CN117092452A - Power distribution network high-resistance ground fault detection and isolation method based on broadband current signals - Google Patents
Power distribution network high-resistance ground fault detection and isolation method based on broadband current signals Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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
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Abstract
The invention relates to a power distribution network high-resistance ground fault detection and isolation method based on broadband current signals, which comprises the following steps: the method is based on a traveling wave positioning type secondary deep fusion on-column circuit breaker device, and provides a high-resistance fault detection and isolation method combining high-frequency traveling wave and traditional transient signal detection, so that the detection and treatment capacity of weak characteristic faults such as high-resistance grounding, hidden danger discharge and the like are greatly improved; the high-frequency traveling wave is not influenced by a line operation mode and a fault transition resistance, and the single-phase fault detection technology of the 10kV power distribution network based on the high-frequency traveling wave detection has a wide application prospect.
Description
Technical Field
The invention relates to the technical field of power faults, in particular to a power distribution network high-resistance ground fault detection and isolation method based on broadband current signals.
Background
The grid structure of the distribution network is complex, the branches of the lines are numerous, the running environment is changeable, faults frequently occur, single-phase earth faults account for more than 80% of the total faults of the medium-voltage distribution network, and the two-phase or three-phase short circuit is developed by single-phase earth. The single-phase grounding fault detection and isolation have very important significance for quickly checking faults and improving the reliability of the power grid. However, the medium-voltage distribution network in China mostly adopts a neutral point non-effective grounding operation mode, and single-phase grounding fault current is smaller, so that difficulty is brought to fault detection. Currently, many researches are focused on solving the fault detection of a low-current grounding system, but the current method is difficult to properly handle high-resistance grounding and hidden-danger discharge due to the complex fault characteristics and grid structure of a distribution network;
the pull-out method is easy to cause power failure of a non-fault line, the off-line injection methods such as the S injection method, the variable frequency signal method and the like cannot be monitored in real time, the timeliness is low for post-processing, the detection reliability is poor due to insensitive characteristics under the condition of single-phase high-resistance grounding faults based on the power frequency zero sequence detection method, the upper limit cut-off frequency of the current transient fault detection method is generally several kHz, the frequency band is narrow, fault key information is easy to lose, and the detection reliability is poor.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a power distribution network high-resistance ground fault detection and isolation method based on broadband current signals, so as to overcome the defects in the prior art.
The technical scheme for solving the technical problems is as follows: a power distribution network high-resistance ground fault detection and isolation method based on broadband current signals comprises an FTU, a circuit breaker and a connecting cable, wherein a traveling wave acquisition module is integrated in the FTU, and the method comprises the following steps:
step S1: extracting A, B, C three-phase traveling wave current and three-phase traveling wave voltage signals through broadband PT and CT, and transmitting the three-phase traveling wave current and the three-phase traveling wave voltage signals to the inside of the FTU through multiplexing signal cables to realize current wave quantity acquisition;
step S2: processing transient signals; determining a characteristic frequency band range SFB, filtering the sampled zero sequence voltage and zero sequence current in the SFB range when the FTU acquires the transient signal, and solving a direction coefficient D by the filtered zero sequence transient voltage and zero sequence transient current;
step S3: processing traveling wave signals; setting a traveling wave voltage and traveling wave current trigger threshold, and recording the traveling wave voltage and traveling wave current when the traveling wave trigger condition is met at the same time after traveling wave trigger acquisition; calculating the phase information of the traveling wave, reserving traveling wave data meeting the condition, calculating the average time of the traveling wave stacks, judging the power frequency periodicity between adjacent traveling wave stacks, calculating the average power once for each discharge of the effective stacks meeting the power frequency periodicity, and recording the sum of all the average powers in the statistical period dt as；
Step S4: fault isolation; counting the number of the traveling wave stacks with power frequency periodicity in a specified counting period dt time, wherein the counted number is Num; by the direction coefficient D, the number Num of the traveling wave stacks with power frequency periodicity and all average sums in the statistical period dtJudging whether the line has faults or not and whether the fault point is positioned at the upstream or downstream of the detection point, and carrying out hierarchical protection and isolation.
