Low-current grounding fault line selection method for power distribution network containing same-tower parallel lines

Abstract

The invention discloses a low-current grounding fault line selection method for a power distribution network containing parallel lines on the same tower, and relates to the field of relay protection, and the method specifically comprises the following steps: S1, grouping double parallel lines on the same tower in the power distribution network, and solving the same component and the inverse component of the zero-sequence current of each group; s2, carrying out intra-group boundary line selection according to the zero-sequence current inverse component, wherein the intra-group boundary line selection specifically comprises two parts of amplitude judgment for screening fault groups and reactive power calculation for fault group line selection; and S3, performing out-of-group out-of-boundary line selection according to the same component of the zero-sequence current, wherein the out-of-group out-of-boundary line selection specifically comprises two parts of amplitude screening for selecting a possible fault line and phase comparison for determining a fault line. According to the method, the double-circuit lines on the same tower are grouped, the distribution network line selection process is divided into the in-boundary line selection process and the out-boundary line selection process, the line selection sensitivity is improved, the problem of misjudgment caused by small fault characteristics of short feeders is avoided through two times of amplitude judgment, and fault processing of related power distribution systems is facilitated.

Description

Technical Field

[0001] The invention relates to the field of optical fiber lasers that output high repetition rate mode-locked pulses, and in particular to a method for selecting a line for a small current grounding fault in a distribution network containing lines mounted on the same pole. Background Art

[0002] In recent years, with the increase in people's demand for electricity, in order to meet economic benefits and maintain the safe and reliable operation of the power system, the distribution network often processes and transforms the existing lines, transforming the single-circuit line into a line on the same pole. This saves the floor space and reduces the construction cost of the tower while increasing the capacity of the distribution line. In addition to phase-to-phase coupling, the lines on the same pole also have line-to-line coupling, which may change the fault characteristics when a small current grounding fault occurs in the system containing the lines on the same pole. At present, the research on the line selection of the distribution network containing the lines on the same pole is even rarer. At present, it is urgent to study the relevant theories, analyze the applicability of the existing line selection methods, and further propose new line selection methods for the distribution network containing the lines on the same pole. Summary of the invention

[0003] In order to solve the above-mentioned problems, the present invention provides a method for selecting a line for a small current grounding fault in a distribution network containing lines installed on the same pole. Based on a simulation model, the influence of the installation on the same pole on the single-phase grounding fault characteristics of the distribution network is explored, and further a method for selecting a steady-state line for a single-phase grounding fault in a system containing a double-circuit line installed on the same pole with an ungrounded neutral point is provided. By grouping the double-circuit lines installed on the same pole, the line selection process of the distribution network is divided into an in-boundary line selection process for selecting lines within the group of lines installed on the same pole and an out-boundary line selection process for selecting other single-circuit lines, thereby improving the sensitivity of line selection, avoiding the problem of misjudgment caused by the small fault characteristics of the short feeder through two amplitude judgments, and facilitating the fault handling of related distribution systems.

[0004] To achieve the above object, the present invention provides a method for selecting a small current ground fault line in a distribution network containing lines on the same pole, step S1: grouping the double-circuit lines on the same pole in the distribution network, and obtaining the same component and the opposite component of the zero-sequence current of each group; Step S2: selecting the line within the group according to the zero-sequence current reverse component, specifically including two parts: amplitude determination for screening the fault group and reactive power calculation for the line selected for the fault group; Step S3: selecting the out-of-bounds line outside the group according to the zero-sequence current component, specifically including two parts: selecting the amplitude screening of the possible fault line and determining the phase comparison of the fault line.

[0005] Preferably, in step S1, when a fault occurs, it is determined whether a single-phase grounding fault occurs in each group of double-circuit lines installed on the same pole; If a fault occurs, the fault group is selected within the boundary; If all groups of common-sensing lines are non-fault lines, perform out-of-bounds line selection on the single-circuit lines outside the group; Based on the idea of ​​the six-sequence component method, the zero-sequence current of the double-circuit line on the same pole is transformed into zero-sequence same component and zero-sequence opposite component, as shown in the following formula: ; in i T It refers to the same component of instantaneous zero-sequence current, which is the sum of zero-sequence currents of double-circuit lines on the same pole. i F It refers to the reverse component of the instantaneous zero-sequence current, which is the difference between the zero-sequence currents of the double-circuit lines on the same pole. i 01 and i 02 are the instantaneous zero-sequence currents flowing through the bus outlet of the lines L1 and L2 on the same pole, respectively. i F To select a line in the boundary, use i T Make an out-of-bounds line selection.

