CN111929630B - Method and device for detecting saturation of current transformer - Google Patents
Method and device for detecting saturation of current transformer Download PDFInfo
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- CN111929630B CN111929630B CN202010666823.3A CN202010666823A CN111929630B CN 111929630 B CN111929630 B CN 111929630B CN 202010666823 A CN202010666823 A CN 202010666823A CN 111929630 B CN111929630 B CN 111929630B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/02—Testing or calibrating of apparatus covered by the other groups of this subclass of auxiliary devices, e.g. of instrument transformers according to prescribed transformation ratio, phase angle, or wattage rating
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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
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- 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
Abstract
The invention provides a method and a device for detecting the saturation of a current transformer, which are used for collecting instantaneous current data when a bus terminal fails; selecting boundary coefficients required by detection by combining the instantaneous current data; judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program, and recording the fault starting time; calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus; calculating dissimilarisation coefficients of the two currents according to the cross correlation coefficients; comparing the dissimilarisation coefficient calculated in real time with a dissimilarisation coefficient set value to determine CT saturation time; and calculating the time difference of the CT saturation time, judging whether the time difference is larger than one eighth period or not to judge the CT saturation condition when the fault occurs, wherein the time difference between the fault identification and the CT saturation start is utilized, the differentiation coefficient is used for determining the CT saturation start time, and the first derivative of the terminal current is used for calculating the fault start time.
Description
Technical Field
The invention relates to the technical field of measuring devices, in particular to a method and a device for detecting saturation of a current transformer.
Background
With the development and construction of a high-voltage direct-current transmission system, the status of a converter station with more and more transmission capacity in a power system is increasingly important, and the safety and stability of the converter station and a main grid frame are directly affected by the occurrence of faults of a bus of the converter station. The basic requirement for bus protection is the fast and reliable operation of the protection scheme, and tripping faults during internal faults or external faults as well as false trips during normal operation may catastrophically affect the safety of the power supply system and may even lead to complete outages.
With the increasing expansion of the power grid scale, the improvement of the voltage class of the power system puts more strict requirements on the accuracy and the speed of bus protection. The principle of bus protection is generally based on the principle of current differential. The differential current is obtained through CT measurement, when faults occur, the current is large and contains transient components, CT is easy to saturate, judgment and action of protection are affected, and in the related technology, the detection efficiency of the saturation of CT in the detection process is low.
Disclosure of Invention
The invention aims to provide a method and a device for detecting the saturation of a current transformer, which solve the problem of low detection efficiency of CT saturation in the detection process in the prior art.
In order to solve the technical problems, the invention adopts the following technical scheme:
according to one aspect of the present invention, there is provided a method for detecting saturation of a current transformer, including: collecting instantaneous current data when a bus terminal fails; selecting boundary coefficients required by detection by combining the instantaneous current data; judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program, and recording the fault starting time; calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus; calculating the differentiation coefficients of the two currents according to the cross correlation coefficients; comparing the dissimilarity coefficient calculated in real time with a dissimilarity coefficient set value to determine CT saturation time; and calculating the time difference of the CT saturation time, and judging whether the time difference is larger than one eighth period or not so as to judge the CT saturation condition when faults occur.
According to an aspect of the present disclosure, there is provided a detection apparatus for saturation of a current transformer, including: the collecting module is used for collecting instantaneous current data when the bus terminal fails; the selecting module is used for selecting boundary coefficients required by detection in combination with the instantaneous current data; the recording module is used for judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program and recording the fault starting time; the first calculation module is used for calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus; the second calculation model is used for calculating dissimilarisation coefficients of the two currents according to the cross-correlation coefficients; the determining module is used for comparing the dissimilarity coefficient calculated in real time with a dissimilarity coefficient set value to determine CT saturation time; and the third calculation module is used for calculating the time difference of the CT saturation time and judging whether the time difference is larger than one eighth period so as to judge the CT saturation condition when the fault occurs.
According to an aspect of the present disclosure, there is provided a computer readable program medium storing computer program instructions which, when executed by a computer, cause the computer to perform a method according to the above.
According to an aspect of the present disclosure, there is provided an electronic apparatus including: a processor; and a memory having stored thereon computer readable instructions which, when executed by the processor, implement the method described above.
