CN117572155A - Flexible grounding system high-resistance fault line selection method based on low-frequency transient zero-sequence current distortion rate - Google Patents
Flexible grounding system high-resistance fault line selection method based on low-frequency transient zero-sequence current distortion rate Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
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Abstract
The invention discloses a high-resistance fault line selection method of a flexible grounding system based on low-frequency transient zero-sequence current distortion rate, belonging to the field of fault line selection of power distribution networks; in the flexible grounding system, the problem of low transition resistance is commonly existed in single-phase grounding protection based on steady-state fault characteristics, and the problem is further highlighted after the parallel small resistor is put into operation; therefore, the invention provides a flexible grounding system high-resistance fault line selection method based on low-frequency transient zero-sequence current distortion rate, which comprises the steps of firstly realizing accurate identification of bus faults and outgoing line faults by calculating the low-frequency transient zero-sequence current distortion rate ratio of each feeder line in a specific time window, and further identifying fault lines; the method is not influenced by the reverse polarity connection of the zero sequence voltage transformer and the zero sequence current transformer, is hardly influenced by the fault distance, and has low requirement on the precision of the transformer.
Description
Technical Field
The invention relates to the field of fault line selection of power distribution networks, in particular to a flexible grounding system high-resistance fault line selection method based on low-frequency transient zero-sequence current distortion rate.
Background
The flexible grounding mode is a novel grounding mode which combines the advantages of the resonance grounding mode and the small-resistance grounding mode, can overcome the problems of high overvoltage level and difficult line selection after the resonance grounding mode is failed, and can also solve the problems that the small-resistance grounding mode cannot distinguish instant grounding faults from permanent grounding faults and has low power supply reliability. The basic idea of the flexible grounding mode is to put in an arc suppression coil during normal operation and transient grounding faults, put in a small parallel resistor after judging the fault type as permanent grounding faults, and realize flexible conversion of the neutral point grounding mode. At present, the flexible grounding mode is popularized and used in partial areas of China, and the national power grid company and the southern power grid company also sequentially issue related regulations and related technical demonstration results.
The flexible grounding system generally adopts zero-sequence overcurrent protection of the small-resistance grounding system, the setting value of the zero-sequence overcurrent protection is often set according to the maximum capacitance current to ground of each feeder line, the setting value is generally 40A to 60A, and the maximum transition resistance capability is not more than 140 omega. And single-phase high-resistance grounding faults larger than 140 omega often occur in a power distribution network, and after the faults occur, protection refuses to act so that the faults exist for a long time, the faults are easily amplified, and even the personal safety is threatened. In addition, the current line selection technology installed in the power distribution network has the accuracy rate lower than 20% when facing single-phase high-resistance ground faults. Therefore, research on high-resistance ground faults of a flexible grounding system is needed to be carried out, and the problem that the existing protection is easy to reject and difficult to select lines under the single-phase high-resistance ground faults is solved.
Disclosure of Invention
In order to solve the problems in the background technology, the invention provides a flexible grounding system high-resistance fault line selection method based on low-frequency transient zero-sequence current distortion rate.
In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme: a flexible grounding system high-resistance fault line selection method based on low-frequency transient zero-sequence current distortion rate comprises the following steps:
step 1: monitoring neutral point current in real time and calculating neutral point current amplitude mutation quantityIf it meets->Starting a fault detection system;
step 2: after short delay, if the fault disappears, returning to the step 1, namely, reducing the neutral point current amplitude to be below a threshold value, otherwise, putting into a parallel small resistor, and entering into the step 3;
step 3: filtering the original waveform of the zero sequence current of each outgoing line to obtain the waveform of the low-frequency transient zero sequence current of each outgoing line, and calculating the distortion rate and the polar error ratio of the low-frequency transient zero sequence current of each outgoing line in a specific time window；
Step 4: according toJudging the fault type->Judging that the bus is faulty, and judging that +.>And judging the line to be a line fault and regarding the line with the lowest low-frequency transient zero sequence current distortion rate as a fault line.
