Differential current waveform characteristic-based excitation surge current identification method for transformer sent out by wind power plant and application of excitation surge current identification method

Abstract

The invention relates to the technical field of relay protection, in particular to a method for identifying excitation surge current of a transformer sent out by a wind power plant based on differential current waveform characteristics and application of the method. Compared with a traditional second harmonic braking method, the method has the advantages that the time window is short, the magnetizing inrush current of the transformer can be quickly identified, and the protection reliability of the sending-out transformer of the wind power plant is improved. The objective of the invention is to solve the problem of how to reliably identify the magnetizing inrush current fault of the wind power plant transformer.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of relay protection, in particular to a wind farm sending transformer excitation inrush current identification method based on differential current waveform characteristics and application thereof. BACKGROUND

[0002] When a large-scale wind farm sending transformer fails, it is usually necessary to quickly and accurately identify whether the fault is an excitation inrush current in a short time, otherwise the protection will be misoperated due to the excitation inrush current. However, since most wind turbines in the current wind farm are double-fed induction generators, the frequency offset characteristics and the increased secondary harmonic content characteristics of the wind farm cause the secondary harmonic braking element in the traditional transformer protection to be challenged.

[0003] The secondary harmonic braking element in the traditional transformer protection is mainly based on the detection of the secondary harmonic content. When the secondary harmonic content is greater than a threshold value, it is determined that an excitation inrush current occurs. However, the secondary harmonic content of the large-scale wind farm system is obviously increased compared with the traditional power grid, and the traditional secondary harmonic braking element may not be able to accurately identify the excitation inrush current of the transformer. On the other hand, the related excitation inrush current identification method based on the traditional power frequency quantity cannot meet the high-speed protection requirements of the large-scale wind farm.

[0004] In view of this, the application provides a new excitation inrush current identification method for a wind farm sending transformer, aiming to realize reliable identification of the wind farm transformer fault. SUMMARY

[0005] The main purpose of the application is to provide an excitation inrush current identification method for a wind farm sending transformer based on differential current waveform characteristics, aiming to solve the problem of how to reliably identify the excitation inrush current fault of the wind farm transformer.

[0006] To achieve the above purpose, the application provides an excitation inrush current identification method for a wind farm sending transformer based on differential current waveform characteristics, which comprises the following steps: S10, calculating differential current according to the transient current collected on both sides of the sending transformer; S20, determining the maximum value point of the differential current when the amplitude of the differential current is greater than a preset first threshold value; S30, calculating the numerical difference between the sampling points symmetrically on both sides of the maximum value point, and taking the maximum value of the normalized numerical differences of the maximum value point; S40, judging whether the maximum value is greater than a preset second threshold value; S50, if yes, judging that the sending transformer has an excitation inrush current.

[0007] Optionally, the expression of the numerical difference is:

[0008] In the formula, representing the maximum point the left side n-th sampling point, representing the maximum point the right side n-th sampling point; m = 1, 2, 3…; n = 1, 2, 3…

[0009] Optionally, the expression of the maximum value is:

[0010] In the formula, is the maximum point of the differential current, is the numerical difference.

[0011] Optionally, after the S50, the method further comprises: S60, performing lockout protection.

[0012] Optionally, after the S40, the method further comprises: S70, if no, judging that the sending transformer has internal fault.

[0013] Optionally, after the S10, the method further comprises: S80, when the amplitude of the differential current is less than or equal to a preset first threshold value, continuously performing the step S10.

[0014] In addition, to achieve the above-mentioned purposes, the application further provides an application of the wind farm sending transformer excitation inrush current identification method based on the differential current waveform features in the wind farm fault detection.

[0015] In addition, to achieve the above-mentioned purposes, the application further provides a transformer, which comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, and the computer program realizes the steps of the wind farm sending transformer excitation inrush current identification method based on the differential current waveform features when executed by the processor.

[0016] In addition, to achieve the above-mentioned purposes, the application further provides a relay protection system, which comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, and the computer program realizes the steps of the wind farm sending transformer excitation inrush current identification method based on the differential current waveform features when executed by the processor.

