CN111257699A - Low-current grounding power grid line selection system based on impedance detection - Google Patents
Low-current grounding power grid line selection system based on impedance detection 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
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- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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Abstract
The invention discloses a small current grounding power grid line selection system based on impedance detection, which comprises: the device comprises a data acquisition module, a spectrum analysis module, an impedance calculation module and a line selection algorithm module. The data acquisition module acquires zero-sequence voltage signals and branch zero-sequence current signals of a power grid. And the frequency spectrum analysis module is used for carrying out frequency spectrum analysis on the zero-sequence voltage signals and the branch zero-sequence current signals of the power grid. And the impedance calculation module searches a grounding characteristic frequency band on the basis of the frequency spectrum analysis result and calculates the characteristic impedance of each branch circuit in the characteristic frequency band. And the line selection algorithm module is used for identifying the ground fault and performing line selection algorithm analysis according to the characteristic impedance data of each branch circuit so as to judge the ground branch circuit. The line selection system is based on the impedance characteristics of each branch in the power grid, and is irrelevant to the running state of the power grid, the specific grounding process and the like. The grounding circuit can be reliably, accurately and quickly selected according to different impedance characteristics of each branch circuit.
Description
Technical Field
The invention relates to the field of power systems, in particular to a low-current grounding power grid line selection system based on impedance detection.
Background
In the 6-66 kV power grid in China, a neutral point non-effective grounding mode, namely a grounding mode that a neutral point is not grounded or is grounded through an arc suppression coil, is mainly adopted, and the power grid adopting the two grounding modes is generally called a low-current grounding power grid.
In a low-current grounding power grid, the most common single-phase grounding fault accounts for more than 80% of the total faults. After the single-phase earth fault occurs, the normal two-phase earth-to-earth voltage can rise to the line voltage, which can cause the voltage of the whole power grid to rise, and cause the potential insulation weak link of the power grid to be punctured, so that the single-phase earth fault develops into an interphase short-circuit fault, the line is tripped, the equipment and personnel safety are damaged, and the reliable operation of the power grid is seriously influenced.
Therefore, when a single-phase grounding fault occurs in the power grid, a line with the single-phase grounding must be found as soon as possible, namely, the 'grounding line selection' is carried out, so that the fault can be eliminated as soon as possible, the fault is prevented from being expanded, the safety of equipment and personnel is ensured, and the power grid can run safely.
The existing line selection can be roughly divided into a transient method, an injection method and the like, wherein:
the transient method mainly analyzes high-frequency transient signals contained in voltage and current signals in the grounding process, and finds the branch with the largest transient signal in all branches, namely the grounding branch. The core of the transient method is extraction of transient signals in the grounding process, and as the frequency bands of the transient signals grounded each time are different, the corresponding grounding transient signals to be extracted are also different. However, the transient method can only extract signals of a certain frequency band from the aspects of calculation amount and algorithm implementation, which causes a fault identification error of a part of the transient method. Meanwhile, for faults with high grounding resistance, due to the inhibition effect of the resistance, no obvious transient process exists, the extraction of a transient signal is difficult, and a transient method cannot be used.
The injection method is to inject a special signal into the zero sequence loop of the power grid, the signal can only flow back to the power grid from the grounding loop, and as long as the special signal is detected, the branch where the special signal is located is the grounding branch. When the injection method is implemented, signal injection equipment is additionally added in a power grid besides primary line selection equipment, so that the equipment cost is undoubtedly increased. Meanwhile, in order to ensure that the injected signals do not have negative effects on the power grid, the injected signals cannot be too large, and in addition, the loss of the power grid to the injected signals is reduced, so that the special signals which can be actually fed back to the power grid are very small, and the detection is difficult.
Document CN103048582A describes a negative sequence impedance angle-based single-phase grounding line selection method, which calculates the phase angle of the negative sequence impedance of each branch by collecting the three-phase voltage of the power grid and the three-phase current of each branch, and then uses the range of the negative sequence impedance phase angle to judge the grounding branch. In practice, the negative sequence component of the branch occurs mainly in the phase-to-phase short-circuit process, not in the single-phase grounding process. The single-phase grounding process is more essential to the impedance of the zero-sequence loop. Document CN105067948A describes a small current grounding line selection device and a single-phase grounding detection method, which are implemented by detecting line impedance variation and voltage-current phase difference. The calculated impedance is the amplitude of the load complex impedance at the fundamental frequency (50Hz), and the voltage-current phase angle difference is actually the phase angle of the load complex impedance. Both negative sequence impedance and load impedance are seriously influenced by the load condition and fault process of the line, and different line loads and different fault processes have different negative sequence impedance and load impedance, namely different impedance amplitudes and impedance phase angles. It is practically difficult to accurately determine the ground branch by the negative sequence or load impedance phase angle alone.
