A new small current grounding line selection equipment and grounding line selection method

Abstract

The application discloses a new small-current grounding line selection complete equipment and a grounding line selection method thereof, and provides the method which comprises the following steps: starting calculation of a bus zero sequence voltage; based on the starting calculation result, recording the fault of the bus zero sequence voltage and zero sequence currents of each line, searching for a fault starting point based on the fault recording data, and obtaining fault components of the bus zero sequence voltage and the zero sequence currents of each line based on the fault starting point; determining the effective value of the fault components of the zero sequence currents of each line, obtaining remaining to-be-selected lines, calculating corresponding judgment variables of transient state method and steady state method for the remaining to-be-selected lines through a group or bootstrap method, performing fusion algorithm and consistency determination on the line selection results of the transient state method and the steady state method, and judging the grounding fault line.The application is suitable for metallic grounding, high-resistance grounding, zero-crossing grounding, arc grounding and other grounding fault conditions in a small-current grounding system in China, reliably and accurately realizes grounding line selection, and the line selection result has high reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ground selection, in particular to a new small current grounding selection complete equipment and a grounding selection method thereof. BACKGROUND

[0002] The fault line selection of distribution network is difficult, and many experts and scholars have developed many small current grounding selection devices (hereinafter referred to as selection device). However, the actual on-site selection accuracy is still not ideal, and the technical requirements of reliable selection are not met. The power supply department urgently hopes to develop a reliable and practical small current grounding selection complete equipment. The small current grounding selection of the transformer substation needs to install a zero sequence current transformer once and a selection device secondly. At present, the zero sequence current transformer and the selection device are designed and installed independently without unified standard design.

[0003] The zero sequence current transformer configured on site is generally configured according to the current transformer for protection. After a single-phase grounding fault occurs in the distribution network, the fault zero sequence current usually operates at the lower limit of the current transformer measurement range (1% to 5% of the rated current value or lower), which cannot meet the selection device and zero sequence current sampling accuracy requirements.

[0004] The existing grounding selection algorithm of the selection device either simply uses the steady-state method for grounding selection or uses the transient method which has been rising in recent years. However, both methods have different degrees of defects and cannot meet the accuracy of grounding selection, and cannot meet the practical technical requirements. SUMMARY

[0005] To solve the problem of insufficient grounding selection accuracy in the prior art, the present application provides a new small current grounding selection complete equipment, which is composed of a high-precision zero sequence current transformer and a matching small current grounding selection device. The present application also provides a new grounding selection method for the small current grounding selection device, which combines group selection and bootstrap selection based on high-precision zero sequence current transformer sampling data, and combines transient method and steady-state method for practical fusion judgment and selection method, which can improve the precision and accuracy of grounding selection.

[0006] The new small current grounding selection complete equipment provided by the present application specifically comprises a small current grounding selection device and a plurality of high-precision zero sequence current transformers.

[0007] The small current grounding selection device is installed in the main control room of the transformer substation, and the plurality of high-precision zero sequence current transformers are installed in a plurality of transformer substation switch cabinets.

[0008] The small current grounding selection device is connected with the plurality of high-precision zero sequence current transformers.

[0009] The high-precision zero sequence current transformer is used for collecting zero sequence currents in each line;

[0010] The small current grounding line selection device is used for collecting zero sequence voltages in the bus and zero sequence currents in each line, and simultaneously performing grounding line selection processing based on the zero sequence voltages in the bus and the zero sequence currents in each line;

[0011] The small current grounding line selection device is provided with an analog sampling channel;

[0012] The analog sampling channel comprises a zero sequence current sampling channel and a voltage sampling channel;

[0013] The zero sequence current sampling channel is used for synchronously and high-speed parallel sampling of multiple zero sequence currents;

[0014] The voltage sampling channel is used for synchronously and high-speed parallel sampling of multiple zero sequence voltages.

[0015] Optionally, the zero sequence current sampling channel comprises a small current transformer, an IV current transformer, an AD converter and a zero sequence current programmable logic chip;

[0016] The voltage sampling channel comprises a voltage transformer, an AD converter and a voltage programmable logic chip.

[0017] The application further provides a new small current grounding line selection method, comprising,

[0018] Collecting zero sequence voltages in the bus and zero sequence currents in each line, and performing fault research and judgment starting calculation based on the zero sequence voltages in the bus;

[0019] Based on the fault research and judgment starting calculation result, performing high-precision fault recording on the zero sequence voltages in the bus and the zero sequence currents in each line, obtaining fault recording data, performing fault starting point searching based on the fault recording data, obtaining the fault starting point, obtaining the first cycle zero sequence voltage fault component and the zero sequence current fault component in each line based on the fault starting point;

[0020] Performing effective value calculation on the zero sequence current fault components in each line, and obtaining remaining candidate lines after research and selection;

[0021] When the number of the remaining candidate lines M=0, a grounding line selection result without fault is obtained;

[0022] When the number of the remaining candidate lines M≥3, performing group research and judgment on the fault recording data based on the remaining candidate lines, and obtaining a grounding line selection result;

[0023] When the number of the remaining candidate lines M<3, performing bootstrap research and judgment on the fault recording data based on the remaining candidate lines, and obtaining a grounding line selection result.

