A power transmission line adaptive reclosing method based on delay cancellation operator

Abstract

The application discloses a power transmission line adaptive reclosing method based on a delay cancellation operator, which comprises the following steps: first, when a fault occurs, a circuit breaker trips, and a fault phase terminal voltage waveform is measured; second, CDSC is used to extract fault features of the measured fault phase terminal voltage; third, a three-dimensional graph is established according to the fault features, and a fault feature area and a threshold value are calculated; fourth, the fault feature area and the threshold value are compared, the fault type is judged, and whether to start a reclosing system is judged. The method is easy to implement, has small calculation amount, is not affected by long-term interference such as voltage imbalance and harmonics, is started after a single-phase trip of the circuit breaker, is not affected by arc extinction time, and can accurately judge arc extinction in about half a beat frequency period after fault arc extinction in theory. EMTP simulation and actual recording data verify the feasibility and superiority of the method.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection, and specifically relates to an adaptive reclosing method for transmission lines based on a delayed phase cancellation operator. Background Technology

[0002] Extensive operational experience shows that over 80% of faults in high-voltage overhead transmission lines are transient, a large portion of which are arcing faults caused by air insulation breakdown. Using automatic reclosing devices to put disconnected faulty lines back into operation can quickly restore normal power supply and effectively improve the stability of the power system. However, traditional automatic reclosing devices employ a fixed-interval blind reclosing scheme, which, while bringing significant economic benefits, also presents several problems:

[0003] When reclosing occurs during a transient fault, the insulation recovery time at the fault point is affected by the line voltage level, line load, wind speed, and whether the line is operating with a shunt reactor. If the reclosing time is less than the insulation recovery time at the fault point, the arc will reignite after reclosing, leading to reclosing failure. If the arc at the fault point extinguishes quickly (such as in transmission lines with shunt reactor compensation), for single-phase ground faults, using fixed-time reclosing will increase the non-full-phase operation time of the line. In this case, a large negative-sequence current will induce a frequency-doubled current on the surface of the generator rotor, which may cause localized high temperatures in areas with large rotor current shunting, potentially burning the rotor.

[0004] The paper "Criterion for Identifying the Nature of Single-Phase Adaptive Reclosing Faults in Ultra-High Voltage / Extra-High Voltage Transmission Lines with Parallel Reactors" by Liu Haofang et al. separates the amplitude of the free component by subtracting data from two fundamental frequency cycles within several power frequency cycles. However, in practical applications, this method requires the secondary arc to be extinguished, and since the arc extinguishing time is unknown, the criterion's activation time is constrained by the arc extinguishing time. The papers "Principle of Single-Phase Adaptive Reclosing Fault Identification in Ultra-High Voltage Lines Based on the Prony Method" by Hu Yaping et al. and "Permanent Fault Identification in Transmission Lines with Parallel Reactors at Both Ends" by Sonam Gyal et al. use the Prony algorithm to extract the amplitude of the free component in the recovery voltage within half a beat frequency cycle, but this requires a high sampling frequency and a large computational load. The papers "A New Method for Identifying Permanent Single-Phase Automatic Reclosing Faults in Transmission Lines with Shunt Reactors" by Sonam Gyaltsen et al. and "A Novel Single-Phase Adaptive Reclosure Scheme for Transmission Lines with Shunt Reactors" by Jiale Suonan et al. proposed a new method to determine the nature of a fault based on the ratio of the difference between the calculated current and the measured current of the faulted phase shunt reactor to the amplitude of the neutral point small reactor current. However, the calculation of the amplitude of the current power frequency component is greatly affected by the free component. Summary of the Invention

[0005] Traditional reclosing schemes are affected by system oscillations and cannot extract this beat frequency characteristic. Therefore, this invention proposes an adaptive reclosing method for transmission lines based on a delayed cancellation operator to accurately distinguish between transient and permanent faults in different system configurations, and to quickly detect the arc extinction time of transient faults.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0007] Step 1: When a fault occurs, the circuit breaker trips, and the voltage waveform at the faulty phase terminal is measured;

[0008] Step 2: Use CDSC to extract fault features from the measured fault phase terminal voltage;

[0009] Step 3: Create a 3D map based on the fault characteristics, and calculate the fault characteristic area and threshold.