As can be seen from the technical scheme, the embodiment of the invention has at least the following advantages and positive effects:
in the technical scheme provided by some embodiments of the invention, instantaneous current data when a bus terminal fails is collected; selecting boundary coefficients required by detection by combining the instantaneous current data; judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program, and recording the fault starting time; calculating the number of correlations of the currents between the two equivalent terminals of the bus; calculating dissimilarisation coefficients of the two currents according to the cross correlation coefficients; comparing the dissimilarisation coefficient calculated in real time with a dissimilarisation coefficient set value to determine CT saturation time; and calculating the time difference of the CT saturation time, judging whether the time difference is larger than one eighth period or not to judge the CT saturation condition when the fault occurs, wherein the time difference between fault identification and CT saturation start is utilized, the dissimilation coefficient is used for determining the CT saturation start time, and the first derivative of the terminal current is used for calculating the fault start time, so that the detection efficiency and the detection precision of the CT saturation in the detection process are effectively improved.
Drawings
Fig. 1 is a flow chart illustrating a method of detecting saturation of a current transformer according to an exemplary embodiment.
Fig. 2 is a basic flow chart illustrating a method of detecting saturation of a current transformer according to an exemplary embodiment.
Fig. 3 is a block diagram of a current transformer saturation detection apparatus according to an exemplary embodiment.
Fig. 4 is a hardware diagram of an electronic device, according to an example embodiment.
Fig. 5 is a computer readable storage medium illustrating a method of detecting saturation of a current transformer according to an exemplary embodiment.
Fig. 6 is a constant parameter distributed transmission line model shown according to an exemplary embodiment.
FIG. 7 is a schematic diagram illustrating real-time acquired current data according to an exemplary embodiment.
Detailed Description
Exemplary embodiments that embody features and advantages of the present invention will be described in detail in the following description. It will be understood that the invention is capable of various modifications in various embodiments, all without departing from the scope of the invention, and that the description and illustrations herein are intended to be by way of illustration only and not to be construed as limiting the invention.
With the development and construction of a high-voltage direct-current transmission system, the status of a converter station with more and more transmission capacity in a power system is increasingly important, and the safety and stability of the converter station and a main grid frame are directly affected by the occurrence of faults of a bus of the converter station. The basic requirement for bus protection is the fast and reliable operation of the protection scheme, and tripping faults during internal faults or external faults as well as false trips during normal operation may catastrophically affect the safety of the power supply system and may even lead to complete outages. Thus, it is extremely important to consolidate the accuracy and reliability factors in the design of bus bar protection schemes. Today, microprocessor-based differential relays are widely used to protect bus bars, and the fundamental application problem of these bus bar differential functions is false tripping due to CT saturation during external fault closure, so how to quickly and accurately determine if a fault is caused by CT saturation is of great significance.
The bus is connected with electric equipment such as a generator, a transformer, a transmission line, a distribution line and the like, and plays a role in receiving and distributing electric energy, so that the bus is an important electric equipment. Although the bus bar protection is set and the probability of bus bar failure is small relative to the transmission line, if the failure cannot be timely removed, a significant effect will be caused. With the increasing expansion of the power grid scale, the improvement of the voltage level of the power system puts more strict requirements on the accuracy and the speed of bus protection. The principle of bus protection is generally based on the current differential principle. The differential current is obtained through CT measurement, when faults occur, the current is large and contains transient components, CT is easy to saturate, and judgment and action of protection are affected.
The conventional CT saturation detection method for bus differential protection is divided into two algorithms. One algorithm is to compare the angular difference between the second harmonics of the first derivative signals of the differential operating current and the suppression current, which is only valid for fast CT (when CT saturation occurs in the first period after the start of the fault) but no later CT saturation can be detected. The second algorithm is applicable to fault trajectories in the operating current and constraint current graphs, which is effective for late CT saturation when the fault current is extremely high due to high dc component in the fault resulting in late CT saturation and fast CT saturation.