[0017] In addition, to achieve the above object, the application further provides a computer readable storage medium, wherein the computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the steps of the method for identifying the magnetizing inrush current of the wind farm sending transformer based on the differential current waveform feature.

[0018] The application has at least the following beneficial effects: (1) Compared with the method based on the traditional second harmonic braking, the method based on the differential current waveform feature has higher accuracy and sensitivity; (2) The time window of the application is short, which can quickly identify the internal fault and magnetizing inrush current of the transformer, and improve the reliability of the wind farm sending transformer protection. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A wind farm grid-connected system simulation model topological graph related to the embodiments of the application; Figure 2 A flowchart of the method for identifying the magnetizing inrush current of the wind farm sending transformer based on the differential current waveform feature related to the embodiments of the application; Figure 3 A waveform curve graph of the numerical difference of the sampling points on both sides of the extreme value point of the sending transformer under the magnetizing inrush current related to the embodiments of the application; Figure 4 A waveform curve graph of the numerical difference of the sampling points on both sides of the extreme value point of the high-voltage side of the sending transformer under the A-phase ground fault related to the embodiments of the application; Figure 5 A waveform curve graph of the numerical difference of the sampling points on both sides of the extreme value point of the high-voltage side of the sending transformer under the BC two-phase short circuit fault related to the embodiments of the application; Figure 6 A waveform curve graph of the numerical difference of the sampling points on both sides of the extreme value point of the high-voltage side of the sending transformer under the A-phase ground fault with a transition resistance of 100 Ω related to the embodiments of the application; Figure 7 An architecture schematic diagram of the hardware running environment of the relay protection system related to the embodiments of the application.

[0020] The implementation of the object, functional features and advantages of the application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0021] For a better understanding of the above technical solutions, the exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art.

[0022] First embodiment In this embodiment, the topology diagram of the wind farm grid-connected system simulation model is shown in Figure 1 The total installed capacity of the wind farm is 200 MW, the low voltage ride-through mode of the wind turbine generator is divided into input crowbar and continuous excitation by frequency converter, and the voltage level is 220 kV. The excitation inrush current of the sending transformer is set, and the sampling rate is 10 kHz.

[0023] With reference to Figure 2 , in this embodiment, a method for identifying the excitation inrush current of the sending transformer of the wind farm based on the waveform characteristics of the differential current is provided, and the method comprises the following steps: S10, calculating the differential current according to the transient current collected on both sides of the sending transformer; In this embodiment, the transient current on both sides of the sending transformer is collected, and the differential current is calculated.

[0024] S20, when the amplitude of the differential current is greater than a preset first threshold value, determining the maximum value point of the differential current; Further, it is judged whether the differential current amplitude is out of limit, if yes, the criterion for identifying the excitation inrush current is started.

[0025] Exemplarily, the discriminant is:

[0026] In the formula, Δ i is the differential current, i set is a preset first threshold value.

[0027] In some optional embodiments, the preset first threshold value i set is 0.2.

[0028] S30, calculating the numerical difference between the symmetric sampling points on both sides of the maximum value point, and taking the maximum value of each normalized numerical difference through the maximum value point; In this step, the sampling point pairs symmetrically between the maximum value points are taken in turn, the numerical difference of the sampling point pair is calculated and normalized, and since there are multiple sampling point pairs, the maximum value needs to be taken.

[0029] Specifically, the expression of the numerical difference is:

[0030] 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….

[0031] 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.

[0032] Specifically, the expression for the maximum value is:

[0033] In the formula, This is the point of maximum differential current. The difference is numerical.

[0034] 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.

[0035] In this embodiment, the determination If the current exceeds the threshold, it is determined that the sending transformer has experienced inrush current.

[0036] In some alternative implementations, the second threshold is preset to 0.2.

[0037] It should be noted that the principle behind selecting this criterion in this embodiment is as follows: 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.