[0010] Step 4: Compare the fault feature area with the threshold value to determine the fault type and whether to activate the reclosing system.

[0011] Furthermore, after the line fault occurs in the first step, the second step is performed. The CDSC algorithm is used to extract fault features from the fault phase terminal voltage measured after the fault occurs. The delayed signal cancellation DSC operator is represented by equation (1):

[0012] (1)

[0013] The input of DSC is from It indicates that it contains , The delayed signal of the αβ frame, This is the system cycle time, where n is the delay factor. It is a 2×2 matrix, defined as:

[0014] (2)

[0015] Where h * It is the target harmonic number.

[0016] Furthermore, equation (1) in Rewritten in the domain as:

[0017] (3)

[0018] make Further simplify the transfer function for:

[0019] (4)

[0020] By setting h in equation (4) * With the value of n, the DSC operator preserves the target harmonic component h = h * And eliminate other harmonic components.

[0021] Furthermore, the h * =1, n=2.

[0022] Furthermore, the third step is achieved by using the phase angle and amplitude change rate extracted from the fault features as criteria to identify transient and permanent faults in transmission lines with parallel reactors.

[0023] Furthermore, the first derivative of the mean square RMS of the signal is extracted to describe the RMC, and it is defined as follows:

[0024] (5)

[0025] The first derivative of the extracted signal can be described as:

[0026] (6)

[0027] in It is the angular frequency of the fundamental component.

[0028] Furthermore, assuming Then the RMS of equation (6) can be expressed as follows.

[0029] (7)

[0030] Furthermore, the phase angle area error rate per unit period (ERPAA) is used to describe the phase angle distortion:

[0031] (8)

[0032] In the formula The area of ​​the ideal phase angle within a unit period. δ is the area of ​​the phase angle, and δ is the ERPAA.

[0033] Furthermore, fault characteristic data is obtained using a sliding data window (SDW), and then the maximum and minimum values ​​of RMS and δ within the sliding data window are extracted.

[0034] Furthermore, the area of ​​the region formed by the fault characteristics is used to distinguish between transient and permanent faults, as defined in the following formula:

[0035] (9)

[0036] Where S SDW The area of ​​the region formed by the fault characteristics. and These are the maximum and minimum RMS values ​​within SDW. and These are the maximum and minimum values ​​of δ within the SDW, respectively;

[0037] and The threshold is defined as:

[0038] (10)

[0039] (11)

[0040] The maximum permissible frequency variation range in a power system is 50 ± 0.5 Hz. Therefore, and The threshold is calculated by the following formula:

[0041] (12)

[0042] (13)

[0043] Where δ 49.5 and δ 50.5 The maximum distortion rates are 49.5 and 50.5 Hz.

[0044] Substituting equations (10)-(13) into equation (9), S SDW The threshold is obtained by the following formula, where ε is set.

[0045] (14)

[0046] The method for distinguishing between transient and permanent faults by utilizing the area formed by fault characteristics is as follows:

[0047] Step 1: After a fault occurs, the criteria are activated three power frequency cycles after the circuit breaker trips to extract features from the faulty phase voltage and calculate the area S of the fault feature region within the sliding data window. SDW and its discrimination ε;

[0048] Step 2: Calculate the S SDW Compare with ε:

[0049] (1) When S SDW When the fault is ≥ε, it is determined to be a transient fault, and the reclosing system is activated.