According to an embodiment of the present disclosure, there is provided a method for detecting saturation of a current transformer, as shown in fig. 1 and 2, including:
step S110, collecting instantaneous current data when a bus terminal fails;
step S120, selecting boundary coefficients required by detection by combining the instantaneous current data;
step S130, judging whether current data acquired in real time meet the starting standard of a detection program, if so, starting a fault detection program, and recording the fault starting time;
step S140, calculating the cross correlation coefficient of the currents between two equivalent terminals of the bus;
step S150, calculating dissimilarisation coefficients of the two currents according to the cross correlation coefficients;
step S160, comparing the dissimilarisation coefficient calculated in real time with a dissimilarisation coefficient set value to determine CT saturation time;
step S170, calculating the time difference of CT saturation time and judging whether the time difference is larger than one eighth of a period so as to judge the CT saturation condition when faults occur.
In some embodiments of the invention, instantaneous current data is collected when a bus terminal fails based on the foregoing scheme; selecting boundary coefficients required by detection by combining the instantaneous current data; judging whether current data acquired in real time meets the starting standard of a detection program, if so, starting a fault detection program, and recording the fault starting time; calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus; calculating dissimilarisation coefficients of the two currents according to the cross correlation coefficients; comparing the real-time calculated dissimilarity coefficient with a dissimilarity coefficient set value to determine CT saturation time; and calculating the time difference of the CT saturation time, judging whether the time difference is larger than one eighth period or not to judge the CT saturation condition when the fault occurs, wherein the time difference between fault identification and CT saturation start is utilized, the dissimilation coefficient is used for determining the CT saturation start time, and the first derivative of the terminal current is utilized for calculating the fault start time, so that the detection efficiency and the detection precision of the CT saturation in the detection process are effectively improved.
These steps are described in detail below.
As shown in fig. 1 and 2, in step S110, instantaneous current data when a bus terminal fails is collected;
the instantaneous current data is collected at the bus terminal, so that the fault state can be timely detected, and the instantaneous current data when the bus terminal fails can be collected.
In addition, before collecting the instantaneous current data when the bus terminal fails, the method further comprises the following steps:
when out-of-zone faults occur, the bus differential protection differential flow contains obviously intermittent periodic pulse waveforms; and the out-of-zone fault time difference flow varies substantially continuously; the CT is determined to be in saturation. The CT saturation condition can be obviously determined through the variation of the periodic pulse waveform, and the detection efficiency and the detection precision of the CT saturation are improved.
In step S120, the boundary coefficients required for detection will be selected in combination with the instantaneous current data.
Step S120 includes: in steady state, the instantaneous current connected to the bus bar terminal is expressed as
Wherein i is φk ，I φkm ，ω，θ k The instantaneous current value, the effective value, the angular frequency and the phase shift of the kth terminal are shown, respectively.
When only the absolute value is considered to be present,
when the current takes the maximum value, i.e., |sin (ωt+θ) k ) When the value of l=1,
when the current effective value is constant during steady state, I φkm (t)＝I φkm (T-T), wherein T is a period,
when it isBarrier causes i φk (t) the occurrence of a mutation,
the boundary coefficients are determined in combination with a boundary constant,
the boundary constant is greater than 1.
By judging different states, corresponding algorithms are adopted for the different states, so that errors in the overall algorithm are reduced, the change degree of instantaneous current is effectively determined, and the universality of the detection method of the saturation of the current transformer is improved.
Alternatively, the value of S should be greater than 1 according to the current condition at the time of CT saturation failure in the history data.
In step S130, it is determined whether the current data collected in real time meets the starting standard of the detection program, if yes, the fault detection program is started, and the fault starting time is recorded.
By adopting a detection pneumatic mechanism, whether current data acquired in real time meet the starting standard of a detection program is judged so as to trigger the starting of a fault detection program, and the detection efficiency and the detection precision of CT saturation are effectively ensured.
Judging whether the current data acquired in real time meets the starting standard of the detection program, if so, starting the fault detection program, and recording the fault starting time, wherein the method further comprises the following steps:
if a fault occurs, the current of the bus terminal will be suddenly changed;
taking whether the fault current is larger than the set current or not as a fault detection starting condition;
if the currents of all the terminals connected to the bus bar meet the following formula, indicating that a fault occurs, a detection algorithm can be started to detect the fault;
at this time, the time satisfying the formula is recorded, and T is set 1 ＝t，T 1 Indicating the start time of the fault.
In step S140, calculating a cross correlation coefficient of currents between two equivalent terminals of the bus bar includes: the dissimilarisation factor of two currents represents the degree of correlation of the currents in the event of a fault, and can be calculated by the following equation: a is that φ ＝1-(r φ ) 2 Wherein, r is φ The relationship of the two current signals is shown, where phi represents the A, B or C phase.