[0006] Preferably, in step S2, the process of selecting the line within the group based on the zero-sequence current reverse component is as follows: After a single-phase grounding fault occurs, the zero-sequence voltage is used to start the line selection process to select the line within the boundary, and the effective value of the zero-sequence current reverse component is I F When making amplitude determination and performing steady-state analysis of single-phase grounding fault according to the fault equivalent circuit, the series impedance of the zero mode and line mode of the equivalent circuit is ignored, and only the transition resistance is retained. The zero-sequence current phases of the fault feeder and the non-fault feeder are completely opposite. The zero-sequence current phase of the non-fault feeder leads the zero-sequence voltage of the bus by 90°, and the zero-sequence current phase of the fault feeder lags the zero-sequence voltage of the bus by 90°. When lines L1 and L2 are non-fault lines, the zero-sequence current phasor value flowing through lines L1 and L2 at the bus outlet is , , the calculation process is as follows: ; Among them C 0_1s , C 0_2s They are the equivalent non-parallel line capacitance to ground of the parallel line L1 and line L2, is the system zero-sequence voltage phasor value, j is the rotation factor, is the system operating frequency, , The instantaneous values ​​of , , and the effective values ​​are recorded as 、 ; When the double-circuit lines on the same pole are non-fault lines, the zero-sequence current phasor values ​​of the two feeders on the same pole should be consistent: , at this time the effective value of the zero-sequence current reverse component ; When the double-circuit lines are not completely installed on the same pole, the lengths of the two feeder lines are different. , but the zero-sequence currents on the two feeders are in phase, and the effective value of the zero-sequence current reverse component is the effective value of the zero-sequence current of line L1 And the effective value of zero-sequence current of line L2 The difference is expressed as: ; In the case of a faulty line in a double-circuit line on the same pole, the zero-sequence currents of the two feeders are in opposite phases. I F It is approximately the sum of the effective values ​​of the zero-sequence currents of the two feeders. Since the zero-sequence currents of the other feeders outside the boundary all flow to the fault line, at this time I F Larger, ; When no internal fault occurs, I F Small, after an internal fault occurs, I F Larger, by setting the threshold α ,right I F The amplitude is used to determine whether an in-bounds fault has occurred: ; If the amplitude judgment determines that an in-boundary fault has occurred, the two lines on the same pole are selected. In the equivalent circuit, the non-fault line is equivalently represented by zero-sequence capacitance. Reactive power flows from the line to the busbar, and the zero-sequence reactive power measured at the busbar outlet is negative. In the fault line, reactive power flows from the busbar to the line, and the zero-sequence reactive power measured at the busbar outlet is positive. i F The calculated reactive power is exactly the reactive power of line L1 Reactive power of line L2 The positive and negative values ​​of the difference are used to select the fault line of the two lines within the boundary. For the lines L1 and L2 that are completely installed on the same pole, there are , correspondingly If no success If it is positive, line L1 is faulty; If no effect If it is negative, line L2 is faulty; For lines that are not completely installed on the same pole, i F Make corrections, , using the corrected The reactive power calculation criteria and line selection results are consistent with those when all the cables are installed on the same pole. If the amplitude determines that the double-circuit line on the same pole is a non-fault line, out-of-bounds line selection is performed.

[0007] Preferably, in step S3, the process of selecting the outer-boundary line outside the group according to the zero-sequence current component is as follows: the condition for starting the outer-boundary line selection is that the inner-boundary line selection determines that the double-circuit lines on the same pole are all non-fault lines, i 01 and i 02 In phase, the effective value of the zero-sequence current component is expressed as For an ungrounded system, the zero-sequence current of the faulty feeder is the sum of the zero-sequence currents of the non-faulty feeders. The zero-sequence current on the line with a single-phase grounding fault is not less than the sum of the effective values ​​of the zero-sequence currents of the same components of the lines on the same pole. ,based on Setting Thresholds β To screen the faulty lines and filter out the shorter lines that are easily misjudged in the zero-sequence current phase comparison, the threshold β According to the actual distribution network structure, the following settings are made in the example: ; If the zero-sequence current of a single-circuit line outside the boundary is less than β , indicating a busbar fault; if there is a zero-sequence current greater than β The sum of the zero-sequence current and the instantaneous zero-sequence current is Compare the phases, the one with opposite phase is the faulty line, if they are all in phase, it is determined to be a bus fault.

[0008] Preferably, after completing the case analysis of the line selection method under the typical distribution network structure, a simulation verification is carried out: a typical 10kv distribution network MATLAB / Simulink simulation model is built, and the faults are set to occur in the short feeders installed on the same pole, the incomplete feeders installed on the same pole with different length differences, the short feeders installed on different poles, the long feeders installed on different poles and the busbars.

