tuning circuit; Step 5: Utilize the equidistant characteristics of wavelet transform in the frequency domain to extract wavelet energy from the acquired fault signals; Step 6: Calculate the high-frequency wavelet energy collected by the measuring points on both sides of the CLC tuning circuit; Step 7: Take the ratio of the high-frequency wavelet energy at the measurement points on both sides of the CLC tuning circuit, and take the logarithm of the ratio of the wavelet energy at the measurement points on both sides. Step 8: Take the sign function of the logarithm of the high-frequency wavelet energy ratio at both measuring points on the tuning circuit. ; Step 9: Construct a directional element based on a CLC tuning circuit.

2. The method for constructing a quasi-directional element based on a CLC tuned circuit according to claim 1, characterized in that, Step 1 specifically refers to: The parameters of the constructed π-type CLC tuning circuit are determined as follows: （1）； In the formula, Capacitance to ground Interphase capacitance; The π-type tuning circuit is equivalent to a segment of phase constant. , length is For the transmission line, the equivalent surge impedance of the π-type tuned circuit is the same as that of the original line. It can satisfy: （2）。 3. The method for constructing a quasi-directional element based on a CLC tuning circuit according to claim 1, characterized in that, Step 2 specifically includes: The transfer characteristics of the π-type CLC tuning circuit include the transfer voltage ratio characteristic and the transfer current ratio characteristic. The transfer voltage ratio characteristic of the π-type CLC tuning circuit is as follows: （3）； （4）； The transfer current ratio characteristic of the π-type CLC tuning circuit is as follows: （5）； （6）； In the formula, For the transfer function of a π-type CLC lumped circuit, Where ω is the angular frequency, C is the equivalent capacitance, and L is the equivalent inductance.

4. The method for constructing a quasi-directional element based on a CLC tuned circuit according to claim 1, characterized in that, Step 3 specifically refers to: Define the transfer function of CT as follows: （7）； In the formula, , For the primary and secondary currents on the system side; By establishing the equivalent circuit of CT, the transfer function of CT is derived as follows: （8）； In the formula, This represents the line resistance.

5. The method for constructing a quasi-directional element based on a CLC tuning circuit according to claim 1, characterized in that, Step 5 specifically includes: The wavelet energy expression is defined as follows: （9）； In the formula, Let m be the wavelet energy of the k-th layer signal, and m be the width of the time window data. These are the wavelet transform coefficients of the k-th layer; The wavelet energy spectrum sequence of discrete wavelet transform is: （10）； The energy spectrum at eight scales of wavelet transform is selected for calculation, and the time-frequency eigenvector matrix is ​​defined as follows: （11）； In the formula, and These are the lengths of the time window and the frequency window, respectively.

6. The method for constructing a quasi-directional element based on a CLC tuning circuit according to claim 1, characterized in that, Step 6 specifically refers to: The measurement point on the M-end busbar side is specified as follows: The corresponding voltage and current are respectively , The line side measuring point is The corresponding voltage and current are respectively , ; Define measurement points , The wavelet high-frequency energies are respectively , ,but: （12）； （13）； In the formula, The wavelet high-frequency energy of the k-th layer signal at the M-end bus side measurement point. The high-frequency energy of the wavelet signal at the k-th layer of the line-side measurement point at terminal M is given.

7. The method for constructing a quasi-directional element based on a CLC tuning circuit according to claim 1, characterized in that, Step 7 specifically refers to: The ratio of the high-frequency wavelet energies at the measurement points on both sides of the CLC tuning circuit is taken as... And take the logarithm of the ratio of the high-frequency wavelet energies at both measuring points: .

8. The method for constructing a quasi-directional element based on a CLC tuning circuit according to claim 1, characterized in that, Step 9 specifically refers to: Through symbolic functions The value of is used as a fault direction criterion for constructing directional elements of CLC tuning circuits; When the logarithm of the wavelet energy ratio is greater than 0, ; When the logarithm of the wavelet energy ratio is less than 0, ; The positive direction of the current is defined as the direction from the busbar to the line. like If so, it is determined to be a positive direction fault; like If so, it is determined to be a fault in the opposite direction.

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