The beneficial effects of the invention are as follows: the high-resistance fault detection and isolation method based on the traveling wave positioning type secondary depth fusion on-column circuit breaker device utilizes the combination of high-frequency traveling wave and traditional transient signal detection, and greatly improves the detection and treatment capacity of weak characteristic faults such as high-resistance grounding, hidden danger discharging and the like; the high-frequency traveling wave is not influenced by a line operation mode and a fault transition resistance, and the single-phase fault detection technology of the 10kV power distribution network based on the high-frequency traveling wave detection has a wide application prospect.
On the basis of the technical scheme, the invention can be improved as follows.
Further, the transient signal processing in step S2 is specifically:
step S21: determining a characteristic frequency band range SFB, wherein the upper limit is 2kHz, the lower limit is 0.1kHz in a resonance grounding grid, a neutral point is not grounded, the lower limit is 0Hz, and when an FTU acquires a transient signal, filtering the sampled zero sequence voltage and zero sequence current in the SFB range;
step S22: setting zero sequence transient threshold value overrun triggering acquisition, and when any one of zero sequence transient voltage and zero sequence transient current exceeds a limit value, starting synchronous triggering acquisition of two zero sequence transient signals and carrying out SFB range digital filtering;
step S23: deriving the zero sequence transient voltage after filtering in SFB to obtain；
Step S24: and solving a direction coefficient D according to a formula by the filtered zero sequence transient voltage and zero sequence transient current.
Further, the calculation formula of the direction coefficient D in step S24 is:
wherein: t is the duration of the transient process, and generally takes 0.01-0.04 s according to the actual running condition.
Further, the processing of the traveling wave signal in step S3 specifically includes:
step S31: setting a traveling wave voltage and traveling wave current trigger threshold, forming a discrete array after traveling wave trigger acquisition, setting the traveling wave voltage array as U n, setting the traveling wave current array as I n, and if only one of the traveling wave voltage and the traveling wave current is triggered, invalidating the current trigger and clearing the current data; only when both meet the triggering condition, the traveling wave voltage and the traveling wave current are effective, and the traveling wave processing is waited to enter the next stage of traveling wave processing;
step S32: in the step S31, the traveling wave voltage and the traveling wave current always appear at the same time, and further the phase information of the traveling wave needs to be calculated, and only any traveling wave phase is calculated; firstly, extracting traveling wave time information, wherein the traveling wave time is related to voltage data at corresponding time by the aid of the wave recording function of three-phase power frequency voltage and three-phase power frequency current existing in the FTU, and the voltage phase at the time is the traveling wave phase;
step S33: setting the phase of the traveling wave as phi; judgingAnd->If the two criteria are met, the traveling wave data is considered to be effective in the current stage, the next processing is carried out, otherwise, the traveling wave data is not effective, and the data is required to be cleared;
step S34: calculating the traveling wave stacking average time through a formula；
Step S35: judging the power frequency periodicity between adjacent travelling wave stacks; judgingOr->Whether or not to do so, ->Generally taking 1-2 ms; when either of the two criteria is true, consider +.>And->All traveling waves in the corresponding traveling wave stackThe power frequency periodicity rule is satisfied; on the contrary, if neither criterion is fulfilled, then +.>And->All traveling waves in the corresponding traveling wave stack do not meet the power frequency periodicity rule, the traveling wave data are judged to be invalid, and +.>And->All traveling wave data in the corresponding traveling wave stack; />The unit is ms, and the accuracy is required to be within 0.1 ms;
step S36: judging the direction of the traveling wave; when step S35 judges that the traveling wave stack meets the power frequency periodicity, calculating the average power of each group of traveling waves, and recording the sum of all the average powers in the statistical period dt asBy->To determine whether the fault or potential discharge is upstream or downstream of the detection point.
Further, the formula for calculating the traveling wave stack average time in step S34 is as follows:
wherein: k is assuming that k sets of discharges are generated near a peak point, corresponding to k groups of traveling wave voltage and traveling wave current,for the average time of the traveling wave stack +.>For GPS time corresponding to the data point of the first traveling wave current amplitude value,/for GPS time corresponding to the data point of the first traveling wave current amplitude value>The magnitude of the first traveling wave current, and so on.
