CN110703040B - Distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference - Google Patents
Distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference Download PDFInfo
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- 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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- 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
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Abstract
The invention discloses a distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference, when a single-phase earth fault occurs in a distribution network, three-phase current data information of each section is acquired from a related current data acquisition device, and the three-phase current mutation of each section is calculated according to the information; then, processing the waveform of the phase current abrupt change quantity of each section by using the proposed waveform difference calculation method to obtain the difference characteristic quantity of each section; and finally, distinguishing upstream and downstream faults and healthy sections according to the difference characteristic quantity, and determining specific fault lines according to the power grid topology model. The method is not influenced by a system grounding mode and fault conditions, is not limited by a specific time period and a frequency band after the fault occurs, and has high positioning sensitivity and reliability.
Description
Technical Field
The invention relates to the field of power system relay protection, in particular to a distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference.
Background
A small-current grounding system is widely adopted in a 10kV medium-voltage distribution network in China, namely two grounding modes of a neutral point grounding without grounding or grounding through an arc suppression coil are adopted. Single-phase earth faults are the most common faults in low-current earthed power distribution networks, exceeding 80% of the total number of faults occurring thereon. After the power distribution system has single-phase earth faults, the three-phase line voltages still keep a symmetrical relation, continuous power supply to loads is not influenced, and therefore the power distribution system still allows the power distribution system to operate with faults for 1-2 hours so as to improve the reliability of power supply. However, if the fault is not eliminated for a long time, a series of more serious consequences such as burning of the electrical equipment can be caused.
Therefore, after a single-phase earth fault occurs in the low-current earth system, a fault point needs to be quickly found and cut off under the condition of ensuring uninterrupted power supply, so as to ensure safe and reliable operation of the power distribution network. However, in China, the distribution network line structure is complex, the neutral point grounding modes are not uniform, the distribution network single-phase grounding fault types are various, the fault rules are usually changeable and difficult to accurately grasp, and meanwhile, the single-phase grounding fault in the low-current grounding system also has the problems of weak steady-state electrical quantity, short transient process and the like which directly influence fault positioning, and the accurate positioning of the distribution network single-phase grounding fault is still very difficult.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems, the invention provides a distribution network single-phase earth fault positioning method based on the difference of the current mutation of the fault phase and the non-fault phase, which can be used for quickly and reliably positioning faults.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference comprises the following steps:
(1) judging that a single-phase earth fault occurs in the power distribution network, and acquiring three-phase current data of each section from a related current data acquisition device;
(2) calculating the three-phase current abrupt change quantity of each section;
(3) calculating the waveform difference of the phase current mutation quantity between every two phases of each section, and selecting the maximum value from the three results as the characteristic quantity of the phase current mutation quantity difference of the fault phase and the non-fault phase of the section;
(4) comparing the phase current mutation quantity difference characteristic quantities of all sections, judging the section with larger difference characteristic quantity as a fault upstream section, and judging the section with smaller difference characteristic quantity as a sound and fault downstream section;
(5) and (4) determining a specific fault section by combining the power distribution network topological structure according to the judgment result in the step 4.
Further, in step 1, the acquired three-phase current data information of each segment at least includes phase current data of a non-fault normal operation state in two cycles before the fault occurs to phase current data of a fault operation state in three cycles after the fault occurs.
Further, in step 2, a three-phase current sudden change calculation formula after each section fails is shown:
wherein, Δ inRepresents the phase current abrupt change, t, corresponding to the nth sampling point in the period after the fault0At the approximate time of failure, T is the power frequency period, NsIs the number of sampling points contained in a power frequency period, n is an integer and is not less than 0<Ns。
Further, in the step 3, the waveform difference calculating method includes:
wherein d isA-BRepresenting the waveform difference between waveform A and waveform B, iA(n)、iB(N) correspond to the sample values, N, of the waveform A, B at the nth sample point, respectivelysIs the number of sampling points contained in a power frequency period, n is an integer and is not less than 0<Ns。
Further, in the step 4, the method for defining the size of the difference feature quantity includes: and judging the section with the difference characteristic quantity greater than 70% of the maximum difference characteristic quantity as a fault upstream section, and judging the section with the difference characteristic quantity less than or equal to 70% of the maximum difference characteristic quantity as a sound and fault downstream section.
Further, in step 5, fault location is performed according to the following logic: if the parts previously determined as the upstream sections are all adjacent sections, the part determined as the upstream section, which is positioned at the rearmost end (farthest from the bus) of the topology, is a faulty section; if the sections are determined to be partially distributed or the majority of the sections in the system are determined to be upstream sections, the bus fault is determined to occur.
