CN115372683A - Novel fault direction discrimination method based on superimposed impedance - Google Patents
Novel fault direction discrimination method based on superimposed impedance Download PDFInfo
- Publication number
- CN115372683A CN115372683A CN202210881168.2A CN202210881168A CN115372683A CN 115372683 A CN115372683 A CN 115372683A CN 202210881168 A CN202210881168 A CN 202210881168A CN 115372683 A CN115372683 A CN 115372683A
- Authority
- CN
- China
- Prior art keywords
- fault
- current
- impedance
- phase
- fault occurs
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/14—Indicating direction of current; Indicating polarity of voltage
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/08—Measuring resistance by measuring both voltage and current
-
- 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
-
- 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
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
A novel fault direction judging method based on superimposed impedance comprises the steps of calculating normal working current of each phase circuit based on a mathematical model of a current power grid structure, and multiplying the working current by a reliable coefficient to serve as a fixed value for judging whether a fault occurs or not. Then the phase current and the phase voltage are sampled according to the set frequency,
and calculating and subtracting the result. And then comparing the difference result with a fixed value for judging whether the fault occurs or not to judge whether the short-circuit fault occurs or not. The variation of the voltage and current caused by the fault is calculated, and a superimposed impedance matrix is calculated. And finally, judging the direction of the fault according to the positive and negative of the superimposed impedance value. The superimposed impedance is positive and a fault occursIn the positive direction of protection, the superimposed impedance is negative, and the fault occurs in the reverse direction of protection. The method can not only correctly judge the fault direction under the condition of common faults, but also correctly judge under the conditions of high-impedance faults and serious faults close to the protection installation position.
Description
Technical Field
The invention relates to the technical field of relay protection of a power grid after a distributed power supply is connected, in particular to a novel fault direction judging method based on superimposed impedance.
Background
The distributed power supply is usually directly connected to a power distribution network below 35kV, and in order to timely cut off a short-circuited fault line in the low-voltage power distribution networks, simple and reliable current protection is usually adopted as main protection of the low-voltage power distribution networks connected to the distributed power supply. Due to the fact that the fault current direction is not fixed due to the fact that the distributed power source is connected, false operation of traditional current protection can be caused, and the novel relay protection capable of reliably judging the fault direction is important.
Today, many transmission networks, mesh distribution networks and modern smart grids have access to distributed power supplies, and these systems usually use the difference in voltage and current angle to determine the direction of a fault, but this method is unreliable in the event of a severe fault at high impedance and near-protection installations, and therefore new methods are needed to reliably determine the direction of a fault.
Disclosure of Invention
In order to solve the problems, a novel fault direction judging method based on superimposed impedance is provided.
The object of the invention is achieved in the following way:
a novel fault direction judging method based on superimposed impedance comprises the following steps:
step 1: firstly, calculating the normal working current of each phase circuit based on a mathematical model of the current power grid structure, and multiplying the working current by a reliable coefficient to be used as a fixed value for judging whether a fault occurs or not; then, the phase current and the phase voltage are sampled according to the set frequency, and the current i of the kth sampling point is sampled a (k) And the k-N sampling point current i a (k-N) by a (k)-i a (k-N) l is calculated, and the current i of the k-N sampling point is calculated a (k-N) and (k-2N) th sampling point current i a (k-2N) proceed with | i a (k-N)-i a (k-2N) | and taking the difference between the two calculated results; then comparing the difference result with a fixed value for judging whether the fault occurs to judge whether the short-circuit fault occurs;
step 2: when the judgment result is that the short-circuit fault occurs, calculating the variable quantity of voltage and current caused by the fault through phase voltage and phase current sampling values, and substituting the variable quantity into a fault direction criterion to calculate a superimposed impedance matrix; finally, judging the direction of the fault according to the positive and negative of the superimposed impedance value; if the superposed impedance is positive, the fault occurs in the positive direction of protection; if the superimposed impedance is negative, the fault occurs in the opposite direction of protection.
