Detection method for current transformer secondary circuit disconnection fault based on pulsating voltage

Abstract

The invention discloses a pulsating voltage-based current transformer secondary circuit disconnection fault detection method, and belongs to the technical field of power distribution network fault detection. According to the invention, the correlation between the real-time voltage signal induced by the voltage transformer and the reference voltage is considered on the basis of the current transformer secondary circuit disconnection difference current criterion; the method has the core effects that the current transformer secondary circuit disconnection fault and the high-resistance grounding fault of the power transmission current are distinguished according to the pulsation rhythm with the specific length in the correlation coefficient between the real-time voltage signal and the reference voltage information, so that the small-amplitude sinusoidal current distinguishing capability of a power transformation secondary system device is improved; and the detection accuracy of the secondary circuit disconnection fault of the current transformer of the power transmission line is greatly improved.

Description

Technical Field

[0001] This invention provides a method for detecting open circuit faults in the secondary circuit of a current transformer based on pulsating voltage, belonging to the field of power distribution network fault detection technology. Background Technology

[0002] Relay protection devices are key equipment in substations. They perform various protection functions by sensing characteristic quantities such as current. Current, as the most important electrical characteristic quantity, directly affects the correctness of protection operation. For a long time, the integrity of the current loop has been a key focus of protection device operation and maintenance. A current transformer (CT) open circuit, i.e., a break in the secondary circuit of the current transformer, is a typical current loop anomaly. Conventional CT open circuit judgments generally use electrical quantities such as differential current for identification, comparing these quantities with a threshold value to determine if a CT is open.

[0003] The current detection current loop primarily uses differential current as the criterion for determining CT disconnection. This criterion is employed by protection systems such as GE-B90, SEL 487B, and REB500, which compares the differential current sensed by the protection with the disconnection lockout value. For example, if a phase CT disconnects on a line, the current in that phase is almost zero. If the differential current calculated from the currents of each phase of each line exceeds the lockout value (this value is much smaller than the operating setpoint, typically 0.15In), a time-delay alarm and line protection are triggered. However, when a high-resistance ground fault occurs, if the differential current exceeds the lockout value and persists for a period (exceeding the Ts delay), this high-resistance ground fault is easily misjudged as a CT disconnection, leading to the lockout of the protection device and delaying timely fault clearing. Summary of the Invention

[0004] The technical problem to be solved by this invention is: how to improve the detection accuracy of open circuit faults in the secondary circuit of current transformers.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is: a method for detecting open circuit faults in the secondary circuit of a current transformer based on pulsating voltage, involving a transmission line, a first protection device, a second protection device, a first current transformer, a second current transformer, a first voltage transformer, and a second voltage transformer; the first protection device, the first current transformer, and the first voltage transformer are installed at the beginning of the transmission line; the second protection device, the second current transformer, and the second voltage transformer are installed at the end of the transmission line; the sampling frequency of the first protection device and the second protection device... Both are 1200Hz, and the detection method includes the following steps:

[0006] Step 1: Set the detection period T for secondary open circuit faults of the current transformer in the transmission line. The detection period T includes n current signal cycles in the transmission line. The n is a natural number greater than 4, and the current signal period is... It takes 0.02 seconds;

[0007] Step 2: The first protection device operates according to the sampling frequency. The instantaneous values ​​of the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer within one detection period T are acquired in real time and collected to form an initial real-time signal sequence of the secondary voltage at the beginning of the transmission line. As shown in equation (1) below,

[0008] (1)

[0009] In equation (1), The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer within one detection cycle T. The instantaneous value collected during the next sampling; The first protection device performs this within one detection cycle T. The instantaneous value of the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer during the t-th sampling in the sampling process; The first protection device performs [the detection] within one detection cycle T. The instantaneous values ​​of the secondary voltages of phases A, B, and C of the line head secondary voltage signal generated by the first voltage transformer in the t-th sampling during the sampling process.

[0010] The second protection device is based on the sampling frequency. Real-time acquisition of the instantaneous values ​​of the secondary voltage signal at the end of the transmission line generated by the second voltage transformer within one detection period T, and collection of these values ​​to form an initial real-time signal sequence of the secondary voltage at the end of the transmission line. As shown in equation (1) below,

[0011] (1)

[0012] In equation (1), The second protection device performs the first, second, and third detections on the secondary voltage signal at the end of the transmission line generated by the second voltage transformer within one detection cycle T. The instantaneous value collected during the next sampling; The second protection device performs this within one detection cycle T. The instantaneous value of the secondary voltage signal at the end of the transmission line generated by the second voltage transformer in the t-th sampling during the sampling process; The second protection device performs the detection within one detection cycle T. The instantaneous values ​​of the secondary voltages of phases A, B, and C of the line end secondary voltage signal generated by the second voltage transformer in the t-th sampling during the sampling process.

[0013] Step 3: Obtain the amplitude value as 57.7. A three-phase sinusoidal reference voltage signal with a frequency of 50Hz and a duration of one detection period T is used, with the sampling frequency... The A, B, and C phases of the three-phase sinusoidal reference voltage signal are respectively subjected to... The data collected and gathered form a real-time reference voltage signal matrix. As shown in equation (3) below,

[0014] (3)

[0015] In equation (3), , ,...arrive These are respectively the first, second, and third operations performed on the three-phase sinusoidal reference voltage signal. The data acquisition process includes the instantaneous values ​​of the first and second reference voltage phases (A-phase) to the... Instantaneous value of the reference voltage phase A; , ,...arrive These are respectively the first, second, and third operations performed on the three-phase sinusoidal reference voltage signal. The instantaneous values ​​of the first and second reference voltage phases B in the data acquisition were collected. Instantaneous value of the reference voltage in phase B; , ,...arrive These are respectively the first, second, and third operations performed on the three-phase sinusoidal reference voltage signal. The instantaneous values ​​of the first and second reference voltages (phase C) during the data acquisition phase are as follows: Instantaneous value of the reference voltage in phase C;

[0016] Step 4: Initialize the real-time signal sequence of the secondary voltage at the beginning of the line. All data is standardized to Within the specified range, all standardized data are collected to form a real-time signal matrix for determining the secondary voltage at the beginning of the line. As shown in equation (4) below,

[0017] (4)

