A method and device for checking polarity and phase sequence of common winding CT of autotransformer

Abstract

The present invention discloses a method and device for verifying the polarity and phase sequence of a common winding CT of an autotransformer. The method comprises obtaining the current on each side of the autotransformer and the current of the common winding; judging whether the autotransformer is in an empty-charge state based on the current on each side; if in the empty-charge state, calculating the split-side differential current based on the current on each side and the current of the common winding; if the split-side differential current is greater than a preset first threshold, judging that the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong; if not in the empty-charge state, judging whether the autotransformer is operating normally based on the current on each side; if operating normally, calculating the split-side differential current and the longitudinal differential current based on the current on each side and the current of the common winding; if the split-side differential current is greater than a preset second threshold and the longitudinal differential current is less than a preset third threshold, judging that the polarity or phase sequence of the common winding CT is wrong; the present invention can solve the problem that the polarity and phase sequence of the common winding CT of the autotransformer are difficult to verify, resulting in malfunction of zero-difference protection during an out-of-zone single-phase grounding fault.

Description

Technical Field

[0001] The invention relates to a method and a device for checking the polarity and phase sequence of a common winding CT of an autotransformer, and belongs to the technical field of transformers. Background Art

[0002] Autotransformers have the advantages of low material consumption, low cost, low losses, and high efficiency, and are therefore widely used in power systems. Because the polarity of the zero-sequence CT on the grounded neutral line of a transformer is difficult to verify, the zero-difference protection of the transformer is generally composed of self-generated zero-sequence currents on the high-voltage and medium-voltage sides and the common winding. This makes it highly sensitive to ground faults on the star winding side of the transformer and is unaffected by the transformer's excitation current, inrush current, on-load voltage regulation, and overexcitation, resulting in excellent quick response. Zero-difference protection is widely used to protect autotransformers and is of great significance for ensuring the safe and stable operation of power grids. However, in recent years, there have been numerous cases of zero-difference protection malfunctioning due to incorrect polarity or phase sequence connection of the common winding CT during out-of-zone ground faults.

[0003] Homodyne protection is used to protect against ground short-circuit faults within the star winding zone of the transformer. When a ground fault occurs outside the protection zone, the zero-sequence current is a through-current within the transformer's zero-differential protection range, and the zero-differential differential current is zero, ensuring reliable and reliable zero-differential protection without false tripping. On-site load testing is conducted to verify the polarity of the CTs on each side of the transformer, including the common winding CT, to ensure correct polarity and phase sequence. However, there are cases where the common winding CTs are incorrectly connected in polarity or phase sequence. If all three phases of the common winding CTs are incorrectly connected in polarity or phase sequence, the zero-sequence current generated by the CTs on the high- and medium-voltage sides and the common winding during normal load operation of the transformer is zero, the zero-differential differential current is normal, and the device does not generate any abnormal alarms. However, if a ground fault occurs outside the protection zone, the zero-differential protection will malfunction. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method and device for calibrating the polarity and phase sequence of the common winding CT of an autotransformer, thereby solving the technical problem that the polarity and phase sequence of the common winding CT of the autotransformer are difficult to calibrate, resulting in false operation of the zero-difference protection during an out-of-zone single-phase grounding fault.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] In a first aspect, the present invention provides a method for verifying the polarity and phase sequence of a common winding (CT) of an autotransformer, comprising:

[0007] Obtain the current on each side of the autotransformer and the common winding current, each side including the high voltage side, medium voltage side and low voltage side;

[0008] Determine whether the autotransformer is in an empty charging state based on the current on each side;

[0009] If it is in the empty-charge state, the split-side differential current is calculated based on the currents on each side and the common winding current. If the split-side differential current is greater than a preset first threshold, it is determined that the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong;

[0010] If it is not in the empty-charge state, the normal operation of the autotransformer is judged based on the current on each side;

[0011] If it operates normally, the side differential current and the longitudinal differential current are calculated based on the currents on each side and the common winding current. If the side differential current is greater than the preset second threshold and the longitudinal differential current is less than the preset third threshold, it is determined that the polarity or phase sequence of the common winding CT is wrong.

[0012] Optionally, judging whether the autotransformer is in an empty-charge state based on the currents on each side includes:

[0013] If there is no current on each side, and any phase of the current on any side satisfies the following formula, then the autotransformer is empty-charged from that side, and that side is determined to be the empty-charge side;

[0014]

[0015] Where, I a , I b , I c is the A, B, and C phase current on either side of the autotransformer, I N is the secondary CT value of this side.

[0016] Optionally, the calculating of the side difference flow includes:

[0017]

[0018] Where, I fcda , I fcdb , I fcdc They are the differential currents of phases A, B and C respectively. They are respectively the high voltage side, medium voltage side and common winding A phase current, They are respectively the high voltage side, medium voltage side, and common winding B phase current, They are high voltage side, medium voltage side and common winding C phase current respectively.

