Secondary harmonic-based main transformer CT polarity judgment method and device

Abstract

The invention discloses a secondary harmonic-based main transformer CT polarity judgment method and device, and the method comprises the steps: responding to the starting of a CT polarity judgment function, configuring a voltage transformer at the high-voltage side of a transformer, and executing a CT polarity judgment process with the voltage transformer; and in response to starting of the CT polarity discrimination function and no voltage transformer configured on the high-voltage side of the transformer, executing a CT polarity discrimination process without the voltage transformer. According to the method, the reliability and accuracy of CT polarity judgment in new energy scenes such as pumped storage, nuclear power and offshore wind power are improved, meanwhile, the complexity of CT polarity judgment is reduced, and the reliability of transformer substation operation is improved.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, specifically relating to a method and device for determining the polarity of a main transformer CT based on second harmonics. Background Technology

[0002] The current loop is a crucial component of relay protection, directly impacting the correct operation of relay protection devices and the safe and stable operation of the power system. Current transformers, as vital components of the current loop, primarily function to convert large primary currents into smaller secondary currents based on the principle of electromagnetic induction, supplying power to measurement and protection circuit devices. They offer advantages such as safety, standardization, and speed, providing timely and accurate primary system current information, playing a vital role in rapidly isolating fault areas and ensuring reliable system operation. With the increasing proportion of clean energy sources such as wind power, photovoltaics, nuclear power, and pumped storage power plants in the power system, and in current applications such as nuclear power and other clean energy substations, pumped storage power plants, and offshore wind power, when generator sets and transformers are shut down for maintenance, the standby transformer is activated. Incorrect CT polarity wiring in the standby transformer branch can lead to protection devices failing to operate or malfunctioning, threatening the safe and stable operation of the substation. Therefore, for current clean energy applications such as nuclear power in substations, pumped storage power plants, and offshore wind power, the polarity of the standby transformer branch must be verified before commissioning to ensure the correct CT polarity.

[0003] In existing technologies, for traditional substations already in operation, load tests are commonly used to determine the correctness of CT polarity. When each bus bay is engaged, if the bus differential current is zero, the CT polarity of each bay is correct; if a differential current exists, the CT polarity of the bay is incorrect. For renovated and expanded substations, independent power sources are used to conduct current-carrying tests on the primary side of the CT, and a phase meter is used to test the current phase in the secondary circuit. The correctness of the CT polarity is determined based on the voltage-current angle difference displayed by the phase meter. If the current phase in the secondary circuit lags the voltage phase, and the angle difference is less than 90 degrees, the CT polarity is considered correct; otherwise, the CT polarity is considered incorrect. However, in new energy scenarios such as pumped storage, nuclear power, and offshore wind power, standby transformers may experience no load, extremely low secondary current, and long distances. Therefore, manual verification of standby transformer CT polarity has low reliability and is complex to operate, posing certain risks during commissioning and jeopardizing the safe and stable operation of the substation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and device for determining the polarity of a main transformer CT based on second harmonics. This improves the reliability and accuracy of CT polarity determination in new energy scenarios such as pumped storage, nuclear power, and offshore wind power. At the same time, it reduces the complexity of CT polarity determination and improves the reliability of substation operation.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, a method for determining the polarity of a transformer current transformer (CT) based on second harmonics is provided, comprising: in response to activating the CT polarity determination function and a voltage transformer is configured on the high-voltage side of the transformer, executing a CT polarity determination process with a voltage transformer; in response to activating the CT polarity determination function and a voltage transformer is not configured on the high-voltage side of the transformer, executing a CT polarity determination process without a voltage transformer.

[0006] Furthermore, the voltage transformer (CT) polarity determination process includes: calculating the fundamental and second harmonic content of the voltage and current in the main transformer bay; in response to the second harmonic content being greater than a set harmonic content threshold, calculating the harmonic angle difference between the second harmonic voltage and the second harmonic current in the main transformer branch; in response to the harmonic angle difference between two or more phases being less than the harmonic angle difference threshold, determining that the main transformer CT polarity is correct; in response to the harmonic angle difference between two or more phases being greater than or equal to the harmonic angle difference threshold, determining that the main transformer CT polarity is incorrect.

[0007] Furthermore, in response to the second harmonic content being less than or equal to the set harmonic content threshold, the fundamental angle difference between the fundamental voltage and fundamental current of the main transformer branch is calculated; in response to the fundamental angle difference between two or more phases being greater than the fundamental angle difference threshold, it is determined that the polarity of the main transformer CT is correct; in response to the fundamental angle difference between two or more phases being less than or equal to the fundamental angle difference threshold, it is determined that the polarity of the main transformer CT is incorrect.

