A method and device for braking excitation inrush current after fault removal for transformer protection

Abstract

The present invention discloses a method and device for braking excitation inrush current after fault removal for transformer protection, which measures and calculates the duration and primary time constant of the excitation inrush current when a newly installed transformer is put into operation without load; an algorithm is used to detect whether the transformer is running with load; after the protection is started, the current sampling value of each sampling point on each side of the transformer is obtained; a differential algorithm is used to filter out the non-periodic components of each current sampling point, and the differential current is calculated; the results of the three-phase differential current after inrush current discrimination are sorted and reassigned; the second harmonic component of the reassigned three-phase current is calculated; the three-phase processed current is compared with the effective value of the fundamental current; if the proportion exceeds the set value, the sample current is determined to be an excitation inrush current, and the differential protection is braked; compared with the existing algorithm, the present invention can more effectively identify the excitation inrush current caused by voltage recovery after fault removal, thereby achieving reliable braking, with a small amount of calculation and a faster response.

Description

Technical field:

[0001] The present invention relates to the field of transformer differential protection, and in particular to a method and device for braking excitation inrush current after fault removal of transformer protection. Background technology:

[0002] Transformer longitudinal differential protection has always served as the primary protection for transformers. However, when the transformer is put into operation without load or the voltage recovers after the external fault is cleared, the transformer will generate a transient excitation current, also known as the excitation inrush current, which may cause the longitudinal differential protection to trip erroneously. How to distinguish between the excitation inrush current and the internal fault current has been a research hotspot for many years. Because the excitation inrush current contains a large amount of second harmonics, the second harmonic principle has long been used to brake the excitation inrush current to prevent false operation. However, traditional second harmonic braking methods are mainly used to prevent false operation of the longitudinal differential protection when the main transformer is unloaded. The braking method generally adopts two extreme braking methods: braking by phase or braking by the phase with the largest harmonic component, and the algorithm is too rigid.

[0003] Because there is no current before the main transformer is empty and charging, the only current between empty and normal transformers is the magnetizing inrush current, so traditional methods are still feasible. However, when an external fault occurs in the transformer, the faulty phase itself carries a large residual voltage. After the external fault is cleared, the magnetizing inrush current generated by the faulty phase voltage recovery is generally smaller than the inrush current during empty charging. Existing second harmonic braking methods cannot adapt to the complex situation of magnetizing inrush current and different short-circuit currents. Frequently, the inrush current is not braked after the fault is cleared, leading to malfunction of the longitudinal differential protection. Summary of the invention:

[0004] The technical problem to be solved by the present invention is that the existing braking method has the problem that the excitation surge current is not braked after the external fault is removed, resulting in malfunction of the longitudinal differential protection.

[0005] To solve the above technical problems, the present application provides a technical solution: providing a method for braking excitation inrush current after fault removal for transformer protection, comprising the following steps:

[0006] Step 1: Measure and calculate the duration T of the magnetizing inrush current and the primary time constant τ of the newly installed transformer when it is put into operation without load.

[0007] Step 2: When both sides of the transformer are loaded, proceed to the next step, otherwise repeat step 2;

[0008] Step 3: When the transformer is in load operation, obtain the current sampling value of each sampling point on each side of the transformer after the protection is started;

[0009] Step 4: Use a differential algorithm to filter out the non-periodic components at each current sampling point and calculate the differential current;

[0010] Step 5: sort the results of the three-phase differential current after inrush current discrimination and re-assign them; Step 6: calculate the second harmonic component of the re-assigned three-phase current;

[0011] Step 7: Compare the three-phase processed current with the effective value of the fundamental current. If the proportion exceeds the set value, the current is determined to be an excitation inrush current and the differential protection is braked. If the proportion does not exceed the set value, return to step 2.

[0012] Furthermore, in step 2, the method for determining whether each side of the transformer is loaded is: each phase current of each side is greater than 5% of the rated current.

[0013] Furthermore, in step 4, the differential algorithm is:

[0014] y(n)=x(n)-x(n–1) (1)

[0015] Where n is the sampling point.

