A method and system for preventing maloperation of transformer differential protection

Abstract

The application discloses a method and system for preventing maloperation of transformer differential protection, and the method comprises the following steps: step 1, obtaining sampling value data of N sampling points based on a current differential current sampling point and N-1 sampling points before the current differential current sampling point; step 2, setting a maximum cycle number M and initializing m=1; step 3, selecting m sampling value data with the maximum absolute value in the N sampling value data as a first data set, and the remaining data as a second data set; step 4, calculating the average value of the absolute values of all sampling value data in the second data set, and calculating the ratio of the average value to the maximum absolute value in the sampling value data; step 5, if the ratio is less than or equal to a preset threshold value, and the current differential current sampling point is the sampling point corresponding to the data in the first data set, it is determined that there are m abnormal large number points in the data window, and the current sampling point is an abnormal large number point; and step 6, shielding the abnormal large number point to prevent the transformer differential protection from acting.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection, and more particularly, to a method and system for preventing malfunction of transformer differential protection. Background Art

[0002] As a key component of the power system, the safe and reliable operation of power transformers is crucial. When an internal fault occurs in a transformer, the transformer's relay protection device detects and clears the fault, ensuring both transformer safety and the stable operation of the power system.

[0003] Current differential protection, the primary protection for transformers, is widely used due to its simple principle and excellent selectivity. Conventional differential protection employs corresponding blocking elements to prevent malfunctions due to abnormal conditions other than internal faults, such as CT saturation and magnetizing inrush current. Therefore, the operating time of conventional differential protection is closely linked to the performance of these blocking elements. Furthermore, to prevent the blocking elements from affecting the protection's operating speed and preventing it from quickly clearing the fault in the event of a severe internal transformer fault, transformer protection devices are often equipped with differential fast-tripping protection elements that do not require any blocking. Relevant technical standards require differential protection to operate within 30ms and differential tripping within 20ms. However, in recent years, severe faults have led to the rapid rise of fault currents, resulting in rapid energy accumulation and heat dissipation, which can ultimately lead to transformer explosions and combustion. To address this issue, fast differential tripping protection algorithms have been proposed. However, these algorithms, which rely on sample value integration, are significantly affected by abnormal sample values. When an out-of-zone fault occurs, accompanied by an abnormally large number of sample values, these protection algorithms can malfunction.

[0004] Therefore, a method for preventing transformer differential protection from malfunctioning is needed. Summary of the Invention

[0005] The present invention provides a method and system for preventing malfunction of transformer differential protection, so as to solve the problem of how to prevent malfunction of transformer differential protection.

[0006] In order to solve the above problem, according to one aspect of the present invention, a method for preventing malfunction of transformer differential protection is provided, the method comprising:

[0007] Step 1: Based on the current differential current sampling point and the N-1 sampling points before it, obtain the sampling value data of N sampling points;

[0008] Step 2, set the maximum number of loops M and initialize m=1;

[0009] Step 3: Select m sample value data with the largest absolute value among N sample value data as the first data set, and the remaining data as the second data set;

[0010] Step 4, averaging the absolute values ​​of all sampled data in the second data set, and calculating the ratio of the average value to the maximum absolute value in the sampled data;

[0011] Step 5: If the ratio is less than or equal to a preset threshold, and the current differential current sampling point is a sampling point corresponding to the data in the first data set, then it is determined that there are m abnormally large points in the data window, and the current sampling point is an abnormally large point;

[0012] Step 6: shielding the abnormally large number points to prevent the transformer differential protection from operating.

[0013] Preferably, the method further comprises:

[0014] If the ratio is less than or equal to the preset threshold, and the current differential current sampling point is not the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is not an abnormally large point.

[0015] Preferably, the method further comprises:

[0016] If the ratio is greater than the preset threshold, it is determined whether m<M is satisfied. If so, m=m+1 is updated and the calculation is returned to step 3 to be recalculated. If not, it is determined that there are no abnormally large points in the data window.

[0017] Preferably, the preset threshold is 0.01.