[0008] Furthermore, the threshold values ​​are: harmonic content 15%; harmonic angle difference 180°; and fundamental frequency angle difference 180°.

[0009] Furthermore, the CT polarity determination process without voltage transformers includes: calculating the fundamental values ​​of the three-phase currents of the charging branch and the main transformer branch, as well as the three-phase current angles and the branch current angle differences; in response to the branch current angle difference of two or more phases being greater than the branch current angle difference threshold, determining that the main transformer CT polarity is correct; in response to the branch current angle difference of two or more phases being less than or equal to the branch current angle difference threshold, determining that the main transformer CT polarity is incorrect.

[0010] Furthermore, the threshold value for the branch current angle difference is 180°.

[0011] Furthermore, the CT polarity determination function is activated under the following conditions: 1) the high-voltage side voltage of the main transformer is normal; 2) the position of the high-voltage side circuit breaker of the main transformer changes from open to closed, or the current in the main transformer branch changes from zero to current. The condition for determining that the high-voltage side voltage of the main transformer is normal is as follows: ; in, , , The effective values ​​of phase A, phase B, and phase C voltages on the high-voltage side of the main transformer. This is the secondary voltage rating. The zero-sequence voltage on the high-voltage side of the main transformer. The negative sequence voltage on the high-voltage side of the main transformer; The threshold value for the main transformer branch current to change from zero to current is 0.05. , This is the secondary rated value of the current.

[0012] Secondly, a transformer CT polarity determination device based on second harmonics is provided, comprising: a CT polarity determination module with a voltage transformer, used to execute a CT polarity determination process with a voltage transformer in response to the activation of the CT polarity determination function and the high-voltage side of the transformer being equipped with a voltage transformer; and a CT polarity determination module without a voltage transformer, used to execute a CT polarity determination process without a voltage transformer in response to the activation of the CT polarity determination function and the high-voltage side of the transformer not being equipped with a voltage transformer.

[0013] Thirdly, a computer device is provided, comprising: a memory for storing instructions; and a processor for executing the instructions, causing the device to perform operations implementing the second harmonic-based main variable CT polarity determination method as described in the first aspect.

[0014] Fourthly, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the polarity determination method of the main variable CT based on second harmonics as described in the first aspect.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: When the CT polarity discrimination function is activated, the present invention executes the CT polarity discrimination process with voltage transformers when voltage transformers are configured on the high-voltage side of the transformer, and executes the CT polarity discrimination process without voltage transformers when voltage transformers are not configured on the high-voltage side of the transformer. This improves the reliability and accuracy of CT polarity judgment in new energy scenarios such as pumped storage, nuclear power and offshore wind power. At the same time, it reduces the complexity of CT polarity judgment and improves the reliability of substation operation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the main process of a main variable CT polarity determination method based on second harmonics provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the polarity verification test in an embodiment of the present invention; Figure 3 This is a schematic diagram of the CT polarity determination function of the main transformer branch 1 in an embodiment of the present invention, wherein (a) is the voltage condition, (b) is the current condition of the main transformer branch 1, and (c) is the CT polarity determination function condition. Figure 4 These are the second harmonic waveforms of the voltage and the second harmonic waveforms of the current in the main transformer branch 1 in this embodiment of the invention (taking a 0-degree closing angle as an example); wherein, (a) is the voltage and main transformer branch current waveforms when the CT polarity is correct and the closing angle is 0 degrees; (b) is the voltage amplitude and phase angle when the CT polarity is correct and the closing angle is 0 degrees; (c) is the main transformer branch current amplitude and phase angle when the CT polarity is correct and the closing angle is 0 degrees. Figure 5 These are the fundamental voltage and fundamental current waveforms of the main transformer branch 1 in this embodiment of the invention (taking a 60-degree closing angle as an example); where (a) is the voltage and main transformer branch current waveforms when the CT polarity is correct and the closing angle is 60 degrees; (b) is the voltage amplitude and phase angle when the CT polarity is correct and the closing angle is 60 degrees; and (c) is the main transformer branch current amplitude and phase angle when the CT polarity is correct and the closing angle is 60 degrees. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0018] Example 1 A method for determining the polarity of a transformer current transformer (CT) based on second harmonics includes: in response to activating the CT polarity determination function and a voltage transformer is configured on the high-voltage side of the transformer, executing a CT polarity determination process with a voltage transformer; in response to activating the CT polarity determination function and a voltage transformer is not configured on the high-voltage side of the transformer, executing a CT polarity determination process without a voltage transformer.