[0024] Optionally, the fault judgment starting calculation specific steps of performing fault judgment processing include

[0025] Based on the bus zero sequence voltage, the bus zero sequence voltage fault component ΔU 0k is obtained, and the obtaining process is as follows:

[0026] ΔU 0k = U k - U k-5*N ;

[0027] Wherein, U k is a sampling point of a current cycle, and U k-5*N is a sampling point corresponding to the previous 5 cycles of the current cycle.

[0028] Based on the bus zero sequence voltage fault component ΔU 0k , the bus zero sequence voltage fault component effective value ΔU 0故 is calculated, when ΔU 0故 ≥ ΔU 0SET , fault recording data saving is performed; wherein, ΔU 0SET is a zero sequence voltage fixed value, and ΔU 0SET = min{15V, 5 times the maximum historical unbalanced voltage value}.

[0029] Optionally, the specific steps of finding the fault starting point based on the fault recording data include:

[0030] Based on the fault recording data, the zero sequence voltage fault component waveform curve is obtained;

[0031] Based on the zero sequence voltage fault component waveform curve, the fault starting point is found by the sudden change variable difference calculation method, and the fault starting point is obtained.

[0032] Optionally, based on the fault starting point, the first cycle zero sequence voltage fault component and the zero sequence current fault component after the fault are calculated, and the specific steps include:

[0033] Based on the fault starting point, the first cycle zero sequence voltage fault component ΔU 暂0k and the zero sequence current fault component ΔI 暂0ik of each line after the fault are calculated, and the process is as follows:

[0034] ΔU 暂0k = U 0k - U 0k-1

[0035] ΔI 暂0ik = I 0ik - I 0ik-1

[0036] Wherein, U 0kU is a sampling value at the first zero sequence voltage k time after the fault 0k-1 I is a sampling value at the k time corresponding to the one cycle zero sequence voltage before the fault 0ik I is a zero sequence current sampling value at the k time of the first cycle of the i-th line after the fault 0ik-1 I is a zero sequence current sampling value at the k time corresponding to the one cycle of the i-th line before the fault

[0037] Optionally, the specific steps of obtaining the remaining candidate lines comprise:

[0038] The root mean square of the zero sequence current fault component of each line is calculated to obtain the root mean square effective value I RMS The calculation process is as follows:

[0039]

[0040] Wherein, N is a sampling point of one cycle, and x(n) is a discrete sampling point of the zero sequence current fault component in each line n;

[0041] The root mean square effective value is determined, and the lines with a root mean square effective value lower than a certain value are removed to obtain the remaining candidate lines through research and selection.

[0042] Optionally, when the number M of the remaining candidate lines is greater than or equal to 3, the specific process of group research and judgment based on the remaining candidate lines comprises:

[0043] The group research and judgment transient method research variable calculation is carried out based on the recording wave data of the remaining candidate lines;

[0044] Wherein, the group transient research variable calculation includes: the initial angle of the transient zero sequence voltage fault component, the waveform correlation coefficient of the transient zero sequence current fault component and the decay direct current component;

[0045] The group research and judgment steady-state method research variable calculation is carried out based on the recording wave data of the remaining candidate lines;

[0046] Wherein, the group steady-state research variable calculation includes: the fundamental amplitude and phase angle of the zero sequence current fault component of the candidate line, the fundamental angle of the zero sequence voltage fault component and the zero sequence current fault component, the fifth harmonic amplitude and phase angle of the steady-state zero sequence current fault component of the candidate line, and the angle comprehensive correlation coefficient of the zero sequence current fault component of the candidate line;

[0047] According to the neutral point grounding mode, the corresponding group transient method line selection result is calculated according to the group research and judgment transient method research variable calculation result;

[0048] According to the neutral point grounding mode, the corresponding group steady-state method line selection result is calculated according to the group research and judgment steady-state method research variable calculation result;

[0049] Based on the line selection results of the group transient method and the group steady-state method, the final line selection result is obtained through fusion algorithm and consistency judgment.

[0050] Optionally, when the number M of the remaining lines to be selected is less than 3, the specific process of performing bootstrapping analysis based on the remaining lines to be selected includes:

[0051] Performing bootstrap transient analysis method analysis variable calculation based on the recorded data of the remaining candidate lines;

[0052] Among them, the bootstrap transient analysis and judgment variables calculation includes: the transient zero-sequence voltage fault starting angle of the selected line, the effective value of the transient zero-sequence current fault component of each selected line, the first cycle sudden change intensity value of the transient zero-sequence current fault component of each selected line, the correlation coefficient between the derivative of the transient zero-sequence voltage fault component and the zero-sequence current fault component of each selected line, and the correlation coefficient between the transient zero-sequence voltage fault component and the zero-sequence current fault component of each selected line;

[0053] Performing bootstrap steady-state method analysis and judgment variable calculation based on the recorded data of the remaining candidate lines;

[0054] The bootstrap steady-state analysis and judgment variables are calculated as follows: the fundamental amplitude of the steady-state zero-sequence current fault component of each candidate line, the angle between the fundamental waves of the zero-sequence voltage fault component and the zero-sequence current fault component of each candidate line;

[0055] According to the neutral point grounding mode, the line selection result of the bootstrap transient method is calculated based on the calculation results of the bootstrap transient analysis variables;

[0056] According to the neutral point grounding mode, the line selection result of the bootstrap steady-state method is obtained according to the calculation results of the bootstrap steady-state analysis variables;

[0057] Based on the line selection results of the bootstrapped transient method and the bootstrapped steady-state method, the final line selection result is obtained through fusion algorithm and consistency judgment.