[0050] (2) When S SDWWhen the value is less than ε, the fault is determined to be a permanent fault, and the reclosing system is blocked.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] 1. This invention analyzes a single-phase fault circuit model of a transmission line with a parallel reactor to obtain the spectral characteristics of the fault phase voltage. A delayed cancellation operator (CDSC) is used to extract the fundamental period and its nearby components to construct a frequency distortion rate criterion. This scheme avoids the influence of high-frequency harmonics, has low computational complexity, and is easy to implement. The criterion is activated after the circuit breaker trips a single phase, unaffected by the arc extinction time. Theoretically, it can accurately determine arc extinction within approximately half a beat frequency cycle after the fault extinguishes. This method can reliably identify the fault nature and detect the arc extinction time, and is unaffected by the fault location and transition resistance.

[0053] 2. The method of this invention analyzes a single-phase fault circuit model of a transmission line with a parallel reactor to obtain the spectral characteristics of the fault phase voltage. It then uses the Delay Cancellation Operator (CDSC) to extract the fundamental period and its nearby components, constructing a frequency distortion rate criterion.

[0054] 3. The method of this invention is easy to implement, requires little computation, and is unaffected by long-term interference such as voltage imbalance and harmonics; the criterion is initiated after a single-phase trip of the circuit breaker, unaffected by the arc extinction time; theoretically, it can accurately determine arc extinction within approximately half a beat frequency cycle after the fault arc is extinguished. EMTP simulation and actual waveform recording data verify its feasibility and superiority. Furthermore, the obtained simulation results and field data confirm the performance of the proposed method.

[0055] 4. The new method proposed in this invention for extracting fault features can accurately distinguish between transient and permanent faults in different system configurations. Attached Figure Description

[0056] Figure 1 This is a flowchart of the adaptive reclosing method for transmission lines based on the delayed cancellation operator;

[0057] Figure 2 It is DSC n Operator structure diagram;

[0058] Figure 3 This is the amplitude response diagram of DSC1 2;

[0059] Figure 4 Amplitude response plot;

[0060] Figure 5 Diagram of transient fault;

[0061] Figure 6 For permanent fault diagrams;

[0062] Figure 7 A 3D diagram of the fault characteristics. Figure 7 (a) is a three-dimensional diagram of transient fault characteristics. Figure 7 (b) is a three-dimensional diagram of the characteristics of a permanent fault;

[0063] Figure 8 A diagram of a power system simulation model;

[0064] Figure 9 Figure 9(a) shows the permanent fault waveform, and Figure 9(b) shows the permanent fault voltage waveform. And threshold map;

[0065] Figure 10 It is a transient fault diagram. Figure 10 (a) is a voltage waveform diagram. Figure 10 (b) is Detection time and threshold graph. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. It should be noted that the embodiments described herein are illustrative, but not limiting, and therefore this invention is not limited to the above embodiments. Based on the principles of this invention, all other implementation methods obtained by those skilled in the art without creative effort are considered to be within the protection scope of this invention.

[0067] like Figure 1 The flowchart shown illustrates that this embodiment provides an adaptive reclosing method for transmission lines based on a delayed cancellation operator, comprising the following steps:

[0068] Step 1: When a fault occurs, the circuit breaker trips, and the voltage waveform at the faulty phase terminal is measured;

[0069] Step 2: Use CDSC to extract fault features from the measured fault phase terminal voltage;

[0070] Step 3: Create a 3D map based on the fault characteristics, and calculate the fault characteristic area and threshold.

[0071] Step 4: Compare the fault feature area with the threshold value to determine the fault type and whether to activate the reclosing system.

[0072] (I) CDSC Algorithm Design

[0073] In this invention, after a line fault occurs in the first step, a second step is performed, in which the CDSC algorithm is used to extract fault features from the fault phase terminal voltage measured after the fault occurs.

[0074] Typically, the Delayed Signal Cancellation (DSC) operator is represented by equation (1):

[0075] (1)

[0076] This is the input to DSC. It indicates that it contains , The delayed signal of the αβ frame, This is the system cycle time, where n is the delay factor. It is a 2×2 matrix, defined as:

[0077] (2)

[0078] Where h * It is the target harmonic number.