[0019] like Figures 1-5 As shown, the determination of the polarity of the main transformer CT based on the second harmonic includes the following steps.

[0020] Step 1: Obtain real-time current and voltage information for each bay and information on the high-voltage side circuit breaker of the main transformer based on the bus protection device.

[0021] Acquire current and voltage information for each interval and information about the high-voltage side circuit breakers of the main transformer. Specifically, sample the three-phase voltage and three-phase current of the main transformer branch at a constant sampling frequency to obtain the first... k Instantaneous three-phase voltage values ​​at each sampling point , , and instantaneous value of three-phase current , , The three-phase current of the charging branch is sampled at a constant sampling frequency to obtain the first... k Instantaneous values ​​of three-phase voltage and three-phase current at each sampling point , , .

[0022] Step 2: Determine whether the CT polarity discrimination function is activated based on the location and current / voltage information of the main transformer high-voltage side circuit breaker; if the conditions for the CT polarity discrimination function are met, proceed to Step 3.

[0023] The CT polarity determination function is activated under the following conditions: 1) The voltage on the high-voltage side of the main transformer is normal; 2) The circuit breaker position on the high-voltage side of the main transformer changes from open to closed, or the current in the main transformer branch changes from zero to current. (1) The voltage on the high-voltage side of the main transformer is normal. The criteria for determining this are: ; in, , , The effective values ​​of phase A, phase B, and phase C voltages on the high-voltage side of the main transformer. This is the secondary voltage rating. The zero-sequence voltage on the high-voltage side of the main transformer. It is the negative sequence voltage on the high-voltage side of the main transformer.

[0024] (2) The position of the high-voltage side circuit breaker of the main transformer changes from open to closed, or the current in the main transformer branch changes from zero to current. Current in the main transformer branch means: I a >0.05 I n , I b >0.05 I n , I c >0.05 I n ; in, , , The effective values ​​of phase A, phase B, and phase C currents on the high-voltage side of the main transformer. This is the secondary rated value of the current. That is, the threshold value for the main transformer branch current to change from zero to current is 0.05. .

[0025] Step 3: When a voltage transformer is configured on the high-voltage side of the transformer, proceed to Step 4 (i.e., in response to the activation of the CT polarity determination function and the presence of a voltage transformer on the high-voltage side of the transformer, execute the CT polarity determination process with a voltage transformer); otherwise, proceed to Step 5 (i.e., in response to the activation of the CT polarity determination function and the absence of a voltage transformer on the high-voltage side of the transformer, execute the CT polarity determination process without a voltage transformer).

[0026] Step 4: Calculate the fundamental voltage and current and second harmonic content of the main transformer interval; if the second harmonic content is greater than the harmonic content threshold (in this invention, the harmonic content threshold is set to 15%), proceed to step 6; otherwise, proceed to step 7.

[0027] The fundamental and second harmonic electrical quantities of voltage and current in the main transformer bay are calculated, and the fundamental phasor of the three-phase current is calculated using the Fourier algorithm. , , and second harmonic phasor , , and the second harmonic phasor of the three-phase current , , Specifically: ; ; ; In the formula, F 1() represents the Fourier algorithm for the fundamental frequency. F 2() is the Fourier algorithm for the second harmonic. , , These are the instantaneous current values ​​of phase A, phase B, and phase C at the k-th sampling point of the main transformer branch, respectively. , , These are the instantaneous voltage values ​​of phase A, phase B, and phase C at the kth sampling point of the main transformer branch, respectively.

[0028] The modulus of the phasor is taken to obtain the effective value of the fundamental frequency. , , and the effective value of the second harmonic , , ; ; The second harmonic content is calculated as follows: ; in, , , These represent the second harmonic content of phases A, B, and C of the main transformer branch, respectively. , , When any value is greater than 0.15, the second harmonic method is used to verify the CT polarity. , , When all values ​​are less than 0.15, the fundamental wave direction method is used to verify the polarity of the CT.