[0018] In equation (4), , ,...arrive The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the line induced by the first voltage transformer within one detection cycle T. The instantaneous values ​​of the secondary voltage phase A at the beginning of the first line and the instantaneous values ​​of the secondary voltage phase A at the beginning of the second line were collected during the sampling. The instantaneous values ​​of the secondary voltage phase A at the beginning of the line, after standardization, are the standard values ​​of the secondary voltage phase A at the beginning of the first line and the standard values ​​of the secondary voltage phase A at the beginning of the second line, up to the... Standard value of phase A secondary voltage at the beginning of the line; , ,...arrive The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the line induced by the first voltage transformer within one detection cycle T. The instantaneous values ​​of phase B of the secondary voltage at the beginning of the first line and the instantaneous values ​​of phase B of the secondary voltage at the beginning of the second line were collected during the sampling. The instantaneous values ​​of phase B of the secondary voltage at the beginning of the line, after standardization, are the standard values ​​of phase B of the secondary voltage at the beginning of the first line and the standard values ​​of phase B of the secondary voltage at the beginning of the second line. Standard value of phase B secondary voltage at the beginning of the line; , ,...arrive The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the line induced by the first voltage transformer within one detection cycle T. The instantaneous values ​​of the C-phase secondary voltage at the beginning of the first line and the instantaneous values ​​of the C-phase secondary voltage at the beginning of the second line were collected during the sampling. The instantaneous values ​​of the C-phase secondary voltage at the beginning of the line, after standardization, are the standard values ​​of the C-phase secondary voltage at the beginning of the first line and the standard values ​​of the C-phase secondary voltage at the beginning of the second line. Standard value of C-phase secondary voltage at the beginning of the line;

[0019] Step 5: Determine the real-time signal matrix for the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the beginning of each phase A line are generated into a data set using the sliding window method. The sliding window method employs... The data is used as the size of the data group, and the unit slides through the total number of data points. Generated from the standard value of the secondary voltage at the beginning of each phase A line The data sets are collected and formed into a sequence of secondary voltage data sets at the beginning of the first phase A line. As shown in equation (5) below,

[0020] (5)

[0021] In equation (5), Real-time signal matrix for judging the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the head end of each phase A line are generated using the sliding window method, resulting in the first, second, and third sets of secondary voltage data for the head end of the phase A line, and so on. The first A-phase line head end secondary voltage data group;

[0022] For the real-time signal matrix of the reference voltage The Communist Party of China The instantaneous values ​​of the A-phase reference voltage are generated using a sliding window method to create a data set. The sliding window method employs... The data is used as the size of the data group, and the unit slides through the total number of data points. The instantaneous value of the A-phase reference voltage is generated The data sets are collected and formed into the first phase A reference voltage data set sequence. As shown in equation (6) below,

[0023] (6)

[0024] In equation (6), These are the real-time signal matrices of the reference voltage. CCP The instantaneous values ​​of the A-phase reference voltage are generated using the sliding window method, resulting in the first, second, and third sets of the first A-phase reference voltage data, and so on. The first A-phase reference voltage data set;

[0025] Step 6: Sequence of the secondary voltage data group at the beginning of the first phase A line and the first A-phase reference voltage data group sequence All data groups are substituted sequentially into the following formula (7) to calculate the total difference between the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The first A-phase correlation coefficient,

[0026] (7)

[0027] In equation (7), It is the sum of the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The i-th first A-phase correlation coefficient in the first A-phase correlation coefficient; It is the sequence of secondary voltage data groups at the beginning of the first phase A line. The i-th first A-phase line head end secondary voltage data group in the data; It is the first A-phase reference voltage data group sequence The i-th first A-phase reference voltage data group in the data; It is the aforementioned The variance; It is the aforementioned The variance;

[0028] Total The first phase A correlation coefficients are collected in the order of calculation to form a first phase A correlation coefficient sequence. ;

[0029] Repeat steps 5 and 6 above to calculate the first phase B correlation coefficient sequence. Correlation coefficient sequence with the first C phase ;

[0030] Step 7: Determine the real-time signal matrix for the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the beginning of each phase A line are generated into data sets using a progressively expanding window method. This progressively expanding window method employs... The first sample size is set at 100 data points, and the size is gradually increased by 100 units until a total of 100 data points are obtained. Generated from the standard value of the secondary voltage at the beginning of each phase A line The data sets were collected and formed into a sequence of secondary voltage data sets at the beginning of the second phase A line. As shown in equation (8) below,

[0031] (8)

[0032] In equation (8), These are the real-time signal matrices for judging the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the head end of the second-phase A-phase line are generated using the progressively expanding window method, resulting in the first, second, and third sets of secondary voltage data for the head end of the second-phase A-phase line, and so on. One set of secondary voltage data at the beginning of the second phase A line;

[0033] For the real-time signal matrix of the reference voltage The Communist Party of China The instantaneous values ​​of the A-phase reference voltage are generated using a progressively expanding window method to create a data set. This progressively expanding window method employs... The first sample size is determined by a set of data points, and unit-expanded sliding sampling is performed on a total of [number] data points. The instantaneous value of the A-phase reference voltage is generated The data sets are collected and formed into a second phase A reference voltage data set sequence. As shown in equation (9) below,

[0034] (9)

[0035] In equation (9), These are the real-time signal matrices of the reference voltage. CCP The instantaneous values ​​of the A-phase reference voltage are generated using a progressively expanding window method, resulting in the first, second, third, ..., second phase A reference voltage data sets. One second A-phase reference voltage data set;

[0036] Step 8: Sequence of the secondary voltage data group at the beginning of the second phase A line and the second phase A reference voltage data group sequence All data groups are substituted sequentially into the following formula (10) to calculate the total difference between the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The second A-phase correlation coefficient,

[0037] (10)

[0038] In equation (10), It is the sum of the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The i-th second A-phase correlation coefficient among the second A-phase correlation coefficients; It is the sequence of secondary voltage data groups at the beginning of the first phase A line. The i-th secondary voltage data group at the beginning of the second phase A line; It is the second phase A reference voltage data group sequence The i-th second phase A reference voltage data group in the data; It is the aforementioned The variance; It is the aforementioned The variance;

[0039] Total The correlation coefficients of phase A are collected in the order of calculation to form a sequence of phase A correlation coefficients. ;

[0040] Repeat steps 7 and 8 above to calculate the second phase B correlation coefficient sequence. Second C phase correlation coefficient sequence ;

[0041] Step 9: Perform differential current judgment on the first current transformer. If the first current transformer meets the differential current criterion, and the correlation coefficient sequence of the first A phase is... The first phase B correlation coefficient sequence The first C-phase correlation coefficient sequence The second phase A correlation coefficient sequence The second phase B correlation coefficient sequence and the second C-phase correlation coefficient sequence All exist with For sequences exhibiting periodic pulsating rhythms, at least one correlation coefficient greater than or equal to the pulsating rhythm correlation coefficient threshold is required. If the signal is positive, it indicates that the first current transformer at the beginning of the transmission line has experienced a secondary circuit disconnection fault within one detection cycle T.