[0058] The present invention has the following technical effects:

[0059] The present invention proposes a new small current grounding line selection equipment set, which consists of a high-precision zero-sequence current transformer and a matching small current grounding line selection device as an overall design. The equipment has a high degree of integration and can well meet the sampling accuracy requirements when measuring actual zero-sequence current in the line selection device and distribution network, and has high accuracy in data collection of zero-sequence current and zero-sequence voltage.

[0060] The present invention proposes a new line selection method for a small current grounding line selection device. Based on high-precision zero-sequence current sampling data, the transient method and the steady-state method are combined for analysis and judgment. The practical fusion analysis and selection method combines group line selection and bootstrap line selection. The method is suitable for various grounding fault conditions such as metallic grounding, high-resistance grounding, zero-crossing grounding, and arc grounding in my country's small current grounding system. It can achieve reliable and accurate grounding line selection, and the line selection results are highly credible, and have strong promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0062] Figure 1 A schematic diagram of a system provided by an embodiment of the present invention;

[0063] Figure 2 A schematic diagram of a high-precision zero-sequence current sampling channel provided by an embodiment of the present invention;

[0064] Figure 3 A schematic diagram of a method flow chart provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0066] like Figure 1 , the present invention provides a new small current grounding line selection equipment set, including: a small current grounding line selection device and a number of high-precision zero-sequence current transformers;

[0067] The small current grounding line selection device is installed in the substation main control room, and several high-precision zero-sequence current transformers are installed in several substation switch cabinets. The small current grounding line selection device is connected to several high-precision zero-sequence current transformers. The high-precision zero-sequence current transformers are used to collect the zero-sequence current in each line. The small current grounding line selection device is used to collect the zero-sequence voltage in the busbar and the zero-sequence current in each line, and simultaneously performs grounding line selection based on the zero-sequence voltage in the busbar and the zero-sequence current in each line. The small current grounding line selection device is provided with an analog sampling channel.

[0068] likeFigure 2 As shown, the analog sampling channel includes a zero-sequence current sampling channel and a voltage sampling channel; the zero-sequence current sampling channel is used to perform synchronous high-speed parallel sampling of multiple zero-sequence currents; the voltage sampling channel is used to perform synchronous high-speed parallel sampling of multiple zero-sequence voltages. The zero-sequence current transformer uses a high-precision zero-sequence current transformer, and the rated current ratio of the high-precision zero-sequence current transformer is generally designed to be 100A / 1A or 50A / 1A, that is, I n =100A or 50A, the secondary current output is output according to the 1A standardized interface. The high-precision zero-sequence current transformer specifies the accuracy level: 0.2S level + 5P10, and the technical indicators are shown in Table 1:

[0069] Table 1

[0070]

[0071]

[0072] That is, at the rated current I n Above, up to 10I n Meet the accuracy requirements of protective current transformers, as low as 1% I below rated current n The rated current meets the accuracy requirements of metering current transformers, standardizes the technical indicators of zero-sequence current transformers, and achieves high-precision and accurate measurement of zero-sequence current transformers across the entire transient and steady-state range. The secondary load of the high-precision zero-sequence current transformer is designed for light loads, with a typical design value of 0.5Ω to 1Ω, which is adjustable and matched based on the cable length between the zero-sequence current transformer and the low-current grounding line selection device on site.

[0073] The low-current grounding line selection device has a built-in high-precision analog sampling channel to achieve accurate sampling of the secondary output current of the high-precision zero-sequence current transformer and the secondary output voltage of the voltage transformer installed on site.

[0074] The high-precision analog sampling channel includes a high-precision zero-sequence current sampling channel and a high-precision voltage sampling channel. The high-precision zero-sequence current sampling channel ensures accurate sampling of multiple high-precision zero-sequence current secondary outputs within the low-current grounding line selection device (ratio and phase differences meet 0.2S+5P10 accuracy requirements), enabling accurate measurement transmission throughout the entire process from primary sampling to secondary conversion. The high-precision zero-sequence current sampling channel consists of a small current transformer, an IV current converter, a high-precision A / D converter, and a large-scale programmable logic chip, enabling synchronous, high-speed, parallel sampling of multiple zero-sequence currents.

[0075] The low current converter uses 1A / 0.01A and the accuracy level is 0.01SS level.

[0076] IV converter, secondary resistance, to realize current-voltage conversion, and interface matching with AD converter.

[0077] Large-scale programmable chip, high-performance FPGA is selected, to realize synchronous work of multiple AD conversion chips (typically 8 AD conversion chips), and AD data storage and reading tasks.

[0078] The other components of the small current grounding line selection device are arranged with an alarm loop, a tripping loop, a man-machine interface display loop, a communication interface loop, a power module loop and other functional components.

[0079] As shown in Figure 3 , the application also provides a new small current grounding line selection method, which comprises

[0080] S1. Collecting bus zero sequence voltage and each line zero sequence current, based on bus zero sequence voltage, starting calculation for fault research; the specific steps comprise: based on bus zero sequence voltage, obtaining bus zero sequence voltage fault component ΔU 0k , the obtaining process is as follows:

[0081] ΔU 0k = U k -U k-5*N ;

[0082] Wherein, U k is the sampling point of the current cycle, and U k-5*N is the corresponding sampling point of the previous 5 cycles (the actual cycle number can be set); the fault component is calculated by subtracting the corresponding sampling point of 5 cycles from the sampling point of the current cycle. Typically, 512 points are sampled per cycle, that is, N = 512.