[0009] Preferably, the simulation feature verification result is: The fault characteristics of the lines installed on the same pole vary under different transition resistances, fault point locations, and fault initial phase angle parameters: The larger the transition resistance, the smaller the first half-wave peak value of the zero-sequence current of the fault line, the faster the transient decay speed, and the steady-state current is determined by the current of other feeders to the ground, with little overall change. There is a slight distortion when the transition resistance is high. As the fault point is farther from the busbar, the amplitude of the first half-wave of the zero-sequence current is smaller, the transient main resonant frequency is lower, and the zero-sequence steady-state current of the fault line is determined by the zero-sequence current of the non-fault feeder, and is less affected by the change of the fault point location. The initial phase angle of the fault only has a great influence on the transient amplitude of the zero-sequence current. The coupling relationship of the lines installed on the same pole has no effect on the steady-state zero-sequence current of the faulty feeder. However, when the faulty line is a line installed on the same pole, the transient zero-sequence current changes, which is manifested as an increase in the transient resonant main frequency.

[0010] Therefore, the present invention adopts the above-mentioned method for selecting a line for a small current grounding fault in a distribution network containing lines on the same pole, which has the following beneficial effects: (1) Based on the simulation model, the present invention explores the influence of the same-pole installation on the single-phase grounding fault characteristics of the distribution network, and further provides a single-phase grounding fault steady-state line selection method for a system with a double-circuit line installed on the same pole and an ungrounded neutral point. By grouping the double-circuit lines installed on the same pole, the distribution network line selection process is divided into an in-boundary line selection process for selecting lines within the same-pole line group and an out-boundary line selection process for selecting other single-circuit lines. This improves the sensitivity of line selection, avoids the problem of misjudgment caused by the small fault characteristics of short feeders through two amplitude judgments, and is beneficial to the fault handling of related distribution systems.

[0011] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A distribution network model containing lines installed on the same pole constructed in the first embodiment of the present invention; Figure 2 It is a zero-sequence current waveform diagram of the fault feeder under different transition resistances measured by the same-pole erection system in the present invention; Figure 3 It is a transient waveform diagram of zero-sequence current of a fault feeder under different transition resistances of the same-pole erection system in the present invention; Figure 4 It is a steady-state waveform diagram of zero-sequence current of fault feeder under different transition resistances of the same-pole erection system in the present invention; Figure 5 It is a steady-state waveform diagram of zero-sequence current of the fault feeder at different fault point positions in the same pole erection system of the present invention; Figure 6 It is a transient waveform diagram of zero-sequence current of a fault feeder at different fault point positions in the same pole erection system of the present invention; Figure 7 It is a transient waveform diagram of zero-sequence current of fault feeder under different fault initial phase angles of the same pole erection system in the present invention; Figure 8 It is a steady-state waveform diagram of zero-sequence current of metallic grounding fault feeder under different parallel racks in the present invention; Fig. 9 It is a transient waveform diagram of zero-sequence current of metallic grounding fault feeder under different parallel racks in the present invention; Fig.10 It is the line selection flow chart of the present invention; Fig.11 The distribution network model is analyzed for the example constructed in the third embodiment of the present invention; Fig.12 This is the phase comparison image in the third embodiment of the present invention. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0014] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0015] The words "include" or "comprises" and the like used in the present invention mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of also including other elements. The orientation or position relationship indicated by the terms "inside", "outside", "upper", "lower", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention. When the absolute position of the described object changes, the relative position relationship may also change accordingly. In the present invention, unless otherwise clearly specified and limited, the terms "attachment" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral body; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0016] Embodiment 1 This embodiment discloses the influence of the same-pole installation on the single-phase grounding fault characteristics of the distribution network, and specifically includes the following steps: Step (1) build a simulation model of a distribution network with two parallel lines on the same pole and an equivalent distribution network simulation model without a parallel system under the same operating conditions; Step (1) build a simulation model of a distribution network with two parallel lines on the same pole and an equivalent distribution network simulation model without a parallel system under the same operating conditions: like Figure 1 As shown, there are 6 overhead lines in total, of which L1 and L2 are installed on the same pole, and L4 and L5 are installed on the same pole.

[0017] For a single loop, set the line mode resistance to 0.12Ω / km, the zero mode resistance to 0.29Ω / km, and the line mode inductance to 1.08×10 - 3 H / km, zero mode inductance 4.49×10 -3 H / km, line mode capacitance 11.49×10 -9 F / km, zero mode capacitance 5.475×10 -9F / km.

[0018] For the lines on the same pole, a six-phase distributed parameter line model is used for simulation. The corresponding single-loop line parameters are used, and the corresponding phase model parameters are calculated by Karenbauer transformation. After taking into account the zero-sequence coupling, the resistance matrix, inductance matrix, and capacitance matrix are formed respectively. The parameters are self-resistance 0.177Ω / km, phase-to-phase mutual resistance 0.057Ω / km, line-to-line mutual resistance 0.08Ω / km, self-inductance 2.215×10 -3 H / km, phase-to-phase mutual inductance 1.133×10 -3 H / km, line mutual inductance 0.913×10 -3 H / km, self capacitance 12.09×10 -9 F / km, phase-to-phase mutual capacitance -2×10 -9 F / km, line mutual capacitance -0.87×10 -9 F / km.