[0079] Equation (1) can be used in Rewritten in the domain as:

[0080] (3)

[0081] make Further simplify the transfer function for:

[0082] (4)

[0083] By setting h in equation (4) * With respect to the value of n, the DSC operator can preserve the target harmonic component h = h * It also eliminates other harmonic components. From a digital signal processing perspective, the DSC operator is similar to a comb filter. Figure 2 It explains in detail Operator structure.

[0084] To better understand the principles of the DSC operator Figure 3 This explains h * =1 and n=2 affect the amplitude through equation (4). In the figure, a single DSC operator cannot block all harmonics, but can only eliminate the h=2k (k=±1,±2,±3…) harmonics and keep the h=2k-1 (k=±1,±2,±3…) harmonics. Therefore, it is essential to construct multiple DSC operators, which can eliminate specific harmonic components step by step while keeping the target harmonic components. When the proposed algorithm is activated, The amplitude response is as follows Figure 4 As shown, where Unaffected by low-frequency components around 50Hz, this algorithm extracts only the target harmonic components.

[0085] (II) Criterion Design

[0086] The third step involves using the phase angle and amplitude change rate extracted from the fault features as criteria to identify transient and permanent faults in transmission lines with parallel reactors. Based on these features, a three-dimensional map is generated, and the area is calculated.

[0087] The first derivative of the root mean square (RMS) of the extracted signal is used to describe the RMC, and it is defined as follows:

[0088] (5)

[0089] The first derivative of the extracted signal can be described as:

[0090] (6)

[0091] in It is the angular frequency of the fundamental component.

[0092] Assumption Then the RMS of equation (6) can be expressed as follows:

[0093] (7)

[0094] Furthermore, phase distortion is not noticeable in practice because the area of ​​the phase angle is constant within a unit period for the fundamental component. This invention uses the phase area error rate per unit period (ERPAA) to describe phase distortion.

[0095] (8)

[0096] In the formula The area of ​​the ideal phase angle within a unit period. δ is the area of ​​the phase angle, and δ is the ERPAA.

[0097] Fault characteristic data are acquired using a sliding data window (SDW). Then, the maximum and minimum values ​​of RMS and δ within the sliding data window are extracted.

[0098] Figure 5 (a) and Figure 6 (a) The voltage waveforms at the faulty phase terminals are shown. The secondary arc was found to extinguish at 0.4s. The voltage waveform from 0.3s to 0.7s was extracted and amplified to obtain the voltage waveform. Figure 5 (b) and Figure 6 (b), and the RMS value is calculated using equation (7), such as Figure 5 (c) and Figure 6As shown in (c), a three-dimensional diagram of the fault characteristics is used, such as Figure 7 As shown.

[0099] The amplitude fluctuation of the signal is represented by RMS on the Y-axis;

[0100] The phase angle distortion of the signal is represented by δ on the X-axis;

[0101] Time is represented by t on the Z-axis for easier observation and analysis, and equal time intervals are taken as follows: 0.36s, 0.46s, 0.56s, 0.66s, and 0.76s.

[0102] Figure 7 (a) shows a transient fault. Due to the presence of the natural frequency, the phase angle distortion and amplitude change rate fluctuation are caused, resulting in the area of ​​the RMS and δ region after the arc is extinguished (0.46s, 0.56s, 0.66s, 0.76s) being larger than that before the arc is extinguished (0.36s).

[0103] Figure 7 (b) shows a permanent fault, the result of which is exactly the opposite of that of a transient fault. The area of ​​the region formed by RMS and δ before the arc is extinguished (0.36s) is larger than that before the arc is extinguished (0.46s, 0.56s, 0.66s, 0.76s).

[0104] Therefore, the area of ​​the region formed by the fault characteristics can be used to distinguish between transient and permanent faults, as defined in the following formula:

[0105] (9)

[0106] Where S SDW The area of ​​the region formed by the fault characteristics. and These are the maximum and minimum RMS values ​​within SDW. and These are the maximum and minimum values ​​of δ within SDW, respectively.