Further, the formula for calculating the average power of each set of traveling waves in step S36 is:
wherein P is the average power of the traveling wave, and N is the length of one traveling wave data, namely the total point number of the discrete data points.Andrespectively traveling wave current and traveling wave voltage.
Further, the fault isolation in step S4 is specifically;
step 41, synchronously monitoring, namely collecting transient and high-frequency traveling wave signals in real time, wherein the traveling wave signals need to be synchronously monitored in time sequence by a plurality of switches, counting the number of the traveling wave stacks with power frequency periodicity in the dt time of a specified statistical period, and counting as Num;
step S42, fault or hidden danger discharging criterion; the following conditions are met, namely, the line is regarded as having a ground fault or hidden discharge:
case 1:，/>the line fails, and the failure point is positioned at the downstream of the detection point;
case 2:，/>line of circuitA fault occurs, and the fault point is positioned at the upstream of the detection point;
case 3:，/>，/>the method comprises the steps of carrying out a first treatment on the surface of the The line is in fault, and the fault point is positioned at the downstream of the detection point;
case 5: otherwise, the circuit has no ground fault or hidden trouble discharge;
wherein: a and b are settable parameters, a can be set to be 3-10 according to the circuit structure and the scale setting;
step S43: hierarchical protection and isolation; by setting level difference coordination, FS3, FS2, FS1 can respectively set delay time of 0s, 0.3s, 0.6s for protection,at time +dt, each circuit breaker of the line completes the judgment of the fault, and for FS3, the fault point is upstream, so that FS3 does not operate, FS1 is longer than FS2 in time delay, so that FS2 operates preferentially at ∈2>The fault is removed after the time delay of 0.3s at the moment of +dt; if the fault point occurs downstream of FS3, FS3 is +.>At time +dt, the fault is immediately removed.
Drawings
FIG. 1 is a schematic flow chart of the present invention;
FIG. 2 is a schematic diagram of a distribution network failure according to the present invention;
fig. 3 is a timing diagram of synchronization monitoring according to the present invention.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
Embodiment 1, as shown in fig. 1 to 3, is a method for detecting and isolating a high-resistance ground fault of a power distribution network based on a broadband current signal, including an FTU (intelligent feeder terminal), a circuit breaker and a connection cable, wherein a traveling wave acquisition module is integrated inside the FTU, and includes the following steps:
step S1: extracting A, B, C three-phase traveling wave current and three-phase traveling wave voltage signals through a broadband PT (potential transformer) and a CT (current transformer), and transmitting the three-phase traveling wave current and the three-phase traveling wave voltage signals to the inside of the FTU through a multiplexing signal cable to realize the acquisition of current wave quantity;
step S2: processing transient signals; determining a characteristic frequency band range SFB (characteristic frequency band), filtering the sampled zero sequence voltage and zero sequence current in the SFB range when the FTU acquires the transient signal, and obtaining a direction coefficient D through the filtered zero sequence transient voltage and zero sequence transient current;
step S3: processing traveling wave signals; setting a traveling wave voltage and traveling wave current trigger threshold, and recording the traveling wave voltage and traveling wave current when the traveling wave trigger condition is met at the same time after traveling wave trigger acquisition; calculating the phase information of the traveling wave, reserving traveling wave data meeting the condition, calculating the average time of the traveling wave stacks, judging the power frequency periodicity between adjacent traveling wave stacks, calculating the average power once for each discharge of the effective stacks meeting the power frequency periodicity, and recording the sum of all the average powers in the statistical period dt as；
Step S4: fault isolation; counting the number of the traveling wave stacks with power frequency periodicity in a specified counting period dt time, wherein the counted number is Num, and multiple times of discharge can occur near a voltage peak at a certain moment to generate multiple groups of traveling wave data, namely the traveling wave stacks; by the direction coefficient D, the number Num of the traveling wave stacks with power frequency periodicity and all average sums in the statistical period dtJudging whether the line has faults or not and whether the fault point is positioned at the upstream or downstream of the detection point, and carrying out hierarchical protection and isolation.
The high-resistance fault detection and isolation method based on the traveling wave positioning type secondary depth fusion on-column circuit breaker device utilizes the combination of high-frequency traveling wave and traditional transient signal detection, and greatly improves the detection and treatment capacity of weak characteristic faults such as high-resistance grounding, hidden danger discharging and the like; the high-frequency traveling wave is not influenced by a line operation mode and a fault transition resistance, and the single-phase fault detection technology of the 10kV power distribution network based on the high-frequency traveling wave detection has a wide application prospect.