[0019] Transformer YgD1 is connected, with a rated power of 20MVA. The loads are all set to 1MW constant impedance loads, and the power factor is set to 0.9.

[0020] The fault was set on L1, and multiple simulations were performed by adjusting the fault point location, transition resistance, fault initial phase angle and other parameters. In order to explore the impact of the same pole installation on the fault characteristics, in addition to the above simulation settings, the uncoupled L1 and L2 and the uncoupled all lines were also considered during the simulation.

[0021] Step (2) analyzing the fault waveforms after single-phase grounding faults in parallel rack systems and non-parallel rack systems; Taking transition resistance as a variable, the fault is set to occur on L1 10 km away from the busbar, with an initial fault phase angle of 90°, and the influence of transition resistance on zero-sequence current is explored. Figure 2 , Figure 3 , Figure 4 It is the zero-sequence current of the fault feeder under different transition resistances, and its magnified waveform images in transient and steady states. The larger the transition resistance, the smaller the first half-wave peak value of the zero-sequence current of the fault line, and the faster the transient attenuation speed. The zero-sequence steady-state current of the fault line is determined by the current of other feeders to the ground, and the overall change is not large. Due to the influence of the transition resistance on the zero-sequence voltage of the busbar, the phase is indirectly delayed and the amplitude is reduced when the transition resistance is 1000Ω.

[0022] Taking the fault point location as a variable, the fault is set to occur on L1, the transition resistance is 10Ω, and the initial fault phase angle is 90°, to explore the influence of the fault point location on the zero-sequence current. Figure 5 , Figure 6 It is the transient steady-state zero-sequence current waveform image of the fault feeder at different fault point locations. As the fault point is farther from the busbar, the amplitude of the first half-wave of the zero-sequence current is smaller and the transient main resonant frequency is lower. The zero-sequence steady-state current of the fault line is determined by the current of other feeders to the ground and is less affected by the change of the fault point location.

[0023] Taking the initial phase angle of the fault as a variable, the fault is set to occur at L1 10 km away from the bus, and the transition resistance is 10Ω, and the influence of the initial phase angle of the fault on the zero-sequence current is explored. Figure 7 It is the transient zero-sequence current waveform image of the fault feeder under different fault initial phase angles. The fault initial phase angle only has a greater impact on the transient amplitude of the zero-sequence current. The larger the fault initial phase angle, the larger the transient amplitude, but it has no effect on the transient main resonant frequency.

[0024] In order to explore the impact of the same pole installation on the fault characteristics, in addition to the above simulation settings, the uncoupled L1 and L2 and all line uncoupled conditions are also considered in the simulation. The fault is set to occur at L1 10km away from the busbar, the transition resistance is 0.001Ω, and the initial phase angle of the fault is 90°.

[0025] Figure 8 and Fig. 9 The steady-state and transient zero-sequence currents of the faulty feeder (L1) measured at the bus outlet. In the steady-state waveform of the zero-sequence current of the faulty feeder, the simulation waveforms in the three cases of the faulty feeder being paralleled on the same pole, the non-faulty feeder being paralleled on the same pole, and the non-faulty feeder being paralleled on the same pole completely overlap, and the coupling relationship of the paralleled lines on the same pole has no effect on the steady-state zero-sequence current of the faulty feeder. In the transient waveform, there are certain differences in the simulation waveforms of the three cases. The transient zero-sequence current decays slowly under metallic grounding. It is obvious from the figure that only the waveforms of L4 and L5 being paralleled are approximately consistent with those without paralleled lines, and the zero-sequence current transient resonance main frequency when the faulty feeder L1 is paralleled on the same pole is higher than the former two.

[0026] Multiple simulations were conducted by adjusting parameters such as the fault point location, transition resistance, and initial fault phase angle. The multi-operating waveform characteristics and their changing patterns observed based on the simulation data were consistent with the above typical situations.

[0027] Step (3) proposes the changing rules of fault characteristics.

[0028] The fault characteristics of the lines on the same pole have similar variation rules as those of single-circuit lines under different transition resistances, fault point locations, and fault initial phase angle parameters. The larger the transition resistance, the smaller the first half-wave peak value of the zero-sequence current of the fault line, the faster the transient attenuation speed, and the steady-state current is determined by the ground current of other feeders. The overall change is not large, and there is a slight distortion when the transition resistance is high. As the fault point is farther from the bus, the amplitude of the first half-wave of the zero-sequence current is smaller, the transient main resonant frequency is lower, and the zero-sequence steady-state current of the fault line is determined by the zero-sequence current of the non-fault feeder, and is less affected by the change of the fault point location. The initial phase angle of the fault has a greater impact only on the transient amplitude of the zero-sequence current.

[0029] The coupling relationship of the lines installed on the same pole has no effect on the steady-state zero-sequence current of the faulty feeder. However, when the faulty line is a line installed on the same pole, its transient zero-sequence current changes, which is mainly manifested as an increase in the transient resonant main frequency.