Wherein, the dissimilarity coefficient set value is calculated by historical data, and the calculation method is the same as that of the dissimilarity coefficient. The minimum dissimilarity coefficient calculated when the CT is saturated is used as the set value of the dissimilarity coefficient of the present program by the calculation of the history data.
The calculating the cross correlation coefficient of the current between the two equivalent terminals of the bus comprises the following steps:
cross correlation coefficient r of two current signals φ Can be calculated by the formula:
wherein i is φE1 And i φE2 Is the two equivalent currents derived from the two terminal equivalent representations of the bus, m represents the sample size per cycle.
Wherein the equivalence is to make the two sides of the bus bar equivalent in practice, i φE1 Indicating the total current flowing into the bus, i φE2 Indicating the total current flowing out of the bus bar. Normally, the inflow and outflow currents should be equal, and if CT is saturated, the outflow current will change.
In step S150, a dissimilarity coefficient of the two currents is calculated according to the cross correlation coefficient, and the difference between the two currents is reflected by the dissimilarity coefficient to display the degree of the difference between the two currents in a data manner.
In step S160, the dissimilarisation coefficient calculated in real time is compared with the dissimilarisation coefficient set value to determine the CT saturation time.
In step S170, a time difference of CT saturation time is calculated, and it is determined whether it is greater than one eighth of a period, so as to determine the CT saturation condition when the fault occurs, including: calculating the duration Δt of the fault from the fault start time and the CT saturation time, Δt=t 2 -T 1 The method comprises the steps of carrying out a first treatment on the surface of the If it meets
Then it is indicated that CT is saturated when a fault occurs and unsaturated otherwise.
As can be seen from the technical scheme, the embodiment of the invention has at least the following advantages and positive effects:
in the technical scheme provided by some embodiments of the invention, instantaneous current data when a bus terminal fails is collected; selecting boundary coefficients required by detection by combining the instantaneous current data; judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program, and recording the fault starting time; calculating the number of correlations of the currents between the two equivalent terminals of the bus; calculating dissimilarisation coefficients of the two currents according to the cross correlation coefficients; comparing the dissimilarisation coefficient calculated in real time with a dissimilarisation coefficient set value to determine CT saturation time; and calculating the time difference of the CT saturation time, judging whether the time difference is larger than one eighth period or not to judge the CT saturation condition when the fault occurs, wherein the time difference between fault identification and CT saturation start is utilized, the dissimilation coefficient is used for determining the CT saturation start time, and the first derivative of the terminal current is used for calculating the fault start time, so that the detection efficiency and the detection precision of the CT saturation in the detection process are effectively improved.
In addition, the method uses the dissimilarity coefficient of two instantaneous current signals found from the equivalent models at two ends of the bus, the dissimilarity coefficient is an index of dissimilarity between the two current signals, the dissimilarity coefficient is increased only when external faults occur and the two conditions of CT saturation are satisfied simultaneously, and the dissimilarity coefficient has uniqueness and can rapidly judge the saturation degree of CT.
The dissimilation coefficient index provided by the method is simple in calculation, high in calculation speed, free of phasor calculation in the whole calculation process and small in calculation process error, so that the saturation degree of CT in the fault period can be rapidly and accurately judged, and misoperation of protection caused by CT saturation is avoided.
The calculation data of the method come from instantaneous current signals, the calculation can be completed in real time in the calculation process, and the detection process has no time delay.
Referring to fig. 6, in particular, a simple 230kV test system is described to verify the performance of the proposed CT saturation detection method. In this embodiment, a constant parameter distributed transmission line model is used, with a CT ratio of 1000/5, and the generator is designed as an ideal sinusoidal voltage source with Dai Weining impedance.
Under the condition of CT saturation, collecting instantaneous current data when a bus terminal fails;
the boundary coefficients required for the detection are selected in combination with the collected current data and according to the method proposed by the present invention, in this example:
(1) Calculating the instantaneous current connected to the bus bar terminal in steady state according to equation (1):
(2) When the current takes the maximum value, i.e., |sin (ωt+θ) k ) When |=1, equation (2) can be expressed as:
the effective value of the current is constant during steady state, therefore, I φkm (t)＝I φkm (T-T), wherein T is a period. With the above assumption in mind, equation (3) may be changed to equation (4):
however, a transient event (i.e., a fault) will result in i φk (t) mutates and thus results in the relationship of equation (5).