Document 103207352a describes a fault line selection method for achieving single-phase grounding of a power distribution network by using a line selection impedance magnitude characteristic. The zero sequence voltage of the power grid before and after the switching of the middle resistor and the zero sequence current of each branch are measured, then the zero sequence current before the switching of the middle resistor is converted into the zero sequence current after the switching of the middle resistor, and finally the so-called line selection impedance is calculated. The essence is that the current generated by the medium resistance can only flow back to the system through the grounding branch circuit, so that the current of the grounding branch circuit is increased; and the current after the normal branch circuit is converted is approximately unchanged. Therefore, the 'line selection impedance' of the grounding branch is smaller, and the 'line selection impedance' of the normal branch is larger. However, in actual operation, especially when the neutral point voltage is low and the current increment generated after the medium resistor is put into use is small, the calculated "line selection impedance" will be relatively high and is difficult to distinguish from the "line selection impedance" of the normal branch, and therefore the line selection accuracy is greatly reduced.
Therefore, no matter the transient method, the injection method or the existing impedance-based line selection, the problems of blind spots which cannot be processed, influence of line operation conditions, influence of a grounding process and the like exist. It is most reliable only to find a line selection that does not depend on the operating conditions of the power grid, on the specific grounding process, on additional equipment, or on the characteristics of the line itself.
Disclosure of Invention
The invention provides a low-current grounding power grid line selection system based on impedance detection, aiming at the problems in the prior art, the system only reflects the zero-sequence impedance to the ground of the characteristic of each branch by measuring the independence of the grounding process and the external signal of each branch in the power grid after grounding occurs, and realizes reliable, accurate and rapid selection of a grounding line in the low-current grounding power grid, thereby improving the operation safety and reliability of the power grid and ensuring the safety of equipment and personnel.
In order to solve the technical problems, the invention is realized by the following technical scheme:
the invention provides a small current grounding power grid line selection system based on impedance detection, which is characterized by comprising the following components: the system comprises a data acquisition module, a spectrum analysis module, an impedance calculation module and a line selection algorithm module;
and the data acquisition module is used for acquiring power grid zero-sequence voltage and branch zero-sequence current signals required by impedance detection. And transmitting the collected power grid zero sequence voltage and branch zero sequence current signals to the frequency spectrum analysis module and the line selection algorithm module.
And the frequency spectrum analysis module receives a starting command from the line selection algorithm module, receives power grid zero sequence voltage and branch zero sequence current signals of the data acquisition module, and performs frequency spectrum analysis on the signals. The result of the spectrum analysis is input to an impedance calculation module.
The impedance calculation module receives the spectrum analysis result from the spectrum analysis module, finds the characteristic frequency band when the ground is connected, calculates the characteristic impedance of each branch in the characteristic frequency band, and inputs the calculated characteristic impedance of each branch into the line selection algorithm module.
The line selection algorithm module receives the voltage signal from the acquisition module, identifies faults and starts the spectrum analysis module after the faults occur; and receiving branch characteristic impedance data from the impedance calculation module, and performing line selection algorithm analysis according to the data so as to judge the grounding branch.
Preferably, the small-current grounding power grid line selection system based on impedance detection is characterized in that the data acquisition module acquires zero-sequence voltage signals and branch zero-sequence current signals of a power grid. In order to ensure the accuracy of subsequent spectrum analysis and impedance calculation, the module adopts the multi-path synchronous and high-speed sampling technology. Wherein:
the multi-path synchronous sampling can meet the requirement of full synchronous acquisition of 100 paths of alternating voltage or current with a synchronous error not exceeding 1 mu S, and ensures that the phase error of each alternating current is minimum during subsequent spectrum analysis and impedance calculation;
the multi-path high-speed sampling can carry out high-speed acquisition of each path of alternating voltage or current above 12.8kHz, and ensures that the subsequent frequency spectrum analysis and impedance calculation have enough frequency bandwidth.