[0016] Furthermore, in step 5, the result is ranked as 1 Imax , I mid , I min ; The assignment method is: I' Imax ←I Imax 、I' mid ←I mid +k(I Imax -I mid ), I' min ←I min +k(I Imax -I min ).

[0017] Furthermore, the k value is set to be:

[0018]

[0019] Among them, f bph is the unbalance degree of the zero-sequence current variation on each side;

[0020]

[0021] Where N is the sampling point expressed in electrical degrees.

[0022] To solve the above technical problems, another technical solution provided by the present application is to provide a post-fault removal excitation inrush current braking system for transformer protection, comprising a detection module, a control module and a protection module, wherein:

[0023] Detection module: measures and calculates the duration T of the magnetizing inrush current and the primary time constant τ when a newly installed transformer is put into operation without load; and determines whether the transformer is in load operation based on whether the current of each phase on each side of the transformer is greater than 5% of the rated current;

[0024] Control module: During the transformer's under-load operation, after protection is activated, the current sampling value of each sampling point on each side of the transformer is obtained; a differential algorithm is used to filter out the non-periodic components at each current sampling point, and the differential current is calculated; the results of the three-phase differential current after inrush current discrimination are sorted and reassigned; the second harmonic component of the reassigned three-phase current is calculated; the processed three-phase current is compared with the effective value of the fundamental current. If the proportion exceeds the set value, the current is determined to be an excitation inrush current and a differential protection signal is generated;

[0025] Protection module: Receives the differential protection signal generated by the control module and performs braking differential protection.

[0026] To solve the above technical problems, another technical solution provided by the present application is to provide a post-fault removal excitation inrush current braking system for transformer protection, comprising:

[0027] Memory: used to store computer programs;

[0028] Processor: used to read and execute the computer program stored in the memory. When the computer program is executed, the processor executes the above-mentioned method for braking excitation inrush current after fault removal for transformer protection.

[0029] In order to solve the above technical problems, another technical solution provided by the present application is: providing a computer-readable storage medium, in which instructions are stored. When the computer instructions are executed on a computer, the computer executes the above-mentioned method for excitation inrush current braking after fault removal for transformer protection.

[0030] The beneficial effects of the present invention are:

[0031] The present invention uses the change in zero-sequence current after fault removal and the decay time characteristics of the transformer system as variable parameters, and obtains an intermediate state between the two algorithms of phase braking and maximum harmonic component phase braking according to the inverse time characteristic. This more reliably brakes differential protection malfunction caused by excitation inrush current generated by voltage recovery after the external fault of the transformer disappears, and is applicable to transformers with various connections and fault conditions on either side.

[0032] Compared with the current common time-frequency transmission scheme, the present application adopts this encoding method to transmit frequency and achieve the transmission of time at the same time, which can effectively reduce the complexity of hardware circuit design while maintaining high-precision transmission of signals at any time. Description of the drawings:

[0033] In order to more clearly illustrate the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only two of the drawings of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A flowchart of a method for braking excitation inrush current after fault removal for transformer protection;

[0035] Figure 2 A schematic diagram of the structural framework of a post-fault clearing excitation inrush current braking system for transformer protection;

[0036] Figure 3 A schematic diagram of the structural framework of a post-fault clearing excitation inrush current braking device for transformer protection;

[0037] Figure 4 A schematic diagram of the structural framework of a computer-readable storage medium. Specific implementation method:

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0039] like Figure 1 As shown, a method for braking excitation inrush current after fault removal of transformer protection is provided, comprising the following steps:

[0040] Step S1, measuring and calculating the duration T of the magnetizing inrush current and the primary time constant τ of the newly installed transformer when it is put into operation without load;

[0041] Step S2: When both sides of the transformer are loaded, proceed to the next step; otherwise, repeat step S2;

[0042] Step S3: During the transformer's loaded operation, after the protection is activated, obtain the current sampling value of each sampling point on each side of the transformer;

[0043] Step S4: using a differential algorithm to filter out the non-periodic component at each current sampling point and calculate the differential current;

[0044] Step S5: sorting the results of the three-phase differential current after inrush current discrimination and re-assigning them;

[0045] Step S6: Calculate the second harmonic component of the re-assigned three-phase current;

[0046] Step S7: Compare the three-phase processed current with the effective value of the fundamental current. If the proportion exceeds the set value, the current is determined to be an excitation inrush current and the differential protection is braked. If the proportion does not exceed the set value, return to step S2. According to convention, the setting value of the second harmonic brake ratio is 15%.