[0018] According to another aspect of the present invention, a system for preventing malfunction of transformer differential protection is provided, the system comprising:

[0019] A data acquisition unit is used to acquire sampling value data of N points based on the current differential current sampling point and the N-1 sampling points before it;

[0020] A setting unit is used to set the maximum number of loops M and initialize m=1;

[0021] A data selection unit is used to select m sample value data with the largest absolute value from N sample value data as a first data set, and the remaining data as a second data set;

[0022] a ratio determination unit, configured to average the absolute values ​​of all sampled value data in the second data set, and calculate a ratio of the average value to a maximum absolute value in the sampled value data;

[0023] an abnormally large number point determining unit, configured to determine that there are m abnormally large number points in the data window and that the current sampling point is an abnormally large number point if the ratio is less than or equal to a preset threshold and the current differential current sampling point is a sampling point corresponding to data in the first data set;

[0024] The data shielding unit is used to shield the abnormally large number points to prevent the transformer differential protection from operating.

[0025] Preferably, the abnormally large number point determining unit is further configured to:

[0026] If the ratio is less than or equal to the preset threshold, and the current differential current sampling point is not the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is not an abnormally large point.

[0027] Preferably, the abnormally large number point determining unit further includes:

[0028] If the ratio is greater than a preset threshold, it is determined whether m<M is satisfied. If so, m=m+1 is updated and the calculation is returned to the data selection unit for recalculation. If not, it is determined that there are no abnormally large points in the data window.

[0029] Preferably, the preset threshold is 0.01.

[0030] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, the program implements any step of a method for preventing malfunction of transformer differential protection.

[0031] According to another aspect of the present invention, the present invention provides an electronic device, comprising:

[0032] The computer-readable storage medium described above; and

[0033] One or more processors are configured to execute the program in the computer-readable storage medium.

[0034] The present invention provides a method and system for preventing transformer differential protection from malfunctioning. The method comprises: step 1, based on a current differential current sampling point and N-1 sampling points before it, obtaining sampling value data of N sampling points; step 2, setting a maximum number of cycles M and initializing m=1; step 3, selecting m sampling value data with the largest absolute values ​​among the N sampling value data as a first data set, and the remaining data as a second data set; step 4, averaging the absolute values ​​of all sampling value data in the second data set, and calculating the ratio of the average value to the maximum absolute value in the sampling value data; step 5, if the ratio is less than or equal to a preset threshold value and the current differential current sampling point is the sampling point corresponding to the data in the first data set, determining that m abnormally large points exist in the data window and the current sampling point is an abnormally large point; and step 6, shielding the abnormally large point to prevent the transformer differential protection from operating. The present invention can identify multiple abnormally large number points and shield the abnormally large number points after identifying the abnormal sampling, thereby ensuring the safety of the fast differential algorithm, that is, avoiding protection malfunctions caused by the existence of abnormally large numbers in the event of out-of-zone faults or other disturbances. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0036] Figure 1 Flowchart of a method 100 for preventing malfunction of transformer differential protection according to an embodiment of the present invention;

[0037] Figure 2 1. An exemplary diagram of a method for preventing malfunction of transformer differential protection according to an embodiment of the present invention;

[0038] Figure 3 1 is a grid-side three-phase current waveform diagram when a single-phase grounding fault occurs at the busbar-side outlet of the grid-side CT of the transformer according to an embodiment of the present invention;

[0039] Figure 4 Schematic diagram of three abnormally large points appearing in the simulation of valve-side A-phase current sampling according to an embodiment of the present invention;

[0040] Figure 5 Schematic diagram of three-phase differential current when a single-phase grounding fault occurs at the busbar-side outlet (outside the small differential area) of the grid-side CT of the transformer according to an embodiment of the present invention;

[0041] Figure 6 A waveform diagram of an abnormally large number point identification result of a differential current according to an embodiment of the present invention;

[0042] Figure 7(a) and (b) are respectively grid-side and valve-side three-phase current waveforms when a single-phase grounding fault occurs at phase A at the transformer-side CT outlet via a 44Ω transition resistor according to an embodiment of the present invention;

[0043] Figure 8 A waveform diagram of an abnormally large number point identification wave according to an embodiment of the present invention;

[0044] Figure 9 A schematic diagram of an abnormally large number point recognition result according to an embodiment of the present invention;

[0045] Figure 10 1 is a schematic structural diagram of a system 1000 for preventing malfunction of transformer differential protection according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0047] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0048] Figure 1 FIG. 1 is a flow chart of a method 100 for preventing transformer differential protection from malfunction according to an embodiment of the present invention. Figure 1 As shown, the method for preventing transformer differential protection malfunction provided by an embodiment of the present invention can identify multiple abnormally large number points and, after identifying abnormal sampling, shield the abnormally large number points, thereby ensuring the safety of the fast differential algorithm, that is, avoiding protection malfunction caused by the presence of abnormally large numbers in the event of an out-of-zone fault or other disturbance. The method 100 for preventing transformer differential protection malfunction provided by an embodiment of the present invention begins at step 101. In step 101, based on the current differential current sampling point and the N-1 sampling points before it, sample value data of N sampling points is obtained.