Example 2, as shown in fig. 1 to 3, this example is a further improvement on the basis of example 1, and is specifically as follows:
the transient signal processing in step S2 specifically includes:
step S21: determining a characteristic frequency band range SFB, wherein the upper limit is 2kHz, the lower limit is 0.1kHz in a resonance grounding grid, a neutral point is not grounded, the lower limit is 0Hz, and when an FTU acquires a transient signal, filtering the sampled zero sequence voltage and zero sequence current in the SFB range;
step S22: setting zero sequence transient threshold value overrun triggering acquisition, and when any one of zero sequence transient voltage and zero sequence transient current exceeds a limit value, starting synchronous triggering acquisition of two zero sequence transient signals and carrying out SFB range digital filtering;
step S23: deriving the zero sequence transient voltage after filtering in SFB to obtain；
Step S24: and solving a direction coefficient D according to a formula by the filtered zero sequence transient voltage and zero sequence transient current.
Example 3 this example is a further improvement over example 2, as shown in fig. 1-3, which is specifically as follows:
the calculation formula of the direction coefficient D in step S24 is:
wherein: t is the duration of the transient process, and generally takes 0.01-0.04 s according to the actual running condition.
Example 4 as shown in fig. 1 to 3, this example is a further improvement on the basis of example 1, and is specifically as follows:
the processing of the traveling wave signal in step S3 specifically includes:
step S31: setting a traveling wave voltage and traveling wave current trigger threshold, forming a discrete array after traveling wave trigger acquisition, setting the traveling wave voltage array as U n, setting the traveling wave current array as I n, and if only one of the traveling wave voltage and the traveling wave current is triggered, invalidating the current trigger and clearing the current data; only when both meet the triggering condition, the traveling wave voltage and the traveling wave current are effective, and the traveling wave processing is waited to enter the next stage of traveling wave processing;
step S32: in the step S31, the traveling wave voltage and the traveling wave current always appear at the same time, and further the phase information of the traveling wave needs to be calculated, and only any traveling wave phase is calculated; firstly, extracting traveling wave time information, wherein the traveling wave time is related to voltage data at corresponding time by the aid of the wave recording function of three-phase power frequency voltage and three-phase power frequency current existing in the FTU, and the voltage phase at the time is the traveling wave phase;
step S33: setting the phase of the traveling wave as phi, wherein the traveling wave is necessarily present near a positive peak value or a negative peak value of the voltage according to the previous description about discharge; judgingAnd->If the two criteria are met, the traveling wave data is considered to be effective in the current stage, the next processing is carried out, otherwise, the traveling wave data is not effective, and the data is required to be cleared;
step S34: calculating the traveling wave stacking average time through a formula；
Step S35: judging the power frequency periodicity between adjacent travelling wave stacks; judgingOr (b)Whether or not to do so, ->Generally taking 1-2 ms; when either of the two criteria is true, consider +.>And->All traveling waves in the corresponding traveling wave stacks meet the power frequency periodicity rule; on the contrary, if neither criterion is fulfilled, then +.>And->All traveling waves in the corresponding traveling wave stack do not meet the power frequency periodicity rule, the traveling wave data are judged to be invalid, and the traveling wave data are clearedAnd->All traveling wave data in the corresponding traveling wave stack; />The unit is ms, and the accuracy is required to be within 0.1 ms;
step S36: judging the direction of the traveling wave; when step S35 determines that the traveling wave stack satisfies the power frequency periodicity, calculating the average power of each traveling wave group, wherein each discharge is required to calculate the average power of each traveling wave group for the effective stack satisfying the power frequency periodicity, and the sum of all the average powers in the statistical period dt is recorded asBy->To determine whether the fault or potential discharge is upstream or downstream of the detection point.