[0019] Optionally, if the device is in an empty-charge state, a delay of 100ms is performed before determining whether the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong.

[0020] Optionally, judging whether the autotransformer operates normally based on the currents on each side includes:

[0021] If there is current on the high-voltage side, the medium-voltage side, and the common winding, the autotransformer is operating normally. The conditions for judging whether there is current are:

[0022]

[0023] Where, I a , I b , I c is the A, B, and C phase current on either side of the autotransformer, I N is the secondary CT value of this side.

[0024] Optionally, calculating the longitudinal difference flow includes:

[0025]

[0026] Where, I da , I db , I dc They are the longitudinal differential currents of phases A, B and C respectively. They are the A-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively. They are respectively the B phase current on the high voltage side, medium voltage side and low voltage side, They are the C-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively.

[0027] Optionally, if the device is not in an empty-charge state, a delay of 10 seconds is performed before determining whether the common winding CT polarity or phase sequence is wrong.

[0028] In a second aspect, the present invention provides a device for checking the polarity and phase sequence of a common winding (CT) of an autotransformer, comprising:

[0029] A current acquisition module is used to obtain the current on each side of the autotransformer and the current on the common winding, each side including the high voltage side, the medium voltage side and the low voltage side;

[0030] An empty-charge state judgment module is used to judge whether the autotransformer is in an empty-charge state based on the current on each side;

[0031] A first verification module is configured to calculate a split-side differential current based on the currents on each side and the common winding current if the circuit is in an empty-charge state, and determine that a polarity or phase sequence error exists in the common winding CT or the empty-charge side CT if the split-side differential current exceeds a preset first threshold;

[0032] A normal operation judgment module is used to judge whether the autotransformer is operating normally based on the current on each side if it is not in an empty charging state;

[0033] The second verification module is used to calculate the side differential current and the longitudinal differential current based on the current on each side and the common winding current if it is operating normally. If the side differential current is greater than the preset second threshold and the longitudinal differential current is less than the preset third threshold, it is determined that the polarity or phase sequence of the common winding CT is wrong.

[0034] In a third aspect, the present invention provides a device for checking the polarity and phase sequence of a common winding CT of an autotransformer, comprising a processor and a storage medium;

[0035] The storage medium is used to store instructions;

[0036] The processor is configured to operate according to the instructions to execute the steps of the above method.

[0037] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above method when executed by a processor.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention provides a method and device for verifying the polarity and phase sequence of the common winding CT of an autotransformer. By using the current on each side to determine when the transformer is empty-charged from a certain side, the split-side differential current is calculated to determine if the common winding CT or the transformer empty-charge side CT has a polarity or phase sequence error. During normal transformer operation, the split-side differential current and longitudinal differential current are calculated to determine if the common winding CT has a polarity or phase sequence error. This method can determine whether the common winding CT has a polarity or phase sequence error by operating the transformer empty-charged under no-load conditions, and can accurately determine whether the common winding CT has a polarity or phase sequence error under normal load conditions. This method solves the problem of difficulty in verifying the polarity and phase sequence of the common winding CT of an autotransformer, which can lead to malfunction of the zero-difference protection during an out-of-zone single-phase grounding fault, thereby improving the reliability of the transformer's zero-difference protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of a method for checking the polarity and phase sequence of a common winding CT of an autotransformer provided in the first embodiment of the present invention;

[0041] Figure 2 This is a wiring schematic diagram of longitudinal differential protection and homodyne protection provided in the first embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0043] Example 1:

[0044] like Figure 1 As shown, the present invention provides a method for checking the polarity and phase sequence of the common winding CT of an autotransformer, comprising:

[0045] 1. Obtain the current on each side of the autotransformer and the common winding current, including the high voltage side, medium voltage side, and low voltage side.

[0046] 2. Determine whether the autotransformer is in an empty charge state based on the current on each side; specifically:

[0047] If there is no current on each side, and any phase of the current on any side satisfies the following formula, then the autotransformer is empty-charged from that side, and that side is determined to be the empty-charge side;

[0048]

[0049] Where, I a , I b , I c is the A, B, and C phase current on either side of the autotransformer, I N is the secondary CT value of this side.

[0050] 3. If the system is in the empty-charge state, the split-side differential current is calculated based on the current on each side and the common winding current. If the split-side differential current is greater than the preset first threshold, it is determined that the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong;

[0051] 3.1、Calculation of side differential flow includes:

[0052]

[0053] Where, I fcda , I fcdb , I fcdc They are the differential currents of phases A, B and C respectively. They are respectively the high voltage side, medium voltage side and common winding A phase current, They are respectively the high voltage side, medium voltage side, and common winding B phase current, They are high voltage side, medium voltage side and common winding C phase current respectively.