[0030] This embodiment provides the single-phase grounding fault characteristics of a distribution network containing double-circuit lines on the same pole and the impact of the same-pole installation on the single-phase grounding fault characteristics of the distribution network compared to a non-parallel system. The lines on the same pole have similar fault characteristic variation patterns as single-circuit lines under different transition resistances, fault point locations, and fault initial phase angle parameters. The coupling relationship of the lines on the same pole has no effect on the steady-state zero-sequence current of the fault feeder and the non-fault feeder. The line selection of the system on the same pole can be studied based on the steady-state characteristics of the zero-sequence current after the equivalent non-parallel line fault.

[0031] Embodiment 2 This embodiment provides a method for selecting a line for a small current grounding fault in a distribution network containing lines on the same pole, reveals the influence of the same pole installation on the characteristics of a single-phase grounding fault in a distribution network; proposes a method for selecting a line for a single-phase grounding fault in a system containing double-circuit lines on the same pole with an ungrounded neutral point; completes a case analysis of the line selection method under a typical distribution network structure, and verifies the effectiveness of the line selection method proposed in the present invention through a typical distribution network model. The specific line selection process is as follows: Fig.10 As shown, the specific steps are as follows: Step S1: grouping the double-circuit lines on the same pole in the distribution network, and obtaining the same component and opposite component of the zero-sequence current of each group; In step S1, when a fault occurs, it is determined whether a single-phase grounding fault occurs in each group of double-circuit lines on the same pole; If a fault occurs, the fault group is selected within the boundary; If all groups of common-sensing lines are non-fault lines, perform out-of-bounds line selection on the single-circuit lines outside the group; Based on the idea of ​​the six-sequence component method, the zero-sequence current of the double-circuit line on the same pole is transformed into zero-sequence same component and zero-sequence opposite component, as shown in the following formula: ; in iT It refers to the same component of instantaneous zero-sequence current, which is the sum of zero-sequence currents of double-circuit lines on the same pole. i F It refers to the reverse component of the instantaneous zero-sequence current, which is the difference between the zero-sequence currents of the double-circuit lines on the same pole. i 01 and i 02 They are the instantaneous zero-sequence currents flowing through the bus outlet of the lines L1 and L2 on the same pole, and the instantaneous zero-sequence current flowing through the bus outlet of the single-circuit line L3 i 03 .use i F To select a line in the boundary, use i T Make an out-of-bounds line selection.

[0032] Step S2: selecting the line within the group according to the zero-sequence current reverse component, specifically including two parts: amplitude determination for screening the fault group and reactive power calculation for the line selected for the fault group; In step S2, the process of selecting the line within the group based on the zero-sequence current reverse component is as follows: After a single-phase grounding fault occurs, the zero-sequence voltage is used to start the line selection process to select the line within the boundary, and the effective value of the zero-sequence current reverse component is I F When making amplitude determination and performing steady-state analysis of single-phase grounding fault according to the fault equivalent circuit, the series impedance of the zero mode and line mode of the equivalent circuit is ignored, and only the transition resistance is retained. The zero-sequence current phases of the fault feeder and the non-fault feeder are completely opposite. The zero-sequence current phase of the non-fault feeder leads the zero-sequence voltage of the bus by 90°, and the zero-sequence current phase of the fault feeder lags the zero-sequence voltage of the bus by 90°. When lines L1 and L2 are non-fault lines, the zero-sequence current phasor value flowing through lines L1 and L2 at the bus outlet is i 01n , i 02n , the calculation process is as follows: ; Among them C 0_1s , C 0_2s They are the equivalent non-parallel line capacitance to ground of the parallel line L1 and line L2, is the system zero-sequence voltage phasor value, j is the rotation factor, is the system operating frequency, , The instantaneous values ​​of , , and the effective values ​​are recorded as 、 ; When the double-circuit lines on the same pole are non-fault lines, the zero-sequence current phasor values ​​of the two feeders on the same pole should be consistent: , at this time the effective value of the zero-sequence current reverse component ; When the double-circuit lines are not completely installed on the same pole, there is a certain difference in the length of the two feeder lines. , but the zero-sequence currents on the two feeders are in phase, and the effective value of the zero-sequence current reverse component is the effective value of the zero-sequence current of line L1 And the effective value of zero-sequence current of line L2 The difference is expressed as: ; In the case of a faulty line in a double-circuit line on the same pole, the zero-sequence currents of the two feeders are in opposite phases. I F It is approximately the sum of the effective values ​​of the zero-sequence currents of the two feeders. Since the zero-sequence currents of the other feeders outside the boundary all flow to the fault line, at this time I F Larger, ; When no internal fault occurs, I F Small, after an internal fault occurs, I F Larger, by setting the threshold α ,right I F The amplitude is used to determine whether an in-bounds fault has occurred: ; If the amplitude judgment determines that an in-boundary fault has occurred, the two lines on the same pole are selected. In the equivalent circuit, the non-fault line is equivalently represented by zero-sequence capacitance. Reactive power flows from the line to the busbar, and the zero-sequence reactive power measured at the busbar outlet is negative. In the fault line, reactive power flows from the busbar to the line, and the zero-sequence reactive power measured at the busbar outlet is positive. i F The calculated reactive power is exactly the reactive power of line L1 Reactive power of line L2 The positive and negative values ​​of the difference are used to select the fault line of the two lines within the boundary. For the lines L1 and L2 that are completely installed on the same pole, there are , correspondingly ; If no effect If it is positive, line L1 is faulty; If no effect If it is negative, line L2 is faulty; For lines that are not completely installed on the same pole, i F Make corrections, , using the corrected The reactive power calculation criteria and line selection results are consistent with those when all the cables are installed on the same pole. If the amplitude determines that the double-circuit line on the same pole is a non-fault line, out-of-bounds line selection is performed.