When a high-resistance grounding fault occurs to a line, a fault point can generate a discontinuous discharge signal, and the discharge generally occurs near a positive peak value or a negative peak value of the operating phase voltage of the line, so that the collected traveling wave series is triggered to have power frequency periodicity, generally at intervals of about 10ms or 20ms, and the periodic rule of the traveling wave is calculated, if the periodic rule is met, the discharge can be caused by the line discharge, namely the high-frequency discharge can occur, and the realization benefits are as follows:
the influence of signals such as instantaneous interference, non-periodic interference and the like can be completely avoided, and misoperation of the switch is caused;
the characteristic of the discharge periodicity physical rule is combined, and the high-resistance ground fault identification accuracy is greatly improved.
Example 5, as shown in fig. 1 to 3, this example is a further improvement on the basis of example 4, and is specifically as follows:
the formula for calculating the traveling wave stack average time in step S34 is as follows:
wherein: k is assuming that k sets of discharges are generated near a peak point, corresponding to k groups of traveling wave voltage and traveling wave current,for the average time of the traveling wave stack +.>For GPS time corresponding to the data point of the first traveling wave current amplitude value,/for GPS time corresponding to the data point of the first traveling wave current amplitude value>The magnitude of the first traveling wave current, and so on.
The average time of the waveform pile can be made to be as close as possible to the time of the traveling wave with large amplitude, namely, the traveling wave with larger amplitude can reflect the intensity degree of high-resistance grounding, and the traveling wave occupies larger dominant weight in calculation, so that the actual objective rule is met. The final calculation result is more in line with the actual situation.
Example 6, as shown in fig. 1 to 3, this example is a further improvement on the basis of example 4, and is specifically as follows:
the formula for calculating the average power of each traveling wave group in step S36 is:
wherein P is the average power of the traveling wave, and N is the length of one traveling wave data, namely the total point number of the discrete data points.And->Respectively traveling wave current and traveling wave voltage.
And multiplying the arrays corresponding to the traveling wave voltage and the traveling wave current by the number of points in sequence, and finally summing, wherein the positive and negative of the arrays can reflect the traveling wave direction of the ground fault. In the traditional method, the positive and negative polarities of the traveling wave are directly taken, and in this way, the traveling wave polarity calculation is possibly wrong under the influence of the traveling wave form (the vibration process exists in part of the traveling wave main wavefront). The calculation method can avoid the problem of polarity judgment error caused by the travelling wave form, and improves the judgment accuracy.
Example 7, as shown in fig. 1 to 3, this example is a further improvement on the basis of example 1, and is specifically as follows:
the fault isolation in the step S4 is specifically as follows;
and step S41, synchronous monitoring, and collecting transient and high-frequency traveling wave signals in real time, wherein the traveling wave signals need to be synchronously monitored in time sequence by a plurality of switches. Firstly, setting fixed time points, generally suggesting that each whole time point is taken as the fixed time points, and 24 hours a day correspond to 24 fixed time points;when the time is=00:00:00 0 mm 0us, the three circuit breakers independently detect traveling waves, count the number of the traveling wave stacks with power frequency periodicity in the specified counting period dt time, count as Num, and the counting period dt can be flexibly set according to the line condition, and can be generally set to be 5 s-5 min>+dt, i.e. +.in FIG. 2>Outputting a judging result at a moment;
step S42, fault or hidden danger discharging criterion; the following conditions are met, namely, the line is regarded as having a ground fault or hidden discharge:
case 1:，/>the line fails, and the failure point is positioned at the downstream of the detection point;
case 2:，/>the line fails and the fault point is positioned at the upstream of the detection point;
case 3:，/>，/>the method comprises the steps of carrying out a first treatment on the surface of the The line is in fault, and the fault point is positioned at the downstream of the detection point;
case 4:，/>，/>the line fails and the fault point is positioned at the upstream of the detection point;
case 5: otherwise, the circuit has no ground fault or hidden trouble discharge;
wherein: a and b are settable parameters, a is set according to the circuit structure and the scale, and is required to be adjusted according to actual conditions during operation, and b can be set to be 3-10;
step S43: hierarchical protection and isolation; by setting level difference coordination, FS3, FS2, FS1 can respectively set delay time of 0s, 0.3s, 0.6s for protection,at time +dt, each circuit breaker of the line completes the judgment of the fault, and for FS3, the fault point is upstream, so that FS3 does not operate, FS1 is longer than FS2 in time delay, so that FS2 operates preferentially at ∈2>The fault is removed after the time delay of 0.3s at the moment of +dt; if the fault point occurs downstream of FS3, FS3 is +.>At time +dt, the fault is immediately removed.