Preferably, the small-current grounding power grid line selection system based on impedance detection is characterized in that the spectrum analysis module performs spectrum analysis on voltage and current signals. In order to process the high-frequency signal generated in the grounding process and avoid the frequency spectrum aliasing caused by the high-frequency signal, a fast Fourier analysis algorithm of adding a Hamming window is adopted.
Preferably, the small-current grounding power grid line selection system based on impedance detection is characterized in that the impedance calculation module calculates a characteristic frequency band of zero-sequence voltage and characteristic impedance of each branch by taking frequency spectrum characteristic data of zero-sequence voltage and zero-sequence current signals from the frequency spectrum analysis module as input. Wherein:
the characteristic frequency band of the zero sequence voltage is based on different grounding processes after grounding occurs, the frequency bands of the generated zero sequence voltage signals are different, and the frequency band with the most obvious grounding corresponding to the zero sequence voltage signal needs to be found for each grounding. Generally speaking, in the grounding process, the frequency range included by the adjacent 3 frequency points with the maximum zero sequence voltage amplitude is the characteristic frequency band of the zero sequence voltage. And the central frequency point of the characteristic frequency band is a characteristic frequency. The interval frequency of adjacent frequency points is 50 Hz.
The characteristic impedance of each branch is the vector sum of the zero sequence voltage of the power grid after grounding and the vector ratio of each frequency point of the zero sequence current of each branch in the characteristic frequency band. Since the characteristic frequency band generally includes 3 frequency points, the calculation method of the characteristic impedance is as follows:
after the grounding occurs, the characteristic impedance of each branch reflects the parallel sum of the ground zero sequence impedances of other normal branches for the grounding branch; for the normal branch, it reflects the zero sequence impedance to ground of the normal branch itself. The characteristic impedance of the ground branch is therefore the smallest of all branches and the direction of its impedance differs the most from the normal branch.
Preferably, the line selection system of the low-current grounded power grid based on impedance detection is characterized in that the line selection algorithm module further includes: fault identification submodule, fault phase judge submodule, line selection judge submodule, wherein:
and the fault identification submodule receives the zero-sequence voltage data from the data acquisition module and then calculates the effective value of the zero-sequence voltage by adopting a root-mean-square algorithm. When the zero sequence voltage effective value exceeds a preset fault voltage value, a fault is considered to occur, the initial time of the fault occurrence is recorded, and a spectrum analysis module is started; and when the zero sequence voltage is recovered to be below the set fault voltage value, the fault is considered to be ended, the end time of the fault is recorded, and the spectrum analysis module is stopped.
And the fault phase judgment submodule receives the system three-phase voltage data from the data acquisition module and then calculates the effective value of each phase voltage by adopting a root mean square algorithm. And after the fault identification submodule judges that the fault occurs, the submodule identifies and records the phase with the lowest phase voltage as the fault phase.
The line selection judgment submodule receives the characteristic impedance of each branch from the impedance calculation module, firstly finds the first three branches with the minimum characteristic impedance module value and the impedance module value smaller than the set impedance maximum value, and then finds the branch with the maximum phase difference between every two branches in the impedance direction as the grounding branch. And if the branch meeting the condition cannot be found, the bus is judged to be grounded.
Preferably, the low-current grounding power grid line selection system based on impedance detection is characterized in that the line selection result of the grounding line selection module includes: one or more of a grounding branch, a grounding bus, a grounding phase, grounding time and recovery time;
the grounding branch circuit is used for indicating the actually grounded branch circuit, and if no branch circuit is grounded, the bus is indicated to be grounded;
the grounding bus is used for indicating the bus where the grounding branch is located;
the grounding phase is used for indicating a fault phase in which a grounding fault occurs;
the grounding time is used for indicating the initial time of the occurrence of the grounding fault;
the recovery time is used to indicate an end time at which the ground fault disappears.
Preferably, the impedance detection-based low-current grounding power grid line selection is characterized in that the spectrum analysis module and the impedance calculation module only need to operate after a grounding fault occurs. When the power grid has no ground fault, the zero-sequence voltage of the power grid is very small and the zero-sequence current of each branch is also very small according to the electrical characteristics of the power grid, and the calculated characteristic frequency and characteristic impedance are inaccurate and cannot be used for calculating a line selection algorithm. Only when the system is in single-phase grounding, the zero sequence voltage and the zero sequence current of each branch are high enough, the calculated characteristic frequency band and the calculated characteristic impedance are accurate enough, and the characteristic frequency band and the calculated characteristic impedance can be used for line selection calculation.