[0042] Conversely, this indicates that the first current transformer at the beginning of the transmission line has no secondary circuit open circuit fault within one detection cycle T.

[0043] Step 10: Repeat steps 4 to 9 to complete the detection of secondary open circuit faults of the second current transformer at the end of the transmission line within one detection cycle T.

[0044] Furthermore, the specific details of the differential current determination of the first current transformer in step 9 are as follows:

[0045] Step 9.1: The first protection device operates according to the sampling frequency. The instantaneous values ​​of the secondary current signal at the beginning of the transmission line generated by the first current transformer within one detection period T are acquired in real time and collected to form an initial real-time signal sequence of the secondary current at the beginning of the transmission line. As shown in equation (11) below,

[0046] (11)

[0047] In equation (11), The first protection device performs the first, second, and third detections on the secondary current signal at the beginning of the transmission line generated by the first current transformer within a detection cycle T. The instantaneous value collected during the next sampling; The first protection device performs this within one detection cycle T. The instantaneous value of the secondary current of the secondary current signal at the beginning of the line, acquired during the t-th sampling in the sampling process; , and The first protection device performs [the detection] within one detection cycle T. The instantaneous values ​​of the secondary currents of phases A, B, and C of the secondary current signal at the beginning of the line, collected during the t-th sampling in the sampling process;

[0048] The second protection device is based on the sampling frequency. The instantaneous values ​​of the secondary current signal at the end of the transmission line generated by the second current transformer within one detection period T are acquired in real time and collected to form an initial real-time signal sequence of the secondary current signal at the end of the transmission line. As shown in equation (12),

[0049] (12)

[0050] In equation (12), The second protection device performs the first, second, and third detections on the secondary current signal at the end of the transmission line generated by the second current transformer within one detection cycle T. The instantaneous value collected during the next sampling; The second protection device performs this within one detection cycle T. The instantaneous value of the secondary current of the secondary current signal at the end of the line is collected during the t-th sampling in the sampling process. , and The second protection device performs the detection within one detection cycle T. During the t-th sampling process, the instantaneous values ​​of the secondary currents of phases A, B, and C at the end of the line are collected.

[0051] The initial real-time signal sequence of the secondary current at the beginning of the line and the initial real-time signal sequence of the secondary current signal at the end of the line The difference is used to form the secondary current difference matrix between the secondary current signals at the beginning and end of the line. As shown in equation (13) below,

[0052] (13)

[0053] In equation (13), , ,...arrive It refers to the difference between the secondary current signals at the beginning and end of the line, specifically the difference between the first A-phase secondary current and the second A-phase secondary current. The difference in secondary current of each phase A line; , ,...arrive It refers to the difference between the first B-phase secondary current of the line and the difference between the second B-phase secondary current of the line and the line end secondary current. The difference in secondary current of each phase B line; , ,...arrive It refers to the difference between the first C-phase secondary current and the second C-phase secondary current between the secondary current signal at the beginning and end of the line, and the difference between the second and third C-phase secondary currents. The difference in secondary current of each C-phase line;

[0054] Step 9.2: For the secondary current difference matrix... CCP The secondary current difference values ​​of each phase A line are generated into a data set using the sliding window method. The sliding window method employs... The data is used as the size of the data group, and the unit slides through the total number of data points. Generated from the secondary current difference of each phase A line These data sets are collected to form a sequence of secondary current difference data sets for phase A line. As shown in equation (14),

[0055] (14);

[0056] In equation (14), For the secondary current difference matrix respectively CCP The secondary current difference data of phase A lines were generated using the sliding window method, including the first set of secondary current difference data of phase A lines, the second set of secondary current difference data of phase A lines, and so on. One set of secondary current difference data for phase A line;

[0057] Step 9.3: Sequence the secondary current difference data group of the A-phase line. The total The data from each data set are summed sequentially, and the arithmetic square root of the sum is calculated. The calculation results are collected as the effective value sequence for judging the A-phase differential current of the first current transformer;

[0058] Step 9.4: Repeat steps 9.2 to 9.3 to obtain the effective value sequence of the differential current judgment of phase B and phase C of the first current transformer respectively. If there is a data in the effective value sequence of the differential current judgment of phase A, phase B and phase C that is greater than the secondary disconnection blocking value of the current transformer, it means that the first current transformer satisfies the differential current criterion within one detection period T.

[0059] Conversely, the first current transformer does not meet the differential current criterion within one detection period T.

[0060] The beneficial effects of this invention are as follows: Based on the existing differential current criterion for open circuit in the secondary circuit of current transformers, this invention adds consideration of the correlation between the real-time voltage signal induced by the voltage transformer and the reference voltage. The core effect of this invention is to distinguish between open circuit faults in the secondary circuit of current transformers and high-resistance grounding faults in transmission current by observing the pulsating rhythm of the correlation coefficient between the real-time voltage signal and the reference voltage information. This improves the ability of substation secondary system devices to distinguish small-amplitude sinusoidal currents and greatly improves the detection accuracy of open circuit faults in the secondary circuit of current transformers in transmission lines. Attached Figure Description

[0061] Figure 1 This is a schematic diagram of the correlation coefficient of the first phase A in this embodiment.

[0062] Figure 2 This is a schematic diagram of the correlation coefficient of the second phase A in this embodiment. Detailed Implementation

[0063] The following description, in conjunction with specific embodiments and accompanying drawings, further illustrates the present invention's method for detecting open circuit faults in the secondary circuit of a current transformer based on pulsating voltage.