[0033] Step S3: selecting the outer-boundary line outside the group based on the zero-sequence current component, specifically including the amplitude screening of the possible fault line and the phase comparison of the fault line. In step S3, the process of selecting the outer-boundary line outside the group based on the zero-sequence current component is as follows: The condition for starting the out-of-bounds line selection is that the in-bounds line selection determines that the double-circuit lines on the same pole are all non-fault lines. i 01 and i 02 In phase, the effective value of the zero-sequence current component is expressed as For an ungrounded system, the zero-sequence current of the faulty feeder is the sum of the zero-sequence currents of the non-faulty feeders. The zero-sequence current on the line with a single-phase grounding fault is not less than the sum of the effective values ​​of the zero-sequence currents of the same components of the lines on the same pole. ,based on Setting Thresholds β To screen the faulty lines and filter out the shorter lines that are easily misjudged in the zero-sequence current phase comparison, the threshold β According to the actual distribution network structure, the following settings are made in the example: ; If the zero-sequence current of a single-circuit line outside the boundary is less than β , indicating a busbar fault; if there is a zero-sequence current greater than β The sum of the zero-sequence current and the instantaneous zero-sequence current is Compare the phases, the one with opposite phase is the faulty line, if they are all in phase, it is determined to be a bus fault.

[0034] Embodiment 3 After completing the case analysis of the line selection method under the typical distribution network structure, simulation verification is carried out: a typical 10kV distribution network matlab / simulink simulation model is built, and the faults are set to occur in the short feeders on the same pole, the feeders with different length differences that are not completely on the same pole, the short feeders on different poles, the long feeders on different poles, and the busbars. Fig.11As shown, a total of 8 lines L1-L8 are set, lines L1-L6 are parallel lines on the same pole, and lines L7 and L8 are single-circuit lines. Among them, line L1 and line L2 are completely parallel lines on the same pole with a length of 5km, simulating the shorter parallel double-circuit lines on the same pole in the system; line L3 and line L4, line L5 and line L6 are not completely parallel on the same pole, and the parallel lengths are all 10km, simulating the incomplete parallel lines on the same pole with length differences in the system, among which line L5 and line L6 have a large length difference; the length of the single-circuit line L7 is 5km, simulating a short line that is easy to misjudge the phase in the system; the length of the single-circuit line L8 is 30km. In this embodiment, the system parameters, the parallel lines on the same pole and the single-circuit line parameters are consistent with those in Example 1, and will not be repeated here. It is respectively set that lines L2 to L8 have a single-phase grounding fault at the end of the line and a single-line grounding fault occurs on the busbar. Simulations are carried out under a variety of transition resistances to verify the proposed line selection method.

[0035] First, the lines on the same pole are grouped, with lines L1 and L2 as group 1, lines L3 and L4 as group 2, and lines L5 and L6 as group 3. The process of selecting lines within the boundary is introduced by taking a single-phase grounding fault with a transition resistance of 10Ω at the end of line L3 as an example.

[0036] After the fault occurs, the amplitude of the reverse component of the zero-sequence current of each group of lines on the same pole within the boundary is first determined. The relevant data are shown in Table 1: Table 1 ;

[0037] After determining that group 2 has a fault, calculate the reactive power generated by the reverse component of the zero-sequence current of group 2. After correcting the reverse component of the zero-sequence current, the measured reactive power Q F2 = 4617var>0, the line 1 in the group, i.e. line L3, is the faulty line, and the line selection is completed.

[0038] The process of selecting the line outside the boundary is introduced by taking a single-phase grounding fault with a transition resistance of 1000Ω at the end of line L8 as an example.

[0039] After the fault occurs, the amplitude of the reverse component of the zero-sequence current of each group of lines on the same pole within the boundary is first determined. The relevant data are shown in Table 2: Table 2 ;

[0040] Determine if an out-of-bounds fault occurs, threshold β =0.497, I 07 =0.041A, I 08 =0.662A. The single-circuit line L8 may be a faulty line. To determine whether it is a busbar fault, it is also necessary to i08 and The phase of is compared. Fig.12 As shown, the two are in reverse phase, and line L8 is judged to be a faulty line.