The traditional direction coefficient method is combined with the high-frequency traveling wave, when a low-resistance fault occurs, the traditional direction coefficient method can achieve a good effect, and when a high-resistance fault occurs, the traveling wave method effectively solves the problem that the high-resistance fault detection effect of the traditional method is unreliable.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (7)
1. The utility model provides a distribution network high resistance ground fault detection and isolation method based on wide band current signal, its characterized in that includes FTU, circuit breaker and connecting cable, the inside integration of FTU has travelling wave collection module, includes following step:
step S1: extracting A, B, C three-phase traveling wave current and three-phase traveling wave voltage signals through broadband PT and CT, and transmitting the three-phase traveling wave current and the three-phase traveling wave voltage signals to the inside of the FTU through multiplexing signal cables to realize current wave quantity acquisition;
step S2: processing transient signals; determining a characteristic frequency band range SFB, filtering the sampled zero sequence voltage and zero sequence current in the SFB range when the FTU acquires the transient signal, and solving a direction coefficient D by the filtered zero sequence transient voltage and zero sequence transient current;
step S3: processing traveling wave signals; setting a traveling wave voltage and traveling wave current trigger threshold, and recording the traveling wave voltage and traveling wave current when the traveling wave trigger condition is met at the same time after traveling wave trigger acquisition; calculating the phase information of the traveling wave, reserving traveling wave data meeting the condition, calculating the average time of the traveling wave stacks, judging the power frequency periodicity between adjacent traveling wave stacks, calculating the average power once for each discharge of the effective stacks meeting the power frequency periodicity, and recording the sum of all the average powers in the statistical period dt as；
Step S4: fault isolation; counting the number of the traveling wave stacks with power frequency periodicity in the specified counting period dt time, wherein the counted number is Num; by the direction coefficient D, the number Num of the traveling wave stacks with power frequency periodicity and all average sums in the statistical period dtJudging whether the line has faults or not and whether the fault point is positioned at the upstream or downstream of the detection point, and carrying out hierarchical protection and isolation.
2. The method for detecting and isolating a high-resistance ground fault of a power distribution network based on a broadband current signal according to claim 1, wherein the processing of the transient signal in step S2 is specifically:
step S21: determining a characteristic frequency band range SFB, wherein the upper limit is 2kHz, the lower limit is 0.1kHz in a resonance grounding grid, a neutral point is not grounded, the lower limit is 0Hz, and when an FTU acquires a transient signal, filtering the sampled zero sequence voltage and zero sequence current in the SFB range;
step S22: setting zero sequence transient threshold value overrun triggering acquisition, and when any one of zero sequence transient voltage and zero sequence transient current exceeds a limit value, starting synchronous triggering acquisition of two zero sequence transient signals and carrying out SFB range digital filtering;
step S23: deriving the zero sequence transient voltage after filtering in SFB to obtain；
Step S24: and solving a direction coefficient D according to a formula by the filtered zero sequence transient voltage and zero sequence transient current.
3. The method for detecting and isolating a high-impedance ground fault of a power distribution network based on a broadband current signal according to claim 2, wherein the calculation formula of the direction coefficient D in the step S24 is as follows:
wherein: t is the duration of the transient process, and generally takes 0.01-0.04 s according to the actual running condition.