[0064] Example

[0065] The detection method in this embodiment involves a transmission line, a first protection device, a second protection device, a first current transformer, a second current transformer, a first voltage transformer, and a second voltage transformer; the first protection device, the first current transformer, and the first voltage transformer are installed at the beginning of the transmission line; the second protection device, the second current transformer, and the second voltage transformer are installed at the end of the transmission line; and the sampling frequency of the first protection device and the second protection device... Both are 1200Hz, and the detection method includes the following steps:

[0066] Step 1: Set the detection period T for secondary open circuit faults in the current transformer of the transmission line. The detection period T includes n current signal cycles in the transmission line. n is a natural number greater than 4, and the current signal period is... It takes 0.02 seconds;

[0067] Step 2: The first protection device operates according to the sampling frequency. The instantaneous values ​​of the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer within one detection period T are acquired in real time and collected to form the initial real-time signal sequence of the secondary voltage at the beginning of the transmission line. As shown in equation (1) below,

[0068] (1)

[0069] In equation (1), The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer within a detection cycle T. The instantaneous value collected during the next sampling; The first protection device is tested within one detection cycle T. The instantaneous value of the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer during the t-th sampling process; The first protection device is tested within a detection cycle T. The instantaneous values ​​of the secondary voltages of phases A, B, and C of the secondary voltage signal generated at the beginning of the transmission line by the first voltage transformer during the t-th sampling process.

[0070] The second protection device operates according to the sampling frequency. The instantaneous values ​​of the secondary voltage signal at the end of the transmission line generated by the second voltage transformer within one detection period T are acquired in real time and collected to form the initial real-time signal sequence of the secondary voltage at the end of the line. As shown in equation (1) below,

[0071] (1)

[0072] In equation (1), The second protection device performs the first, second, and third detections on the secondary voltage signal at the end of the transmission line generated by the second voltage transformer within a detection cycle T. The instantaneous value collected during the next sampling; The second protection device is activated within a detection cycle T. The instantaneous value of the secondary voltage signal at the end of the transmission line generated by the second voltage transformer induced by the second voltage transformer during the t-th sampling in the sampling process; The second protection device is tested within a detection cycle T. The instantaneous values ​​of the secondary voltages of phases A, B, and C of the secondary voltage signal at the end of the transmission line generated by the second voltage transformer during the t-th sampling process.

[0073] Step 3: Obtain the amplitude value as 57.7. A three-phase sinusoidal reference voltage signal with a frequency of 50Hz and a duration of one detection period T is used, with a sampling frequency of... The A, B, and C phases of the three-phase sinusoidal reference voltage signal were each subjected to... The data collected and gathered form a real-time reference voltage signal matrix. As shown in equation (3) below,

[0074] (3)

[0075] In equation (3), , ,...arrive These are the first, second, and third operations performed on the three-phase sinusoidal reference voltage signal, respectively. The data acquisition process includes the instantaneous values ​​of the first and second reference voltage phases (A-phase) to the... Instantaneous value of the reference voltage phase A; , ,...arrive These are the first, second, and third operations performed on the three-phase sinusoidal reference voltage signal, respectively. The instantaneous values ​​of the first and second reference voltage phases B in the data acquisition were collected. Instantaneous value of the reference voltage in phase B; , ,...arrive These are the first, second, and third operations performed on the three-phase sinusoidal reference voltage signal, respectively. The instantaneous values ​​of the first and second reference voltages (phase C) during the data acquisition phase are as follows: Instantaneous value of the reference voltage in phase C;

[0076] Step 4: Initial real-time signal sequence of secondary voltage at the beginning of the line. All data is standardized to Within the specified range, all standardized data are collected to form a real-time signal matrix for determining the secondary voltage at the beginning of the line. As shown in equation (4) below,

[0077] (4)

[0078] In equation (4), , ,...arrive The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the line induced by the first voltage transformer within a detection cycle T. The instantaneous values ​​of the secondary voltage phase A at the beginning of the first line and the instantaneous values ​​of the secondary voltage phase A at the beginning of the second line were collected during the sampling. The instantaneous values ​​of the secondary voltage phase A at the beginning of the line, after standardization, are the standard values ​​of the secondary voltage phase A at the beginning of the first line and the standard values ​​of the secondary voltage phase A at the beginning of the second line, up to the... Standard value of phase A secondary voltage at the beginning of the line; , ,...arrive The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the line induced by the first voltage transformer within a detection cycle T. The instantaneous values ​​of phase B of the secondary voltage at the beginning of the first line and the instantaneous values ​​of phase B of the secondary voltage at the beginning of the second line were collected during the sampling. The instantaneous values ​​of phase B of the secondary voltage at the beginning of the line, after standardization, are the standard values ​​of phase B of the secondary voltage at the beginning of the first line and the standard values ​​of phase B of the secondary voltage at the beginning of the second line. Standard value of phase B secondary voltage at the beginning of the line; , ,...arrive The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the line induced by the first voltage transformer within a detection cycle T. The instantaneous values ​​of the C-phase secondary voltage at the beginning of the first line and the instantaneous values ​​of the C-phase secondary voltage at the beginning of the second line were collected during the sampling. The instantaneous values ​​of the C-phase secondary voltage at the beginning of the line, after standardization, are the standard values ​​of the C-phase secondary voltage at the beginning of the first line and the standard values ​​of the C-phase secondary voltage at the beginning of the second line. Standard value of C-phase secondary voltage at the beginning of the line;

[0079] Step 5: Determine the real-time signal matrix for the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the beginning of each phase A line are generated using a sliding window method to create a data set. The sliding window method employs... The data is used as the size of the data group, and the unit slides through the total number of data points. Generated from the standard value of the secondary voltage at the beginning of each phase A line The data sets are collected and formed into a sequence of secondary voltage data sets at the beginning of the first phase A line. As shown in equation (5) below,

[0080] (5)

[0081] In equation (5), Real-time signal matrix for judging the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the head end of each phase A line are generated using the sliding window method, resulting in the first, second, and third sets of secondary voltage data for the head end of the phase A line, and so on. The first A-phase line head end secondary voltage data group;

[0082] Real-time signal matrix of reference voltage The Communist Party of China The instantaneous values ​​of the A-phase reference voltage are generated using a sliding window method to create a data set. The sliding window method employs... The data is used as the size of the data group, and the unit slides through the total number of data points. The instantaneous value of the A-phase reference voltage is generated The data sets are collected and formed into the first phase A reference voltage data set sequence. As shown in equation (6) below,

[0083] (6)

[0084] In equation (6), These are the real-time signal matrices of the reference voltage. CCP The instantaneous values ​​of the A-phase reference voltage are generated using the sliding window method, resulting in the first, second, and third sets of the first A-phase reference voltage data, and so on. The first A-phase reference voltage data set;