[0083] Based on bus zero sequence voltage fault component ΔU 0k , the bus zero sequence voltage fault component effective value ΔU 0故 is calculated every 10 ms, whether it exceeds the set value is judged, when ΔU 0故 ≥ ΔU 0SET , if the set value is exceeded, the fault research is started, the small current grounding line selection process is entered, and fault recording is performed; if the set value is not exceeded, the task of periodically monitoring the bus zero sequence voltage fault component is continued. Wherein, ΔU 0SET is the zero sequence voltage set value, and ΔU 0SET = min{15V, 5 times the maximum historical unbalanced voltage value}. ΔU 0SETThe zero-sequence voltage setting value adopts a fixed value and is selected according to the maximum value of the maximum unbalanced voltage to meet the high-resistance grounding starting requirements.

[0084] S2. Based on the fault analysis and startup calculation results, perform high-precision fault recording of the busbar zero-sequence voltage and busbar zero-sequence current. Based on the fault recording data, locate the fault initiation point and obtain the fault initiation point. Based on the fault initiation point, obtain the zero-sequence current fault component of each line.

[0085] After the fault analysis is started, wait for 240ms (i.e., according to the time setting for avoiding instantaneous ground fault) to record the waveform after the fault, and then temporarily store the zero-sequence voltage, three-phase voltage, and all zero-sequence current waveforms of the bus where the 4-cycle data before the fault and the 12-cycle data after the fault start (a total of 16 cycles) are located (i.e., U0, U1, U2, U3). a 、U b 、U c , I 01 , I 02 ...I 0N ).

[0086] S2.1. First, calculate the three-phase voltage and zero-sequence voltage fundamental RMS values ​​for the 10th to 12th cycles after the fault to determine whether it is a transient fault or a false ground fault. If it is a transient fault or a false ground fault, the ground line selection algorithm returns to the original state and the recorded data is stored.

[0087] S2.2 The specific steps of locating the fault initiation point based on the fault recording data include: obtaining a zero-sequence voltage fault component waveform curve, i.e., a Δ3U0 waveform curve, based on the fault recording data, by subtracting the data corresponding to the point in the first cycle from the data corresponding to the points in the second to sixteenth cycles. Based on the zero-sequence voltage fault component waveform curve, a sudden change difference calculation method is used to locate the fault initiation point, thereby obtaining the fault initiation point.

[0088] S2.3. Based on the determined fault starting point, calculate the transient zero-sequence voltage fault component of the first cycle after the fault and the zero-sequence current fault component of each line below the busbar.

[0089] Based on the fault starting point, the process of calculating the zero-sequence voltage fault component and the zero-sequence current fault component of each line is as follows:

[0090] ΔU 暂0k =U 0k -U 0k-1

[0091] ΔI 暂0ik =I 0ik -I 0ik-1

[0092] Wherein, i∈(all the outgoing lines of the bus 0~n), k takes value from the fault point to the whole 1 cycle after the fault.

[0093] S3. The effective value of each line zero sequence current fault component is determined, and the remaining candidate lines are obtained. The specific steps of obtaining the remaining candidate lines include:

[0094] The root mean square effective value of the zero sequence current fault component of the above n lines is calculated, which is ΔI 01RMS , ΔI 02RMS ..... ΔI 0nRMS

[0095] The root mean square calculation formula is as follows:

[0096]

[0097] Wherein, N is the sampling point, and x(n) is the discrete sampling point of the zero sequence current fault component in each line n;

[0098] From the above root mean square effective value sequence of the zero sequence current fault component, remove the candidate lines whose calculated value is lower than 1A (the fixed value can be set), and the remaining candidate lines are as follows ΔI 01RMS , ΔI 02—RMS ..... ΔI 0iRMS .

[0099] S4. If the number of remaining candidate lines M=0, it is considered that there is no fault, abnormal disturbance, and three-phase zero sequence voltage 3U0 alarm prompt is returned.

[0100] S5. When the number of remaining candidate lines M≥3, based on the remaining candidate lines, the group research and judgment of the fault recording data is carried out, the fault line selection is carried out, and the line selection result is obtained.

[0101] S5.1 When the number of remaining candidate lines M≥3, the specific process of group research and judgment based on the remaining candidate lines includes: group research and judgment of transient state method based on the recording data of the remaining candidate lines.

[0102] Wherein, the group transient state research variable calculation includes: the initial angle of the transient zero sequence voltage fault component, the waveform correlation coefficient of the transient zero sequence current fault component and the decay direct current component;

[0103] The calculation method of the initial angle α 起始角 of the transient zero sequence voltage fault component is to extract the 5th whole cycle zero sequence voltage waveform after the determined fault starting point, and calculate the initial phase angle α 起始角N＝5 by Fourier transform, and the initial phase angle ≈ α 起始角

[0104] The waveform correlation coefficient ρi Calculation method:

[0105] The following formula is used to perform pairwise correlation analysis on the transient zero-sequence current fault component waveforms of each candidate line within the first half-wave 1 / 8 cycle after the fault, and the pairwise correlation coefficients between the candidate lines are obtained to form a correlation matrix S.

[0106]

[0107]

[0108] According to the correlation matrix S, the comprehensive waveform correlation coefficient ρ of the selected line is calculated WAVEi

[0109]

[0110] Attenuation DC component ΔI 0DCi Calculation method:

[0111]

[0112] The attenuated DC component is calculated according to the value of one cycle data after avoiding the first half-wave impact component, that is, the DC component from 1 / 8 cycle to the first cycle data after the fault.

