Method for identifying excitation inrush of wind farm sending transformer based on differential current waveform characteristics and application thereof

Abstract

This application relates to the field of relay protection technology, and in particular to a method for identifying inrush current in wind farm transmission transformers based on differential current waveform characteristics and its application. By utilizing the characteristics of the differential current waveform to construct the inrush current fault criterion for the transformer, compared with the traditional second harmonic restraint method, the time window is shorter, enabling rapid identification of the transformer's inrush current and improving the reliability of the wind farm transmission transformer protection. The aim is to solve the problem of how to reliably identify inrush current faults in wind farm transformers.

Description

Technical Field

[0001] This application relates to the field of relay protection technology, and in particular to a method for identifying inrush current of wind farm transmission transformers based on differential current waveform characteristics and its application. Background Technology

[0002] When a fault occurs in the power transmission transformer of a large-scale wind farm, it is usually necessary to quickly and accurately identify whether the fault is caused by inrush current within a short period of time; otherwise, the protection will malfunction due to the inrush current. However, since most wind turbines in wind farms are currently doubly-fed induction generators, the frequency deviation characteristics and increased second harmonic content of wind farms pose challenges to the second harmonic restraint components in traditional transformer protection.

[0003] Traditional transformer protection second harmonic restraint elements mainly detect second harmonic content. When the second harmonic content exceeds a threshold, it is identified as an inrush current. However, the second harmonic content in large-scale wind farm systems is significantly higher than that in traditional power grids. Traditional second harmonic restraint elements may not be able to accurately identify the inrush current of transformers. On the other hand, the relevant inrush current identification methods based on traditional power frequency quantities cannot meet the high-speed protection requirements of large-scale wind farms.

[0004] In view of this, this application proposes a new method for identifying inrush current in wind farm power transmission transformers, aiming to achieve reliable identification of transformer faults in wind farms. Summary of the Invention

[0005] The main objective of this application is to provide a method for identifying inrush current in wind farm power transmission transformers based on differential waveform characteristics, aiming to solve the problem of how to reliably identify inrush current faults in wind farm transformers.

[0006] To achieve the above objectives, this application provides a method for identifying inrush current in wind farm transmission transformers based on differential current waveform characteristics, the method comprising:

[0007] S10, calculate the differential current based on the transient currents collected on both sides of the output transformer;

[0008] S20, when the amplitude of the differential current is greater than a preset first threshold, determine the maximum value point of the differential current;

[0009] S30, calculate the numerical difference between the sampling points symmetrical on both sides of the maximum point, and normalize each numerical difference through the maximum point and take the maximum value among them;

[0010] S40, determine whether the maximum value is greater than a preset second threshold;

[0011] S50, if so, determine that the output transformer has an inrush current.

[0012] Optionally, the expression for the numerical difference is:

[0013]

[0014] In the formula, Represents the maximum point The nth sampling point on the left, Represents the maximum point The nth sampling point on the right; m=1, 2, 3…; n=1, 2, 3….

[0015] Optionally, the expression for the maximum value is:

[0016]

[0017] In the formula, This is the point of maximum differential current. The difference is numerical.

[0018] Optionally, after S50, the following steps are also included:

[0019] S60, executes interlocking protection.

[0020] Optionally, after S40, the method further includes:

[0021] S70, if not, determine that the output transformer has an internal fault.

[0022] Optionally, after S10, the method further includes:

[0023] S80, when the amplitude of the differential current is less than or equal to a preset first threshold, step S10 continues to be executed.

[0024] In addition, to achieve the above objectives, this application also provides an application of the wind farm sending transformer excitation inrush current identification method based on differential current waveform characteristics as described in any of the preceding claims in wind farm fault detection.

[0025] In addition, to achieve the above objectives, this application also provides a transformer, the transformer comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, it implements the steps of the wind farm output transformer excitation inrush current identification method based on differential current waveform characteristics as described in any of the preceding claims.

[0026] In addition, to achieve the above objectives, this application also provides a relay protection system, which includes: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, it implements the steps of the wind farm output transformer inrush current identification method based on differential current waveform characteristics as described in any of the preceding claims.

[0027] In addition, to achieve the above objectives, this application also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the wind farm output transformer inrush current identification method based on differential current waveform characteristics as described in any of the preceding claims.

[0028] This application has at least the following beneficial effects:

[0029] (1) Compared with the traditional second harmonic braking method, the method of this application using differential current waveform characteristics has higher accuracy and sensitivity;

[0030] (2) The application has a short time window, which can quickly identify internal faults and inrush currents of the transformer, thus improving the reliability of the protection of the wind farm's output transformer. Attached Figure Description

[0031] Figure 1 This is a simulation model topology diagram of the wind farm grid-connected system involved in the embodiments of this application;

[0032] Figure 2 This is a flowchart illustrating the inrush current identification method for wind farm output transformers based on differential current waveform characteristics, as described in an embodiment of this application.