[0049] In step 102, the maximum number of loops M is set, and m=1 is initialized.

[0050] In step 103 , m sampling value data with the largest absolute values ​​among N sampling value data are selected as the first data set, and the remaining data are selected as the second data set.

[0051] In step 104, an average value is obtained for the absolute values ​​of all the sampled data in the second data set, and a ratio of the average value to the maximum absolute value in the sampled data is calculated.

[0052] In step 105, if the ratio is less than or equal to the preset threshold, and the current differential current sampling point is the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is an abnormally large point.

[0053] In step 106, the abnormally large number point is shielded to prevent the transformer differential protection from operating.

[0054] Preferably, the method further comprises:

[0055] If the ratio is less than or equal to the preset threshold, and the current differential current sampling point is not the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is not an abnormally large point.

[0056] Preferably, the method further comprises:

[0057] If the ratio is greater than the preset threshold, it is determined whether m<M is satisfied. If so, m=m+1 is updated and the calculation is returned to step 3 to be recalculated. If not, it is determined that there are no abnormally large points in the data window.

[0058] Preferably, the preset threshold is 0.01.

[0059] Combine Figure 2 As shown, M=3 is taken as an example for description.

[0060] In the present invention, the first step is to identify the abnormally large number of differential current points. The current k-th differential current sampling point and the N-1 points before it, a total of N differential current sampling values, are used to identify the abnormally large number of differential current points. Figure 2 As shown, the judgment process is:

[0061] First, the N sampling points in the data window are calculated as shown in formula (1). That is, the sampling value with the largest absolute value among the N sampling values ​​is selected, and then the absolute values ​​of all sampling values ​​except this maximum value are averaged. Next, the ratio of this average value to the maximum absolute value is calculated to obtain the ratio λ1. If λ1 is less than a certain value k1, it is determined that there is an abnormally large value among the N differential flow sampling points. Further determine whether the current sampling point is the sampling point with the largest absolute value selected previously. If so, the current sampling point is an abnormally large value. Otherwise, it indicates that there is an abnormally large value in the current data window, but it is not the current differential flow sampling point. If the calculated λ1 is greater than a certain value, it is necessary to determine the two abnormally large values. The ratio λ2 is calculated using formula (2).

[0062] The calculation of λ2 is similar to λ1. When calculating the average value, the maximum and second-largest absolute values ​​are subtracted, and only the average value of N-2 points is calculated. The obtained λ2 is compared with the fixed value k2. If the ratio is less than the fixed value, it is determined that there are two abnormally large values ​​among the N differential flow sampling points. Further judgment is made as to whether the current sampling point belongs to the previously selected sampling point with the largest or second-largest absolute value. If so, it is determined that the current sampling point is one of the two abnormally large values. Otherwise, it indicates that there are two abnormally large values ​​in the current data window, but they are not the current differential flow sampling point. If the calculated λ2 is still greater than a certain value, it is necessary to judge the three abnormally large values. Calculate λ3 using formula (3).

[0063] The calculation of λ3 is similar to that of λ1 and λ2. When calculating the average value, simply subtract the maximum, second-largest, and third-largest values, and only calculate the average value of N-3 points. Comparing λ3 with the constant k3, if the ratio is less than the constant, it is determined that there are three abnormally large values ​​among the N differential flow sampling points. Further determination is made as to whether the current sampling point belongs to the previously selected sampling point with the largest, second-largest, or third-largest absolute value. If so, it is determined that the current sampling point is one of the three abnormally large values. Otherwise, it indicates that there are three abnormally large values ​​in the current data window, but they are not the current differential flow sampling point. If the calculated λ3 is still greater than a certain constant k3, it is determined that there are no abnormally large values ​​among the N sampling points.