[0113] The group steady-state method is used to calculate the variables for group judgment based on the recorded data of the remaining candidate lines. The group steady-state judgment variables include: the fundamental amplitude and phase angle of the zero-sequence current fault component of the candidate line, the angle between the fundamental waves of the zero-sequence voltage fault component and the zero-sequence current fault component of the candidate line, the amplitude and phase angle of the fifth harmonic of the steady-state zero-sequence current fault component of the candidate line, and the comprehensive correlation coefficient of the angle of the zero-sequence current fault component of the candidate line.

[0114] According to the determined fault starting point and based on the fault recording data, the zero-sequence voltage fault component of the steady-state process of the 10th cycle after the fault and the zero-sequence current fault component of each line under the bus are calculated.

[0115] ΔU 暂0k =U 0k+10N -U 0k-N

[0116] ΔI 暂0ik =I 0ik+10N -I 0ik-N

[0117] S5.2 The calculation method of the population steady-state judgment variable is as follows

[0118] The fundamental amplitude and phase angle of the zero-sequence current fault component of the selected line, i.e. ΔI 0x Fundamental wave amplitude and phase calculation method: Use Fourier algorithm to calculate the fundamental wave amplitude ΔI0 of the selected lineiamplitude and phase angle ΔI0 iangle

[0119] The fundamental angle α between the zero-sequence voltage fault component and the zero-sequence current fault component of the selected line U0-I0i Calculation method:

[0120] According to the zero-sequence voltage and zero-sequence current fault component waveform data in the steady-state process, the fundamental initial phase angle α of voltage and current is obtained respectively through the fundamental Fourier algorithm. U0i , α I0i ,

[0121] α U0-I0i =α U0i -α I0i .

[0122] The fifth harmonic ΔI0 of the steady-state zero-sequence current fault component of the selected line 5i The calculation method of the fifth harmonic amplitude and phase: According to the zero-sequence current fault component waveform data in the steady-state process, the fifth harmonic amplitude ΔI0 of the selected line is calculated by Fourier algorithm. 5iamplitude and phase angle ΔI0 5iangle .

[0123] Comprehensive correlation coefficient of the zero-sequence current fault component angle of the selected line ρ ANGLEi Calculation method: The calculated phase angle ΔI0 iangle According to the following rule, the two-way correlation coefficient is used to form the angle correlation matrix S. The rule is: for the neutral point ungrounded system, the angle between the two is (160 degrees to 200 degrees), ρ xy =-1, otherwise ρ xy =1, for the neutral point through the arc suppression system, the angle between the two is greater than 5 degrees, ρ xy =-1, otherwise ρ xy =1

[0124]

[0125] According to the angle correlation matrix S, the comprehensive waveform correlation coefficient ρ of the selected line is calculated ANGLEi .

[0126]

[0127] S5.3 is based on the calculation of group transient judgment variables and group steady-state judgment variables, and obtains the final line selection result through fusion analysis and consistency judgment.

[0128] The following convenient, simple and reliable fusion analysis and on-site line selection method is adopted

[0129] For a neutral point ungrounded system, the following algorithm is used to calculate two line selection results and then perform a fusion analysis:

[0130] a) Transient method, transient zero sequence current fault component waveform correlation analysis method is used to calculate the line selection result. Judgment method: In ρ WAVEi Among them, select the maximum value ρ max and the minimum value ρ min , if ρ max >0.5 and ρ min <-0.5, the line number where the minimum value is located is the fault line number, otherwise, it is a bus fault

[0131] b) Steady-state method, steady-state zero-sequence current fault component fundamental wave amplitude phase line selection method

[0132] Judgment method: In ΔI0 iamplitude Select the maximum value ΔI0 imax1 , submaximum ΔI0 imax2 . Detect whether the fundamental wave phase angles corresponding to the maximum value and the second maximum value are in phase or inversely related. If ΔI0 imax1 >ΔI0 imax2 If the fundamental wave phase angles are inversely related to each other, the line number with the largest one is the fault line number, otherwise it is a bus fault.

[0133] c) Method of integrating the results of transient method and steady-state method: If the results of transient method and steady-state method are consistent, the analysis and judgment results are directly determined. If the results of transient method and steady-state method are inconsistent, the transient method is taken as the priority result and the steady-state method is taken as the secondary result to determine the analysis and judgment results, which will be used as a reference for decision-making on the test tripping of the grounding line selection device or the scheduling of the test pull sequence.

[0134] The neutral point passes through the arc suppression coil system, and the following algorithms are used to calculate the following four line selection results and then conduct integrated analysis:

[0135] a) Transient method, transient zero sequence current fault component waveform correlation analysis method is used to calculate the line selection result. Judgment method: In ρ WAVEi Among them, select the maximum value ρ max and the minimum value ρ min , if ρ max >0.5 and ρ min <-0.5, the line number where the minimum value is located is the fault line number, otherwise, it is a bus fault

[0136] b) Transient method, transient zero-sequence decay DC component analysis method to calculate line selection results

[0137] Judgment method: If α 起始角 ∈(-15°~15°), execute the following transient attenuation DC judgment method, otherwise this method is invalid. 0DCi Select the maximum value I 0DCmax1 , submaximum I 0DCmax2 , if I0DCmax1 >10×I 0DCmax2 and I 0DCmax1 If >2A is satisfied, the maximum line number is the fault line number, otherwise it is the bus fault.