[0029] Step 5: Calculate the fundamental values ​​of the three-phase currents, the three-phase current angles, and the branch current angle differences for the charging branch and the main transformer branch. Use the phase comparison method to determine the CT polarity. If the angle difference between two or more branch currents is greater than the branch current angle difference threshold, the CT polarity of the main transformer bay is correctly determined (i.e., in response to the angle difference between two or more branch currents being greater than the branch current angle difference threshold, the main transformer CT polarity is determined to be correct). If the angle difference between two or more phases is less than or equal to the branch current angle difference threshold, the CT polarity determination for the main transformer bay and the charging bay is reversed (i.e., in response to the angle difference between two or more branch currents being less than or equal to the branch current angle difference threshold, the main transformer CT polarity is determined to be incorrect).

[0030] Calculate the fundamental values ​​and angles of the three-phase currents in the charging branch and the main transformer branch, specifically as follows: Fundamental values ​​of the three-phase current in the charging branch: ; in, , , These are the fundamental phasors for phases A, B, and C of the charging interval, respectively. , , These are the instantaneous current values ​​of phases A, B, and C of the charging branch, respectively.

[0031] Three-phase current angles of the charging branch and the main transformer branch: ; in, , , These represent the current angles of phases A, B, and C of the main transformer bay, respectively. , , These represent the current angles of phases A, B, and C during the charging interval. This represents the phase angle calculation function.

[0032] The three-phase current angle difference between the charging branch and the main transformer branch is calculated as follows: when Greater than , Greater than , Greater than At that time, the angle difference between the main transformer interval and the charging interval is: ; when Less than , Less than , Less than At that time, the angle difference between the main transformer interval and the charging interval is: ; in, The angle difference between the main transformer interval and the charging interval (phase A) The angle difference between the main transformer interval and the charging interval (phase B) The difference in phase C is the angle between the main transformer interval and the charging interval.

[0033] If the angle difference between the currents of two or more branches is greater than the corresponding threshold value (i.e., the branch current angle difference threshold value is set to 180° in this invention), that is... , , If at least two angle differences satisfy the following conditions, the CT polarity determination of the main variable interval is correct (i.e., the CT polarity of the main variable is correct). ; in, The constant is 180°. This is the threshold value for the angle difference.

[0034] If the angle difference between the currents in two or more branches is less than the corresponding threshold value, that is... , , If at least two angle differences satisfy the following conditions, the CT polarity determination of the main transformer interval and the charging interval is incorrect (i.e., the main transformer CT polarity is incorrect). .

[0035] Step Six: Calculate the harmonic angle difference between the second harmonic voltage and the second harmonic current of the main transformer branch (i.e., in response to the second harmonic content being greater than the set harmonic content threshold value, calculate the harmonic angle difference between the second harmonic voltage and the second harmonic current of the main transformer branch). If the harmonic angle difference between two or more phases is less than the corresponding harmonic angle difference threshold value, the polarity determination of the main transformer interval CT is correct (i.e., in response to the harmonic angle difference between two or more phases being less than the harmonic angle difference threshold value, the determination is: the polarity of the main transformer CT is correct). If the harmonic angle difference between two or more phases is greater than or equal to the harmonic angle difference threshold value, the polarity determination of the CTs of the main transformer interval and the charging interval is reversed (i.e., in response to the harmonic angle difference between two or more phases being greater than or equal to the harmonic angle difference threshold value, the determination is: the polarity of the main transformer CT is incorrect).

[0036] The harmonic phase angle difference (i.e., harmonic angle difference) between the second harmonic voltage and the second harmonic current in the main transformer branch is calculated as follows: ; in, This represents the harmonic angle difference between the second harmonic voltage and the second harmonic current of phase A in the main transformer branch. This represents the harmonic angle difference between the second harmonic voltage and the second harmonic current of phase B in the main transformer branch. This represents the harmonic angle difference between the second harmonic voltage and the second harmonic current of phase C in the main transformer branch.

[0037] like , , If at least two harmonic angle differences are less than 180 degrees (i.e., the harmonic angle difference threshold is 180°), then the CT polarity of the main transformer branch is determined to be correct (i.e., the main transformer CT polarity is correct); if , , If there are at least two angle differences greater than 180 degrees, it is determined that the CT polarity of the main transformer branch is incorrect (i.e., the main transformer CT polarity is incorrect).

[0038] Step 7: Calculate the fundamental angle difference between the fundamental voltage and fundamental current of the main transformer branch (i.e., in response to the second harmonic content being less than or equal to the set harmonic content threshold value, calculate the fundamental angle difference between the fundamental voltage and fundamental current of the main transformer branch). If the angle difference between two or more phases is greater than the fundamental angle difference threshold value, the polarity determination of the main transformer interval CT is correct (i.e., in response to the fundamental angle difference between two or more phases being greater than the fundamental angle difference threshold value, the determination is: the polarity of the main transformer CT is correct). If the angle difference between two or more phases is less than or equal to the fundamental angle difference threshold value, the polarity determination of the main transformer interval CT is reversed (i.e., in response to the fundamental angle difference between two or more phases being less than or equal to the fundamental angle difference threshold value, the determination is: the polarity of the main transformer CT is incorrect).

[0039] The fundamental phase angle difference between the fundamental voltage and fundamental current of the main transformer branch is calculated as follows: ; In the formula, This represents the fundamental angle difference between the fundamental current and the fundamental voltage of phase A in the main transformer branch. This represents the fundamental angle difference between the fundamental voltage and fundamental current of phase B in the main transformer branch. This represents the fundamental angle difference between the fundamental voltage and fundamental current of phase C in the main transformer branch.

[0040] like , , If at least two fundamental frequency angle differences are greater than 180 degrees (i.e., the fundamental frequency angle difference threshold is 180°), then the CT polarity of the main transformer branch is determined to be correct (i.e., the main transformer CT polarity is correct); if , , If there are at least two fundamental wave angle differences less than 180 degrees, it is determined that the CT polarity of the main transformer branch is incorrect (i.e., the main transformer CT polarity is incorrect).

[0041] Figure 3 for Figure 2 The logic diagram of the start conditions for the CT polarity discrimination function of the main transformer 1 bay is as follows: when the voltage of the main transformer 1 bay is normal, the circuit breaker position changes from open to closed, or the three-phase current changes from no current to current, the CT polarity discrimination function is started.

[0042] Figure 4 When the closing angle is 0°, Figure 2 According to the method of this invention, the second harmonic waveforms of the voltage and current in the first branch of the main transformer are such that the second harmonic content is greater than 0.15. The polarity of the transformer current transformer (CT) in the transformer branch is determined by the angular relationship between the second harmonic current and the second harmonic voltage. , , The angle difference is less than 180 degrees, indicating that the CT polarity of the main transformer branch is correct.

[0043] Figure 5 When the closing angle is 60°, Figure 2 According to the method of this invention, the second harmonic waveforms of the voltage and current in the first branch of the main transformer are such that the second harmonic content is greater than 0.15. The polarity of the transformer current transformer (CT) in the transformer branch is determined by the angular relationship between the second harmonic current and the second harmonic voltage. , , The angle difference was also less than 180 degrees, indicating that the CT polarity of the main transformer branch was correct.

[0044] This invention first acquires real-time voltage and current information for each bay, as well as information about the main transformer bay circuit breakers. Based on the acquired main transformer bay current information, it calculates the second harmonic content and determines whether the second harmonic content exceeds a threshold value. Secondly, based on the location change information or current change characteristics of the main transformer high-voltage side circuit breakers and the main transformer branch voltage information, it determines whether to activate the CT polarity discrimination function. Finally, based on the configuration of voltage transformers on the main transformer high-voltage side, it adaptively uses the second harmonic content of the main transformer bay and the phase angle difference characteristics of the second harmonic, fundamental current, and corresponding voltage, or the phase angle difference characteristics of the charging branch and the main transformer bay current, to discriminate the polarity of the main transformer CT. Compared with existing technologies, this invention can effectively utilize the second harmonic component, which has the highest content in the inrush current, adaptively adapt to the second harmonic of the inrush current, and integrate the fundamental wave to determine the CT polarity direction. This solves the problems of low reliability and complexity in manually verifying the polarity of standby transformer CTs in new energy scenarios such as pumped storage, nuclear power, and offshore wind power, thereby improving the operational reliability of substations.

[0045] Example 2 Based on the second harmonic-based transformer CT polarity determination method described in Embodiment 1, this embodiment provides a second harmonic-based transformer CT polarity determination device, including: a CT polarity determination module with a voltage transformer, used to execute a CT polarity determination process with a voltage transformer in response to the activation of the CT polarity determination function and the high-voltage side of the transformer being equipped with a voltage transformer; and a CT polarity determination module without a voltage transformer, used to execute a CT polarity determination process without a voltage transformer in response to the activation of the CT polarity determination function and the high-voltage side of the transformer not being equipped with a voltage transformer.

[0046] Example 3 Based on the second harmonic-based main transformer CT polarity determination method described in Embodiment 1, this embodiment provides a computer device, including: a memory for storing instructions; and a processor for executing the instructions, causing the device to perform operations implementing the second harmonic-based main transformer CT polarity determination method described in Embodiment 1.

[0047] Example 4 Based on the second harmonic-based main transformer CT polarity determination method described in Embodiment 1, this embodiment provides a computer-readable storage medium storing a computer program thereon. When the computer program is executed by a processor, it implements the second harmonic-based main transformer CT polarity determination method as described in Embodiment 1.

[0048] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0049] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0050] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0051] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0052] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for determining the polarity of a main variable CT based on second harmonics, characterized in that, include: In response to the activation of the CT polarity determination function, and given that a voltage transformer is configured on the high-voltage side of the transformer, the CT polarity determination process with the voltage transformer is executed. In response to the activation of the CT polarity determination function, and since no voltage transformer is configured on the high-voltage side of the transformer, the CT polarity determination process without a voltage transformer is executed.

2. The method for determining the polarity of a main variable CT based on second harmonics according to claim 1, characterized in that, The process for determining the polarity of a current transformer (CT) with a voltage transformer includes: Calculate the fundamental and second harmonic content of the voltage and current in the main transformer bay; In response to the second harmonic content exceeding the set harmonic content threshold, the harmonic angle difference between the second harmonic voltage and the second harmonic current of the main transformer branch is calculated. If the harmonic angle difference between two or more phases is less than the harmonic angle difference threshold, it is determined that the polarity of the main transformer CT is correct. If the harmonic angle difference between two or more phases is greater than or equal to the harmonic angle difference threshold, it is determined that the polarity of the main transformer CT is incorrect.

3. The method for determining the polarity of a main variable CT based on second harmonics according to claim 2, characterized in that, In response to the second harmonic content being less than or equal to a set harmonic content threshold, the fundamental angle difference between the fundamental voltage and fundamental current of the main transformer branch is calculated. If the fundamental angle difference between two or more phases is greater than the fundamental angle difference threshold, it is determined that the polarity of the main transformer CT is correct. If the fundamental angle difference between two or more phases is less than or equal to the fundamental angle difference threshold, it is determined that the main transformer CT polarity is incorrect.

4. The method for determining the polarity of a main variable CT based on second harmonics according to claim 2 or 3, characterized in that, The threshold values ​​for harmonic content are 15%; the threshold values ​​for harmonic angle difference are 180°; and the threshold values ​​for fundamental frequency angle difference are 180°.

5. The method for determining the polarity of a main variable CT based on second harmonics according to claim 1, characterized in that, The CT polarity determination process without voltage transformers includes: Calculate the fundamental values ​​of the three-phase currents, the three-phase current angles, and the branch current angle differences for the charging branch and the main transformer branch; If the angle difference between two or more phase branch currents is greater than the branch current angle difference threshold, it is determined that the polarity of the main transformer CT is correct. If the angle difference between the currents of two or more phases is less than or equal to the threshold value of the angle difference between the currents of the two phases, it is determined that the polarity of the main transformer CT is incorrect.

6. The method for determining the polarity of a main variable CT based on second harmonics according to claim 5, characterized in that, The threshold value for the branch current angle difference is 180°.

7. The method for determining the polarity of a main variable CT based on second harmonics according to claim 1, characterized in that, To activate the CT polarity determination function, the following conditions must be met: 1) The voltage on the high-voltage side of the main transformer is normal; 2) The position of the circuit breaker on the high-voltage side of the main transformer changes from open to closed, or the current in the main transformer branch changes from zero to current. The criteria for determining normal voltage on the high-voltage side of the main transformer are as follows: ； in, , , The effective values ​​of phase A, phase B, and phase C voltages on the high-voltage side of the main transformer. This is the secondary voltage rating. The zero-sequence voltage on the high-voltage side of the main transformer. The negative sequence voltage on the high-voltage side of the main transformer; The threshold value for the main transformer branch current to change from zero to current is 0.

05. , This is the secondary rated value of the current.

8. A polarity determination device for a main variable CT based on second harmonics, characterized in that, include: A CT polarity determination module with a voltage transformer is used to respond to the activation of the CT polarity determination function, and the high-voltage side of the transformer is equipped with a voltage transformer to execute the CT polarity determination process with the voltage transformer. The CT polarity determination module without voltage transformer is used to execute the CT polarity determination process in response to the activation of the CT polarity determination function and when no voltage transformer is configured on the high-voltage side of the transformer.

9. A computer device, characterized in that, include: Memory, used to store instructions; A processor is configured to execute the instructions, causing the device to perform operations that implement the main variable CT polarity determination method based on second harmonics as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the main variable CT polarity determination method based on second harmonics as described in any one of claims 1 to 7.

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