Referring to fig. 7, according to the above steps, in the present embodiment, the value of S is set to 2.0.
Current signal for CT fast saturation occurs at t=47 ms during AG external fault
Judging whether current data acquired in real time meet the starting standard of a detection program, if so, starting a fault detection program, and recording CT saturation starting time T1;
in an embodiment, it is determined according to equation (6) provided in claim step 3 that the fault start time is 47ms, so the detection procedure starts at t=47 ms, where t1=47 ms.
According to the detection method, calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus;
according to
A cross correlation coefficient between the two terminal currents is calculated.
Calculating the dissimilarisation coefficient A of two currents according to the calculated cross correlation coefficient φ The differentiation coefficient A to be calculated in real time φ Set value A of dissimilarisation coefficient x A comparison is made to determine if it has failed and the time T2 is recorded. A is that φ ＝1-(r φ ) 2 The dissimilarisation coefficient between the terminal currents is calculated, i.e. in this embodiment:
A φ ＝1-(r φ ) 2 ＞A x
so as to determine that the bus fails, there may be CT saturation, and record the time at that moment, i.e. t2=50.2 ms.
Calculating the time difference and judging whether the time difference is larger than one eighth periodThe saturation condition of CT when the fault happens is broken, and a detection result is output, so that the time difference between the fault starting time T1 and the CT saturation time T2 is calculated, namely: Δt=t 2 -T 1 =50.2-47=3.2 ms, and there is
To sum up: in an embodiment, for an external fault at F, an abrupt change in instantaneous current to all terminals of the busbar 1 is caused during the fault. When a fault occurs at t1=47 ms, CT saturation of terminal 2 occurs at t2=50.2 ms. The response of the detection at the beginning of the fault and the final response of the proposed CT saturation detector are shown in fig. 1 and 2. As the fault begins, the first derivative of the current momentarily becomes high. Thus, the failure start detector recognizes a failure at t1=47 ms. Current dissimilarisation coefficient a φ At t2=50.2 ms, the time difference (3.2 ms) becomes higher than 1/8 period, so the detection result is output: CT satiety.
The object of the present invention is to propose a method for detecting CT saturation during an external bus fault, which uses the dissimilarisation coefficients of two instantaneous current signals found from the equivalent model at both ends of the bus. The dissimilarisation factor is an indicator of the dissimilarity between the two current signals and only becomes high during an external fault if the CT is saturated. With the appearance of an external fault, the CT will not immediately saturate, and the current waveform remains undistorted for at least about 1/6 of a cycle prior to the first saturated waveform portion. The time difference between fault identification and CT saturation onset is utilized herein, with the differentiation coefficient being used to determine CT saturation onset time and calculate the fault onset time using the first derivative of the termination current. According to the method, the dissimilation coefficient and the fault starting time are calculated from the instantaneous current signal, the calculation load of phase quantity calculation is eliminated in the calculation process, the calculation process is simple, and the judgment is quick, so that the CT saturation can be quickly and accurately detected by the method. Meanwhile, the effectiveness of this method for fast and late CT saturation is demonstrated in the examples, regardless of saturation severity.
The foregoing detailed description is directed to embodiments of the invention which are not intended to limit the scope of the invention, but rather to cover all modifications and variations within the scope of the invention.
As shown in fig. 3, in one embodiment, the device 200 for detecting saturation of a current transformer further includes:
a gathering module 210 for gathering instantaneous current data when the bus terminal fails;
a selecting module 220, configured to select a boundary coefficient required for detection in combination with the instantaneous current data;
the recording module 230 is configured to determine whether current data collected in real time meets a criterion for starting a detection program, and if so, start a fault detection program and record a fault start time;
a first calculation module 240, configured to calculate a cross correlation coefficient of currents between two equivalent terminals of the bus;
a second calculation model 250 for calculating a dissimilarisation factor of the two currents according to the cross correlation factor;
a determining module 260, configured to compare the dissimilarity coefficient calculated in real time with the dissimilarity coefficient set point to determine a CT saturation time;
the third calculation module 270 calculates the time difference of the CT saturation time and determines whether it is greater than one eighth period to determine the CT saturation condition when the fault occurs.