Further, the method for setting the neutral point current amplitude mutation in the step 1 is as follows:
wherein,and->The neutral point current amplitude and the neutral point maximum unbalanced current amplitude are respectively +.>Maximum unbalanced voltage amplitude of system is 144.337V, < >>Frequency angle frequency, reliability coefficient->1.5 @ is taken>And setting the neutral point current amplitude abrupt change amount according to the installed arc suppression coil inductance on site.
Further, in step 2, the short delay time is 2s.
In step 2, the input time of the parallel small resistor is the zero crossing instant of the next neutral point current after 2s of delay.
Further, in step 3, the non-fault line low-frequency transient zero sequence currentThe method comprises the following steps:
wherein,、/>the voltage amplitude of the fault point and the current amplitude of the arc suppression coil before the parallel small resistor is put into operation are respectively +.>、、/>Respectively, non-fault line capacitance to ground and systemTotal capacitance to ground, faulty line capacitance to ground,/->、/>Respectively connecting the instantaneous fault point voltage and the arc suppression coil current initial phase angle of the small parallel resistor,vfor the system detuning degree, +.>Is parallel small resistance value->Is a transition resistance;
further, in step 3, the low-frequency transient zero-sequence current of the fault lineThe method comprises the following steps:
wherein,and (3) the capacitance to ground for the fault line.
In step 3, the specific time window is 0s-0.02s after the parallel connection of the small resistors.
Further, in step 3, the filter cuts to a frequency of 360Hz.
Further, in step 3, the distortion ratio is:
wherein,、/>respectively is the instituteThe maximum value and the minimum value of the distortion rate of the low-frequency transient zero sequence current in the outgoing line are provided.
In step 4, the line selection step is as follows:
step 4.1, if the distortion rate is extremely poorJudging that the bus fails, and ending line selection;
step 4.2, if the distortion rate is extremely poorAnd judging that the line is out of line fault, and timely cutting off the line with the lowest low-frequency transient zero-sequence current distortion rate as the fault line.
The high-resistance fault line selection method for the flexible grounding system based on the low-frequency transient zero-sequence current distortion rate disclosed by the invention is simple and feasible in principle, does not need to change the original protection device of the line, is simple to operate and high in practicability, and can avoid the influence of the reverse polarity connection of the zero-sequence voltage transformer and the zero-sequence current transformer; meanwhile, the method also solves the problem that the steady-state fault component drops sharply after the parallel small resistor is put into operation, greatly reduces the accuracy requirement of the transformer, and is hardly influenced by the fault distance.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a simulated topology;
FIG. 3 is a waveform diagram of the original waveform of the zero sequence current of each feeder;
fig. 4 is a waveform diagram of zero sequence current after filtering by a filter.
Detailed Description
The present invention will be described in more detail below with reference to the drawings and simulation cases.
The flexible grounding system high-resistance fault line selection method based on the low-frequency transient zero-sequence current distortion rate is shown in fig. 1, and comprises the following steps:
step 1: monitoring neutral point current in real time and calculating neutral point current amplitude mutation quantityIf it meets->Starting a fault detection system;
step 2: after short delay, if the fault disappears, returning to the step 1, namely, reducing the neutral point current amplitude to be below a threshold value, otherwise, putting into a parallel small resistor, and entering into the step 3;
step 3: filtering the original waveform of the zero sequence current of each outgoing line to obtain the waveform of the low-frequency transient zero sequence current of each outgoing line, and calculating the distortion rate and the polar error ratio of the low-frequency transient zero sequence current of each outgoing line in a specific time window；
Step 4: according toJudging the fault type->Judging that the bus is faulty, and judging that +.>And judging the line to be a line fault and regarding the line with the lowest low-frequency transient zero sequence current distortion rate as a fault line.