[0107] According to GB / T 12323-2008, high-voltage transmission lines are allowed a voltage variation of ±5%. However, in reality, the recovery voltage after the secondary arc is extinguished far exceeds ±5% of the nominal system voltage. Transmission lines with shunt reactors have a higher recovery voltage than those without. Therefore, to improve the reliability of the proposed algorithm, and The threshold can be defined as:

[0108] (10)

[0109] (11)

[0110] The maximum permissible frequency variation range in a power system is 50 ± 0.5 Hz. Therefore, and The threshold can be calculated using the following formula.

[0111] (12)

[0112] (13)

[0113] Where δ 49.5 and δ 50.5 The maximum distortion rates are 49.5 and 50.5 Hz.

[0114] Substituting equations (10)-(13) into equation (9), S SDW The threshold is obtained by the following formula, where ε is set as follows:

[0115] (14)

[0116] To mitigate the interference caused by circuit breaker operation, the proposed algorithm will begin working after 3 cycles.

[0117] This section implements the fourth step: comparing the calculated fault feature area with a threshold. In transient faults, ≥ε. However, the result is exactly the opposite in permanent faults, used to determine whether the reclosing system has started.

[0118] (III) Application Examples

[0119] The power system simulation model of the present invention is as follows: Figure 8 As shown, it can perform digital simulation on 500kV transmission lines with shunt reactors installed at one end, shunt reactors installed at both ends, or no shunt reactors installed, and can realize full-process simulation of transient or permanent single-phase grounding faults in transmission lines.

[0120] Using the arc dynamic equations, the MODELS control module and TACS component in the ATP / EMTP simulation platform were programmed, and the time-varying resistance (type 94) module was used to establish the primary and secondary arc models.

[0121] The system consists of six transmission lines, two of which are equipped with additional parallel compensation reactors.

[0122] Parallel reactors were installed at one end of a 170km long line (TL57) to achieve 40% compensation (Lx=11.46H, Ln=3.82H).

[0123] The 180km long line (TL69) has parallel reactors installed at both ends to achieve 80% compensation (Lx=9.8H, Ln=3.26H).

[0124] The line parameters are set as follows:

[0125] Positive sequence resistance R1 = 0.0182 / km, zero-sequence resistance R0=0.1734 / km;

[0126] Positive-sequence inductance L1 = 0.9081 mH / km, zero-sequence inductance L0 = 2.0878 mH / km;

[0127] Positive sequence capacitance C1 = 0.0132 F / km, zero-sequence capacitance C0=0.0101 F / km.

[0128] (1) If a permanent failure occurs

[0129] The transmission line TL69 was simulated with a 75% fault, 80% line compensation, and a permanent fault resistance of 10Ω.

[0130] Figure 9 (a) is a waveform diagram of the phase terminal voltage of a permanent fault, with no recovery voltage stage and no beat frequency phenomenon.

[0131] Figure 9 (b) is The calculated curve, where ε is the threshold, shows that... The curve does not exceed ε, indicating that the fault is permanent.

[0132] (2) In case of transient failure

[0133] After three loop cycles, the algorithm begins to work.

[0134] A transient fault with a fault resistance of 5Ω was simulated on a transmission line TL69 with a fault at 50% capacity, 80% line compensation, and a fault resistance of 5Ω.

[0135] Figure 10 (a) is a waveform diagram of the phase-terminal voltage during a transient fault. The secondary arc is completely extinguished at 0.4s, and then the voltage recovery phase begins. Due to the superposition of the free oscillation component and the power frequency component, the voltage at the faulty phase-terminal exhibits a significant beat frequency phenomenon.

[0136] like Figure 10 (b) is Detection time and threshold graph, after circuit breaker operation. The time was 433.9ms, indicating that the fault was transient.

[0137] Although exemplary embodiments of the invention have been described and illustrated, those skilled in the art will understand that various changes and substitutions can be made thereto without departing from the spirit of the invention. Furthermore, many modifications can be made to adapt specific situations to the doctrine of the invention without departing from the central concepts of the invention described herein. Therefore, the invention is not limited to the specific embodiments disclosed herein, but may include all embodiments and equivalents that fall within the scope of the invention.