An electronic device 40 according to this embodiment of the invention is described below with reference to fig. 4. The electronic device 40 shown in fig. 4 is only an example and should not be construed as limiting the functionality and scope of use of embodiments of the present invention.
As shown in fig. 4, the electronic device 40 is in the form of a general purpose computing device. Components of electronic device 40 may include, but are not limited to: the at least one processing unit 41, the at least one memory unit 42, a bus 43 connecting the different system components, including the memory unit 42 and the processing unit 41.
Wherein the storage unit stores program code that is executable by the processing unit 41 such that the processing unit 41 performs the steps according to various exemplary embodiments of the present invention described in the above-mentioned "example methods" section of the present specification.
The memory unit 42 may include readable media in the form of volatile memory units, such as Random Access Memory (RAM) 421 and/or cache memory 422, and may further include Read Only Memory (ROM) 423.
The storage unit 42 may also include a program/utility tool 424 having a set (at least one) of program modules 425, such program modules 425 including, but not limited to: an operating system, one or more application programs, other program modules, and program data, each or some combination of which may include an implementation of a network environment.
The bus 43 may be one or more of several types of bus structures including a memory unit bus or memory unit controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.
From the above description of embodiments, those skilled in the art will readily appreciate that the example embodiments described herein may be implemented in software, or may be implemented in software in combination with the necessary hardware. Thus, the technical solution according to the embodiments of the present disclosure may be embodied in the form of a software product, which may be stored in a non-volatile storage medium (may be a CD-ROM, a U-disk, a mobile hard disk, etc.) or on a network, including several instructions to cause a computing device (may be a personal computer, a server, a terminal device, or a network device, etc.) to perform the method according to the embodiments of the present disclosure.
According to an embodiment of the present disclosure, there is also provided a computer-readable storage medium having stored thereon a program product capable of implementing the method described above in the present specification. In some possible embodiments, the various aspects of the invention may also be implemented in the form of a program product comprising program code for causing a terminal device to carry out the steps according to the various exemplary embodiments of the invention as described in the "exemplary methods" section of this specification, when said program product is run on the terminal device.
Referring to fig. 5, a program product 50 for implementing the above-described method according to an embodiment of the present invention is described, which may employ a portable compact disc read only memory (CD-ROM) and include program code, and may be run on a terminal device, such as a personal computer. However, the program product of the present invention is not limited thereto, and in this document, a readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
The program product may employ any combination of one or more readable media. The readable medium may be a readable signal medium or a readable storage medium. The readable storage medium can be, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or a combination of any of the foregoing. More specific examples (a non-exhaustive list) of the readable storage medium would include the following: an electrical connection having one or more wires, a portable disk, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.
The computer readable signal medium may include a data signal propagated in baseband or as part of a carrier wave with readable program code embodied therein. Such a propagated data signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination of the foregoing. A readable signal medium may also be any readable medium that is not a readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code embodied on a readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
Program code for carrying out operations of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device, partly on a remote computing device, or entirely on the remote computing device or server. In the case of remote computing devices, the remote computing device may be connected to the user computing device through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computing device (e.g., connected over the Internet using an Internet service provider).
Furthermore, the above-described drawings are only illustrative of the processes involved in the method according to the exemplary embodiment of the present invention, and are not intended to be limiting. It will be readily appreciated that the processes shown in the above figures do not indicate or limit the temporal order of these processes. In addition, it is also readily understood that these processes may be performed synchronously or asynchronously, for example, in a plurality of modules.
It is to be understood that the invention is not limited to the precise arrangements and instrumentalities shown in the drawings, which have been described above, and that various modifications and changes may be effected without departing from the scope thereof. The scope of the invention is limited only by the attached claims.
Claims (10)
1. A method for detecting saturation of a current transformer, comprising:
collecting instantaneous current data when a bus terminal fails;
selecting boundary coefficients required by detection by combining the instantaneous current data;
judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program, and recording the fault starting time;
calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus;
calculating dissimilarisation coefficients of the two currents according to the cross correlation coefficients;
comparing the dissimilarisation coefficient calculated in real time with a dissimilarisation coefficient set value to determine CT saturation time;
and calculating the time difference of the CT saturation time, and judging whether the time difference is larger than one eighth period or not so as to judge the CT saturation condition when faults occur.