[0038] 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 3It can be seen that the difference on both sides of the excitation inrush waveform vertex is large. And it can be calculated that the maximum value point i p ( m ) is normalized and the maximum value i d ( n ) is calculated i dmax is 0.41. It can be seen that the maximum value i dmax is greater than the threshold value 0.2, so it can be judged that the excitation inrush of the outgoing transformer occurs.

[0039] In the technical scheme provided in the embodiment, the differential current waveform characteristics are used to form the excitation inrush fault criterion of the transformer. Compared with the method based on the traditional second harmonic braking, the time window is shorter, the excitation inrush of the transformer can be quickly identified, and the reliability of the outgoing transformer protection of the wind farm is improved.

[0040] Further and optionally, in the embodiment, after step S50 of judging that the excitation inrush of the outgoing transformer occurs, the following step is performed: S60, performing a blocking protection.

[0041] Further and optionally, in the embodiment, if it is judged that the maximum value is less than or equal to a preset second threshold value, then: S70, judging that the outgoing transformer has an internal fault.

[0042] Further and optionally, after step S10, the following step is further included: S80, when the amplitude of the differential current is less than or equal to a preset first threshold value, continuously performing step S10.

[0043] Second embodiment Based on the first embodiment, in the embodiment, the wind farm grid-connected system simulation model is also as shown in Figure 1 The remaining settings are the same as those in the first embodiment, and the difference lies in that the fault occurs at the high-voltage side of the outgoing transformer, and the fault types are set as an A-phase ground fault and B and C two-phase short-circuit faults.

[0044] Referring to the waveform curve diagram of the numerical difference of the sampling points on both sides of the maximum value point of the outgoing transformer high-voltage side under the A-phase ground short-circuit fault as shown in Figure 4 i p ( m ) is normalized and the maximum value i d ( n ) is calculated 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.

[0045] 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.

[0046] 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 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 0.11, which is less than the threshold of 0.2, it can be determined that an internal fault has occurred in the transmitting transformer.

[0047] 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.

[0048] For details regarding the application of the wind farm fault detection, please refer to the content in the first or second embodiment.

[0049] 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.

[0050] 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.

[0051] like Figure 7As shown, the relay protection system can 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 realize the connection communication between the components. The user interface 1003 can include a display screen (Display), an input unit such as a keyboard (Keyboard), and the optional user interface 1003 can also include a standard wired interface, a wireless interface. The network interface 1004 can optionally include a standard wired interface, a wireless interface (such as a WI-FI interface). The memory 1005 can be a high-speed RAM memory, or a stable memory (non-volatile memory) such as a disk memory. The memory 1005 can also be an independent storage device from the aforementioned processor 1001.

[0052] Those skilled in the art can understand that, Figure 7 The relay protection system architecture shown in the figure does not constitute a limitation on the relay protection system, and can include more or fewer components than the figure, or combine certain components, or different component arrangements.

[0053] As Figure 7 As shown, the memory 1005 as a storage medium can include an operating system, a network communication module, a user interface module, and a computer program. The operating system is a program that manages and controls the hardware and software resources of the relay protection system, and the running of the computer program and other software or programs.

[0054] In Figure 7 In the relay protection system shown, the user interface 1003 is mainly used to connect the terminal and communicate data with the terminal; the network interface 1004 is mainly used for the background server and communicates data with the background server; and the processor 1001 can be used to call the computer program stored in the memory 1005.

[0055] 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: When the processor 1001 calls the computer program stored in the memory 1005, the following operations are performed: S10, according to the transient current collected on both sides of the outgoing transformer, calculating the differential current; S20, when the amplitude of the differential current is greater than a preset first threshold, determining the maximum value point of the differential current; S30, calculating the numerical difference between the sampling points symmetrically on both sides of the maximum value point, and taking the maximum value of the normalized numerical difference through the maximum value point; S40, judging whether the maximum value is greater than a preset second threshold value; S50, if yes, judging that the sending transformer has a magnetizing inrush current.