[0033] Figure 3 This is a waveform curve showing the numerical difference between sampling points on both sides of the peak of the excitation inrush current of the output transformer involved in the embodiments of this application;

[0034] Figure 4 This is a waveform curve of the numerical difference between sampling points on both sides of the maximum value point when a phase A ground fault occurs on the high-voltage side of the transmitting transformer involved in the embodiments of this application.

[0035] Figure 5 This is a waveform curve of the numerical difference between sampling points on both sides of the maximum value point under a two-phase short-circuit fault (BC) on the high-voltage side of the power transmission transformer involved in the embodiments of this application.

[0036] Figure 6 This is a waveform curve of the difference between the sampling points on both sides of the maximum value point when a phase A ground fault occurs on the high-voltage side of the transmitting transformer involved in this application, and the transition resistance is 100 Ω.

[0037] Figure 7 This is a schematic diagram of the hardware operating environment of the relay protection system involved in the embodiments of this application.

[0038] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0039] To better understand the above technical solutions, exemplary embodiments of this disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0040] First Embodiment

[0041] In this embodiment, the topology diagram of the wind farm grid-connected system simulation model is as follows: Figure 1 As shown, the total installed capacity of the wind farm is 200 MW. The low-voltage ride-through methods for the wind turbines are divided into two types: crowbar operation and continuous excitation by a frequency converter, with a voltage level of 220 kV. An inrush current is generated by the output transformer, and the sampling rate is 10 kHz.

[0042] Reference Figure 2 This embodiment provides a method for identifying inrush current in wind farm power transmission transformers based on differential current waveform characteristics. The method includes the following steps:

[0043] S10, calculate the differential current based on the transient currents collected on both sides of the output transformer;

[0044] In this embodiment, transient currents on both sides of the output transformer are collected, and differential current is calculated.

[0045] S20, when the amplitude of the differential current is greater than a preset first threshold, determine the maximum value point of the differential current;

[0046] Furthermore, it is determined whether the differential current amplitude exceeds the limit; if so, the criteria for inrush current identification are activated.

[0047] For example, the discriminant is:

[0048]

[0049] In the formula, ∆ i For differential current, i set This is the preset first threshold.

[0050] In some optional implementations, a first threshold is preset. iset Take 0.2.

[0051] S30, calculate the numerical difference between the sampling points symmetrical on both sides of the maximum point, and normalize each numerical difference through the maximum point and take the maximum value among them;

[0052] In this step, we take symmetrical sampling point pairs between the two sides of the maximum point, calculate the numerical difference between the sampling point pairs and normalize it. Since there are multiple sampling point pairs, we need to take the maximum value among them.

[0053] Specifically, the expression for the numerical difference is:

[0054]

[0055] In the formula, Represents the maximum point The nth sampling point on the left, Represents the maximum point The nth sampling point on the right; m=1, 2, 3…; n=1, 2, 3….

[0056] For example, refer to Figure 3 The waveform curve showing the difference in values ​​between sampling points on both sides of the peak of the inrush current waveform of the transmitting transformer is shown. It can be seen that the difference between the two sides of the maximum value point changes with time, thus determining that there is a large gap between the two sides of the peak of the inrush current waveform.

[0057] Specifically, the expression for the maximum value is:

[0058]

[0059] In the formula, This is the point of maximum differential current. The difference is numerical.

[0060] S40, determine whether the maximum value is greater than a preset second threshold;

[0061] S50, if so, determine that the output transformer has an inrush current.

[0062] In this embodiment, the determination If the current exceeds the threshold, it is determined that the sending transformer has experienced inrush current.

[0063] In some alternative implementations, the second threshold is preset to 0.2.

[0064] It should be noted that the principle behind selecting this criterion in this embodiment is as follows:

[0065] Due to the influence of the second harmonic, the inrush current exhibits asymmetrical characteristics, with certain differences in the waveforms on both sides of the peak. Except for the discontinuous angle portion, there is a significant difference in the waveform difference between the two sides of the peak. However, under internal fault conditions, the waveform exhibits a more obvious sinusoidal characteristic, and the waveforms on both sides of the peak are approximately symmetrical, resulting in a smaller difference. Therefore, by calculating the maximum point of the differential current waveform and using this as the peak, the difference between the sampling points on both sides of the peak can be obtained. Then, the difference can be normalized using the maximum point, and the maximum value can be obtained. This allows for the accurate identification of the inrush current and internal faults in the output transformer.