[0047] In step S2, the method for determining whether each side of the transformer is loaded is: each phase current of each side is greater than 5% of the rated current.

[0048] In step S4, the difference algorithm is:

[0049] y(n)=x(n)-x(n–1) (1)

[0050] Where n is the sampling point.

[0051] In this embodiment, taking the △→Y rotation angle method as an example, the differential current is calculated as:

[0052]

[0053] Among them, the three-phase currents on each side are values converted by the balance coefficient.

[0054] In step S5, the result is sorted as 1 Imax , I mid , I min ; The assignment method is: I' Imax ←I Imax 、I' mid ←I mid +k(I Imax -I mid ), I' min ←I min +k(I Imax -I min ).

[0055] In this embodiment, the k value is set according to the inverse time characteristic as follows:

[0056]

[0057] Among them, f bph is the unbalance degree of the zero-sequence current variation on each side;

[0058]

[0059] Where N is the sampling point expressed in electrical degrees.

[0060] Based on the current sampling data collected from multiple cases of longitudinal differential protection malfunction caused by excitation inrush current after the external fault of the transformer was removed, after calculation using this application, the second harmonic characteristics with smaller inrush current characteristics can be increased, and reliable braking can be provided for such situations, which can more reliably and effectively prevent the longitudinal differential protection malfunction caused by the inrush current generated by voltage recovery.

[0061] like Figure 2 As shown, a post-fault removal excitation inrush current braking system for transformer protection is provided, comprising a detection module 21, a control module 22 and a protection module 23, wherein:

[0062] Detection module 21: measures and calculates the duration T of the magnetizing inrush current and the primary time constant τ of the newly installed transformer when it is put into operation without load; and determines whether the transformer is in load operation based on whether the current of each phase on each side of the transformer is greater than 5% of the rated current;

[0063] Control module 22: During the transformer's loaded operation, after protection is activated, obtains the current sampling value of each sampling point on each side of the transformer; uses a differential algorithm to filter out the non-periodic component at each current sampling point and calculates the differential current; sorts the results of the three-phase differential current after inrush current discrimination and reassigns them; calculates the second harmonic component of the reassigned three-phase current; compares the processed three-phase current with the effective value of the fundamental current; if the proportion exceeds the set value, the current is determined to be an excitation inrush current and a differential protection signal is generated;

[0064] Protection module 23: receives the differential protection signal generated by the control module and performs braking differential protection.

[0065] like Figure 3 As shown, a post-fault removal excitation inrush current braking device for transformer protection is provided, comprising:

[0066] Memory 31: used to store computer programs;

[0067] Processor 32: configured to read and execute the computer program stored in the memory. When the computer program is executed, the processor executes the above-mentioned method for braking excitation inrush current after fault removal for transformer protection.

[0068] The processor is configured to execute program instructions stored in the memory to implement the steps of any of the aforementioned embodiments of the method for braking excitation inrush current after fault removal for transformer protection. In a specific implementation scenario, the device for braking excitation inrush current after fault removal for transformer protection may include, but is not limited to, a microcomputer and a server. Furthermore, the device for braking excitation inrush current after fault removal for transformer protection may also include a mobile device such as a laptop computer or a tablet computer, which is not limited herein.

[0069] Specifically, the processor is used to control itself and the memory to implement the steps of the embodiment of the excitation inrush current braking method after fault removal of any of the above-mentioned transformer protection. The processor can also be called a CPU (Central Processing Unit). The processor may be an integrated circuit chip with signal processing capabilities. The processor can also be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. In addition, the processor can be implemented by an integrated circuit chip.

[0070] In the several embodiments provided in this application, it should be understood that the disclosed methods and devices can be implemented in other ways. For example, the device implementation methods described above are only schematic. For example, the division of modules or units is only a logical function division. There may be other division methods in actual implementation. For example, units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, and the indirect coupling or communication connection of devices or units can be electrical, mechanical or other forms.