[0041] All simulation data assuming that a single-line grounding fault occurs at the line ends and busbars of lines L2 to L8 are shown in Table 3: Table 3 ;

[0042] The steps and methods involved in the above embodiments 2 and 3 are based on the embodiment 1.

[0043] The simulation feature verification results are: The fault characteristics of the lines installed on the same pole vary under different transition resistances, fault point locations, and fault initial phase angle parameters: The larger the transition resistance, the smaller the first half-wave peak value of the zero-sequence current of the fault line, the faster the transient decay speed, and the steady-state current is determined by the current of other feeders to the ground, with little overall change. There is a slight distortion when the transition resistance is high. As the fault point is farther from the busbar, the amplitude of the first half-wave of the zero-sequence current is smaller, the transient main resonant frequency is lower, and the zero-sequence steady-state current of the fault line is determined by the zero-sequence current of the non-fault feeder, and is less affected by the change of the fault point location. The initial phase angle of the fault only has a great influence on the transient amplitude of the zero-sequence current. The coupling relationship of the lines installed on the same pole has no effect on the steady-state zero-sequence current of the faulty feeder. However, when the faulty line is a line installed on the same pole, the transient zero-sequence current changes, which is manifested as an increase in the transient resonant main frequency.

[0044] Therefore, the present invention adopts the above-mentioned method for selecting a small current grounding fault line in a distribution network containing lines on the same pole, and uses negative dispersion ytterbium-doped fiber as the gain medium of a high repetition rate fiber laser to simplify dispersion management, reduce the threshold, optimize nonlinear effect control, and improve repetition rate performance, and ultimately obtains a low-threshold mode-locked pulse output with a repetition rate of hundreds of GHz.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for selecting a line for a small current ground fault in a distribution network containing lines on the same pole, characterized in that: The specific steps include: Step S1: grouping the double-circuit lines on the same pole in the distribution network, and obtaining the same component and opposite component of the zero-sequence current of each group; Step S2: selecting the line within the group according to the zero-sequence current reverse component, specifically including two parts: amplitude determination for screening the fault group and reactive power calculation for the line selected for the fault group; Step S3: selecting the out-of-bounds line outside the group according to the zero-sequence current component, specifically including two parts: selecting the amplitude screening of the possible fault line and determining the phase comparison of the fault line.

2. According to the method for selecting a line for a small current ground fault in a distribution network containing lines in parallel on the same pole as described in claim 1, it is characterized in that: In step S1, when a fault occurs, it is determined whether a single-phase grounding fault occurs in each group of double-circuit lines on the same pole; If a fault occurs, the fault group is selected within the boundary; If all groups of common-sensing lines are non-fault lines, perform out-of-bounds line selection on the single-circuit lines outside the group; Based on the idea of ​​the six-sequence component method, the zero-sequence current of the double-circuit line on the same pole is transformed into zero-sequence same component and zero-sequence opposite component, as shown in the following formula: ； in i T It refers to the same component of instantaneous zero-sequence current, which is the sum of zero-sequence currents of double-circuit lines on the same pole. i F It refers to the reverse component of the instantaneous zero-sequence current, which is the difference between the zero-sequence currents of the double-circuit lines on the same pole. i 01 and i 02 are the instantaneous zero-sequence currents flowing through the bus outlet of the lines L1 and L2 on the same pole, respectively. i F To select a line in the boundary, use i T Make an out-of-bounds line selection.