[0138] c) steady-state method, steady-state zero sequence current fault component fifth harmonic component phase comparison method.

[0139] Judgment method: select the maximum value ΔI0 5iamplitude and the second maximum value ΔI0 5imax1 in ΔI0 5imax2 , and detect whether the phase angle between the maximum value and the second maximum value corresponding to the fifth harmonic phase angle is in phase or reverse relationship, if ΔI0 5imax1 > ΔI0 5imax2 and the reverse relationship between each other, the maximum line number is the fault line number, otherwise it is the bus fault.

[0140] d) steady-state method, steady-state zero sequence current fault component fundamental phase comparison method

[0141] Judgment method: in ρ ANGLEi , select the maximum value ρ max and the minimum value ρ min , if ρ max =1 and ρ min =-1, the minimum value of the line number is the fault line number, otherwise this method is invalid.

[0142] e) transient method and steady-state method result fusion method

[0143] If there are two results output, the transient method is directly used as the transient method result. If there are two results output, the steady-state method is directly used as the steady-state method result. If the transient method and the steady-state method result are consistent, the research result is directly determined. If the transient method and the steady-state method result are inconsistent, the transient method is used as the priority result, and the steady-state method is used as the secondary result. The grounding line selection result is obtained, and the research result is determined to provide grounding line selection device for trial tripping or dispatching trial pulling sequence.

[0144] S6. When the number of remaining candidate lines M<3, based on the remaining candidate lines, the fault recording data is self-booted and judged, the fault line selection is carried out, and the line selection result is obtained;

[0145] When the number of remaining candidate lines M<3, the specific process of self-booting and judging based on the remaining candidate lines includes,

[0146] S6.1 Based on the recording data of the remaining candidate lines, the self-booting and judging transient method research variable calculation is carried out;

[0147] The bootstrap transient judgment variable calculation includes: a fault starting angle of a transient zero sequence voltage of a candidate line, an effective value of a transient zero sequence current fault component of each candidate line, a first cycle mutation intensity value of the transient zero sequence current fault component of each candidate line, a derivative of a transient zero sequence voltage fault component of each candidate line and a zero sequence current fault component correlation coefficient, and a transient zero sequence voltage fault component and a zero sequence current fault component correlation coefficient of each candidate line.

[0148] The fault starting angle of the transient zero sequence voltage of the candidate line α 起始角 The calculation method is as follows: the zero sequence voltage waveform of the determined fault starting point is extracted, and the initial phase angle α 起始角N＝5 is calculated by Fourier transform. 起始角

[0149] The effective value of the transient zero sequence current fault component of each candidate line ΔI 0x The calculation adopts a root mean square method.

[0150]

[0151] N=64 is taken when the correlation coefficient in the first half wave is calculated.

[0152] The first cycle mutation intensity value of the transient zero sequence current fault component of each candidate line ΔTB 0x The calculation adopts a root mean square method.

[0153]

[0154] That is, the ratio of the effective value of the first 1 / 8 cycle to the effective value of the last 1 / 8 cycle in the first cycle of the zero sequence fault component after the fault is calculated.

[0155] The derivative calculation method of the transient zero sequence voltage fault component adopts a difference method of the zero sequence voltage fault, that is,

[0156] dU(k)=U(k)-U(k-1),

[0157] The correlation coefficient of the transient zero sequence voltage fault component and the zero sequence current fault component of each candidate line ρ 1x The correlation coefficient calculation method of ρ 2x is as follows:

[0158]

[0159] N=64 is taken when the correlation coefficient in the first half wave is calculated.

[0160] The attenuation DC component of the transient zero sequence current fault component of each candidate line ΔI 0DC The calculation method is as follows:

[0161] ​

[0162] The decaying DC component is calculated according to the data value of one cycle after the first half-wave impact component is avoided.

[0163] S6.2 Based on the recording data of the remaining candidate lines, the self-lifting research and judgment steady-state method research and judgment variable calculation is performed.

[0164] The self-lifting steady-state research and judgment variable calculation includes: the steady-state zero sequence current fault component fundamental amplitude of each candidate line, the zero sequence voltage fault component and the zero sequence current fault component fundamental angle of each candidate line.

[0165] The steady-state zero sequence current fault component fundamental amplitude of each candidate line is ΔI 0x The calculation method uses the Fourier algorithm to calculate the fundamental amplitude of the candidate line, and the zero sequence voltage fault component and the zero sequence current fault component fundamental angle of each candidate line is α U0-I0 The calculation method,

[0166] The zero sequence voltage and zero sequence current fault component waveform data in the steady-state process are sequentially obtained by the fundamental Fourier algorithm to obtain the fundamental initial phase angle of the voltage and current, respectively. U0x , and α I0x .

[0167] α U0-I0x = α U0x - α I0x .

[0168] S6.3 Based on the self-lifting transient research and judgment variable calculation and the self-lifting steady-state research and judgment variable calculation, the final line selection result is obtained through fusion analysis, consistency determination.

[0169] The following simple and reliable fusion analysis on-site line selection research and judgment method is adopted

[0170] The line selection result array JD of the candidate line is initialized i = 0 i∈(1~2).