[0085] Step 6: Sequence of the secondary voltage data group at the beginning of the first phase A line and the first phase A reference voltage data group sequence All data groups are substituted sequentially into the following formula (7) to calculate the total difference between the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The first A-phase correlation coefficient,

[0086] (7)

[0087] In equation (7), It is the sum of the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The i-th first A-phase correlation coefficient in the first A-phase correlation coefficient; It is the sequence of secondary voltage data at the beginning of the first phase A line. The i-th first A-phase line head end secondary voltage data group in the data; It is the first A-phase reference voltage data group sequence The i-th first A-phase reference voltage data group in the data; yes The variance; yes The variance;

[0088] Total The first phase A correlation coefficients are collected in the order of calculation to form a first phase A correlation coefficient sequence. ;

[0089] Repeat steps 5 and 6 above to calculate the first phase B correlation coefficient sequence. Correlation coefficient sequence with the first C phase ;

[0090] Step 7: Determine the real-time signal matrix for the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the beginning of each phase A line were generated using a progressively expanding window method to create data sets. The progressively expanding window method employed... The first sample size is set at 100 data points, and the size is gradually increased by 100 units until a total of 100 data points are obtained. Generated from the standard value of the secondary voltage at the beginning of each phase A line The data sets were collected and formed into a sequence of secondary voltage data sets at the beginning of the second phase A line. As shown in equation (8) below,

[0091] (8)

[0092] In equation (8), These are the real-time signal matrices for judging the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the head end of the second-phase A-phase line are generated using the progressively expanding window method, resulting in the first, second, and third sets of secondary voltage data for the head end of the second-phase A-phase line, and so on. One set of secondary voltage data at the beginning of the second phase A line;

[0093] Real-time signal matrix of reference voltage The Communist Party of China The instantaneous values ​​of the A-phase reference voltage are generated using a progressively expanding window method. The progressively expanding window method employs... The first sample size is determined by a set of data points, and unit-expanded sliding sampling is performed on a total of [number] data points. The instantaneous value of the A-phase reference voltage is generated The data sets are collected and formed into a second phase A reference voltage data set sequence. As shown in equation (9) below,

[0094] (9)

[0095] In equation (9), These are the real-time signal matrices of the reference voltage. CCP The instantaneous values ​​of the A-phase reference voltage are generated using a progressively expanding window method, resulting in the first, second, third, ..., second phase A reference voltage data sets. One second A-phase reference voltage data set;

[0096] Step 8: Sequence of secondary voltage data at the beginning of the second phase A line Second Phase A Reference Voltage Data Group Sequence All data groups are substituted sequentially into the following formula (10) to calculate the total difference between the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The second A-phase correlation coefficient,

[0097] (10)

[0098] In equation (10), It is the sum of the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The i-th second A-phase correlation coefficient among the second A-phase correlation coefficients; It is the sequence of secondary voltage data at the beginning of the first phase A line. The i-th secondary voltage data group at the beginning of the second phase A line; It is the second phase A reference voltage data group sequence The i-th second phase A reference voltage data group in the data; yes The variance; yes The variance;

[0099] Total The correlation coefficients of phase A are collected in the order of calculation to form a sequence of phase A correlation coefficients. ;

[0100] Repeat steps 7 and 8 above to calculate the second phase B correlation coefficient sequence. Second C phase correlation coefficient sequence ;

[0101] Step 9: Perform differential current determination on the first current transformer, the details of which are as follows:

[0102] Step 9.1: The first protection device operates according to the sampling frequency. The instantaneous values ​​of the secondary current signal at the head end of the transmission line generated by the first current transformer within one detection period T are acquired in real time and collected to form the initial real-time signal sequence of the secondary current at the head end of the line. As shown in equation (11) below,

[0103] (11)

[0104] In equation (11), The first protection device performs the first, second, and third detections on the secondary current signal at the beginning of the transmission line generated by the first current transformer within a detection cycle T. The instantaneous value collected during the next sampling; The first protection device is tested within one detection cycle T. The instantaneous value of the secondary current of the secondary current signal at the beginning of the line, acquired during the t-th sampling in the sampling process; , and The first protection device is tested within a detection cycle T. The instantaneous values ​​of the secondary currents of phases A, B, and C at the t-th sampling point of the line head-end secondary current signal during the sampling process.

[0105] The second protection device operates according to the sampling frequency. The instantaneous values ​​of the secondary current signal at the end of the transmission line generated by the second current transformer within one detection period T are acquired in real time and collected to form the initial real-time signal sequence of the secondary current signal at the end of the line. As shown in equation (12),

[0106] (12)

[0107] In equation (12), The second protection device performs the first, second, and third detections on the secondary current signal at the end of the transmission line generated by the second current transformer within a detection cycle T. The instantaneous value collected during the next sampling; The second protection device is activated within a detection cycle T. The instantaneous value of the secondary current at the end of the line is collected during the t-th sampling in the sampling process. , and The second protection device is tested within a detection cycle T. During the t-th sampling process, the instantaneous values ​​of the secondary currents of phases A, B, and C at the end of the line are collected.

[0108] The initial real-time signal sequence of the secondary current at the beginning of the line and the initial real-time signal sequence of the secondary current signal at the end of the line The difference is used to form a secondary current difference matrix between the secondary current signals at the beginning and end of the line. As shown in equation (13) below,

[0109] (13)

[0110] In equation (13), , ,...arrive It is the difference between the secondary current signals at the beginning and end of the line, specifically the difference between the secondary current signals of the first A-phase line and the secondary current signals at the end of the line. The difference in secondary current of each phase A line; , ,...arrive It is the difference between the first B-phase secondary current of the line and the secondary current of the line at the beginning and end of the line, and the difference between the second B-phase secondary current of the line and the second B-phase secondary current of the line. The difference in secondary current of each phase B line; , ,...arrive It is the difference between the secondary current of the first C-phase line and the secondary current of the second C-phase line between the secondary current signal at the beginning and end of the line, and the difference between the secondary current of the second C-phase line and the secondary current of the third C-phase line. The difference in secondary current of each C-phase line;

[0111] Step 9.2: Calculate the secondary current difference matrix. CCP The secondary current difference values ​​of each phase A line are generated into a data set using the sliding window method. The sliding window method employs... The data is used as the size of the data group, and the unit slides through the total number of data points. Generated from the secondary current difference of each phase A line These data sets are collected to form a sequence of secondary current difference data sets for phase A line. As shown in equation (14),