3. According to the method for selecting a line for a small current ground fault in a distribution network containing lines in parallel on the same pole as described in claim 2, it is characterized in that: In step S2, the process of selecting the line within the group based on the zero-sequence current reverse component is as follows: After a single-phase grounding fault occurs, the zero-sequence voltage is used to start the line selection process to select the line within the boundary, and the effective value of the zero-sequence current reverse component is I F When making amplitude determination and performing steady-state analysis of single-phase grounding fault according to the fault equivalent circuit, the series impedance of the zero-mode and line-mode of the equivalent circuit is ignored, and only the transition resistance is retained. The zero-sequence current phases of the fault feeder and the non-fault feeder are completely opposite. The zero-sequence current phase of the non-fault feeder leads the zero-sequence voltage of the bus by 90°, and the zero-sequence current phase of the fault feeder lags the zero-sequence voltage of the bus by 90°. When lines L1 and L2 are non-fault lines, the zero-sequence current phasor value flowing through lines L1 and L2 at the bus outlet is , , the calculation process is as follows: ； Among them C 0_1s , C 0_2s They are the equivalent non-parallel line capacitance to ground of the parallel line L1 and line L2, is the system zero-sequence voltage phasor value, j is the rotation factor, is the system operating frequency, , The instantaneous values ​​of , , and the effective values ​​are recorded as 、 ; When the double-circuit lines on the same pole are non-fault lines, the zero-sequence current phasor values ​​of the two feeders on the same pole should be consistent: , at this time the effective value of the zero-sequence current reverse component ; When the double-circuit lines are not completely installed on the same pole, the lengths of the two feeder lines are different. , but the zero-sequence currents on the two feeders are in phase, and the effective value of the zero-sequence current reverse component is the effective value of the zero-sequence current of line L1 And the effective value of zero-sequence current of line L2 The difference is expressed as: ； In the case of a faulty line in a double-circuit line on the same pole, the zero-sequence currents of the two feeders are in opposite phases. I F It is approximately the sum of the effective values ​​of the zero-sequence currents of the two feeders. Since the zero-sequence currents of the other feeders outside the boundary all flow to the fault line, at this time I F Larger, ; When no internal fault occurs, I F Small, after an internal fault occurs, I F Larger, by setting the threshold α ,right I F The amplitude is used to determine whether an in-bounds fault has occurred: ； If the amplitude judgment determines that an in-boundary fault has occurred, the two lines on the same pole are selected. In the equivalent circuit, the non-fault line is equivalently represented by zero-sequence capacitance. Reactive power flows from the line to the busbar, and the zero-sequence reactive power measured at the busbar outlet is negative. In the fault line, reactive power flows from the busbar to the line, and the zero-sequence reactive power measured at the busbar outlet is positive. i F The calculated reactive power is exactly the reactive power of line L1 Reactive power of line L2 The positive and negative values ​​of the difference are used to select the fault line of the two lines within the boundary. For the lines L1 and L2 that are completely installed on the same pole, there are , correspondingly ; If no effect If it is positive, line L1 is faulty; If no effect If it is negative, line L2 is faulty; For lines that are not completely installed on the same pole, i F Make corrections, , using the corrected The reactive power calculation criteria and line selection results are consistent with those when all the cables are installed on the same pole. If the amplitude determines that the double-circuit line on the same pole is a non-fault line, out-of-bounds line selection is performed.

4. A method for selecting a line for a small current ground fault in a distribution network containing lines in parallel on the same pole as claimed in claim 3, characterized in that: In step S3, the process of selecting the outer line outside the group according to the zero-sequence current component is as follows: The condition for starting the out-of-bounds line selection is that the in-bounds line selection determines that the double-circuit lines on the same pole are all non-fault lines. and The same-phase, zero-sequence current component effective value is expressed as For an ungrounded system, the zero-sequence current of the faulty feeder is the sum of the zero-sequence currents of the non-faulty feeders. The zero-sequence current on the line with a single-phase grounding fault is not less than the sum of the effective values ​​of the zero-sequence currents of the same components of the lines on the same pole. ,based on Setting Thresholds β To screen the faulty lines and filter out the shorter lines that are easily misjudged in the zero-sequence current phase comparison, the threshold β According to the actual distribution network structure, the following settings are made in the example: ； If the zero-sequence current of a single-circuit line outside the boundary is less than β , indicating a busbar fault; if there is a zero-sequence current greater than β The sum of the zero-sequence current and the instantaneous zero-sequence current is Compare the phases, the one with opposite phase is the faulty line, if they are all in phase, it is determined to be a bus fault.

5. A method for selecting a line for a small current ground fault in a distribution network containing lines in parallel on the same pole as claimed in claim 4, characterized in that: After completing the case analysis of the line selection method under the typical distribution network structure, simulation verification is carried out: a typical 10kV distribution network matlab / simulink simulation model is built, and the faults are set to occur in short feeders on the same pole, incomplete feeders on the same pole with different length differences, short feeders on different poles, long feeders on different poles and busbars.

6. A method for selecting a line for a small current ground fault in a distribution network containing lines in parallel on the same pole as claimed in claim 5, characterized in that: The simulation feature verification results are: The fault characteristics of the lines installed on the same pole vary under different transition resistances, fault point locations, and fault initial phase angle parameters: The larger the transition resistance, the smaller the first half-wave peak value of the zero-sequence current of the fault line, the faster the transient decay speed, and the steady-state current is determined by the current of other feeders to the ground, with little overall change, and slightly distorted when the transition resistance is high; As the fault point is farther from the busbar, the amplitude of the first half-wave of the zero-sequence current is smaller, the transient main resonant frequency is lower, and the zero-sequence steady-state current of the fault line is determined by the zero-sequence current of the non-fault feeder, and is less affected by the change of the fault point location. The initial phase angle of the fault only has a great influence on the transient amplitude of the zero-sequence current. The coupling relationship of the lines installed on the same pole has no effect on the steady-state zero-sequence current of the faulty feeder. However, when the faulty line is a line installed on the same pole, the transient zero-sequence current changes, which is manifested as an increase in the transient resonant main frequency.

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