2. The method for detecting saturation of a current transformer according to claim 1, wherein said selecting boundary coefficients required for detection in combination with said instantaneous current data comprises:
in steady state, the instantaneous current connected to the bus bar terminal is expressed as
Wherein i is φk ，I φkm ，ω，θ k Respectively representing the instantaneous current value, the effective value, the angular frequency and the phase shift of the kth terminal;
when only the absolute value is considered to be present,
when the current takes the maximum value, i.e., |sin (ωt+θ) k ) When the value of l=1,
when the current effective value is constant during steady state, I φkm (t)＝I φkm (T-T), wherein T is a period,
when a fault results in i φk (t) the occurrence of a mutation,
the boundary coefficients are determined in combination with a boundary constant,
the boundary constant is larger than 1, and the S value is larger than 1 according to the current condition during CT saturation fault in the historical data.
3. The method for detecting saturation of current transformer according to claim 2, wherein said determining whether current data collected in real time satisfies a criterion for starting a detection program, if so, starting a fault detection program, and recording a fault start time, further comprises:
if a fault occurs, the current of the bus terminal will be suddenly changed;
taking whether the fault current is larger than the set current or not as a fault detection starting condition;
if the currents of all the terminals connected to the bus bar meet the following formula, indicating that a fault occurs, a detection algorithm can be started to detect the fault;
at this time, the time satisfying the formula is recorded, and T is set 1 ＝t，T 1 The fault starting time is represented, and the S value is larger than 1 according to the current condition of CT saturation fault in the historical data.
4. The method for detecting saturation of a current transformer according to claim 1, wherein calculating a cross correlation coefficient of currents between two equivalent terminals of a bus bar comprises:
cross correlation coefficient r of two current signals φ Can be calculated by the formula:
wherein i is φE1 And i φE2 Is the two equivalent currents derived from the two terminal equivalent representations of the bus, m represents the sample size per cycle.
5. The method for detecting saturation of a current transformer according to claim 1, wherein calculating a dissimilarisation factor of two currents from the cross correlation factor comprises:
the dissimilarisation factor of two currents represents the degree of correlation of the currents in the event of a fault, and can be calculated by the following equation: a is that φ ＝1-(r φ ) 2 Wherein, r is φ The relationship of the two current signals is shown, where phi represents the A, B or C phase.
6. The method for detecting saturation of current transformer according to claim 1, wherein calculating the time difference of the CT saturation time and judging whether it is greater than one eighth period to judge the CT saturation condition at the time of failure comprises:
calculating the duration Δt of the fault from the fault start time and the CT saturation time, Δt=t 2 -T 1 The method comprises the steps of carrying out a first treatment on the surface of the If it meets
Then it is indicated that CT is saturated when a fault occurs, whereas it is unsaturated, and T2 is the time of the fault.
7. The method for detecting saturation of a current transformer according to claim 1, further comprising, before collecting instantaneous current data when a bus terminal fails:
when out-of-zone faults occur, the bus differential protection differential flow contains obviously intermittent periodic pulse waveforms; and the out-of-zone fault time difference flow varies substantially continuously;
the CT is determined to be in saturation.
8. A current transformer saturation detection device, comprising:
the collecting module is used for collecting instantaneous current data when the bus terminal fails;
the selecting module is used for selecting boundary coefficients required by detection in combination with the instantaneous current data;
the recording module is used for judging whether the current data acquired in real time meet the starting standard of the detection program, if so, starting the fault detection program and recording the fault starting time;
the first calculation module is used for calculating the cross correlation coefficient of the currents between the two equivalent terminals of the bus;
the second calculation model is used for calculating dissimilarity coefficients of the two currents according to the cross correlation coefficient;
the determining module is used for comparing the dissimilarity coefficient calculated in real time with a dissimilarity coefficient set value to determine CT saturation time;
and the third calculation module is used for calculating the time difference of the CT saturation time and judging whether the time difference is larger than one eighth period so as to judge the CT saturation condition when the fault occurs.
9. A computer readable program medium, characterized in that it stores computer program instructions, which when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 7.
10. An electronic device, comprising:
a processor;
a memory having stored thereon computer readable instructions which, when executed by the processor, implement the method of any of claims 1 to 7.
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