Further, the method for setting the neutral point current amplitude mutation in the step 1 is as follows:
wherein,and->The neutral point current amplitude and the neutral point maximum unbalanced current amplitude are respectively +.>Maximum unbalanced voltage amplitude of system is 144.337V, < >>Frequency angle frequency, reliability coefficient->1.5 @ is taken>And setting the neutral point current amplitude abrupt change amount according to the installed arc suppression coil inductance on site.
Further, in step 2, the short delay time is 2s.
In step 2, the input time of the parallel small resistor is the zero crossing instant of the next neutral point current after 2s of delay.
Further, in step 3, the non-fault line low-frequency transient zero sequence currentThe method comprises the following steps:
wherein,、/>the voltage amplitude of the fault point and the current amplitude of the arc suppression coil before the parallel small resistor is put into operation are respectively +.>、、/>The ground capacitance of the non-fault line, the total ground capacitance of the system and the ground capacitance of the fault line are respectively +.>、/>Respectively connecting the instantaneous fault point voltage and the arc suppression coil current initial phase angle of the small parallel resistor,vfor the system detuning degree, +.>Is parallel small resistance value->Is a transition resistance;
further, in step 3, the low-frequency transient zero-sequence current of the fault lineThe method comprises the following steps:
wherein,and (3) the capacitance to ground for the fault line.
In step 3, the specific time window is 0s-0.02s after the parallel connection of the small resistors.
Further, in step 3, the filter cuts to a frequency of 360Hz.
Further, in step 3, the distortion ratio is:
wherein,、/>and the maximum value and the minimum value of the low-frequency transient zero sequence current distortion rate in all outgoing lines are respectively obtained.
In step 4, the line selection step is as follows:
step 4.1, if the distortion rate is extremely poorJudging that the bus fails, and ending line selection;
step 4.2, if the distortion rate is extremely poorAnd judging that the line is out of line fault, and timely cutting off the line with the lowest low-frequency transient zero-sequence current distortion rate as the fault line. Simulation and experimental verification
In order to verify the reliability and effectiveness of the invention, the invention constructs a 10kV radial flexible grounding system simulation model shown in figure 2 based on a real-time digital simulation system (RTDS), the simulation system comprises 4 outgoing lines L1-L4, wherein L1-L3 are a series-parallel connection line of an overhead line and a cable line, L4 is an overhead line, G is an infinite power supply,R N the neutral point is connected with a small resistor in parallel, is set to be a common value of 10 omega on site,Sfor connecting the switch with the small resistance input and the switch with the small resistance output in parallel,L p the neutral point is grounded to the arc suppression coil.
Table 1 line selection effect under different transition resistance ground faults of bus
| Transition resistance/Ω | L1/% | L2/% | L3/% | L4/% | Extremely poor rate of distortion | Line selection result | Whether or not to be accurate |
| 0.01 | 9.60 | 9.78 | 9.97 | 8.50 | 1.17 | Bus bar | Correct and correct |
| 10 | 84.85 | 86.27 | 87.82 | 76.11 | 1.15 | Bus bar | Correct and correct |
| 100 | 219.28 | 220.62 | 221.96 | 209.66 | 1.06 | Bus bar | Correct and correct |
| 500 | 343.31 | 348.75 | 354.58 | 309.59 | 1.15 | Bus bar | Correct and correct |