[0066] Similarly, refer to Figure 3 ,Depend on Figure 3 It can be seen that the numerical difference between the sampling points on both sides of the peak under the excitation inrush current is... The curve variation characteristics conform to the principle described in this embodiment, that is, from... Figure 3 It can be seen that there is a significant difference in the values ​​on both sides of the peak of the excitation inrush current waveform. Furthermore, calculations show that the peak value is reached at the maximum point. i p ( m )right i d ( n Normalize the result and find its maximum value. i dmax The value is 0.41, indicating that the maximum value is under this working condition. i dmax If the value is greater than the threshold of 0.2, it can be determined that an inrush current has occurred in the sending transformer.

[0067] In the technical solution provided in this embodiment, the inrush current fault criterion of the transformer is constructed by using the differential current waveform characteristics. Compared with the traditional second harmonic braking method, the time window is shorter, which can quickly identify the inrush current of the transformer and improve the reliability of the protection of the wind farm's output transformer.

[0068] Further and optionally, in this embodiment, after executing step S50 and determining that the sending transformer has an inrush current, the following steps are performed:

[0069] S60, executes interlocking protection.

[0070] Further and optionally, in this embodiment, if it is determined that the maximum value is less than or equal to a preset second threshold, then:

[0071] S70, it is determined that the output transformer has an internal fault.

[0072] Further and optionally, after step S10, the method further includes:

[0073] S80, when the amplitude of the differential current is less than or equal to a preset first threshold, step S10 continues to be executed.

[0074] Second Embodiment

[0075] Based on the first embodiment, in this embodiment, the simulation model of the wind farm grid connection system is also as follows. Figure 1 As shown, the rest of the settings are the same as in the first embodiment, except that the fault is set to occur on the high-voltage side of the sending transformer, and the fault types are set to A-phase grounding fault and B and C-phase short circuit fault, respectively.

[0076] Reference Figure 4 The diagram shown is a waveform curve of the numerical difference between sampling points on both sides of the maximum value point under the condition of a phase A ground fault on the high-voltage side of the transmitting transformer. i p ( m )right i d ( n Normalize the result and find its maximum value. i dmax If the value is 0.09, which is less than the threshold of 0.2, it can be determined that an internal fault has occurred in the transmitting transformer.

[0077] Reference Figure 5 The diagram shown is a waveform curve of the numerical difference between sampling points on both sides of the maximum value point under a two-phase (BC) short-circuit fault on the high-voltage side of the transmitting transformer. The waveform curve passes through the maximum value point. i p ( m )right i d ( n Normalize the result and find its maximum value. i dmax If the value is 0.07, which is less than the threshold of 0.2, it can be determined that an internal fault has occurred in the transmitting transformer.

[0078] Reference Figure 6 The diagram shown depicts the waveform difference between sampling points on both sides of the maximum value point when a phase A ground fault occurs on the high-voltage side of the transmitting transformer, with a transition resistance of 100 Ω. The waveform passes through the maximum value point. i p ( m )right i d ( n Normalize the result and find its maximum value. i dmax If the value is 0.11, which is less than the threshold of 0.2, it can be determined that an internal fault has occurred in the transmitting transformer.

[0079] Furthermore, as an implementation scheme, the embodiments of this application also relate to the application of a wind farm sending transformer excitation inrush current identification method based on differential current waveform characteristics as described in any of the preceding claims in wind farm fault detection.

[0080] For details regarding the application of the wind farm fault detection, please refer to the content in the first or second embodiment.

[0081] Furthermore, as one implementation, this application embodiment also relates to a transformer, the transformer comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, it implements the steps of the wind farm output transformer excitation inrush current identification method based on differential current waveform characteristics as described in any of the preceding claims.

[0082] Furthermore, as an implementation scheme, Figure 7 This is a schematic diagram of the hardware operating environment of the relay protection system involved in the embodiments of this application.

[0083] like Figure 7 As shown, the relay protection system may include: a processor 1001, such as a CPU; a memory 1005; a user interface 1003; a network interface 1004; and a communication bus 1002. The communication bus 1002 is used to enable communication between these components. The user interface 1003 may include a display screen or an input unit such as a keyboard; optionally, the user interface 1003 may also include a standard wired interface or a wireless interface. The network interface 1004 may optionally include a standard wired interface or a wireless interface (such as a Wi-Fi interface). The memory 1005 may be a high-speed RAM or a stable, non-volatile memory, such as a disk drive. Optionally, the memory 1005 may also be a storage device independent of the aforementioned processor 1001.

[0084] Those skilled in the art will understand that Figure 7 The relay protection system architecture shown does not constitute a limitation on the relay protection system and may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0085] like Figure 7 As shown, the memory 1005, which serves as a storage medium, may include an operating system, a network communication module, a user interface module, and computer programs. The operating system is a program that manages and controls the hardware and software resources of the relay protection system, while the computer programs and other software or programs run.