[0112] (14);

[0113] In equation (14), For the secondary current difference matrix respectively CCP The secondary current difference data of phase A lines were generated using the sliding window method, including the first set of secondary current difference data of phase A lines, the second set of secondary current difference data of phase A lines, and so on. One set of secondary current difference data for phase A line;

[0114] Step 9.3: Sequence the secondary current difference data of phase A line. The total The data from each data set are summed sequentially, and the arithmetic square root of the sum is calculated. The calculation results are collected as the effective value sequence for judging the A-phase differential current of the first current transformer;

[0115] Step 9.4: Repeat steps 9.2 to 9.3 to obtain the effective value sequence of the differential current judgment of phase B and phase C of the first current transformer respectively. If there is a data in the effective value sequence of the differential current judgment of phase A, phase B and phase C that is greater than the secondary disconnection blocking value of the current transformer, it means that the first current transformer satisfies the differential current criterion within one detection period T.

[0116] Conversely, the first current transformer does not meet the differential current criterion within one detection cycle T.

[0117] If the first current transformer satisfies the differential current criterion, and the first A-phase correlation coefficient sequence The first phase B correlation coefficient sequence The first C-phase correlation coefficient sequence The second phase A correlation coefficient sequence The second phase B correlation coefficient sequence Second C phase correlation coefficient sequence All exist with For sequences exhibiting periodic pulsating rhythms, at least one correlation coefficient greater than or equal to the pulsating rhythm correlation coefficient threshold is required. If this is true, it means that the first current transformer at the beginning of the transmission line has experienced a secondary circuit disconnection fault within one detection cycle T.

[0118] Conversely, it indicates that the first current transformer at the beginning of the transmission line has no secondary circuit open circuit fault within one detection cycle T.

[0119] Step 10: Repeat steps 4 to 9 to complete the detection of secondary open circuit faults of the second current transformer at the end of the transmission line within one detection cycle T.

[0120] The following describes the detection of a broken circuit in the secondary circuit of a current transformer on a specific transmission line.

[0121] In this embodiment, the voltage sampling value of the first protection device is 24 points per cycle, and the detection period T is a total of 5 cycles. Taking the voltage data of phase A as an example, there are a total of 120 instantaneous values ​​of the secondary voltage at the first end of phase A, which are standardized to obtain 120 standard values ​​of the secondary voltage at the first end of phase A. Using the sliding window method, with 18 data points as the data window, the 120 standard values ​​of the secondary voltage at the first end of phase A and the 120 reference voltages of phase A are slid-windowed respectively. Based on the sliding window results, they are substituted into formula (7) to generate a total of 103 correlation coefficients for the first phase A, as shown in Table 1 below.

[0122]

[0123]

[0124]

[0125] Table 1

[0126] Based on the data in Table 1 above, plot the first A correlation coefficient graph, as follows: Figure 1 As shown, it is easy to see that If a pulsating rhythm with a period of 12 exists, then the first voltage pulsation criterion is considered satisfied in this example.

[0127] In this embodiment, 18 data points are used as data windows. Sliding windows are applied to 120 standard values ​​of the secondary voltage at the first end of phase A and 120 reference voltages of phase A. The sliding window results are then substituted into formula (10) to generate the second phase A correlation coefficient, as shown in Table 2 below.

[0128]

[0129]

[0130]

[0131] Table 2

[0132] Based on the data in Table 1 above, plot the second A correlation coefficient graph, as follows: Figure 2 As shown, it is easy to see that If a pulsating rhythm with a period of 12 exists, then the second voltage pulsation criterion is considered satisfied in this example.