Has the advantages that: compared with the prior art, the distribution network single-phase earth fault positioning method based on the fault phase non-fault phase current mutation difference has the following remarkable advantages: the analysis and judgment are carried out only through the three-phase current data, and the method can be easily realized under the prior art condition; the fault characteristics of the phase current sudden change quantity are used in the temporary steady-state stage after the single-phase earth fault occurs, the accurate judgment of the fault moment is not relied on, and the influence of a system grounding mode and the single-phase earth fault condition is avoided; the proposed waveform difference calculation method can well distinguish an upstream section from a downstream or healthy section of the single-phase earth fault by combining the waveform of the phase current break variable of the fault non-fault phase of a specific section, and has high positioning reliability.
Drawings
FIG. 1 is a schematic diagram of system current distribution after a single-phase earth fault of a distribution network;
FIG. 2 is a vector diagram of phase voltage step quantities;
fig. 3 is a flow chart of the distribution network single-phase earth fault location of the present invention;
FIG. 4 is a schematic diagram of a PSCAD simulation verification system;
FIG. 5 is a waveform diagram of three-phase current break variables of a fault line in a simulation example;
fig. 6 is a waveform diagram of three-phase current break variables of a non-fault line in a simulation example.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
The invention discloses a distribution network single-phase earth fault positioning method based on phase current mutation difference of fault phases and non-fault phases, and aims to solve the problem of single-phase earth fault positioning of a distribution network.
For the phase current break variable, a distribution network low current grounding system is specifically taken as an example for explanation, and when a single-phase grounding fault occurs, the composition of the current in the system is shown in fig. 1. For the distribution network system before the fault occurs, the phase current of each line in the normal state consists of load current and line-to-ground capacitance current. The amplitude and the phase of the three-phase line current are still kept unchanged after the small current grounding system fails, so that the load current of each phase of the line does not change before and after the fault. Therefore, the phase current variation of each phase of each line is mainly reflected in the variation of the capacitance current to ground.
For each phase of the non-faulted line, the non-faulted phase of the faulted line, and the downstream segment of the faulted phase of the faulted line, the phase current break amount is:
wherein, Δ u is the sudden change of phase voltage of the phase of the line, and C is the capacitance value to ground of the phase of the line.
For the upstream section of the fault phase of the fault line, the phase current abrupt change quantity comprises the change quantity of the capacitance current to the ground, and also comprises the grounding current flowing through the grounding point, namely:
wherein, IkIs the ground current.
Meanwhile, the vector diagram analysis is carried out on the phase voltage abrupt change quantity related to the voltage abrupt change quantity, as shown in fig. 2, the three-phase voltage vector abrupt change quantity vectors of all lines are completely the same after the single-phase earth fault occurs, and the three-phase voltage vector abrupt change quantity vectors are zero sequence voltages, namely delta ua＝Δub＝Δuc＝u0. Therefore, in conjunction with the characteristics associated with the phase voltage abrupt change, the characteristics of the phase current abrupt change may be summarized as follows:
for the non-fault line and the downstream of the fault line, the three-phase voltage sudden change quantity is kept consistent, so the corresponding phase current sudden change quantity is also kept consistent, namely the three-phase current sudden change quantity is equal in amplitude and consistent in waveform.
For the upstream of the fault line, the current abrupt change amount of the phase of the fault phase and the other two non-fault phases on the fault line is obviously different because the grounding current flows to the ground through a fault point on the fault phase.
Based on the characteristics, the single-phase earth fault of the power distribution network can be positioned. Meanwhile, for the phase current sudden change characteristic, the invention provides a waveform difference representation method.
For two waveforms A, B with the same sampling frequency, calculating the amplitude difference of the corresponding sampling points of the two waveforms at the same time and squaring, then accumulating the results in a power frequency period, and finally obtaining a result representing the difference of the two waveforms, as shown in the formula:
wherein N issRepresenting the number of sampling points, i, contained in a power frequency cycleA(n)、iBAnd (n) respectively corresponding to the sampling values of the two different waveforms at the nth sampling point.
By utilizing the waveform difference representation method and combining with phase current mutation fault characteristic analysis, the invention provides a distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference, as shown in fig. 3, the specific steps are as follows:
(1) after the single-phase earth fault of the power distribution network is judged, three-phase current data information of each section is obtained from a related current data acquisition device;
the obtained three-phase current data information of each section at least comprises phase current data of a non-fault normal operation state in two periods before fault occurrence to phase current data of a fault operation state in three periods after fault occurrence.