| 1000 | 433.51 | 441.56 | 449.23 | 385.77 | 1.16 | Bus bar | Correct and correct |
| 2000 | 354.66 | 360.24 | 366.30 | 320.12 | 1.14 | Bus bar | Correct and correct |
| 3000 | 353.35 | 358.91 | 364.91 | 318.58 | 1.15 | Bus bar | Correct and correct |
| 4000 | 356.27 | 361.87 | 367.92 | 321.34 | 1.14 | Bus bar | Correct and correct |
TABLE 2 line selection effect under different transition resistance ground faults occurring at outgoing line L4
| Transition resistance/Ω | L1/% | L2/% | L3/% | L4/% | Extremely poor rate of distortion | Line selection result | Whether or not to be accurate |
| 0.01 | 140.28 | 143.06 | 146.04 | 32.30 | 4.52 | L4 | Correct and correct |
| 10 | 173.42 | 176.96 | 180.76 | 42.20 | 4.28 | L4 | Correct and correct |
| 100 | 296.05 | 300.87 | 306.06 | 46.96 | 6.52 | L4 | Correct and correct |
| 500 | 342.40 | 347.76 | 353.66 | 45.76 | 7.73 | L4 | Correct and correct |
| 1000 | 351.15 | 356.69 | 362.65 | 42.73 | 8.49 | L4 | Correct and correct |
| 2000 | 355.21 | 360.72 | 366.79 | 37.70 | 9.73 | L4 | Correct and correct |
| 3000 | 356.24 | 361.83 | 367.89 | 33.80 | 10.88 | L4 | Correct and correct |
| 4000 | 355.07 | 360.63 | 366.18 | 31.21 | 11.73 | L4 | Correct and correct |
TABLE 3 distortion ratio of feeder current waveform for different fault distances
| Transition resistance/Ω | Distance to failure | L1/% | L2/% | L3/% | L4/% | Line selection result |
| 2000 | 3km | 355.10 | 360.65 | 366.64 | 37.77 | L4 |
| 2000 | 6km | 352.87 | 358.37 | 364.44 | 37.85 | L4 |
| 2000 | 9km | 358.58 | 364.01 | 369.87 | 37.12 | L4 |
| 3000 | 3km | 353.87 | 359.44 | 365.59 | 33.81 | L4 |
| 3000 | 6km | 355.30 | 360.92 | 366.92 | 33.89 | L4 |
| 3000 | 9km | 356.44 | 361.99 | 368.01 | 33.87 | L4 |
In order to further verify the effectiveness of the proposed method, the RTDS is connected with a PA30B type digital simulation power amplifier, the output current of the PA30B type power amplifier is connected to an MG-LJK100J type zero sequence current transformer, the output current of the secondary side of the transformer is connected to a circuit board, the output waveform is recorded through an oscilloscope, and finally, the proposed method is verified, and the experimental results are shown in Table 4:
table 4 experimental data results
| Fault location | Transition resistance/Ω | L1/% | L2/% | L3/% | L4/% | Extremely poor rate of distortion | Line selection result | Whether or not to be correct |
| Bus bar | 2000 | 333.43 | 332.86 | 338.29 | 359.05 | 1.08 | Bus bar | Correct and correct |
| Bus bar | 3000 | 330.83 | 326.15 | 329.36 | 306.51 | 1.08 | Bus bar | Correct and correct |
| Bus bar | 4000 | 321.04 | 305.07 | 333.26 | 332.90 | 1.09 | Bus bar | Correct and correct |
| L4 | 2000 | 323.55 | 320.61 | 338.2 | 39.98 | 8.46 | L4 | Correct and correct |
| L4 | 3000 | 326.99 | 341.93 | 344.39 | 38.21 | 9.01 | L4 | Correct and correct |
| L4 | 4000 | 330.62 | 345.19 | 344.35 | 28.04 | 12.31 | L4 | Correct and correct |
| L3 | 2000 | 328.43 | 344.41 | 147.64 | 320.69 | 2.33 | L3 | Correct and correct |
| L3 | 3000 | 326.42 | 327.84 | 178.03 | 326.10 | 1.84 | L3 | Correct and correct |
| L3 | 4000 | 329.03 | 327.56 | 169.57 | 326.71 | 1.94 | L3 | Correct and correct |
Fig. 3 and fig. 4 show that when a single-phase high-resistance ground fault of 3000 Ω occurs at the tail end of the line L4, the original waveform change diagrams of zero sequence currents of all feeder lines before and after the input of the small parallel resistor and the filtered current waveform diagrams, and as a result, the fault treatment strategy suitable for the flexible grounding system can work correctly under different ground fault resistances, and has higher practicability.