Claims

1. A method for detecting a secondary circuit disconnection fault of a pulsating voltage-based current transformer, involving a transmission line, a first protection device, a second protection device, a first current transformer, a second current transformer, a first voltage transformer and a second voltage transformer. The first protection device, the first current transformer and the first voltage transformer are installed at the head end of the power transmission line; The second protection device, the second current transformer and the second voltage transformer are installed at the tail end of the power transmission line; The sampling frequency of the first protection device and the second protection device is 1200 Hz, characterized in that the detection method comprises the following steps: Step 1: set the detection period T of the current transformer secondary disconnection fault of the power transmission line, the detection period T includes n current signal periods in the power transmission line , the n is a natural number greater than 4, and the current signal period is 0.02s; Step 2: the first protection device according to the sampling frequency The first voltage transformer collects the instantaneous value of the line head secondary voltage signal generated by the transmission line in a detection period T and forms a line head secondary voltage initial real-time signal sequence As shown in the following formula (1), （1） In equation (1), The first protection device performs the first, second, and third detections on the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer within one detection cycle T. The instantaneous value collected during the next sampling; The first protection device performs this within one detection cycle T. The instantaneous value of the secondary voltage signal at the beginning of the transmission line generated by the first voltage transformer during the t-th sampling in the sampling process; The first protection device performs [the detection] within one detection cycle T. The instantaneous values ​​of the secondary voltages of phases A, B, and C of the line head secondary voltage signal generated by the first voltage transformer in the t-th sampling during the sampling process. The second protection device is according to a sampling frequency The second voltage transformer collects the instantaneous value of the secondary voltage signal generated by the transmission line in a detection period T and forms an initial real-time signal sequence of the secondary voltage at the end of the line As shown in the following formula (1), （1） In formula (1), are respectively the instantaneous values of the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer when the second protection device performs first, second, to the nth sampling on the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer in one detection period T; are respectively the instantaneous values of the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer when the second protection device performs first, second, to the nth sampling on the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer in one detection period T; are respectively the instantaneous values of the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer when the second protection device performs first, second, to the nth sampling on the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer in one detection period T; are respectively the instantaneous values of the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer when the second protection device performs first, second, to the nth sampling on the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer in one detection period T; are respectively the instantaneous values of the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer when the second protection device performs first, second, to the nth sampling on the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer in one detection period T; are respectively the instantaneous values of the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer when the second protection device performs first, second, to the nth sampling on the line end secondary voltage signal generated by the power transmission line and sensed by the second voltage transformer in one detection period T; Step 3: Obtain a three-phase sinusoidal reference voltage signal with an amplitude of 57.7 , a frequency of 50 Hz, and a time length of one detection period T, using the sampling frequency , the A-phase, B-phase, and C-phase of the three-phase sinusoidal reference voltage signal are each sampled times and collected to form a real-time reference voltage signal matrix , as shown in the following formula (3), （3） In formula (3), , ,... to are the first reference voltage instantaneous value, the second reference voltage A-phase instantaneous value to the reference voltage A-phase instantaneous value for the first, second to the time data acquisition of the three-phase sinusoidal reference voltage signal, respectively; , ,... to are the first reference voltage B-phase instantaneous value, the second reference voltage B-phase instantaneous value to the reference voltage B-phase instantaneous value for the first, second to the time data acquisition of the three-phase sinusoidal reference voltage signal, respectively; , ,... to are the first reference voltage C-phase instantaneous value, the second reference voltage C-phase instantaneous value to the reference voltage C-phase instantaneous value for the first, second to the time data acquisition of the three-phase sinusoidal reference voltage signal, respectively; Step 4: Standardize all data in the initial real-time signal sequence of the line primary secondary voltage to the interval range of and collect all the standardized data to form a line primary secondary voltage judgment real-time signal matrix as shown in the following formula (4), （4） In formula (4), , ,... to are respectively the first line head secondary voltage A-phase instantaneous value, the second line head secondary voltage A-phase instantaneous value to the nth line head secondary voltage A-phase instantaneous value collected by the first protection device when sampling the line head secondary voltage signal of the first voltage transformer for the first time, the second time to the nth time in one detection period T, the first line head secondary voltage A-phase standard value, the second line head secondary voltage A-phase standard value to the nth line head secondary voltage A-phase standard value after standardization processing of the line head secondary voltage A-phase instantaneous value; , ,... to are respectively the first line head secondary voltage B-phase instantaneous value, the second line head secondary voltage B-phase instantaneous value to the nth line head secondary voltage B-phase instantaneous value collected by the first protection device when sampling the line head secondary voltage signal of the first voltage transformer for the first time, the second time to the nth time in one detection period T, the first line head secondary voltage B-phase standard value, the second line head secondary voltage B-phase standard value to the nth line head secondary voltage B-phase standard value after standardization processing of the line head secondary voltage B-phase instantaneous value; , ,... to are respectively the first line head secondary voltage C-phase instantaneous value, the second line head secondary voltage C-phase instantaneous value to the nth line head secondary voltage C-phase instantaneous value collected by the first protection device when sampling the line head secondary voltage signal of the first voltage transformer for the first time, the second time to the nth time in one detection period T, the first line head secondary voltage C-phase standard value, the second line head secondary voltage C-phase standard value to the nth line head secondary voltage C-phase standard value after standardization processing of the line head secondary voltage C-phase instantaneous value; Step 5: Determine the real-time signal matrix for the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the beginning of each phase A line are generated into a data set using the sliding window method. The sliding window method employs... The data is used as the size of the data group, and the units are slid across the total number of data points. Generated from the standard value of the secondary voltage at the beginning of each phase A line. The data sets are collected and formed into a sequence of secondary voltage data sets at the beginning of the first phase A line. As shown in equation (5) below, （5） In formula (5), respectively judging real-time signal matrix of the line head secondary voltage The first, second, third,..., to the Nth first A-phase line head secondary voltage data groups are generated by using a sliding window method. The first, second, third,..., to the Nth first A-phase line head secondary voltage data groups are generated by using a sliding window method.​ The reference voltage real-time signal matrix In total, in total A sliding window method is used to generate a data set for the instantaneous value of the A-phase reference voltage, in which A total of data is used as the data set size, and a unit slide is performed in a total of A data set is generated in a total of A first A-phase reference voltage data set sequence is formed by collecting As shown in the following formula (6), （6） In formula (6), are respectively the real-time signal matrixes of the reference voltages are respectively the first, second, third,..., and the Nth first A-phase reference voltage data groups generated by the sliding window method for the A-phase reference voltage instantaneous values in the reference voltage real-time signal matrix ​​ Step 6: Calculate the total of first A-phase correlation coefficients between the A-phase signals of the line head secondary voltage data set sequence of the first A-phase line and the A-phase signals of the three-phase sinusoidal wave reference voltage data set sequence of the first A-phase reference voltage data set sequence, respectively, in sequence according to the following formula (7) by substituting all data sets in the sequence into the formula (7) respectively and sequentially. and the first A-phase reference voltage data set sequence ​​ （7） In equation (7), It is the sum of the A-phase signal of the secondary voltage at the beginning of the line and the A-phase signal of the three-phase sinusoidal reference voltage. The i-th first A-phase correlation coefficient in the first A-phase correlation coefficient; It is the sequence of secondary voltage data groups at the beginning of the first phase A line. The i-th first A-phase line head end secondary voltage data group in the data; It is the first A-phase reference voltage data group sequence The i-th first A-phase reference voltage data group in the data; It is the aforementioned The variance; It is the aforementioned The variance; The total number of first A-phase correlation coefficients is collected in the order of calculation to form a first A-phase correlation coefficient sequence ;​ The first B-phase correlation coefficient sequence is calculated by repeating the principles of steps 5 to 6 above in sequence and the first C-phase correlation coefficient sequence ; Step 7: Determine the real-time signal matrix for the secondary voltage at the beginning of the line. CCP The standard values ​​of the secondary voltage at the beginning of each phase A line are generated into data sets using a progressively expanding window method. This progressively expanding window method employs... The first sample size is set at 100 data points, and the size is gradually increased by 100 units until a total of 100 data points are obtained. Generated from the standard value of the secondary voltage at the beginning of each phase A line. The data sets were collected and formed into a sequence of secondary voltage data sets at the beginning of the second phase A line. As shown in equation (8) below, （8） In formula (8), respectively are real-time signal matrixes for judging the secondary voltage of the line head In total The first, second, third,..., and the Nth second A-phase line head secondary voltage data groups of the A-phase line head secondary voltage standard value are generated by the step-by-step expanding window method. The first, second, third,..., and the Nth second A-phase line head secondary voltage data groups of the A-phase line head secondary voltage standard value are generated by the step-by-step expanding window method. The reference voltage real-time signal matrix A total of The step-by-step expanding window method is used to generate data groups for the instantaneous values of the A-phase reference voltage, wherein The step-by-step expanding window method is used to generate data groups for the instantaneous values of the A-phase reference voltage, wherein The step-by-step expanding window method is used to generate data groups for the instantaneous values of the A-phase reference voltage, wherein The step-by-step expanding window method is used to generate data groups for the instantaneous values of the A-phase reference voltage, wherein As shown in the following formula (9), （9） In equation (9), These are the real-time signal matrices of the reference voltage. CCP The instantaneous values ​​of the A-phase reference voltage are generated using a progressively expanding window method, resulting in the first, second, third, ..., second phase A reference voltage data sets. One second A-phase reference voltage data set; Step 8: Calculate the total of second A-phase correlation coefficients between the A-phase signals of the line head secondary voltage data set sequence of the second A-phase line and the A-phase signals of the three-phase sinusoidal wave reference voltage data set sequence of the second A-phase reference voltage data set sequence, respectively, in sequence according to the following formula (10) and all data sets in the second A-phase reference voltage data set sequence ​​ （10） In formula (10), is a sum of the A-phase signal of the line head secondary voltage and the A-phase signal of the three-phase sinusoidal reference voltage is an i-th second A-phase correlation coefficient in the second A-phase correlation coefficients; is an i-th second A-phase line head secondary voltage data group in the sequence of second A-phase line head secondary voltage data groups is an i-th second A-phase line head secondary voltage data group in the sequence of second A-phase line head secondary voltage data groups is an i-th second A-phase reference voltage data group in the sequence of second A-phase reference voltage data groups is an i-th second A-phase reference voltage data group in the sequence of second A-phase reference voltage data groups is a variance of the is a variance of the is a variance of the​ The total number of second A-phase correlation coefficients is collected in the order of calculation to form a second A-phase correlation coefficient sequence ;​ The principle of the above steps 7 to 8 is repeated to obtain the second B-phase correlation coefficient sequence and the second C-phase correlation coefficient sequence ; Step 9: judging the differential current of the first current transformer, if the first current transformer meets the differential current criterion, and the first A-phase correlation coefficient sequence , the first B-phase correlation coefficient sequence , the first C-phase correlation coefficient sequence , the second A-phase correlation coefficient sequence , the second B-phase correlation coefficient sequence , and the second C-phase correlation coefficient sequence all have a pulsation rhythm with a period of , and at least one correlation coefficient in the sequence of the pulsation rhythm is greater than or equal to the pulsation rhythm correlation coefficient judgment threshold , it is determined that the first current transformer at the head end of the power transmission line has a secondary circuit disconnection fault in the detection period T. Conversely, it indicates that the first current transformer at the head end of the power transmission line has no secondary circuit disconnection fault in one detection period T. Step 10: repeat the contents of steps 4 to 9 to complete the detection of the secondary disconnection fault of the second current transformer at the tail end of the power transmission line in one detection period T.