The specific steps of the step 1 are as follows: calculating normal working current I of each phase circuit based on mathematical model of current power grid structure n ，
Wherein S is the load power of the power grid, and U is the voltage of the power grid; the constant value for judging whether a fault occurs is set to 0.2I in consideration of the reliability factor of current protection n ，
Then, the phase current and the phase voltage are sampled according to the set frequency of 1kHz, whether a fault occurs is judged through a fault criterion, wherein the fault criterion is as the following formula (1), i a (k) Is the kth sample value of the current, i a (k-N) is the k-N sample value of the current, i a (k-2N) is the k-2N sampling value of the current, N is the number of current samples in one period, and the value range of k is 1-N;
||i a (k)-i a (k-N)|-|i a (k-N)-i a (k-2N)||≥0.2I n (1)
substituting the collected actual measurement phase current sampling value into the fault criterion to continuously compare with a fixed value for judging whether a fault occurs; and if the sampled value of the actually measured current is changed due to the short circuit, so that the fault discrimination inequality (1) is established, judging that the short circuit fault occurs in the line.
The specific steps of the step 2 are as follows:
calculating the variation delta V of the voltage caused by the fault at N sampling points in one period through phase voltage sampling values a ：
Wherein V a (k)，V a (k-1)，V a (k-N+1)，V a (k-N)，V a (k-1-N)，V a (k-2N + 1) are sampling values of phase voltages at k, k-1,k-N +1,k-N, k-1-N, k-2N +1 sampling points respectively; Δ V a (k)，ΔV a (k-1)，ΔV a (k-N + 1) is the voltage variation at the kth, kth-1 and kth-N +1 sampling points respectively;
these differences can be written in the form of a matrix, written as:
calculating the variation delta I of the current caused by the fault at N sampling points in one period through the phase current sampling value a ：
Wherein I (k), I a (k-1)，I a (k-N+1)，I a (k-N)，I a (k-1-N)，I a (k-2N + 1) are sampling values of phase current at k, k-1,k-N +1,k-N, k-1-N, k-2N +1 sampling points respectively; delta I a (k)，ΔI a (k-1)，ΔI a (k-N + 1) is the current variation at the kth, kth-1 and kth-N +1 sampling points respectively;
these differences can be written in the form of a matrix, written as:
further based on the relation between impedance and voltage and current, calculating a superposed impedance matrix [ Z ]] 1×1 The calculation method is as follows:
calculating the resulting superimposed impedance value [ Z ] according to the above formula] 1×1 Judging the direction of the fault; the superposed impedance is positive, and the fault occurs in the positive direction of protection; the superimposed impedance is negative and the fault occurs in the opposite direction of protection.
The reliability factor is 0.2; the set frequency is 1kHz.
The invention has the beneficial effects that: compared with the prior art, the method uses the sampling values of the instantaneous voltage and the current to calculate the superimposed impedance, not only can correctly judge the fault direction under the condition of general faults, but also can correctly judge under the conditions of high-impedance faults and serious faults which are closer to the protective installation position, and eliminates a plurality of problems and defects existing in the prior method.
Drawings
Fig. 1 is a schematic flow chart illustrating an implementation of a fault direction determination method based on superimposed impedance according to an embodiment of the present invention.
Fig. 2 is a diagram of a simulation circuit for verifying validity of the superimposed impedance-based fault direction determination method according to an embodiment of the present invention.
Fig. 3 is a simulation result diagram of the fault direction determination method when the single-phase short circuit occurs in the simulation circuit in the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure as claimed. Unless otherwise defined, all technical and scientific terms used herein have the same technical meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
The embodiment of the present invention provides a novel fault direction discrimination method based on superimposed impedance, and for better describing the embodiment of the present invention, a specific embodiment of the present invention will now be described with reference to the accompanying drawings, as shown in fig. 1, which is a schematic flow chart of the implementation of the novel fault direction discrimination method based on superimposed impedance, and the method includes:
step 11: firstly, calculating the normal working current of each phase circuit based on a mathematical model of the current power grid structure, and multiplying the working current by a reliability coefficient of 0.2 to be used as a fixed value for judging whether a fault occurs. Then, the phase current and the phase voltage are sampled according to the set frequency of 1kHz, and the kth sampling point is electrically connectedStream i a (k) And the k-N sampling point current i a (k-N) by a (k)-i a (k-N) l is calculated, and the current i of the k-N sampling point is calculated a (k-N) and (k-2N) th sampling point current i a (k-2N) proceed with | i a (k-N)-i a (k-2N) | is calculated, and the two results of the calculation are differenced. And comparing the difference result with a fixed value for judging whether the fault occurs to judge whether the short-circuit fault occurs.