Preferably, the small-current grounding power grid line selection system based on impedance detection is characterized in that the impedance and the characteristic impedance refer to zero-sequence to ground complex impedance of a zero-sequence loop of a line. The characteristic signal can be clearly used as a characteristic signal for identifying the grounding fault, and the grounding branch can be quickly and accurately judged by calculating the characteristic impedance.
Compared with the prior art, the invention has the following advantages:
(1) the invention relates to a small-current grounding power grid line selection system based on impedance detection, which is based on the impedance characteristics of each branch in a power grid, is only related to the electrical design parameters, the manufacturing process and the installation position of the line, and is not related to the operation working condition, the specific grounding process and an external signal of the power grid, so that a grounding line can be selected reliably, accurately and quickly according to the difference of the impedance characteristics of each branch.
(2) The small-current grounding power grid line selection system based on impedance detection can be widely applied to various 6-66 kV power grid systems, comprises a neutral point grounding system through an arc suppression coil and a neutral point non-grounding system, and can well match line selection requirements when equipment such as a medium resistor, a small resistor and an active arc suppression coil (arc suppression cabinet) is adopted in the existing system. The line selection requirements of various field operation conditions are met.
Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.
Drawings
Embodiments of the invention are further described below with reference to the accompanying drawings:
FIG. 1 is a block diagram of the modules that make up the system of the preferred embodiment of the present invention;
FIG. 2 is a system internal data flow diagram of the preferred embodiment of the present invention;
FIG. 3 is a block diagram of a spectrum analysis module according to a preferred embodiment of the present invention;
FIG. 4 is a block diagram of an impedance calculation module according to a preferred embodiment of the present invention;
FIG. 5 is a block diagram of a module structure of a line selection algorithm according to a preferred embodiment of the present invention;
FIG. 6 is a waveform diagram illustrating an exemplary embodiment of the present invention.
FIG. 7 is a voltage spectrum diagram of the preferred embodiment of the present invention.
Fig. 8 is a diagram of the current spectrum of the ground branch according to the preferred embodiment of the present invention.
FIG. 9 is a graph of the calculated characteristic impedance according to the preferred embodiment of the present invention.
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
An embodiment of a low-current grounding power grid line selection system based on impedance detection according to the present invention is described in detail with reference to fig. 1, and as shown in fig. 1, the low-current grounding power grid line selection system includes: the system comprises a data acquisition module 1, a spectrum analysis module 2, an impedance calculation module 3 and a line selection algorithm module 4; the data acquisition module 1 is used for acquiring power grid zero sequence voltage and branch zero sequence current signals required by impedance detection. Transmitting the collected power grid zero sequence voltage and branch zero sequence current signals to a frequency spectrum analysis module 2 and a line selection algorithm module 4; and the frequency spectrum analysis module 2 receives the starting command from the line selection algorithm module 3, receives the power grid zero sequence voltage and branch zero sequence current signals of the data acquisition module 1, and performs frequency spectrum analysis on the signals. The result of the spectrum analysis is input into an impedance calculation module 3; the impedance calculation module 3 receives the spectrum analysis result from the spectrum analysis module 2, finds the characteristic frequency band when the ground is connected, calculates the characteristic impedance of each branch in the characteristic frequency band, and inputs the calculated characteristic impedance of each branch into the line selection algorithm module 4; the line selection algorithm module 4 is used for receiving the voltage signals from the acquisition module 1, identifying faults and starting the spectrum analysis module 2 after the faults occur; and receiving branch characteristic impedance data from the impedance calculation module 3, and performing line selection algorithm analysis according to the data so as to judge the grounding branch.
In the embodiment, three-phase voltages Ua, Ub and Uc of a power grid, zero-sequence voltage U0 and zero-sequence currents of 4 branches, namely a branch I-1 current I01, a branch I-2 current I02, a branch I-3 current I03 and a branch I-4 current I04 are collected. And ground fault simulation was performed on branch I-1.
The specific implementation of each module in the above embodiments is described in detail below:
1. a data acquisition module, as shown in fig. 2:
the module collects three-phase voltages Ua, Ub and Uc from a power grid, zero-sequence voltage U0 and zero-sequence currents I01, I02, I03 and I04 of 4 branches. For the acquired result, the data acquisition module 1 inputs the three-phase voltage Ua, Ub and Uc and the zero-sequence voltage U0 data into the line selection algorithm module 4; the data acquisition module 1 inputs zero sequence voltage U0 and zero sequence currents I01, I02, I03 and I04 of 4 branches into the spectrum analysis module.
The acquisition rate of the data acquisition module is 12.8kHz, the acquisition of all voltage and current signals is completely synchronous, and the time synchronization error among the signals is not more than 1 muS, so that the accuracy of signals required by subsequent frequency spectrum analysis and grounding line selection can be effectively ensured.
2. A spectrum analysis module, as shown in fig. 2 and 3:
the module receives zero sequence voltage U0 and zero sequence currents I01, I02, I03 and I04 of 4 branches from the data acquisition module 1, and carries out FFT operation of adding a Hamming window on each zero sequence voltage and zero sequence current signal, thereby effectively reducing the influence of frequency spectrum mixing caused by high-frequency signals on signal analysis, and further obtaining the accurate frequency spectrum characteristics of each zero sequence voltage and zero sequence current signal.
The module analyzes the accurate frequency spectrum data of each zero sequence voltage and zero sequence current signal and inputs the frequency spectrum data into the impedance calculation module 3.
The operation and the stop of the module are controlled by the line selection algorithm module 4, and after the grounding occurs, the line selection algorithm module 4 starts the operation of the spectrum analysis module 2; and after the grounding disappears, the line selection algorithm module 4 stops the operation of the spectrum analysis module 2.
An example of the results of the spectral analysis of this module is shown in fig. 7 and 8. Wherein fig. 7 is a spectrum analysis result of the zero sequence voltage U0, and fig. 8 is a current spectrum analysis result of the grounding branch I-1.
3. An impedance calculation module, as shown in fig. 2 and 4:
the module uses the frequency spectrum signals of zero sequence voltage U0 and zero sequence currents I01, I02, I03 and I04 of 4 branches transmitted by the frequency spectrum analysis module 2, firstly finds out the frequency with the maximum voltage module value in the frequency spectrum of the voltage U0 as the central frequency, and then two adjacent frequencies (recorded by 50Hz) form a characteristic frequency band together; and then calculating the line characteristic impedance R1, R2, R3, R4 and the line characteristic impedance R04, R2, R3 and R4 corresponding to each branch in the characteristic frequency band for the currents I01, I02, I03 and I04. Because the characteristic frequency band comprises 3 frequency points, the calculation method of the characteristic impedance is as follows:
the calculated characteristic impedance of each branch is input to the line selection algorithm module 4.
An example of the impedance analysis results of this module is shown in fig. 9.
4. A line selection algorithm module, as shown in fig. 2 and 5:
the module receives the three-phase voltage Ua, Ub, Uc of the power grid, the zero sequence voltage U0 signal from the data acquisition module 1, and the characteristic impedance R1, R2, R3, R4 of each branch from the impedance calculation module 3.
The module firstly calculates the effective value of the zero sequence voltage U0, judges whether the zero sequence voltage U0 exceeds the set starting voltage of the ground fault, and if the zero sequence voltage U0 exceeds the starting voltage, the power grid is considered to be grounded in a single phase. At this time, the fault occurrence time is recorded, the judgment of the fault phase is started, and the spectrum analysis module 2 is started at the same time. And the fault phase judgment is to calculate the effective values of three-phase voltages Ua, Ub and Uc by adopting a root-mean-square algorithm, and to judge the fault phase by using the phase with the lowest effective voltage value.
The module judges that the power grid is grounded in a single phase, starts the spectrum analysis module 2, and finds the first 3 branches with the minimum impedance module value and finds the branch with the maximum difference between the impedance direction and other branches in the 3 branches as the grounding branch after the impedance calculation module 3 obtains the characteristic impedances R1, R2, R3 and R4 of the branches. Meanwhile, the bus where the fault branch is located is the grounding bus.
The module continuously monitors the effective value of the zero sequence voltage U0 in the grounding process, and when the value of the zero sequence voltage U0 is lower than the set grounding fault starting voltage, grounding is considered to disappear. At this time, the ground fault disappearance time is recorded, and the operation of the spectrum analysis module is stopped.
The grounding occurrence time, the grounding disappearance time, the grounding fault phase, the grounding branch and the grounding bus recorded by the module form a complete line selection result together.
An example of an analysis of this module is shown in fig. 6, 7, 8, 9. Wherein fig. 6 is a waveform of a ground fault; fig. 7 shows the result of the frequency spectrum analysis of the zero sequence voltage U0; FIG. 8 is the current spectrum analysis result of the grounded branch I-1; fig. 9 shows the impedance analysis result, and it can be seen that it is the impedance of the grounding branch I-1 which is the smallest and the direction which is the largest difference from other normal branches.
According to the small-current grounding power grid line selection system based on impedance detection, accurate and quick judgment of single-phase grounding fault branches in various small-current grounding power grids is achieved. The neutral point grounding system can be widely applied to various 6-66 kV power grid systems, comprises a neutral point grounding system through an arc suppression coil and a neutral point non-grounding system, and can well match the line selection requirements when equipment such as a medium resistor, a small resistor and an active arc suppression coil (arc suppression cabinet) are adopted in the existing system. The line selection requirements of various field operation conditions are met. The method is beneficial to improving the safe and reliable operation of the power grid and reducing the damage of the single-phase earth fault to equipment and personnel.
The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and not to limit the invention. Any modifications and variations within the scope of the description, which may occur to those skilled in the art, are intended to be within the scope of the invention.
Claims (8)
1. A small current grounding power grid line selection system based on impedance detection is characterized by comprising: the system comprises a data acquisition module, a spectrum analysis module, an impedance calculation module and a line selection algorithm module;
the data acquisition module is used for acquiring power grid zero-sequence voltage and branch zero-sequence current signals required by impedance detection; transmitting the collected power grid zero sequence voltage and branch zero sequence current signals to the frequency spectrum analysis module and the line selection algorithm module;
the frequency spectrum analysis module receives a starting command from the line selection algorithm module, receives power grid zero sequence voltage and branch zero sequence current signals of the data acquisition module, and performs frequency spectrum analysis on the signals; the result of the frequency spectrum analysis is input into an impedance calculation module;
the impedance calculation module receives the spectrum analysis result from the spectrum analysis module, finds the characteristic frequency band when the ground is connected, calculates the characteristic impedance of each branch in the characteristic frequency band, and inputs the calculated characteristic impedance of each branch into the line selection algorithm module;
the line selection algorithm module receives the voltage signal from the acquisition module, identifies faults and starts the spectrum analysis module after the faults occur; and receiving branch characteristic impedance data from the impedance calculation module, and performing line selection algorithm analysis according to the data so as to judge the grounding branch.
2. The impedance detection based small-current grounding power grid line selection system according to claim 1, wherein the data acquisition module acquires a power grid zero-sequence voltage and a branch zero-sequence current signal; in order to ensure the accuracy of subsequent spectrum analysis and impedance calculation, the data acquisition module adopts a multi-path synchronous and high-speed sampling technology; wherein:
the multi-path synchronous sampling can meet the requirement of full synchronous acquisition of 100 paths of alternating voltage or current with a synchronous error not exceeding 1 mu S, and ensures that the phase error of each alternating current is minimum during subsequent spectrum analysis and impedance calculation;
the multi-path high-speed sampling can carry out high-speed acquisition of each path of alternating voltage or current above 12.8kHz, and ensures that the subsequent frequency spectrum analysis and impedance calculation have enough frequency bandwidth.
3. The small-current grounding power grid line selection system based on impedance detection as claimed in claim 1, wherein the spectrum analysis module performs spectrum analysis on zero-sequence voltage and zero-sequence current signals; in order to process the high-frequency signals generated in the grounding process and avoid the frequency spectrum aliasing caused by the high-frequency signals, a fast Fourier analysis algorithm of adding a Hamming window is adopted.
4. The small-current grounding power grid line selection system based on impedance detection as claimed in claim 1, wherein the impedance calculation module takes the frequency spectrum characteristic data of the zero-sequence voltage and zero-sequence current signals from the frequency spectrum analysis module as input to calculate the characteristic frequency band of the zero-sequence voltage and the characteristic impedance of each branch; wherein:
the characteristic frequency band of the zero sequence voltage is based on different grounding processes after grounding occurs, the frequency bands of the generated zero sequence voltage signals are different, and the frequency band with the most obvious grounding characteristic corresponding to the zero sequence voltage signal needs to be found in each grounding process; in the grounding process, the frequency range contained by the adjacent 3 frequency points with the maximum zero sequence voltage amplitude is the characteristic frequency band of the zero sequence voltage; the central frequency point of the characteristic frequency band is a characteristic frequency; the interval frequency of adjacent frequency points is 50 Hz;
the characteristic impedance of each branch is the vector sum of the zero sequence voltage of the power grid after grounding and the vector ratio of each frequency point of the zero sequence current of each branch in the characteristic frequency band; since the characteristic frequency band generally includes 3 frequency points, the calculation method of the characteristic impedance is as follows:
after the grounding occurs, the characteristic impedance of each branch circuit reflects the parallel sum of the zero sequence impedance of other normal branch circuits to the ground for the grounding branch circuit; for the normal branch, it reflects the zero sequence impedance of the normal branch itself to the ground; the characteristic impedance of the ground branch is therefore the smallest of all branches and the direction of its impedance differs the most from the normal branch.
5. The small-current grounding power grid line selection system based on impedance detection as claimed in claim 1, wherein the line selection algorithm module further comprises: fault identification submodule, fault phase judge submodule, line selection judge submodule, wherein:
the fault identification submodule receives zero sequence voltage data from the data acquisition module and then calculates the effective value of the zero sequence voltage by adopting a root mean square algorithm; when the zero sequence voltage effective value exceeds a preset fault voltage value, a fault is considered to occur, the initial time of the fault occurrence is recorded, and a spectrum analysis module is started; when the zero sequence voltage is recovered to be below the set fault voltage value, the fault is considered to be ended, the end time of the fault is recorded, and the frequency spectrum analysis module is stopped;
the fault phase judgment submodule receives system three-phase voltage data from the data acquisition module and then calculates an effective value of each phase voltage by adopting a root mean square algorithm; after the fault identification submodule judges that a fault occurs, the submodule identifies and records a phase with the lowest phase voltage as a fault phase;
the line selection judgment submodule receives the characteristic impedance of each branch from the impedance calculation module, firstly finds the first three branches with the minimum characteristic impedance module value and the impedance module value smaller than the set impedance maximum value, and then finds the branch with the maximum phase difference between every two branches in the impedance direction as a grounding branch in the three branches; and if the branch meeting the condition cannot be found, the bus is judged to be grounded.
6. The small-current grounding power grid line selection system based on impedance detection as claimed in claim 1 or 5, wherein the line selection result of the grounding line selection module comprises: one or more of a grounding branch, a grounding bus, a grounding phase, grounding time and recovery time;
the grounding branch circuit is used for indicating the actually grounded branch circuit, and if no branch circuit is grounded, the bus is indicated to be grounded;
the grounding bus is used for indicating the bus where the grounding branch is located;
the grounding phase is used for indicating a fault phase in which a grounding fault occurs;
the grounding time is used for indicating the initial time of the occurrence of the grounding fault;
the recovery time is used to indicate an end time at which the ground fault disappears.
7. The low-current grounding power grid line selection system based on impedance detection as claimed in any one of claims 1 to 6, wherein the spectrum analysis module and the impedance calculation module only need to operate after a grounding fault occurs; when the power grid has no ground fault, the zero-sequence voltage of the power grid is very small and the zero-sequence current of each branch is also very small according to the electrical characteristics of the power grid, and the calculated characteristic frequency and characteristic impedance are inaccurate and cannot be used for calculating a line selection algorithm; only when the system is in single-phase grounding, the zero sequence voltage and the zero sequence current of each branch are high enough, the calculated characteristic frequency band and the calculated characteristic impedance are accurate enough, and the characteristic frequency band and the calculated characteristic impedance can be used for line selection calculation.
8. The small-current grounding power grid line selection system based on impedance detection as claimed in any one of claims 1 to 7, wherein the impedance and the characteristic impedance refer to zero-sequence complex impedance to ground of a zero-sequence loop of a line; the characteristic signal can be clearly used as a characteristic signal for identifying the grounding fault, and the grounding branch can be quickly and accurately judged by calculating the characteristic impedance.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112731047A (en) * | 2020-12-03 | 2021-04-30 | 天津大学 | Fault line selection method suitable for flexible grounding system |
| CN113820620A (en) * | 2021-08-17 | 2021-12-21 | 捍防（深圳）实业有限公司 | Fault analysis method and fault analysis device for power supply system |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112731047A (en) * | 2020-12-03 | 2021-04-30 | 天津大学 | Fault line selection method suitable for flexible grounding system |
| CN113820620A (en) * | 2021-08-17 | 2021-12-21 | 捍防（深圳）实业有限公司 | Fault analysis method and fault analysis device for power supply system |
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