2. The detection method of claim 1, wherein: The specific contents of the differential current judgment of the first current transformer in step 9 are as follows: Step 9.1: The first protection device collects the instantaneous values of the secondary current signal of the first current transformer at a sampling frequency The first current transformer collects the instantaneous values of the secondary current signal of the first current transformer at a sampling frequency As shown in the following formula (11), （11） In equation (11), The first protection device performs the first, second, and third detections on the secondary current signal at the beginning of the transmission line generated by the first current transformer within a detection cycle T. The instantaneous value collected during the next sampling; The first protection device performs this within one detection cycle T. The instantaneous value of the secondary current of the secondary current signal at the beginning of the line, acquired during the t-th sampling in the sampling process; , and The first protection device performs [the detection] within one detection cycle T. The instantaneous values ​​of the secondary currents of phases A, B, and C of the secondary current signal at the beginning of the line, collected during the t-th sampling in the sampling process; The second protection device is according to a sampling frequency The second current transformer collects the instantaneous value of the secondary current signal of the transmission line generated by the second current transformer in a detection period T in real time and forms an initial real-time signal sequence of the secondary current signal of the transmission line As shown in the following formula (12), （12） In equation (12), The second protection device performs the first, second, and third detections on the secondary current signal at the end of the transmission line generated by the second current transformer within one detection cycle T. The instantaneous value collected during the next sampling; The second protection device performs this within one detection cycle T. The instantaneous value of the secondary current of the secondary current signal at the end of the line is collected during the t-th sampling in the sampling process. , and The second protection device performs the detection within one detection cycle T. During the t-th sampling process, the instantaneous values ​​of the secondary currents of phases A, B, and C at the end of the line are collected. said line head-end secondary current initial real-time signal sequence and said line tail-end secondary current signal initial real-time signal sequence forming a secondary current difference matrix between said line head-end secondary current signal and said line tail-end secondary current signal by differencing as shown in equation (13) below, （13） In formula (13), , , is a first A-phase line secondary current difference between the line head end secondary current signal and the line end secondary current signal, a second A-phase line secondary current difference to an Nth A-phase line secondary current difference; , , is a first B-phase line secondary current difference between the line head end secondary current signal and the line end secondary current signal, a second B-phase line secondary current difference to an Nth B-phase line secondary current difference; , , is a first C-phase line secondary current difference between the line head end secondary current signal and the line end secondary current signal, a second C-phase line secondary current difference to an Nth C-phase line secondary current difference; ​​​ Step 9.2: generating the data set of the secondary current difference value of the A-phase line by using the sliding window method The data set of the secondary current difference value of the A-phase line is generated by using the sliding window method in which data is used as the data set size, and the unit sliding is performed in the total of secondary current difference values of the A-phase line to generate data sets and collect them to form a data set sequence of the secondary current difference value of the A-phase line , as shown in the following equation (14)​ （14）； In formula (14), respectively, the secondary current difference matrix In total A-phase line secondary current difference data sets generated by the sliding window method, the second A-phase line secondary current difference data set to the A-phase line secondary current difference data set; Step 9.3: Sequence the secondary current difference data group of the A-phase line. The total The data from each data set are summed sequentially, and the arithmetic square root of the sum is calculated. The calculation results are collected as the effective value sequence for judging the A-phase differential current of the first current transformer; Step 9.4: repeat the contents of steps 9.2 to 9.3 to obtain the B-phase differential current judgment effective value sequence and the C-phase differential current judgment effective value sequence of the first current transformer respectively, if there is data greater than the current transformer secondary disconnection blocking value in the A-phase differential current judgment effective value sequence, the B-phase differential current judgment effective value sequence and the C-phase differential current judgment effective value sequence, it indicates that the first current transformer meets the differential current criterion in one detection period T; Conversely, the first current transformer does not meet the differential current criterion in one detection period T.

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