[0064] in,

[0065]

[0066]

[0067]

[0068] Where k1, k2, and k3 are preset thresholds, with a recommended value of 0.01. N is the number of sampling points, and k represents the kth sampling point.

[0069] In the present invention, the identification of 4, 5, 6, ... multiple abnormally large points can be performed according to the set M.

[0070] In the present invention, after identifying abnormally large number points, the differential algorithm can take corresponding measures to shield the abnormally large number points, thereby ensuring the safety of the fast differential algorithm, that is, avoiding protection malfunctions caused by the existence of abnormally large numbers in the event of out-of-zone faults or other disturbances.

[0071] In the present invention, RTDS is used to carry out internal and external fault simulation verification.

[0072] (1) Out-of-area faults (with abnormally large numbers)

[0073] When a single-phase grounding fault occurs at the busbar outlet of the transformer grid-side CT, the grid-side three-phase current waveform is as follows: Figure 3 As shown in the figure, there are three abnormally large numbers in the current sampling of phase A on the simulated valve side, such as Figure 4 As shown; when a single-phase grounding fault occurs at the transformer grid side CT outlet near the bus side (outside the small difference area), the three-phase differential current is as follows Figure 5 As shown, the waveform of the abnormal large number of differential current identification results is as follows Figure 6 shown.

[0074] In the abnormally large number identification result, the value of the criterion waveform at the current sampling point is an integer N, which means that within the time window of 10 sampling points with the current point as the reference point, there are N sampling points identified as abnormally large numbers, and the current sampling point is one of them.

[0075] If the value of the criterion waveform at the current sampling point is fraction N+0.5, it means that within the time window of 10 sampling points with the current point as the reference point, there are N sampling points identified as abnormally large, and the current sampling point is not identified as an abnormally large sampling point.

[0076] (2) Faults within the area

[0077] When the transformer grid side CT is close to the transformer side outlet, the A phase has a single-phase grounding fault through a 44Ω transition resistor. The original waveforms of the currents on each side and the three-phase current waveforms on the valve side are as follows: Figure 7 As shown in (a) and (b), the original waveform of the differential current is as follows Figure 8 As shown, the waveform of the abnormal large number of differential current identification results is as follows Figure 9 shown.

[0078] As can be seen from the above, the method proposed in this patent can effectively identify abnormally large numbers when there are abnormally large numbers of faults outside the zone, avoid false operations outside the zone, and faults within the zone will not be mistakenly identified as abnormally large numbers. It can effectively solve the problem of the contradiction between improving the protection action speed and the protection safety and reliability under serious faults.

[0079] Figure 10 FIG. 1 is a schematic structural diagram of a system 1000 for preventing malfunction of transformer differential protection according to an embodiment of the present invention. Figure 10 As shown, the system 1000 for preventing misoperation of transformer differential protection provided in an embodiment of the present invention includes: a data acquisition unit 1001, a setting unit 1002, a data selection unit 1003, a ratio determination unit 1004, an abnormally large number point determination unit 1005 and a data shielding unit 1006.

[0080] Preferably, the data acquisition unit 1001 is configured to acquire N sampling value data points based on the current differential current sampling point and the N-1 sampling points before it.

[0081] Preferably, the setting unit 1002 is used to set a maximum number of cycles M and initialize m=1.

[0082] Preferably, the data selection unit 1003 is configured to select m sampling value data with the largest absolute values ​​from N sampling value data as the first data set, and the remaining data as the second data set.

[0083] Preferably, the ratio determination unit 1004 is configured to average the absolute values ​​of all sampled value data in the second data set, and calculate the ratio of the average value to the maximum absolute value in the sampled value data.

[0084] Preferably, the abnormally large number point determining unit 1005 is configured to determine that there are m abnormally large number points in the data window and that the current sampling point is an abnormally large number point if the ratio is less than or equal to a preset threshold and the current differential current sampling point is a sampling point corresponding to the data in the first data set.

[0085] Preferably, the abnormally large number point determining unit 1005 is further configured to:

[0086] If the ratio is less than or equal to the preset threshold, and the current differential current sampling point is not the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is not an abnormally large point.