[0054] 3.2. The phase-side differential flow is greater than the preset first threshold, including: the phase-side differential flow of any phase satisfies the following formula:

[0055]

[0056] Where, σ1 is the preset first threshold;

[0057] 3.3. Delay 100ms before determining whether the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong.

[0058] 4. If it is not in the empty charge state, judge whether the autotransformer is operating normally based on the current on each side; specifically including:

[0059] If there is current on the high-voltage side, medium-voltage side, and common winding, the autotransformer is operating normally. The conditions for judging whether there is current are:

[0060]

[0061] Where, I a , I b , I c is the A, B, and C phase current on either side of the autotransformer, I N is the secondary CT value of this side.

[0062] 5. If it is operating normally, the split-side differential current and longitudinal differential current are calculated based on the current on each side and the common winding current. If the split-side differential current is greater than the preset second threshold and the longitudinal differential current is less than the preset third threshold, it is determined that the polarity or phase sequence of the common winding CT is wrong.

[0063] 5.1. Calculate the differential flow on each side, same as step 3.1;

[0064] 5.2. Calculation of longitudinal differential flow includes:

[0065]

[0066] Where, I da , I db , I dc They are the longitudinal differential currents of phases A, B and C respectively. They are the A-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively. They are respectively the B phase current on the high voltage side, medium voltage side and low voltage side, They are the C-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively.

[0067] 5.3. The phase-side differential flow is greater than the preset second threshold and the longitudinal differential flow is less than the preset third threshold, including: the phase-side differential flow and the phase longitudinal differential flow of any phase satisfy the following formula:

[0068]

[0069] Where, σ2 is the preset second threshold, and σ3 is the preset third threshold;

[0070] 5.4. Delay 10s before determining if the common winding CT polarity or phase sequence is wrong.

[0071] The method provided in this embodiment can determine whether the polarity or phase sequence of the common winding CT may be wrong through the transformer no-load operation under no-load conditions, and can correctly determine whether the polarity or phase sequence of the common winding CT is wrong under normal load conditions, thereby improving the reliability of zero-difference protection.

[0072] like Figure 2 As shown, the wiring schematic diagram of longitudinal differential protection and zero differential protection;

[0073] Under normal circumstances, the polarity of the CT on each side participating in the transformer differential (zero sequence, longitudinal differential) protection is positive when flowing into the transformer. When the transformer is empty and charged, an excitation surge current will be generated, and there will be current only on the empty and charged side and the common winding side. If the polarity and phase sequence of the CT on the empty and charged side and the common winding CT are correct, the current on the empty and charged side and the common winding will be equal in magnitude and opposite in direction, and the split-side differential current will be 0. If the polarity or phase sequence of the CT on the empty and charged side or the common winding side is wrong, a split-side differential current will be generated. When the transformer is operating normally with load, there will be current on the high-voltage side, medium-voltage side, low-voltage side and common winding side. If the polarity and phase sequence of the CT on the high, medium and low-voltage sides are correct, the longitudinal differential current should be 0. If the longitudinal differential current is less than the threshold but the split-side differential current is greater than the threshold, it can be determined that the polarity or phase sequence of the CT on the common winding side is wrong.

[0074] Example 2:

[0075] An embodiment of the present invention provides a device for checking the polarity and phase sequence of a common winding (CT) of an autotransformer, comprising:

[0076] A current acquisition module is used to obtain the current on each side of the autotransformer and the current on the common winding, each side including the high voltage side, the medium voltage side and the low voltage side;

[0077] An empty-charge state judgment module is used to judge whether the autotransformer is in an empty-charge state based on the current on each side;

[0078] A first verification module is configured to calculate a split-side differential current based on the currents on each side and the common winding current if the circuit is in an empty-charge state, and determine that a polarity or phase sequence error exists in the common winding CT or the empty-charge side CT if the split-side differential current exceeds a preset first threshold;

[0079] A normal operation judgment module is used to judge whether the autotransformer is operating normally based on the current on each side if it is not in an empty charging state;

[0080] The second verification module is used to calculate the side differential current and the longitudinal differential current based on the current on each side and the common winding current if it is operating normally. If the side differential current is greater than the preset second threshold and the longitudinal differential current is less than the preset third threshold, it is determined that the polarity or phase sequence of the common winding CT is wrong.

[0081] Example 3:

[0082] Based on the first embodiment, the present invention provides a device for checking the polarity and phase sequence of a common winding CT of an autotransformer, including a processor and a storage medium;

[0083] The storage medium is used to store instructions;

[0084] The processor is configured to operate according to the instructions to execute the steps of the above method.