(2) Calculating the three-phase current abrupt change quantity of each section;
and calculating the three-phase current break variable corresponding to the second period after the fault of each section by the following formula:
wherein, Δ inThe phase current abrupt change quantity, t, corresponding to the nth sampling point of the second period after the fault is shown0At the approximate time of failure, T is the power frequency period, NsIs the number of sampling points contained in a power frequency period, n is an integer and is not less than 0<Ns。
(3) Calculating the waveform difference of the phase current mutation quantity between every two phases of each section, and selecting the largest value from the three results as the characteristic quantity of the phase current mutation quantity difference of the fault non-fault phase of the section;
the waveform difference calculation method comprises the following steps:
wherein d isA-BRepresenting the waveform difference between waveform A and waveform B, iA(n)、iB(N) correspond to the sample values, N, of the waveform A, B at the nth sample point, respectivelysIs a power frequency periodThe number of sampling points contained in the sampling device, n is an integer and is not less than 0<Ns。
(4) Comparing the difference characteristic quantities of phase current abrupt change quantities of all sections, judging the section with larger difference characteristic quantity as a fault upstream section, and judging the section with smaller difference characteristic quantity as a sound and fault downstream section;
the definition method of the difference characteristic quantity comprises the following steps: and judging the section with the difference characteristic quantity greater than 70% of the maximum difference characteristic quantity as a fault upstream section, and judging the section with the difference characteristic quantity less than or equal to 70% of the maximum difference characteristic quantity as a sound and fault downstream section.
(5) And (4) determining a specific fault section by combining the power distribution network topological structure according to the judgment result in the step 4.
Fault location is carried out according to the following logic, specifically: if the parts previously determined as the upstream sections are all adjacent sections, the part determined as the upstream section, which is positioned at the rearmost end (farthest from the bus) of the topology, is a faulty section; if a portion of the segments determined to be upstream segments are distributed or if most of the segments in the system are determined to be upstream segments, then a bus fault is considered to have occurred.
To further prove the correctness of the method of the present invention, a PSCAD simulation model as shown in FIG. 4 was established, i.e., a main transformer of a 35kV substation wired via Y/D was configured with a 10kV system in the form of a single bus, in which 8 different sections including the fault section were set up in total. In addition, the grounding mode of the system is adjusted in a mode that a grounding transformer is connected to a bus, and the grounding mode of the whole system is determined to be ungrounded or grounded through an arc suppression coil by changing the grounding mode of the star-shaped side of the grounding transformer.
The specific simulation and line equipment parameters are as follows:
the system frequency is 50Hz, the simulation duration is 2s, the section 2 generates C-phase single-phase ground fault in the middle section at the moment of 0.5s, the phase current sampling points are all arranged at the front end of each section, the simulation and sampling frequency is 50kHz, wherein:
a circuit: the line types in the system comprise pure overhead, pure cable and cable overhead mixed lines, and are specifically built by a frequency correlation model;
a main transformer: sN2MVA, Y/D wiring;
a distribution transformer: sN0.5MVA, D/Yn wiring;
loading: the load capacity accounts for 80% of the distribution transformer capacity, and the power factor is 85%;
an arc suppression coil: when the system is a system grounded through an arc suppression coil, an overcompensation mode is adopted, and the degree of compensation is 10%.
In the simulation model, when the system grounding mode is that the neutral point is grounded through the arc suppression coil, a metallic grounding fault with a fault initial phase angle of 90 ° occurs at the fault point, the waveforms of the three-phase current abrupt change quantities of the fault section 2 and the non-fault section 6 can be obtained as shown in fig. 5 and 6 according to the process two, and simultaneously, the simulation is performed under three different systems and typical fault conditions that the system is a neutral point ungrounded system, the grounding point transition resistance is 200 ohms, and the fault initial phase angle is 0 °, so that the line difference characteristic quantity and the positioning result shown in table 1 can be respectively obtained, and the current unit in the waveforms and the calculation result is kA.
In order to further highlight the superiority of the method, besides the difference calculation of the phase current mutation amount of the second period after the fault selected in the specific embodiment, the calculation and line selection results of the 3 rd and 4 th periods after the fault are also additionally displayed.
TABLE 1
As can be seen from fig. 5 and 6, the simulation results are consistent with the previous summary of the characteristics of the phase current inrush variables and are applicable to any transient state phase after a fault occurs. Meanwhile, as can be seen from the data and the results in table 1, the fault non-fault phase difference method provided by the invention can show significant numerical difference for the upstream of the fault line, the downstream of the fault line and the non-fault line under various system types and fault conditions, and has very high positioning sensitivity and reliability.