[0171] For the neutral point ungrounded system, the following algorithm is used to calculate the line selection result and then perform fusion research and judgment:

[0172] a) Transient method, if ΔTB 0x > 5, it indicates that the transient process is obvious, and the transient zero sequence voltage derivative current polarity discrimination method is performed: if ρ 1i < -0.5, then JD i ++,

[0173] If ΔTB 0x ≤ 5, it indicates that the transient process is not obvious, and the transient zero sequence voltage and current polarity discrimination method is performed: if ρ 2i < -0.5, then JD i++.

[0174] b) Steady-state method zero sequence voltage current angle discrimination method: if α u0-I0 ∈(65°~115°), then JD i ++,

[0175] c) Result fusion: if remaining 1 line calculation, when JD1≥1, it is judged that the line number is the fault line number, otherwise it is bus fault.

[0176] If there are 2 lines left to calculate, and JD1≥1 and JD2≥1, at this time, the zero sequence fundamental amplitude and the fundamental phase of the two lines are calculated (the method is the same as above), if the direction fundamental phase is opposite, the maximum fundamental amplitude is the fault line number, otherwise it is bus fault.

[0177] For the neutral point arc suppression coil grounding system, the following algorithm is used to calculate the line selection result and then fuse and judge:

[0178] a) Transient method-waveform correlation analysis method, if ΔTB 0x >5, it means that the transient process is obvious, and the transient zero sequence voltage derivative current polarity discrimination method is executed: if ρ 1i <ρ 1SET , then JD i ++,

[0179] If ΔTB 0x ≤5, it means that the transient process is not obvious, and the transient zero sequence voltage current polarity discrimination method is executed: if ρ 2i <ρ 2SET , then JD i ++,

[0180] b) Transient method-decay DC component method, if α 起始角 ∈(-15°~15°), the transient decay DC discrimination method is executed, otherwise this method is invalid, ΔI DCi ≥ΔI DCSET , then JD i ++.

[0181] c) Steady-state method-zero sequence voltage current angle method, zero sequence voltage current angle discrimination method: if α U0-I0 ∈(260°~265°), then JD i ++,

[0182] d) Result fusion: if remaining 1 line calculation, when JD1≥1, it is judged that the line number is the fault line number, otherwise it is bus fault. If there are 2 lines left to calculate, and JD1≥1 and JD2≥1.

[0183] At this time, the attenuation DC method in the transient method is preferred to be judged, and the waveform correlation analysis method in the transient method is used to judge again, the line number in the judgment is taken as the fault line number, otherwise it is a bus fault.

[0184] After fault judgment, the change of three-phase zero sequence voltage 3U0 is monitored in real time, when 3U0 drops below 50% of the starting value (the value can be set), the fault monitoring is returned after 1 second delay, and the real-time variable monitoring under normal conditions is performed again.

[0185] The application provides a new line selection method of a small current grounding line selection device, based on high-precision zero sequence current sampling data, combining the transient method and the steady-state method for judgment, combining the group line selection and the bootstrap line selection, and the practical fusion judgment line selection method is suitable for metallic grounding, high resistance grounding, zero crossing grounding, arc grounding and other grounding fault conditions in the small current grounding system of China, can realize reliable and accurate grounding line selection, the line selection result has high reliability, and has strong popularization and application value.

[0186] The basic principle, main features and advantages of the application are shown and described above. It should be understood by those skilled in the art that the application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principle of the application, and various changes and improvements can be made without departing from the spirit and scope of the application, and these changes and improvements all fall within the scope of the application. The scope of protection of the application is defined by the appended claims and their equivalents.

Claims

1. A new low-current grounding line selection method, characterized by: include, Collect the busbar zero-sequence voltage and each line zero-sequence current, and perform fault analysis and startup calculation based on the busbar zero-sequence voltage; Based on the fault analysis and startup calculation result, high-precision fault recording is performed on the bus zero-sequence voltage and each line zero-sequence current to obtain fault recording data, and a fault starting point is searched based on the fault recording data to obtain the fault starting point. Based on the fault starting point, a zero-sequence voltage fault component of the first cycle after the fault and a zero-sequence current fault component of each line are obtained; Calculate the effective value of the zero-sequence current fault component of each line, and obtain the remaining lines to be selected after analysis and screening; When the number of remaining lines to be selected M=0, a line selection result without faults is obtained; When the number M of the remaining lines to be selected is greater than or equal to 3, performing group analysis on the fault recording data based on the remaining lines to be selected to obtain a line selection result; When the number M of the remaining lines to be selected is less than 3, the fault recording data is bootstrapped and judged based on the remaining lines to be selected to obtain a line selection result; When the number of the remaining candidate routes M is greater than or equal to 3, the specific process of performing group analysis based on the remaining candidate routes includes: Performing group analysis and transient method analysis and variable calculation based on the recorded data of the remaining candidate lines; The calculation of group transient analysis variables includes: the starting angle of the transient zero-sequence voltage fault component, the waveform correlation coefficient of the transient zero-sequence current fault component and the attenuated DC component; Perform group analysis and steady-state method analysis and variable calculation based on the recorded data of the remaining candidate lines; The calculation of group steady-state analysis variables includes: the fundamental amplitude and phase angle of the zero-sequence current fault component of the selected line, the angle between the fundamental wave of the zero-sequence voltage fault component and the zero-sequence current fault component of the selected line, the fifth harmonic amplitude and phase angle of the steady-state zero-sequence current fault component of the selected line, and the comprehensive correlation coefficient of the angle of the zero-sequence current fault component of the selected line; According to the neutral point grounding mode, the corresponding group transient method line selection results are calculated based on the group transient method analysis variable calculation results; According to the neutral point grounding mode, the corresponding group steady-state method line selection results are calculated based on the group steady-state method analysis and judgment variable calculation results; Based on the line selection results of the group transient method and the group steady-state method, the final line selection result is obtained through fusion algorithm and consistency judgment; When the number of the remaining candidate lines M is less than 3, the specific process of bootstrapping and judging based on the remaining candidate lines includes: Performing bootstrap transient analysis method analysis variable calculation based on the recorded data of the remaining candidate lines; Among them, the bootstrap transient analysis and judgment variables calculation includes: the transient zero-sequence voltage fault starting angle of the selected line, the effective value of the transient zero-sequence current fault component of each selected line, the first cycle sudden change intensity value of the transient zero-sequence current fault component of each selected line, the correlation coefficient between the derivative of the transient zero-sequence voltage fault component and the zero-sequence current fault component of each selected line, and the correlation coefficient between the transient zero-sequence voltage fault component and the zero-sequence current fault component of each selected line; Performing bootstrap steady-state method analysis and judgment variable calculation based on the recorded data of the remaining candidate lines; The bootstrap steady-state analysis and judgment variables are calculated as follows: the fundamental amplitude of the steady-state zero-sequence current fault component of each candidate line, the angle between the fundamental waves of the zero-sequence voltage fault component and the zero-sequence current fault component of each candidate line; According to the neutral point grounding mode, the line selection result of the bootstrap transient method is calculated based on the calculation results of the bootstrap transient analysis variables; According to the neutral point grounding mode, the line selection result of the bootstrap steady-state method is obtained according to the calculation results of the bootstrap steady-state analysis variables; Based on the line selection results of the bootstrapped transient method and the bootstrapped steady-state method, the final line selection result is obtained through fusion algorithm and consistency judgment.