[0087] Preferably, the abnormally large number point determining unit 1005 further includes:

[0088] If the ratio is greater than a preset threshold, it is determined whether m<M is satisfied. If so, m=m+1 is updated and the calculation is returned to the data selection unit for recalculation. If not, it is determined that there are no abnormally large points in the data window.

[0089] Preferably, the preset threshold is 0.01.

[0090] Preferably, the data shielding unit 1006 is used to shield the abnormally large number points to prevent the transformer differential protection from operating.

[0091] The system 1000 for preventing malfunction of transformer differential protection according to the embodiment of the present invention corresponds to the method 100 for preventing malfunction of transformer differential protection according to another embodiment of the present invention, and will not be described in detail herein.

[0092] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, the program implements any step of a method for preventing malfunction of transformer differential protection.

[0093] According to another aspect of the present invention, the present invention provides an electronic device, comprising:

[0094] The computer-readable storage medium described above; and

[0095] One or more processors are configured to execute the program in the computer-readable storage medium.

[0096] The present invention has been described with reference to a few embodiments. However, it is apparent to those skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the present invention.

[0097] Generally, all terms used in this disclosure are to be interpreted according to their ordinary meaning in the art, unless explicitly defined otherwise herein. All references to "a / the / the [device, component, etc.]" are to be interpreted openly as referring to at least one instance of the device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0098] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0099] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0100] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0101] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preventing malfunction of transformer differential protection, characterized in that: The method comprises: Step 1: Based on the current differential current sampling point and the N-1 sampling points before it, obtain the sampling value data of N sampling points; Step 2, set the maximum number of loops M and initialize m=1; Step 3: Select m sample value data with the largest absolute value among N sample value data as the first data set, and the remaining data as the second data set; Step 4, averaging the absolute values ​​of all sampled data in the second data set, and calculating the ratio of the average value to the maximum absolute value in the sampled data; Step 5: If the ratio is less than or equal to a preset threshold, and the current differential current sampling point is a sampling point corresponding to the data in the first data set, then it is determined that there are m abnormally large points in the data window, and the current sampling point is an abnormally large point; Step 6: shielding the abnormally large number points to prevent the transformer differential protection from operating; The method further comprises: If the ratio is greater than the preset threshold, it is determined whether m<M is satisfied. If so, m=m+1 is updated and the calculation is returned to step 3 to be recalculated. If not, it is determined that there are no abnormally large points in the data window.

2. The method according to claim 1, characterized in that The method further comprises: If the ratio is less than or equal to the preset threshold, and the current differential current sampling point is not the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is not an abnormally large point.

3. The method according to claim 1, characterized in that The preset threshold is 0.

01.

4. A system for preventing transformer differential protection from malfunctioning, characterized in that: The system comprises: A data acquisition unit is used to acquire sampling value data of N points based on the current differential current sampling point and the N-1 sampling points before it; A setting unit is used to set the maximum number of loops M and initialize m=1; A data selection unit is used to select m sample value data with the largest absolute value from N sample value data as a first data set, and the remaining data as a second data set; a ratio determination unit, configured to average the absolute values ​​of all sampled value data in the second data set, and calculate a ratio of the average value to a maximum absolute value in the sampled value data; an abnormally large number point determining unit, configured to determine that there are m abnormally large number points in the data window and that the current sampling point is an abnormally large number point if the ratio is less than or equal to a preset threshold and the current differential current sampling point is a sampling point corresponding to data in the first data set; A data shielding unit, used for shielding the abnormally large number points to prevent the transformer differential protection from operating; Wherein, the abnormally large number point determining unit further includes: If the ratio is greater than a preset threshold, it is determined whether m<M is satisfied. If so, m=m+1 is updated and the calculation is returned to the data selection unit for recalculation. If not, it is determined that there are no abnormally large points in the data window.

5. The system according to claim 4, characterized in that The abnormally large number point determination unit is further used to: If the ratio is less than or equal to the preset threshold, and the current differential current sampling point is not the sampling point corresponding to the data in the first data set, it is determined that there are m abnormally large points in the data window, and the current sampling point is not an abnormally large point.

6. The system according to claim 4, characterized in that The preset threshold is 0.

01.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 3 are implemented.

8. An electronic device, characterized in that: include: The computer-readable storage medium of claim 7; as well as One or more processors are configured to execute the program in the computer-readable storage medium.

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