[0071] like Figure 4 As shown, a computer-readable storage medium 4 is provided, in which instructions 41 are stored. When the computer instructions 41 are executed on a computer, the computer executes the steps of any of the above-mentioned embodiments of the method for magnetizing inrush current braking after fault removal for transformer protection.

[0072] A computer-readable storage medium may be a non-volatile computer-readable storage medium, such as, but not limited to, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In this application, a computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0073] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0074] The above are merely preferred embodiments of the present invention and do not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for braking an excitation inrush current after fault removal for transformer protection, comprising the following steps: Step 1: Measure and calculate the duration T of the magnetizing inrush current and the primary time constant τ of the newly installed transformer when it is put into operation without load. Step 2: When both sides of the transformer are loaded, proceed to the next step, otherwise repeat step 2; Step 3: When the transformer is in load operation, obtain the current sampling value of each sampling point on each side of the transformer after the protection is started; Step 4: Use a differential algorithm to filter out the non-periodic components at each current sampling point and calculate the differential current; Step 5: Sort the results of the three-phase differential current after inrush current discrimination and reassign them: Step 6: Calculate the second harmonic component of the re-assigned three-phase current; Step 7: Compare the three-phase processed current with the effective value of the fundamental current. If the proportion exceeds the set value, the current is determined to be an excitation inrush current and the differential protection is braked. If the proportion does not exceed the set value, return to step 2. In the step 5, the result is sorted as 1 Imax , I mid , I min ; The assignment method is: I' Imax ←I Imax 、I' mid ←I mid +k(I Imax -I mid ), I' min ←I min +k(I Imax -I min ); The k value is set according to the inverse time characteristic: Among them, f bph is the unbalance degree of the zero-sequence current variation on each side; Where N is the sampling point expressed in electrical degrees.

2. The method for braking excitation inrush current after fault removal for transformer protection according to claim 1, characterized in that: In the step 2, the method for determining whether each side of the transformer is loaded is: the current of each phase on each side is greater than 5% of the rated current.

3. The method for braking excitation inrush current after fault removal for transformer protection according to claim 1, characterized in that: In step 4, the differential algorithm is: y(n)=x(n)-x(n –1) (3) Where n is the sampling point.

4. A post-fault removal excitation inrush current braking system for transformer protection based on the method according to any one of claims 1 to 3, characterized in that: It includes detection module, control module and protection module, among which: Detection module: measures and calculates the duration T of the magnetizing inrush current and the primary time constant τ when a newly installed transformer is put into operation without load; and determines whether the transformer is in load operation based on whether the current of each phase on each side of the transformer is greater than 5% of the rated current; Control module: During the transformer's under-load operation, after the protection is activated, the current sampling value of each sampling point on each side of the transformer is obtained; a differential algorithm is used to filter out the non-periodic components of each current sampling point, and the differential current is calculated; the results of the three-phase differential current after inrush current discrimination are sorted and reassigned; the second harmonic component of the reassigned three-phase current is calculated; the three-phase processed current is compared with the effective value of the fundamental current. If the proportion exceeds the set value, the current is determined to be an excitation inrush current, and a differential protection signal is generated; the change in zero-sequence current after fault removal and the decay time characteristics of the transformer system are used as variable parameters, and the intermediate state between the two algorithms of phase braking or phase braking with the maximum harmonic component is obtained according to the inverse time characteristic, thereby more reliably braking the differential protection malfunction caused by the excitation inrush current generated by voltage recovery after the external fault of the transformer disappears; Protection module: Receives the differential protection signal generated by the control module and performs braking differential protection.

5. A post-fault clearing excitation inrush current braking system for transformer protection, characterized by: include: Memory: used to store computer programs; Processor: used to read and execute the computer program stored in the memory, when the computer program is executed, the processor executes the post-fault removal excitation inrush current braking method for transformer protection according to any one of claims 1 to 3.

6. A computer-readable storage medium, characterized in that The computer-readable storage medium stores instructions, and when the computer instructions are executed on a computer, the computer is caused to execute the post-fault removal excitation inrush current braking method for transformer protection according to any one of claims 1 to 3.

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