2. The new low-current grounding line selection method according to claim 1 is characterized in that: The specific steps of fault analysis and starting calculation for fault analysis and processing include: Based on the bus zero-sequence voltage, obtain the bus zero-sequence voltage fault component , the acquisition process is as follows: ； in, is the sampling point of the current cycle, The sampling points corresponding to the first five cycles of the current cycle; Based on bus zero-sequence voltage fault component , calculate the effective value of the bus zero-sequence voltage fault component △U 0故 , when △U 0故 ≥△U 0SET When , the fault recording data is saved; among them, △U 0SET is the zero sequence voltage constant, △U 0SET =min{15V, 5 times the maximum historical unbalanced voltage value}.

3. The new low-current grounding line selection method according to claim 1 is characterized in that: The specific steps for finding the fault starting point based on fault recording data include: Based on the fault recording data, the zero-sequence voltage fault component waveform curve is obtained; Based on the zero-sequence voltage fault component waveform curve, the fault starting point is found by using the mutation difference calculation method to obtain the fault starting point.

4. The new low-current grounding line selection method according to claim 1 is characterized in that: Based on the fault starting point, calculate the zero-sequence voltage fault component and zero-sequence current fault component of the first cycle after the fault. The specific steps include: Based on the fault starting point, calculate the zero-sequence voltage fault component of the first cycle after the fault and the zero-sequence current fault components of each line The process is: in, is the sampling value of the zero-sequence voltage at time k of the first cycle after the fault, is the sampling value of the zero-sequence voltage at time k before the fault, is the zero-sequence current sampling value of the i-th line at time k in the first cycle after the fault, is the zero-sequence current sampling value of the i-th line at time k in the cycle before the fault.

5. The new low-current grounding line selection method according to claim 1 is characterized in that: The specific steps of obtaining the remaining candidate routes include: The root mean square (RMS) value of the zero-sequence current fault component of each line is calculated to obtain the RMS effective value I RMS , the calculation process is as follows: ； Where N is the sampling point of one cycle, x(n) is the discrete sampling point of the zero-sequence current fault component in each line n; The root mean square effective value is judged, and the routes with root mean square effective value lower than the set value are removed, and the remaining candidate routes are obtained through analysis and screening.

6. A new small current grounding line selection complete set of equipment corresponding to the new small current grounding line selection method according to any one of claims 1 to 5, characterized in that: include: Small current grounding line selection device and several high-precision zero-sequence current transformers; The small current grounding line selection device is installed in the main control room of the substation, and the plurality of high-precision zero-sequence current transformers are installed in a plurality of substation switch cabinets; The small current grounding line selection device is connected to the plurality of high-precision zero-sequence current transformers; The high-precision zero-sequence current transformer is used to collect the zero-sequence current in each circuit; The small current grounding line selection device is used to collect the zero-sequence voltage in the bus and the zero-sequence current in each line, and perform grounding line selection processing based on the zero-sequence voltage in the bus and the zero-sequence current in each line; The small current grounding line selection device is provided with an analog sampling channel; The analog sampling channel includes a zero-sequence current sampling channel and a voltage sampling channel; The zero-sequence current sampling channel is used to perform synchronous high-speed parallel sampling of multiple zero-sequence currents; The voltage sampling channel is used to perform synchronous high-speed parallel sampling on multiple zero-sequence voltages.

7. The new low-current grounding line selection complete equipment according to claim 6 is characterized by: The zero-sequence current sampling channel includes a small current transformer, an IV current converter, an AD converter and a zero-sequence current programmable logic chip; The voltage sampling channel includes a voltage converter, an AD converter, and a voltage programmable logic chip.

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