The method comprises the following specific steps: calculating normal working current I of each phase circuit based on mathematical model of current power grid structure n ，
Wherein S is the load power of the power grid, and U is the voltage of the power grid. The constant value for judging whether the fault occurs is set to 0.2I in consideration of the reliability coefficient of the current protection n 。
Then, the phase current and the phase voltage are sampled according to the set frequency of 1kHz, whether a fault occurs is judged through a fault criterion, wherein the fault criterion is as the following formula (1), i a (k) Is the kth sample value of the current, i a (k-N) is the k-N sample value of the current, i a (k-2N) is the k-2N sampling value of the current, N is the number of current samples in one period, and the value range of k is 1-N;
||i a (k)-i a (k-N)|-|i a (k-N)-i a (k-2N)||≥0.2I n (1)
and substituting the collected actual measurement phase current sampling value into the fault criterion to continuously compare with a fixed value for judging whether the fault occurs. And if the sampled value of the actually measured current is changed due to the short circuit, so that the fault discrimination inequality (1) is established, judging that the short circuit fault occurs in the line.
Step 12: and then, calculating the variable quantities of voltage and current caused by faults through phase voltage and phase current sampling values, and substituting the variable quantities into a fault direction criterion to calculate a superimposed impedance matrix. And finally, judging the fault occurrence direction according to the positive and negative of the superposed impedance values. The superimposed impedance is positive, the fault occurs in the positive direction of protection, the superimposed impedance is negative, and the fault occurs in the negative direction of protection.
Calculating the variation delta V of the voltage caused by the fault at N sampling points in one period through phase voltage sampling values a ：
Wherein V a (k)，V a (k-1)，V a (k-N+1)，V a (k-N)，V a (k-1-N)，V a (k-2N + 1) are sampling values of phase-phase voltage at k, k-1,k-N +1,k-N, k-1-N, k-2N +1 sampling points respectively. Δ V a (k)，ΔV a (k-1)，ΔV a And (k-N + 1) is the voltage variation of the kth, the kth-1 and the kth-N +1 sampling points respectively.
These differences can be written in the form of a matrix, written as:
calculating the variation delta I of the current caused by the fault at N sampling points in one period through the phase current sampling value a ：
Wherein I (k), I a (k-1)，I a (k-N+1)，I a (k-N)，I a (k-1-N)，I a (k-2N + 1) are sampling values of phase current at k, k-1,k-N +1,k-N, k-1-N, k-2N +1 sampling points respectively. Delta I a (k)，ΔI a (k-1)，ΔI a And (k-N + 1) is the current variation of the kth, the kth-1 and the kth-N +1 sampling points respectively.
These differences can be written in the form of a matrix, written as:
further based on the relation between impedance and voltage and current, calculating a superposed impedance matrix [ Z ]] 1×1 The calculation method is as follows:
finally, the obtained superposed impedance value [ Z ] is calculated according to the formula] 1×1 Positive and negative, the direction of the fault occurrence is judged. The superimposed impedance is positive, the fault occurs in the positive direction of protection, the superimposed impedance is negative, and the fault occurs in the negative direction of protection.
The above equations are all exemplified by phase a, and similar equations apply to the other phases.
The above-mentioned novel fault direction discrimination method based on the superimposed impedance is verified by using specific examples.
By utilizing electromagnetic transient simulation software PSCAD, the effectiveness of the novel fault direction judging method based on the superimposed impedance is established by verifying the power grid simulation circuit shown in figure 2. The system voltage is 33kV, the system frequency is 50Hz, the lengths of the AB line and the BC line are both 10km, and the protection R is a relay protection device arranged at the B bus of the BC line.
Positive direction single-phase earth fault occurs: assuming that the system normally operates before the fault, for the protection R, a single-phase ground fault of the line BC in the positive direction occurs as shown in fig. 2 at 0.2s, and the curve in fig. 3 (a) is a superimposed impedance calculation result curve of the method provided by the present patent, it can be seen that the superimposed impedance in fig. 3 (a) becomes a positive value at 0.2s, and it can be correctly determined that the line BC in the positive direction has the fault. Because the positive direction of the fault occurrence protection R belongs to the protection range of the protection R, the protection R sends a tripping signal to trip.