[0085] Example 4:

[0086] Based on the first embodiment, the embodiment of the present invention provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps of the above method are implemented.

[0087] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0088] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0089] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0090] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for checking the polarity and phase sequence of the common winding CT of an autotransformer, characterized in that: include: Obtain the current on each side of the autotransformer and the common winding current, each side including the high voltage side, medium voltage side and low voltage side; Determine whether the autotransformer is in an empty charging state based on the current on each side; If it is in the empty-charge state, the split-side differential current is calculated based on the currents on each side and the common winding current. If the split-side differential current is greater than a preset first threshold, it is determined that the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong; If it is not in the empty-charge state, the normal operation of the autotransformer is judged based on the current on each side; If it is operating normally, the split-side differential current and the longitudinal differential current are calculated based on the currents on each side and the common winding current. If the split-side differential current is greater than a preset second threshold and the longitudinal differential current is less than a preset third threshold, it is determined that the polarity or phase sequence of the common winding CT is wrong; The calculation of the side difference flow includes: Where, I fcda , I fcdb , I fcdc They are the differential currents of phases A, B and C respectively. They are respectively the high voltage side, medium voltage side and common winding A phase current, They are respectively the high voltage side, medium voltage side, and common winding B phase current, They are respectively the high voltage side, medium voltage side and common winding C phase current; The calculation of the longitudinal difference flow comprises: Where, I da , I db , I dc They are the longitudinal differential currents of phases A, B and C respectively. They are the A-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively. They are respectively the B phase current on the high voltage side, medium voltage side and low voltage side, They are the C-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively.

2. The method for checking the polarity and phase sequence of the common winding CT of an autotransformer according to claim 1, characterized in that: The method of judging whether the autotransformer is in an empty-charge state based on the currents on each side includes: If there is no current on each side, and any phase of the current on any side satisfies the following formula, then the autotransformer is empty-charged from that side, and that side is determined to be the empty-charge side; Where, I a , I b , I c is the A, B, and C phase current on either side of the autotransformer, I N is the secondary CT value of this side.

3. The method for checking the polarity and phase sequence of the common winding CT of an autotransformer according to claim 1, characterized in that: If it is in the empty-charge state, the delay before determining whether the polarity or phase sequence of the common winding CT or the empty-charge side CT is wrong is 100ms.

4. The method for checking the polarity and phase sequence of the common winding CT of an autotransformer according to claim 1, characterized in that: The method of judging whether the autotransformer is operating normally based on the currents on each side includes: If there is current on the high-voltage side, the medium-voltage side, and the common winding, the autotransformer is operating normally. The conditions for judging whether there is current are: Where, I a , I b , I c is the A, B, and C phase current on either side of the autotransformer, I N is the secondary CT value of this side.

5. The method for checking the polarity and phase sequence of the common winding CT of an autotransformer according to claim 1, characterized in that: If it is not in the empty charging state, a delay of 10 seconds is performed before determining whether the common winding CT polarity or phase sequence is wrong.

6. A device for checking polarity and phase sequence of common winding CT of autotransformer, characterized in that: include: A current acquisition module is used to obtain the current on each side of the autotransformer and the current on the common winding, each side including the high voltage side, the medium voltage side and the low voltage side; An empty-charge state judgment module is used to judge whether the autotransformer is in an empty-charge state based on the current on each side; A first verification module is configured to calculate a split-side differential current based on the currents on each side and the common winding current if the circuit is in an empty-charge state, and determine that a polarity or phase sequence error exists in the common winding CT or the empty-charge side CT if the split-side differential current exceeds a preset first threshold; A normal operation judgment module is used to judge whether the autotransformer is operating normally based on the current on each side if it is not in an empty charging state; a second checking module, configured to calculate, if normal operation occurs, a split-side differential current and a longitudinal differential current based on the currents on each side and the common winding current, and determine that a polarity or phase sequence error exists in the common winding CT if the split-side differential current is greater than a preset second threshold and the longitudinal differential current is less than a preset third threshold; The calculation of the side difference flow includes: Where, I fcda , I fcdb , I fcdc They are the differential currents of phases A, B and C respectively. They are respectively the high voltage side, medium voltage side and common winding A phase current, They are respectively the high voltage side, medium voltage side, and common winding B phase current, They are respectively the high voltage side, medium voltage side and common winding C phase current; The calculation of the longitudinal difference flow comprises: Where, I da , I db , I dc They are the longitudinal differential currents of phases A, B and C respectively. They are the A-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively. They are respectively the B phase current on the high voltage side, medium voltage side and low voltage side, They are the C-phase currents on the high-voltage side, medium-voltage side, and low-voltage side respectively.

7. A device for checking polarity and phase sequence of common winding CT of autotransformer, characterized in that: including processors and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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