4. The method for detecting and isolating a high-impedance ground fault of a power distribution network based on a broadband current signal according to claim 1, wherein the processing of the traveling wave signal in the step S3 is specifically:
step S31: setting a traveling wave voltage and traveling wave current trigger threshold, forming a discrete array after traveling wave trigger acquisition, setting the traveling wave voltage array as U n, setting the traveling wave current array as I n, and if only one of the traveling wave voltage and the traveling wave current is triggered, invalidating the current trigger and clearing the current data; only when both meet the triggering condition, the traveling wave voltage and the traveling wave current are effective, and the traveling wave processing is waited to enter the next stage of traveling wave processing;
step S32: in the step S31, the traveling wave voltage and the traveling wave current always appear at the same time, and further, the phase information of the traveling wave needs to be calculated, and only any traveling wave phase is calculated; firstly, extracting traveling wave time information, wherein the traveling wave time is related to voltage data at corresponding time by the aid of the wave recording function of three-phase power frequency voltage and three-phase power frequency current existing in the FTU, and the voltage phase at the time is the traveling wave phase;
step S33: setting the phase of the traveling wave as phi; judgingAnd->If the two criteria are met, the traveling wave data is considered to be effective in the current stage, the next processing is carried out, otherwise, the traveling wave data is not effective, and the data is required to be cleared;
step S34: calculating the traveling wave stacking average time through a formula；
Step S35: judging the power frequency periodicity between adjacent travelling wave stacks; judgingOr (b)Whether or not to do so, ->Generally taking 1-2 ms; when either of the two criteria is met, the recognition is madeIs->And->All traveling waves in the corresponding traveling wave stacks meet the power frequency periodicity rule; on the contrary, if neither criterion is fulfilled, then +.>And->All traveling waves in the corresponding traveling wave stack do not meet the power frequency periodicity rule, the traveling wave data are judged to be invalid, and the traveling wave data are clearedAnd->All traveling wave data in the corresponding traveling wave stack; />The unit is ms, and the accuracy is required to be within 0.1 ms;
step S36: judging the direction of the traveling wave; when the step S35 judges that the traveling wave stack meets the power frequency periodicity, calculating the average power of each traveling wave group, and recording the sum of all the average powers in the statistical period dt asBy->To determine whether the fault or potential discharge is upstream or downstream of the detection point.
5. The method for detecting and isolating a high-impedance ground fault of a power distribution network based on a broadband current signal according to claim 4, wherein the formula for calculating the traveling wave stack average time in step S34 is as follows:
wherein: k is assuming that k sets of discharges are generated near a peak point, corresponding to k groups of traveling wave voltage and traveling wave current,for the average time of the traveling wave stack +.>For GPS time corresponding to the data point of the first traveling wave current amplitude value,/for GPS time corresponding to the data point of the first traveling wave current amplitude value>The magnitude of the first traveling wave current, and so on.
6. The method for detecting and isolating high-impedance ground faults of a power distribution network based on broadband current signals according to claim 4, wherein the formula for calculating the average power of each set of traveling waves in step S36 is as follows:
wherein P is the average power of the traveling wave, N is the length of one traveling wave data, namely the total point number of the discrete data points,and->Respectively traveling wave current and traveling wave voltage.
7. The method for detecting and isolating high-resistance ground faults of a power distribution network based on broadband current signals according to claim 1, wherein the fault isolation in the step S4 is specifically;
step 41, synchronously monitoring, namely collecting transient and high-frequency traveling wave signals in real time, wherein the traveling wave signals need to be synchronously monitored in time sequence by a plurality of switches, counting the number of the traveling wave stacks with power frequency periodicity in the dt time of a specified statistical period, and counting as Num;
step S42, fault or hidden danger discharging criterion; the following conditions are met, namely, the line is regarded as having a ground fault or hidden discharge:
case 1:，/>the line fails, and the failure point is positioned at the downstream of the detection point;
case 2:，/>the line fails and the fault point is positioned at the upstream of the detection point;
case 3:，/>，/>the method comprises the steps of carrying out a first treatment on the surface of the The line is in fault, and the fault point is positioned at the downstream of the detection point;
case 4:，/>，/>the line fails and the fault point is positioned at the upstream of the detection point;
case 5: otherwise, the circuit has no ground fault or hidden trouble discharge;
wherein: a and b are settable parameters, a can be set to be 3-10 according to the circuit structure and the scale setting;
step S43: hierarchical protection and isolation; by setting level difference coordination, FS3, FS2, FS1 can respectively set delay time of 0s, 0.3s, 0.6s for protection,at time +dt, each circuit breaker of the line completes the judgment of the fault, and for FS3, the fault point is upstream, so that FS3 does not operate, FS1 is longer than FS2 in time delay, so that FS2 operates preferentially at ∈2>The fault is removed after the time delay of 0.3s at the moment of +dt; if the fault point occurs downstream of FS3, FS3 is +.>At time +dt, the fault is immediately removed.
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