Reverse direction single phase earth fault occurs: assuming that the system normally operates before the fault, for the protection R, a single-phase ground fault of the opposite direction line AB occurs as shown in fig. 2 at 0.2s, the curve in fig. 3 (b) is a superimposed impedance calculation result curve of the method provided by the present patent, and it can be seen that the superimposed impedance in fig. 3 (b) becomes a negative value at 0.2s, and it can be correctly determined that the line AB in the protection opposite direction has a fault. The protection R does not send out a tripping signal because the reverse direction of the protection R does not belong to the protection range of the protection R when the fault occurs.
Simulation results prove the accuracy and effectiveness of the fault direction judging method based on the superimposed impedance to different types of faults under various conditions. Compared with the traditional mode, the method is applicable to common fault conditions, and can correctly judge under the conditions of high-impedance faults and serious faults close to the protection installation position. Meanwhile, the method has the advantages of low calculation burden, short discrimination time and the like.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the overall concept of the present invention, and these should also be construed as the protection scope of the present invention.
Claims (4)
1. A novel fault direction distinguishing method based on superimposed impedance is characterized in that: the method comprises the following steps:
step 1: firstly, calculating the normal working current of each phase circuit based on a mathematical model of the current power grid structure, and multiplying the working current by a reliable coefficient to be used as a fixed value for judging whether a fault occurs or not; then, the phase current and the phase voltage are sampled according to the set frequency, and the current i of the kth sampling point is sampled a (k) And the k-N sampling point current i a (k-N) by a (k)-i a (k-N) l is calculated, and the current i of the k-N sampling point is calculated a (k-N) and (k-2N) th sampling point current i a (k-2N) proceed with | i a (k-N)-i a (k-2N) | and taking the difference between the two calculated results; then comparing the difference result with a fixed value for judging whether the fault occurs to judge whether the short-circuit fault occurs;
step 2: when the judgment result is that the short-circuit fault occurs, calculating the variable quantities of voltage and current caused by the fault through phase voltage and phase current sampling values, and substituting the variable quantities into a fault direction criterion to calculate a superimposed impedance matrix; finally, judging the fault occurrence direction according to the positive and negative of the superposed impedance values; if the superposed impedance is positive, the fault occurs in the positive direction of protection; if the superimposed impedance is negative, the fault occurs in the opposite direction of protection.
2. The novel fault direction judging method based on the superimposed impedance as claimed in claim 1, characterized in that: the specific steps of the step 1 are as follows: calculating normal working current I of each phase circuit based on mathematical model of current power grid structure n ，
Wherein S is the load power of the power grid, and U is the voltage of the power grid; the constant value for judging whether a fault occurs is set to 0.2I in consideration of the reliability factor of current protection n ，
Then, the phase current and the phase voltage are sampled according to the set frequency of 1kHz, and whether a fault occurs is judged through a fault criterion, wherein the fault criterion is as the following formula (1), i a (k) Is the kth sample value of the current, i a (k-N) is the k-N sample value of the current, i a (k-2N) is the k-2N sampling value of the current, N is the number of current samples in one period, and the value range of k is 1-N;
||i a (k)-i a (k-N)|-|i a (k-N)-i a (k-2N)||≥0.2I n (1)
substituting the collected actual measurement phase current sampling value into the fault criterion to continuously compare with a fixed value for judging whether a fault occurs; and if the sampled value of the actually measured current is changed due to the short circuit, so that the fault discrimination inequality (1) is established, judging that the short circuit fault occurs in the line.