The foregoing description and examples are only intended to illustrate the technical aspects of the present application, not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions.
Claims (7)
1. The flexible grounding system high-resistance fault line selection method based on the low-frequency transient zero-sequence current distortion rate is characterized by comprising the following steps of:
step 1: monitoring neutral point current in real time and calculating neutral point current amplitude mutation quantityIf it meets->Starting a fault detection system;
step 2: after short delay, if the fault disappears, returning to the step 1, namely, reducing the neutral point current amplitude to be below a threshold value, otherwise, putting into a parallel small resistor, and entering into the step 3;
step 3: filtering the original waveform of the zero sequence current of each outgoing line to obtain the waveform of the low-frequency transient zero sequence current of each outgoing line, and calculating the distortion rate and the polar error ratio of the low-frequency transient zero sequence current of each outgoing line in a specific time window；
Step 4: according toJudging the fault type->Judging that the bus is faulty, and judging that +.>And judging the line to be a line fault and regarding the line with the lowest low-frequency transient zero sequence current distortion rate as a fault line.
2. The method for selecting a high-resistance fault line of a flexible grounding system based on a low-frequency transient zero-sequence current distortion rate according to claim 1, wherein the abrupt change of the neutral point current amplitude in the step 1 is as follows:
wherein,and->The neutral point current amplitude and the neutral point maximum unbalanced current amplitude are respectively +.>Maximum unbalanced voltage amplitude of system is 144.337V, < >>Frequency angle frequency, reliability coefficient->1.5 @ is taken>Is the arc suppression coil inductance.
3. The flexible grounding system high-resistance fault line selection method based on the low-frequency transient zero-sequence current distortion rate according to claim 1, wherein the non-fault line low-frequency transient zero-sequence current in the step 3 is characterized in thatThe method comprises the following steps:
fault line low frequency transient zero sequence currentThe method comprises the following steps:
wherein,、/>the voltage amplitude of the fault point and the current amplitude of the arc suppression coil before the parallel small resistor is put into operation are respectively +.>、/>、The ground capacitance of the non-fault line, the total ground capacitance of the system and the ground capacitance of the fault line are respectively +.>、/>Respectively connecting the instantaneous fault point voltage and the arc suppression coil current initial phase angle of the small parallel resistor,vfor the system detuning degree, +.>Is parallel small resistance value->Is a transition resistance;
error rate ratio for distinguishing bus fault and outlet faultThe method comprises the following steps:
wherein,、/>and the maximum value and the minimum value of the low-frequency transient zero sequence current distortion rate in all outgoing lines are respectively obtained.
4. The method for high-resistance fault line selection of the flexible grounding system based on the low-frequency transient zero-sequence current distortion rate according to claim 1, wherein the specific time window in the step 3 is as follows: and 0s-0.02s after the input of the parallel small resistor.
5. The method for high-resistance fault line selection of flexible grounding system based on low-frequency transient zero-sequence current distortion rate according to claim 1, wherein the filter cut-off frequency in step 3 is as follows: 360Hz.
6. The method for selecting high-resistance fault lines of flexible grounding system based on low-frequency transient zero-sequence current distortion rate according to claim 1, wherein the method for distinguishing bus faults from outgoing line faults in the step 4 is as follows:it is determined that the bus bar has failed,and judging that the wire is out of order.
7. The method for high-resistance fault line selection of the flexible grounding system based on the low-frequency transient zero-sequence current distortion rate according to claim 1, wherein the line selection method for the line fault in the step 4 is as follows: and taking the line with the lowest low-frequency transient zero-sequence current distortion rate in the specific time window as a fault line.
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