[0086] exist Figure 7In the relay protection system shown, the user interface 1003 is mainly used to connect to the terminal and communicate with the terminal; the network interface 1004 is mainly used to communicate with the back-end server; and the processor 1001 can be used to call the computer program stored in the memory 1005.

[0087] In this embodiment, the relay protection system includes: a memory 1005, a processor 1001, and a computer program stored in the memory and executable on the processor, wherein:

[0088] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0089] S10, calculate the differential current based on the transient currents collected on both sides of the output transformer;

[0090] S20, when the amplitude of the differential current is greater than a preset first threshold, determine the maximum value point of the differential current;

[0091] S30, calculate the numerical difference between the sampling points symmetrical on both sides of the maximum point, and normalize each numerical difference through the maximum point and take the maximum value among them;

[0092] S40, determine whether the maximum value is greater than a preset second threshold;

[0093] S50, if so, determine that the output transformer has an inrush current.

[0094] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0095] The expression for the numerical difference is:

[0096]

[0097] In the formula, Represents the maximum point The nth sampling point on the left, Represents the maximum point The nth sampling point on the right; m=1, 2, 3…; n=1, 2, 3….

[0098] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0099] The expression for the maximum value is:

[0100]

[0101] In the formula, This is the point of maximum differential current. The difference is numerical.

[0102] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0103] S60, executes interlocking protection.

[0104] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0105] S70, if not, determine that the output transformer has an internal fault.

[0106] When processor 1001 calls a computer program stored in memory 1005, it performs the following operations:

[0107] S80, when the amplitude of the differential current is less than or equal to a preset first threshold, step S10 continues to be executed.

[0108] Furthermore, those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program includes program instructions and can be stored in a storage medium, which is a computer-readable storage medium. The program instructions are executed by at least one processor in the relay protection system to implement the process steps of the embodiments of the above methods.

[0109] Therefore, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the various steps of the wind farm output transformer inrush current identification method based on differential current waveform characteristics as described in the above embodiments.

[0110] The computer-readable storage medium can be any computer-readable storage medium capable of storing program code, such as a USB flash drive, portable hard drive, read-only memory (ROM), magnetic disk, or optical disk.

[0111] It should be noted that, since the storage medium provided in the embodiments of this application is the storage medium used to implement the methods of the embodiments of this application, those skilled in the art can understand the specific structure and variations of the storage medium based on the methods described in the embodiments of this application, and therefore will not be repeated here. All storage media used in the methods of the embodiments of this application fall within the scope of protection of this application.

[0112] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application 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.

[0113] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. 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... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0114] 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.

[0115] 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.

[0116] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0117] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for identifying inrush current in wind farm transmission transformers based on differential current waveform characteristics, characterized in that, The method includes the following steps: S10, calculate the differential current based on the transient currents on both sides of the output transformer collected within a 5ms time window; S20, when the amplitude of the differential current is greater than a preset first threshold, determine the maximum value point of the differential current; S30, calculate the numerical difference between the sampling points symmetrical on both sides of the maximum point, and normalize each numerical difference through the maximum point and take the maximum value among them; The expression for the numerical difference is: ； In the formula, Represents the maximum point The nth sampling point on the left, Represents the maximum point The nth sampling point on the right; m=1, 2, 3…; n=1, 2, 3…; The expression for the maximum value is: ； In the formula, This is the point of maximum differential current. The difference is numerical; S40, determine whether the maximum value is greater than a preset second threshold; S50, if so, determine that the output transformer has an inrush current.

2. The method as described in claim 1, characterized in that, Following S50, the following is also included: S60, executes interlocking protection.

3. The method as described in claim 1, characterized in that, Following S40, the following is also included: S70, if not, determine that the output transformer has an internal fault.

4. The method as described in claim 1, characterized in that, Following S10, the following is also included: S80, when the amplitude of the differential current is less than or equal to a preset first threshold, step S10 continues to be executed.

5. An application of the wind farm sending transformer excitation inrush current identification method based on differential current waveform characteristics as described in any one of claims 1 to 4 in wind farm fault detection.

6. A transformer, characterized in that, The transformer includes: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, it implements the steps of the wind farm output transformer excitation inrush current identification method based on differential current waveform characteristics as described in any one of claims 1 to 4.

7. A relay protection system, characterized in that, The relay protection system includes: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, it implements the steps of the wind farm output transformer inrush current identification method based on differential current waveform characteristics as described in any one of claims 1 to 4.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the wind farm outgoing transformer excitation inrush current identification method based on differential current waveform characteristics as described in any one of claims 1 to 4.

Images