3. The novel fault direction judging method based on the superimposed impedance as claimed in claim 1, characterized in that: the specific steps of the step 2 are as follows:
calculating the variation delta V of the voltage caused by the fault at N sampling points in one period through phase voltage sampling values a ：
Wherein V a (k)，V a (k-1)，V a (k-N+1)，V a (k-N)，V a (k-1-N)，V a (k-2N + 1) are sampling values of phase voltage at k, k-1,k-N +1,k-N, k-1-N, k-2N +1 sampling points respectively; Δ V a (k)，ΔV a (k-1)，ΔV a (k-N + 1) is the voltage variation at the kth, kth-1 and kth-N +1 sampling points respectively;
these differences can be written in the form of a matrix, written as:
calculating the variation delta I of the current caused by the fault at N sampling points in one period through the phase current sampling value a ：
Wherein I (k), I a (k-1)，I a (k-N+1)，I a (k-N)，I a (k-1-N)，I a (k-2N + 1) are sampling values of phase current at k, k-1,k-N +1,k-N, k-1-N, k-2N +1 sampling points respectively; delta I a (k)，ΔI a (k-1)，ΔI a (k-N + 1) is the current variation at the kth, kth-1 and kth-N +1 sampling points respectively;
these differences can be written in the form of a matrix, written as:
and calculating a superposed impedance matrix [ Z ] based on the relation between the impedance and the voltage and the current] 1×1 The calculation method is as follows：
Calculating the resulting superimposed impedance value [ Z ] according to the above formula] 1×1 Judging the direction of the fault; the superposed impedance is positive, and the fault occurs in the positive direction of protection; the superimposed impedance is negative and the fault occurs in the opposite direction of protection.
4. The novel fault direction judging method based on the superimposed impedance as claimed in claim 1, characterized in that: the reliability factor is 0.2; the set frequency is 1kHz.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210881168.2A CN115372683A (en) | 2022-07-20 | 2022-07-20 | Novel fault direction discrimination method based on superimposed impedance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210881168.2A CN115372683A (en) | 2022-07-20 | 2022-07-20 | Novel fault direction discrimination method based on superimposed impedance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN115372683A true CN115372683A (en) | 2022-11-22 |
Family
ID=84063480
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202210881168.2A Pending CN115372683A (en) | 2022-07-20 | 2022-07-20 | Novel fault direction discrimination method based on superimposed impedance |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115372683A (en) |
-
2022
- 2022-07-20 CN CN202210881168.2A patent/CN115372683A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Liao et al. | Online optimal transmission line parameter estimation for relaying applications | |
| RU2576340C2 (en) | Method and device for ground fault detection based on change in three-phase current | |
| CN103576053B (en) | A kind of voltage sag source localization method based on limited electric energy quality monitoring point | |
| Gao et al. | Design and evaluation of a directional algorithm for transmission-line protection based on positive-sequence fault components | |
| CN107632281B (en) | Measurement and control method of automatic wiring detection instrument of three-phase three-wire metering device | |
| CN105811383A (en) | Novel positive sequence impedance differential protection method of microgrid | |
| CN110927519B (en) | Active power distribution network fault positioning method based on mu PMU measurement value | |
| CN108614180B (en) | Single-phase earth fault line searching method | |
| CN111781461B (en) | Ground fault line selection and section determination method for small-current grounding power system | |
| CN110120666A (en) | A kind of voltage dip situation estimation method | |
| Katic et al. | Field testing of distribution state estimator | |
| Kang et al. | Analyses and judgment methods of single-phase broken-line fault for loaded distribution line | |
| CN109193595B (en) | Active power distribution network failure separation method based on current phase comparison | |
| CN110058127B (en) | Single-phase earth fault point identification method for non-effectively-grounded power distribution network | |
| Li et al. | Augmented state estimation method for fault location based on on-line parameter identification of PMU measurement data | |
| Katic et al. | Distribution state estimation field testing | |
| Duong et al. | A comparative case study of online voltage instability monitoring | |
| CN115372683A (en) | Novel fault direction discrimination method based on superimposed impedance | |
| Nikander et al. | Methods for earth fault identification and distance estimation in a compensated medium voltage distribution network | |
| CN114034985A (en) | Power distribution network asymmetric fault in-situ positioning method based on distributed power supply information | |
| CN115603286A (en) | Self-adaptive distance protection method for unbalanced short circuit of photovoltaic power supply tie line | |
| CN104578008A (en) | Zero-sequence direction element maloperation prevention method | |
| Wang et al. | Fault detection method for intelligent distribution network based on protected element model | |
| Bao-Wei et al. | Two-terminal fault location scheme based on distributed parameters of cable-overhead hybrid transmission line | |
| Dua et al. | Change in Sum of Power Based Fault Detection Method for Microgrid Utilizing μPMU |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |