CN110907761B - Continuous line selection method and system for single-phase earth fault - Google Patents
Continuous line selection method and system for single-phase earth fault Download PDFInfo
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Abstract
The invention relates to a continuous line selection method and a system for single-phase earth faults, wherein the continuous line selection method comprises the following steps: s1: when the voltage value of the neutral point of the power grid is greater than the set alarm starting voltage value, single-phase grounding initial fault judgment and line selection are carried out, and if the single-phase grounding fault exists, grounding line selection is carried out; s2: if the fault continues to occur after step S1 is completed, the fault phase is determined and the line is selected continuously during the fault continuing process. The method solves the problem that after the first-choice line is tripped due to the fact that the power grid is grounded after single-phase grounding, the fault is continuous and cannot be continuously judged, and improves the efficiency of fault removal.
Description
Technical Field
The invention relates to the technical field of power grids, in particular to a continuous line selection method and system for single-phase earth faults.
Background
The medium-voltage power grid single-phase grounding is allowed to have a fault for a period of time, and under the condition that the knowledge of the national grid on the power supply reliability is gradually improved, the fault needs to be cut off and a fault point needs to be found as soon as possible, so that the fault expansion is avoided. When one line of a power grid is grounded, the other two phase voltages are increased to the line voltage, so that the original normal phase insulation in the system is possibly deteriorated, single-phase grounding occurs again, the single-phase grounding fault is converted into an interphase short circuit, and one line is tripped; the single-phase grounding fault can be continued after tripping, other weak phases can be grounded in a single phase, tripping is carried out again, and the fault environment is repeated.
The existing small current line selection device is basically based on transient state line selection and takes zero sequence voltage as a starting condition. Acquiring zero-sequence current, each phase voltage and zero-sequence voltage on site, determining that a fault occurs when the zero-sequence voltage rises to 30% of the phase voltage, further judging the fault type, and selecting a fault line if the fault type is grounded; however, when the single-phase grounding is continued, the grounding occurs again, the neutral point voltage cannot be changed essentially, and the traditional device cannot realize the restarting judgment above the starting threshold value, so that a fault line can only be searched by a stay wire, the continuous line selection cannot be carried out, and the fault discharge efficiency is low.
Disclosure of Invention
The invention provides a continuous line selection method for single-phase earth faults, which solves the problem that the continuous line selection cannot be carried out after a power grid fails.
The invention is realized by the following technical scheme:
a continuous line selection method for single-phase earth faults comprises the following steps:
s1: when the voltage value of the neutral point of the power grid is larger than the set alarm starting voltage value, carrying out single-phase grounding initial fault judgment and line selection, and if the single-phase grounding fault occurs, carrying out grounding line selection;
s2: if the fault continuously occurs after the step S1 is completed, judging and selecting a fault phase continuously occurring in the fault continuous process;
in the technical scheme, in step S2, when the fault continues to occur, the fault phase determination and the line selection operation can be continued in the fault continuing process, so that the problem that continuous line selection and fault removal cannot be performed is solved, and the fault removal efficiency is improved.
As a further improvement of the present invention, the single-phase ground initial fault judgment in step S1 includes the steps of:
s201: performing FFT operation analysis on the zero sequence voltage to obtain amplitudes and phases of each harmonic of the zero sequence voltage, and judging that the power grid fault is a ferromagnetic resonance fault when any amplitude of each harmonic exceeds an alarm starting voltage value;
s202: calculating an effective value of each branch zero-sequence current by a root-mean-square method, judging the power grid fault to be a PT fault when the sum of the branch zero-sequence currents is smaller than a set minimum grounding current, and judging the power grid fault to be a single-phase grounding fault when the sum of the branch zero-sequence currents is larger than the set minimum grounding current;
step S201 and step S202 are not in sequence; in the technical scheme, the method takes the condition that the neutral point voltage of the power grid in normal operation is larger than a set alarm starting voltage value as a starting condition, and judges that the fault type is ferromagnetic resonance fault or PT fault or single-phase grounding fault by calculating the amplitude and the frequency spectrum of zero-sequence voltage and calculating the amplitude of zero-sequence current of each branch circuit; and after the single-phase earth fault is confirmed, carrying out earth line selection to finish the initial judgment of the power grid fault and prepare for the next line selection.
Further, the ground line selection in step S1 includes the steps of:
s301: performing digital filtering on the zero sequence voltage and each zero sequence current to obtain a transient signal, and entering step S302, wherein the digital filtering in the step is transient filtering;
s302: performing transient line selection according to the transient signal, and if a transient line selection result is obtained, judging that the result is a grounding line selection result, and finishing grounding line selection; if the transient state line selection has no result, the step S303 is executed;
s303: performing digital filtering on the zero-sequence voltage and each zero-sequence current to obtain a steady-state signal, and entering a step S304, wherein the digital filtering in the step is steady-state filtering;
s304: and performing stable state line selection according to the stable state signal to obtain a stable state line selection result and finish grounding line selection.
In the technical scheme, transient state filtering is firstly carried out on the zero sequence voltage acquired in real time and the zero sequence current of each branch circuit to obtain a transient state signal, and line selection is carried out through the transient state signal; only when the transient signal is too small, carrying out steady state filtering on the zero sequence voltage and the zero sequence current of each branch circuit to obtain a steady state signal, and carrying out line selection through the steady state signal; the line selection method based on the electric principle is adopted no matter the transient signal line selection or the steady-state signal line selection; the line selection method based on the electrical principle is to find a branch with the maximum zero sequence current amplitude after grounding, and if the phase of the branch lags behind the zero sequence voltage phase by 90 degrees, the branch is considered to be grounded, otherwise, the bus is considered to be grounded.
Further, the continuous occurrence of the fault in step S2 means that when the grid voltage continuously exceeds 30V, it is determined that the fault continues, and the continuous grounding line selection also continues; and when the zero sequence voltage is recovered to be below 30V, determining that the fault is not continuous.
Further, the determination of the failed phase continuation in step S2 includes the steps of:
s401: performing digital filtering on the three-phase voltage, wherein the digital filtering comprises transient filtering and steady-state filtering to obtain a transient voltage signal and a steady-state voltage signal respectively;
s402: and respectively calculating the transient voltage mutation of each phase voltage and the steady voltage mutation of each phase voltage according to the transient voltage signal or the steady voltage signal, carrying out comprehensive operation on the transient voltage mutation of each phase voltage and the steady voltage mutation of each phase voltage, and judging the continuous fault phase according to the comprehensive operation result.
In the technical scheme, transient voltage mutation of each phase voltage and steady voltage mutation of each phase voltage are respectively calculated according to the transient voltage signal and the steady voltage signal, and weighted comprehensive operation is carried out on the transient voltage mutation of each phase voltage and the steady voltage mutation of each phase voltage to obtain a comprehensive mutation value of each phase, wherein the phase with the largest comprehensive mutation value is a fault-continuing phase.
Further, the line selection in step S2 includes the steps of:
s501: the method comprises the following steps of (1) realizing steady-state current mutation detection by adopting a root mean square value method for zero-sequence current of each branch and realizing transient current mutation detection by adopting transient signal filtering for the zero-sequence current of each branch;
s502: and when the transient sudden change of two adjacent cycles or the steady-state current sudden change of three adjacent cycles exceeds a set current sudden change value, judging the branch circuit as a fault-resuming branch circuit.
In the technical scheme, the real-time current amplitude value and the transient current signal of each branch are obtained by calculating the zero sequence current of each branch in real time and filtering the transient signal. When the current amplitude mutation of a certain branch in three adjacent power frequency periods exceeds the current mutation limit value, or after transient filtering, the transient mutation of two adjacent power frequency periods exceeds the set current mutation limit value, the branch is judged to be a fault-continuing branch, and fault-continuing line selection is completed.
The application further provides a continuous line selection system for the single-phase earth fault, which comprises an alarm module, a primary judgment module, a continuous fault judgment module and a secondary judgment module;
the alarm module is used for comparing the neutral point voltage value of the power grid with the set alarm starting voltage value and sending an alarm signal when the neutral point voltage value of the power grid is greater than the set alarm starting voltage value;
the primary judgment module is used for carrying out single-phase grounding initial fault judgment and line selection when the alarm module judges that the voltage value of the neutral point of the power grid is greater than the set alarm starting voltage value, and carrying out grounding line selection if the voltage value is a single-phase grounding fault;
the continuous fault judgment module is used for judging whether the fault is continuous or not after the single-phase grounding initial fault is judged and the line is selected;
and the secondary judging module is used for judging the continuous fault phase in the fault continuous process and selecting a line when the fault continuously occurs.
Further, the primary judging module comprises a primary fault judging module and a primary line selecting module;
the primary fault judgment module is used for carrying out FFT operation analysis on the zero sequence voltage to obtain each harmonic amplitude and phase of the zero sequence voltage, if any amplitude of each harmonic exceeds an alarm starting voltage value, the power grid fault is judged to be a ferromagnetic resonance fault, or after the zero sequence current of each branch is calculated to have an effective value through a root mean square method, if the sum of the zero sequence current of each branch is smaller than a set minimum grounding current, the power grid fault is judged to be a PT fault, and if the sum of the zero sequence current of each branch is larger than the set minimum grounding current, the power grid fault is judged to be a single-phase grounding fault;
the primary line selection module is used for performing transient filtering on zero sequence voltage and each zero sequence current to obtain a transient signal when the primary fault judgment module judges that the power grid fault is a single-phase earth fault, performing transient line selection according to the transient signal, and judging that the result is an earth line selection result if the transient line selection result is obtained, so as to finish earth line selection; and if the transient signal is small and the transient line selection has no result, performing steady-state filtering on the zero sequence voltage and each zero sequence current to obtain a steady-state signal, performing steady-state line selection according to the steady-state signal to obtain a steady-state line selection result, and completing the grounding line selection.
Further, the secondary judging module comprises a secondary fault judging module and a secondary line selecting module;
the secondary fault judgment module is used for carrying out digital filtering on the three-phase voltage, wherein the digital filtering comprises transient filtering and steady-state filtering, a transient voltage signal and a steady-state voltage signal are obtained respectively, transient voltage mutation of each phase voltage and steady-state voltage mutation of each phase voltage are calculated respectively according to the transient voltage signal and the steady-state voltage signal, comprehensive operation is carried out on the transient voltage mutation of each phase voltage and the steady-state voltage mutation of each phase voltage, and finally, a fault phase is judged to be continuously generated according to a comprehensive operation result;
and the secondary line selection module is used for realizing steady-state current mutation detection by adopting a root mean square value method for the zero-sequence current of each branch, meanwhile, realizing transient current mutation detection by adopting transient signal filtering for the zero-sequence current of each branch, judging a fault-resuming branch, and judging the branch as the fault-resuming branch when the transient mutations of two adjacent cycles or the steady-state current mutations of three adjacent cycles exceed a set current mutation value.
In conclusion, the method has the advantages that after the power grid fault occurs and the primary fault judgment and line selection are carried out, the change of the phase voltage and the zero sequence current increment of the non-grounding branch circuit is monitored by utilizing a real-time wave recording calculation mode in the fault, the direction and the energy of the change are calculated to judge whether the secondary grounding fault occurs and judge the line and the phase category; after one line with the fault trips, during and after fault recovery, the increment and steady-state fault are used for judging the final grounding fault line and phase, and continuous grounding judgment is carried out sequentially and repeatedly until the fault is finished; the method solves the problems that the fault is continuous after the first-choice line is tripped and is possible to be tripped after the fault occurs again, and the fault is continuous and can not be subjected to line selection and fault restoration for multiple times due to the fact that the power grid is grounded again after single-phase grounding occurs.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a flow chart of the algorithm of the present invention;
FIG. 2 is a schematic diagram of the initial fault determination of the present invention;
FIG. 3 is a schematic diagram of the initial fault line selection of the present invention;
FIG. 4 is a schematic diagram of a failure-to-occur determination of the present invention;
fig. 5 is a schematic diagram of line selection for a failure of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1:
as shown in fig. 1, a method for continuously selecting a line of a single-phase earth fault is characterized by comprising the following steps:
s1: when the voltage value of the neutral point of the power grid is larger than the set alarm starting voltage value, carrying out single-phase grounding initial fault judgment and line selection, and if the single-phase grounding fault occurs, carrying out grounding line selection;
s2: if the fault continuously occurs after the step S1 is completed, judging and selecting a fault phase continuously occurring in the fault continuous process;
in step S2, when the fault continues to occur, the fault phase determination and line selection operations can be continued during the fault continuation process, so that the problem that the continuous line selection cannot be performed and the fault is eliminated is solved, and the fault elimination efficiency is improved.
As shown in fig. 2, the single-phase ground fault determination in step S1 is performed by collecting three voltages, a zero-sequence voltage, and zero-sequence currents of each branch, and specifically includes steps S201 to S202:
s201: carrying out FFT operation analysis on the zero sequence voltage to obtain the amplitude and phase of each harmonic of the zero sequence voltage, analyzing the frequency spectrum and the phase angle, and identifying faults, wherein when any amplitude of each harmonic exceeds an alarm starting voltage value, the power grid fault is judged to be a ferromagnetic resonance fault;
s202: calculating an effective value and performing phase angle analysis on the zero sequence current of each branch by a root mean square method, identifying faults, judging the power grid fault to be a PT fault when the sum of the zero sequence current of each branch is less than a set minimum grounding current, and judging the power grid fault to be a single-phase grounding fault when the sum of the zero sequence current of each branch is greater than the set minimum grounding current;
in the step S201, an FFT algorithm is adopted to obtain amplitudes and phases of each harmonic, where 1/2 power frequency is 25Hz, 1/3 power frequency is 17Hz, 2 frequency doubling is 100Hz, 3 frequency doubling is 150Hz, and 5 frequency doubling is 250Hz, and all are used for determining ferromagnetic resonance; when any amplitude value of any harmonic in the zero sequence voltage exceeds the fault starting voltage, the fault is regarded as a ferromagnetic resonance fault; in the step S202, the effective values of the three-phase voltage, the zero-sequence voltage, and the zero-sequence current of each branch are calculated by using a root-mean-square method; when the effective value of the zero sequence voltage is detected to exceed the fault starting voltage, the system is considered to have a fault, and if the sum of the zero sequence currents of the branches is smaller than the set minimum grounding current sum of 0.5A, the fault is judged to be a PT fault; and if the sum of the zero sequence currents is larger than the minimum grounding current, judging the single-phase grounding fault.
As shown in fig. 3, the grounding route selection in step S1 is determined by collecting zero-sequence voltage and zero-sequence current of each branch, and specifically includes steps S301 to S302:
s301: performing digital filtering on the zero sequence voltage and each zero sequence current to obtain a transient signal, and entering step S302, wherein the digital filtering in the step is transient filtering;
s302: performing transient line selection according to the transient signal, and if a transient line selection result is obtained, judging that the result is a grounding line selection result, and finishing grounding line selection; if the transient state line selection has no result, the step S303 is executed;
s303: performing digital filtering on the zero-sequence voltage and each zero-sequence current to obtain a steady-state signal, and entering a step S304, wherein the digital filtering in the step is steady-state filtering;
s304: and performing stable state line selection according to the stable state signal to obtain a stable state line selection result and finish grounding line selection.
In the steps S301 to S302, digital filtering adopts an IIR mode of two frequency bands, which are filters for transient signal processing with a band-pass range of 3 to 11 times of power frequency, i.e., 150Hz to 550Hz, and filters for steady signal processing with a band-pass range of 1 to 2 times of power frequency, i.e., 50 to 100 Hz; performing transient filtering on the zero sequence voltage acquired in real time and the zero sequence current of each branch circuit to obtain a transient signal, and performing line selection through the transient signal; only when the transient signal is too small, carrying out steady state filtering on the zero sequence voltage and the zero sequence current of each branch circuit to obtain a steady state signal, and carrying out line selection through the steady state signal; the line selection method based on the electric principle is adopted no matter the transient signal line selection or the steady-state signal line selection; the line selection method based on the electrical principle is to find a branch with the maximum zero sequence current amplitude after grounding, and if the phase of the branch lags behind the zero sequence voltage phase by 90 degrees, the branch is considered to be grounded, otherwise, the bus is considered to be grounded.
The continuous occurrence of the fault in the step S2 means that when the grid voltage continuously exceeds 30V, it is determined that the fault continues, and the continuous grounding and line selection also continues; and when the zero sequence voltage is recovered to be below 30V, determining that the fault is not continuous.
As shown in fig. 4, the determination of the phase failure in step S2 is performed by collecting three-phase voltages, and specifically includes steps S401 to S402:
s401: performing digital filtering on the three-phase voltage, wherein the digital filtering comprises transient filtering and steady-state filtering, and respectively obtaining a transient voltage signal and a steady-state voltage signal;
s402: respectively calculating transient voltage mutation of the three-phase voltage and steady voltage mutation of the three-phase voltage according to the transient voltage signal and the steady voltage signal, carrying out comprehensive operation on the transient voltage mutation of the three-phase voltage and the steady voltage mutation of the three-phase voltage, and judging a continuous fault phase according to a comprehensive operation result;
judging the fault phase of the continuous occurrence in the step S2, performing digital filtering on the three-phase voltage signal, calculating the steady-state amplitude of the three-phase voltage and the transient-state voltage amplitude of the three-phase voltage from the obtained steady-state signal and the transient-state signal, calculating the transient-state voltage jump of the three-phase voltage and the steady-state voltage jump of the three-phase voltage according to the steady-state amplitude of the temporary three-phase voltage and the transient-state voltage amplitude of the three-phase voltage, and performing weighted comprehensive operation on the transient-state voltage jump of the three-phase voltage and the steady-state voltage jump of the three-phase voltage to obtain a comprehensive sudden change value of each phase, wherein the phase with the largest comprehensive sudden change value is the fault phase of the continuous occurrence; as the optimal selection in this embodiment, the weights of the transient voltage jump of the three-phase voltage and the steady voltage jump of the three-phase voltage each account for 50% of the proportion.
As shown in fig. 5, the line selection in step S2 is determined by collecting zero-sequence currents of each branch, and specifically includes steps S501 to S502:
s501: the method comprises the following steps of (1) realizing steady-state current mutation detection by adopting a root mean square value method for zero-sequence current of each branch and realizing transient current mutation detection by adopting transient signal filtering for the zero-sequence current of each branch;
s502: when the transient sudden change of two adjacent cycles or the steady-state current sudden change of three adjacent cycles exceeds a set current sudden change value, the branch is judged to be a fault-resuming branch;
in the line selection in the step S2, the change of the zero sequence current of each branch is continuously monitored to realize continuous grounding line selection; in order to detect the change of the zero sequence current of the branch circuit, the step adopts a root mean square value method to realize the detection of the steady-state current mutation, and simultaneously adopts a band-pass IIR frequency of 3-11 times of power frequency, namely 150 Hz-550 Hz, to realize the detection of the transient current mutation; when the transient sudden change of two adjacent cycles or the steady-state current sudden change of three adjacent cycles is detected to exceed the set current sudden change value by more than 1.0A, the branch with the sudden change exceeding the limit is considered to be grounded.
Example 2:
the present embodiment provides a continuous line selection system for single-phase ground fault, including: the device comprises an alarm module, a primary judgment module, a continuous fault judgment module and a secondary judgment module;
the alarm module is used for comparing the neutral point voltage value of the power grid with the set alarm starting voltage value and sending an alarm signal when the neutral point voltage value of the power grid is greater than the set alarm starting voltage value;
the primary judgment module is used for sending an alarm signal by the alarm module when the voltage value of the neutral point of the power grid is greater than the set alarm starting voltage value, carrying out single-phase grounding initial fault judgment and line selection, and carrying out grounding line selection if the single-phase grounding fault occurs;
the continuous fault judgment module is used for judging whether the fault is continuous or not after the single-phase grounding initial fault is judged and the line is selected;
and the secondary judging module is used for judging the continuous fault phase in the fault continuous process and selecting a line when the fault continuously occurs.
The primary judging module comprises a primary fault judging module and a primary line selecting module; the primary fault judgment module is used for obtaining the amplitude and the phase of each subharmonic of the zero sequence voltage after the zero sequence voltage is analyzed through FFT (fast Fourier transform) operation, judging the power grid fault to be a ferromagnetic resonance fault if any amplitude of each subharmonic exceeds an alarm starting voltage value, or judging the power grid fault to be a PT fault if the sum of the zero sequence currents of all branches is less than a set minimum grounding current after the effective value of the zero sequence currents of all branches is calculated through a root-mean-square method; if the sum of the zero sequence currents of all the branches is larger than the set minimum grounding current, the power grid fault is judged to be a single-phase grounding fault; the primary line selection module is used for performing transient filtering on zero sequence voltage and each zero sequence current to obtain a transient signal when the primary fault judgment module judges that the power grid fault is a single-phase earth fault, performing transient line selection according to the transient signal, and judging that the result is an earth line selection result if the transient line selection result is obtained, so as to finish earth line selection; and if the transient signal is small and the transient line selection has no result, performing steady-state filtering on the zero sequence voltage and each zero sequence current to obtain a steady-state signal, performing steady-state line selection according to the steady-state signal to obtain a steady-state line selection result, and completing the grounding line selection.
The secondary judging module comprises a secondary fault judging module and a secondary line selecting module; the secondary fault judgment module is used for carrying out digital filtering on the three-phase voltage, wherein the digital filtering comprises transient filtering and steady-state filtering, a transient voltage signal and a steady-state voltage signal are obtained respectively, transient voltage mutation of each phase voltage and steady-state voltage mutation of each phase voltage are calculated respectively according to the transient voltage signal and the steady-state voltage signal, comprehensive operation is carried out on the transient voltage mutation of each phase voltage and the steady-state voltage mutation of each phase voltage, and finally, a fault phase is judged to be continuously generated according to a comprehensive operation result; and the secondary line selection module is used for realizing steady-state current mutation detection by adopting a root mean square value method for the zero-sequence current of each branch and transient-state current mutation detection by adopting transient-state signal filtering for the zero-sequence current of each branch, and when the transient-state mutations of two adjacent cycles or the steady-state current mutations of three adjacent cycles exceed a set current mutation value, the branch is judged to be a fault-resuming branch.
The continuous line selection system for the single-phase earth fault further comprises an intelligent alarm module, and when the power grid is subjected to initial single-phase earth and an earth branch is selected, the intelligent alarm module immediately reports the earth branch to the superior monitoring system and carries out earth alarm; for a continuous fault, when the branch where the continuous fault is located is the same as the previous fault branch, the continuous fault does not alarm the upper-level monitoring system, and repeated alarm is avoided; and if the branch where the failure is continuously sent is different from the previous failure branch, immediately reporting a new failure branch to the upper-level monitoring system.
In the prior art, a grounding line selection device basically only has the function of primary line selection, the accuracy is not high, zero-sequence fault recording is limited to a few cycles or dozens of cycles instead of recording in a full fault period, and the fault of a non-recording section lacks real-time online monitoring and calculation capacity; the invention monitors the change of phase voltage and non-grounding branch zero sequence current increment by a real-time wave recording calculation mode in the fault, calculates the direction and energy of the change to judge whether the secondary grounding fault occurs and judges the line and phase difference; after one line with the fault trips, during and after fault recovery, the increment and the steady-state fault are used for judging the final grounding fault line and phase, and continuous grounding judgment is carried out for multiple times in sequence until the fault is finished; the method solves the problems that the fault is continuous after the first-choice line is tripped and is possible to be tripped after the fault occurs again, and the fault is continuous and can not be subjected to line selection and fault restoration for multiple times due to the fact that the power grid is grounded again after single-phase grounding occurs.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to those skilled in the art without departing from the principles of the present invention may be apparent to those skilled in the relevant art and are intended to be within the scope of the present invention.
Claims (4)
1. A continuous line selection method for single-phase earth faults is characterized by comprising the following steps:
s1: when the voltage value of the neutral point of the power grid is larger than the set alarm starting voltage value, carrying out single-phase grounding initial fault judgment and line selection, and if the single-phase grounding fault occurs, carrying out grounding line selection;
s2: if the fault continuously occurs after the step S1 is completed, judging and selecting a fault phase continuously occurring in the fault continuous process;
the continuous occurrence of the fault in the step S2 means that when the grid voltage continuously exceeds 30V, it is determined that the fault continues, and the continuous grounding and line selection also continues; when the zero sequence voltage is recovered to be below 30V, the fault is determined to be non-continuous;
the determination of the failed phase continuation in step S2 includes the steps of:
s401: performing digital filtering on the three-phase voltage, wherein the digital filtering comprises transient filtering and steady-state filtering to obtain a transient voltage signal and a steady-state voltage signal respectively;
s402: respectively calculating transient voltage mutation of each phase voltage and steady voltage mutation of each phase voltage according to the transient voltage signal and the steady voltage signal, carrying out comprehensive operation on the transient voltage mutation of each phase voltage and the steady voltage mutation of each phase voltage, and judging a failure phase according to a comprehensive operation result;
the line selection in step S2 includes the steps of:
s501: the method comprises the following steps of (1) realizing steady-state current mutation detection by adopting a root mean square value method for zero-sequence current of each branch and realizing transient current mutation detection by adopting transient signal filtering for the zero-sequence current of each branch;
s502: and when the transient sudden change of two adjacent cycles or the steady-state current sudden change of three adjacent cycles exceeds a set current sudden change value, judging the branch as a fault-continuing branch.
2. The method for continuous line selection of single-phase earth fault as claimed in claim 1, wherein the single-phase earth initial fault determination in step S1 includes the steps of:
s201: carrying out fast Fourier transform operation analysis on the zero sequence voltage to obtain the amplitude and the phase of each harmonic of the zero sequence voltage, and judging that the power grid fault is a ferromagnetic resonance fault when any amplitude of each harmonic exceeds an alarm starting voltage value;
s202: calculating an effective value of each branch zero-sequence current by a root-mean-square method, judging the power grid fault as a voltage transformer fault when the sum of the branch zero-sequence currents is smaller than a set minimum grounding current, and judging the power grid fault as a single-phase grounding fault when the sum of the branch zero-sequence currents is larger than the set minimum grounding current;
step S201 and step S202 have no precedence order.
3. The method for continuous line selection of single-phase earth fault as claimed in claim 1, wherein the line selection for grounding in step S1 includes the steps of:
s301: performing digital filtering on the zero sequence voltage and each zero sequence current to obtain a transient signal, and entering step S302, wherein the digital filtering in the step is transient filtering;
s302: performing transient line selection according to the transient signal, and if a transient line selection result is obtained, judging that the result is a grounding line selection result, and finishing grounding line selection; if the transient state line selection has no result, the step S303 is executed;
s303: performing digital filtering on the zero-sequence voltage and each zero-sequence current to obtain a steady-state signal, and entering a step S304, wherein the digital filtering in the step is steady-state filtering;
s304: and performing stable state line selection according to the stable state signal to obtain a stable state line selection result and finish grounding line selection.
4. A continuous line selection system for a single-phase ground fault, comprising: the device comprises an alarm module, a primary judgment module, a continuous fault judgment module and a secondary judgment module;
the alarm module is used for comparing the neutral point voltage value of the power grid with the set alarm starting voltage value and sending an alarm signal when the neutral point voltage value of the power grid is greater than the set alarm starting voltage value;
the primary judgment module is used for carrying out single-phase grounding initial fault judgment and line selection when the alarm module judges that the voltage value of the neutral point of the power grid is greater than the set alarm starting voltage value, and carrying out grounding line selection if the voltage value is a single-phase grounding fault;
the continuous fault judgment module is used for judging whether the fault is continuous or not after the single-phase grounding initial fault is judged and the line is selected;
the secondary judging module is used for judging and selecting a fault phase which is continuously generated in the fault continuous process when the fault continuously occurs;
the primary judging module comprises a primary fault judging module and a primary line selecting module;
the primary fault judgment module is used for carrying out fast Fourier transform operation analysis on the zero sequence voltage to obtain each harmonic amplitude and phase of the zero sequence voltage, if any amplitude of each harmonic exceeds an alarm starting voltage value, the power grid fault is judged to be a ferromagnetic resonance fault, or after the zero sequence current of each branch is calculated to have an effective value through a root-mean-square method, if the sum of the zero sequence current of each branch is less than a set minimum grounding current, the power grid fault is judged to be a voltage transformer fault, and if the sum of the zero sequence current of each branch is greater than the set minimum grounding current, the power grid fault is judged to be a single-phase grounding fault;
the primary line selection module is used for performing transient filtering on zero sequence voltage and each zero sequence current to obtain a transient signal when the primary fault judgment module judges that the power grid fault is a single-phase earth fault, performing transient line selection according to the transient signal, and judging that the result is an earth line selection result if the transient line selection result is obtained, so as to finish earth line selection; if the transient state line selection has no result, performing steady state filtering on the zero sequence voltage and each zero sequence current to obtain a steady state signal, and performing steady state line selection according to the steady state signal to obtain a steady state line selection result to complete grounding line selection;
the secondary judging module comprises a secondary fault judging module and a secondary line selecting module;
the secondary fault judgment module is used for carrying out digital filtering on the three-phase voltage, wherein the digital filtering comprises transient filtering and steady-state filtering, a transient voltage signal and a steady-state voltage signal are obtained respectively, transient voltage mutation of each phase voltage and steady-state voltage mutation of each phase voltage are calculated respectively according to the transient voltage signal and the steady-state voltage signal, comprehensive operation is carried out on the transient voltage mutation of each phase voltage and the steady-state voltage mutation of each phase voltage, and finally, a fault phase is judged to be continuously generated according to a comprehensive operation result;
and the secondary line selection module is used for realizing steady-state current mutation detection by adopting a root mean square value method for the zero-sequence current of each branch, realizing transient-state current mutation detection by adopting transient signal filtering for the zero-sequence current of each branch, judging a fault-resuming branch, and judging the branch as the fault-resuming branch when the transient-state mutations of two adjacent cycles or the steady-state current mutations of three adjacent cycles exceed a set current mutation value.
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