Claims (5)
1. A distribution network single-phase earth fault positioning method based on fault phase and non-fault phase current mutation difference is characterized by comprising the following steps:
(1) judging that a single-phase earth fault occurs in the power distribution network, and acquiring three-phase current data of each section from a related current data acquisition device;
(2) calculating the three-phase current abrupt change quantity of each section;
(3) calculating the waveform difference of the phase current mutation amount between every two phases of each section, and selecting the maximum value from the waveform difference of the phase current mutation amount between every two phases as the characteristic quantity of the phase current mutation amount difference of the fault phase and the non-fault phase of the section; the waveform difference calculation method comprises the following steps:
wherein d isA-BRepresenting the waveform difference between waveform A and waveform B, iA(n)、iB(N) correspond to the sample values, N, of the waveform A, B at the nth sample point, respectivelysIs the number of sampling points contained in a power frequency period, n is an integer and is not less than 0<Ns；
(4) Comparing the phase current mutation quantity difference characteristic quantities of all sections, judging the section with larger difference characteristic quantity as a fault upstream section, and judging the section with smaller difference characteristic quantity as a sound and fault downstream section;
(5) and (4) determining a specific fault section by combining the power distribution network topological structure according to the judgment result in the step 4.
2. The distribution network single-phase ground fault location method based on the difference between the current mutation quantities of the faulted phase and the non-faulted phase according to claim 1, wherein the three-phase current data information of each section obtained in step 1 at least comprises phase current data of a non-faulted normal operation state in two cycles before the fault occurs to phase current data of a faulted operation state in three cycles after the fault occurs.
3. The distribution network single-phase earth fault location method based on the difference between the current jump quantities of the fault phase and the non-fault phase according to claim 1, wherein in the step 2, a calculation formula of the three-phase current jump quantity after the fault of each section is given as follows:
wherein, Δ inRepresents the phase current abrupt change, t, corresponding to the nth sampling point in the period after the fault0At the approximate time of failure, T is the power frequency period, NsIs the number of sampling points contained in a power frequency period, n is an integer and is not less than 0<Ns。
4. The distribution network single-phase earth fault location method based on the difference between the phase current mutation of the fault phase and the phase current mutation of the non-fault phase as claimed in claim 1, wherein in the step 4, the definition method of the difference characteristic quantity is as follows: and judging the section with the difference characteristic quantity greater than 70% of the maximum difference characteristic quantity as a fault upstream section, and judging the section with the difference characteristic quantity less than or equal to 70% of the maximum difference characteristic quantity as a sound and fault downstream section.
5. The distribution network single-phase earth fault location method based on the difference of the current mutation of the fault phase and the non-fault phase according to claim 1, wherein in the step 5, fault location is performed according to the following logic:
if the parts previously determined as the upstream sections are all adjacent sections, the part determined as the upstream section at the last end of the topological structure is a fault section;
if the sections are determined to be partially distributed or the majority of the sections in the system are determined to be upstream sections, the bus fault is determined to occur.
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| CN111208387B (en) * | 2020-02-17 | 2022-03-11 | 国电南瑞南京控制***有限公司 | Distribution network single-phase grounding line selection method based on synchronous phase current fault component comparison |
| CN111983510B (en) * | 2020-07-17 | 2023-08-18 | 珠海许继电气有限公司 | Single-phase ground fault phase selection method and system based on phase voltage and current abrupt change |
| CN112255499B (en) * | 2020-10-10 | 2021-09-07 | 重庆大学 | Phase current amplitude based power distribution network disconnection fault positioning and identifying method and system |
| CN112485588B (en) * | 2020-11-11 | 2024-02-06 | 云南电网有限责任公司临沧供电局 | Permanent high-resistance fault section positioning method based on cascade H-bridge control |
| CN112782528B (en) * | 2020-12-31 | 2023-07-18 | 西安理工大学 | Power distribution network fault section positioning method by utilizing PMU |
| CN113156267B (en) * | 2021-04-27 | 2024-02-02 | 福州大学 | Power distribution network ground fault section selection method and system |
| CN113341272A (en) * | 2021-06-01 | 2021-09-03 | 陕西理工大学 | Transient quantity-based power distribution network single-phase earth fault section positioning system and method |
| CN114552581A (en) * | 2022-04-26 | 2022-05-27 | 国网天津市电力公司电力科学研究院 | Regional autonomous method, device and equipment for power distribution network |
| CN114879085B (en) * | 2022-07-12 | 2022-10-04 | 北京智芯半导体科技有限公司 | Single-phase earth fault identification method and device, electronic equipment and medium |
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| CN104865496B (en) * | 2015-04-28 | 2018-02-13 | 国家电网公司 | Distribution line fault section location method based on differential offset degree |
| CN105842583B (en) * | 2016-03-25 | 2018-09-04 | 西安交通大学 | Distribution single-phase earthing Section Location based on faulted phase voltage and jump-value of current |
| CN106154116B (en) * | 2016-08-09 | 2018-12-04 | 国电南瑞科技股份有限公司 | A kind of distribution net work earthing fault localization method |
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