Claims

1. A power transmission line adaptive reclosing method based on a delay cancellation operator, characterized by, Includes the following steps: Step 1: When a fault occurs, the circuit breaker trips, and the voltage waveform at the faulty phase terminal is measured; Step 2: Use CDSC to extract fault features from the measured fault phase terminal voltage; Step 3: Use the phase angle and amplitude change rate in the extracted fault features as criteria to identify transient and permanent faults in transmission lines with parallel reactors. Create a three-dimensional map based on the fault features and calculate the fault feature area and threshold. Step 4: Compare the fault feature area with the threshold value to determine the fault type and whether to activate the reclosing system; The area formed by the fault characteristics is used to distinguish between transient and permanent faults, as defined in equation (1): ； (1) where S SDW is the area of the region formed by the fault feature, and are the maximum and minimum values of the RMS within the SDW, and are the maximum and minimum values of δ within the SDW, respectively; and The threshold definitions of and are given by equations (2) and (3), respectively: ； (2) ； (3) The maximum allowed variation range of the frequency in the power system is 50 ± 0.5 Hz, then, and The threshold values are obtained from equation (4) and equation (5): ； (4) ； (5) where δ 49.5 and δ 50.5 are the maximum distortion rates of 49.5 and 50.5 Hz, respectively. Substituting formulae (2) - (5) into formula (1), S SDW The threshold value of ε is given by formula (6), where ； (6) The method for distinguishing between transient and permanent faults by utilizing the area formed by fault characteristics is as follows: Step 1: After a fault occurs, the criteria are activated three power frequency cycles after the circuit breaker trips to extract features from the faulty phase voltage and calculate the area S of the fault feature region within the sliding data window. SDW and its discrimination ε; Step 2: The calculated S SDW Compare with ε: (1) When S SDW ≥ ε, the fault is determined to be transient, and the reclosing system is started. (2) When S SDW < ε, the fault is determined as permanent and the reclosing system is blocked.

2. The delay cancellation operator based adaptive reclosing method for power transmission lines according to claim 1, wherein, After the line fault occurs in the first step, the second step is performed. The CDSC algorithm is used to extract fault features from the fault phase terminal voltage measured after the fault occurs. The delayed signal cancellation DSC operator is represented by equation (7): ； (7) The input to the DSC is given by where the input signal is given by , is the delayed signal of the αβ-frame, is the system period time, n is the delay factor, is a 2x2 matrix defined as: ； (8) where h * is the target harmonic number.

3. The delay cancellation operator based adaptive reclosing method for power transmission lines according to claim 2, wherein, Formula (7) is rewritten in the domain as: Formula (7) is rewritten in the domain as: ； (9) Let Further simplifying the transfer function is: ； (10) By setting the values of h * and n in equation (10), the DSC operator retains the target harmonic component h = h * and eliminates the other harmonic components.

4. The delay cancellation operator based adaptive reclosing method for power transmission lines according to claim 3, wherein, The h * = 1, n = 2.

5. The delay-opposition-operator-based transmission line adaptive reclosing method according to claim 1, wherein, The first derivative of the mean square RMS of the extracted signal is used to describe the RMC, and it is defined as follows: ； (11) The first derivative of the extracted signal is described as follows: ； (12) wherein is the angular frequency of the fundamental component.

6. The delay cancellation operator based adaptive reclosing method for power transmission lines according to claim 5, wherein, Assume The RMS of equation (12) can be expressed as follows: (13)。 7. The delay-opposition-operator-based transmission line adaptive reclosing method according to claim 1, characterized in that, The phase angle area error rate per unit period (ERPAA) is used to describe phase angle distortion. ； (14) wherein is the ideal phase angle area in a unit period, is the phase angle area, and δ is the ERPAA.

8. The delay cancellation operator based transmission line adaptive reclosing method of claim 1, wherein, Fault characteristic data is obtained using a sliding data window (SDW), and then the maximum and minimum values ​​of RMS and δ within the sliding data window are extracted.

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