[0056] When the processor 1001 invokes the computer program stored in the memory 1005, the following operations are performed: The expression of the numerical difference is:

[0057] In the formula, The maximum value point is represented by The left n-th sampling point, The maximum value point is represented by The right n-th sampling point; m = 1, 2, 3…; n = 1, 2, 3…

[0058] When the processor 1001 invokes the computer program stored in the memory 1005, the following operations are performed: The expression of the maximum value is:

[0059] In the formula, The maximum value point of the differential current is represented by The numerical difference is represented by

[0060] When the processor 1001 invokes the computer program stored in the memory 1005, the following operations are performed: S60, performing the lockout protection.

[0061] When the processor 1001 invokes the computer program stored in the memory 1005, the following operations are performed: S70, if no, judging that the sending transformer has an internal fault.

[0062] When the processor 1001 invokes the computer program stored in the memory 1005, the following operations are performed: S80, when the amplitude of the differential current is less than or equal to a preset first threshold value, the step S10 is continuously performed.

[0063] In addition, it can be understood by those skilled in the art that all or part of the processes in the method for implementing the above embodiments can be completed by a computer program instructing related hardware. The computer program includes program instructions, and the computer program 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 above-mentioned embodiments of the method.

[0064] Therefore, the application further provides a computer readable storage medium, which stores a computer program. The computer program is executed by a processor to implement each step of the method for identifying the magnetizing inrush current of a wind farm sending transformer based on a differential current waveform feature.

[0065] The computer readable storage medium can be a U disk, a mobile hard disk, a read-only memory (ROM), a magnetic disk or an optical disk, or any other computer readable storage medium that can store program codes.

[0066] It should be noted that the storage medium provided by the embodiments of the application is a storage medium used to implement the method of the embodiments of the application. Therefore, based on the method introduced in the embodiments of the application, those skilled in the art can understand the specific structure and modifications of the storage medium, and thus will not be described here. Any storage medium used by the method of the embodiments of the application belongs to the scope of protection of the application.

[0067] Those skilled in the art should understand that the embodiments of the application can be provided as a method, a system or a computer program product. Therefore, the application can be in the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware aspects. Moreover, the application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program codes.

[0068] The application is described with reference to flowcharts and / or block diagrams according to the methods, devices (systems) and computer program products of the embodiments of the application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one flow or multiple flows and / or blocks Figure 1 The devices that implement the functions specified in one block or multiple blocks.

[0069] These computer program instructions can also be stored in a computer readable storage medium that can guide the computer or other programmable data processing devices to work in a specific way, so that the instructions stored in the computer readable storage medium produce a product including instruction devices that implement the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one flow or multiple flows and / or blocks Figure 1 The devices that implement the functions specified in one block or multiple blocks.

[0070] These computer program instructions can also be loaded into computer or other programmable data processing devices, so that a series of operations steps are performed on the computer or other programmable devices to generate computer-implemented processes, thus the instructions executed on the computer or other programmable devices provide processes for implementing the functions specified in the flowcharts Figure 1 one flowchart or multiple flowcharts and / or blocks Figure 1 one flowchart or multiple flowcharts and / or blocks

[0071] Although the preferred embodiments of the application have been described, those skilled in the art will be able to make additional modifications and variations to these embodiments without departing from the spirit and scope of the application. Accordingly, it is intended that the appended claims be construed to include all such modifications and variations as fall within the scope of the application.

[0072] Obviously, various modifications and changes are possible in the present application without departing from the spirit and scope of the application. It is to be understood that the above description is intended to be illustrative and not restrictive. The scope of the application should be determined by the appended claims and their equivalents.

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 collected on both sides of the output transformer; 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; 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, 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….

3. The method as described in claim 1, characterized in that, The expression for the maximum value is: ； In the formula, This is the point of maximum differential current. The difference is numerical.

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

5. 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.

6. 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.

7. 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 6 in wind farm fault detection.

8. 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 6.

9. 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 6.

10. 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 6.

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