A low voltage protection method, system and storage medium for a low frequency transformer

Abstract

The application discloses a low-frequency transformer low-voltage protection method and system and a storage medium in the technical field of low-frequency power transmission. The method comprises the following steps: judging whether a current starting element is started; in the case that the current starting element is not started, identifying whether a PT line is disconnected or a short-circuit fault occurs according to the sudden change of the phase voltage on each side of the low-frequency transformer; and performing a low-voltage protection action after the short-circuit fault occurs. The application can effectively avoid the problem that the low-frequency transformer protection device of the low-frequency power transmission system is misjudged as a PT line disconnection when a fault occurs, thereby locking the low-voltage protection.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology, specifically relating to a low-voltage protection method, system, and storage medium for low-frequency transformers. Background Technology

[0002] The construction of low-frequency power transmission systems can support island energy development and new energy transmission, contributing to the development of new power systems. Furthermore, it can continuously optimize and improve the power transmission and distribution network structure, enhance the grid's disaster prevention and mitigation capabilities, and effectively ensure a safer, more economical, and more reliable power supply. Low-frequency transformers are the core equipment of low-frequency power transmission systems. The low-voltage protection of low-frequency transformers, as the overall backup protection in the low-frequency power transmission system, is closely related to the safe operation of the system. Compared with power frequency power systems, the valve control devices present in low-frequency power transmission systems cause different changes in electrical quantities during system faults compared to normal power systems. This may affect the correct operation of low-voltage protection and thus impact the safe operation of the low-frequency power transmission system.

[0003] When a fault occurs in a normal power frequency system, the undervoltage protection can be activated by the current-starting element. However, for the protection device of the low-frequency transformer in the low-frequency transmission system, the valve control device will quickly suppress the fault current when the system is faulty, which may cause the current-starting element to fail to start. This may lead to a misjudgment of the PT being disconnected, thus blocking the undervoltage protection. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-voltage protection method, system, and storage medium for low-frequency transformers, which can effectively avoid the problem that the current-starting element of the low-frequency transformer protection device in a low-frequency power transmission system fails to start when a fault occurs, thus misjudging it as a PT disconnection.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, a low-voltage protection method for a low-frequency transformer is provided, comprising: determining whether a current-initiating element has been activated; if the current-initiating element has not been activated, identifying whether the fault is a PT disconnection or a short-circuit fault based on the sudden changes in phase voltage on each side of the low-frequency transformer; and executing a low-voltage protection action after a short-circuit fault occurs.

[0007] Furthermore, the process of determining whether the current-starting element has started is as follows: collect the phase current of each side of the low-frequency transformer, and calculate the line current mutation, negative sequence current and zero sequence current based on the phase current of each side of the low-frequency transformer;

[0008] If the current on either side satisfies any one of the following equations in either phase, then the current-initiating element is determined to have started.

[0009]

[0010] Where ΔI is the line current mutation, I2 is the negative sequence current, I0 is the zero sequence current, δ1 is the line current mutation threshold, δ2 is the negative sequence current threshold, and δ3 is the zero sequence current threshold.

[0011] Furthermore, based on the voltage fluctuations on each phase of the low-frequency transformer, it is determined whether the fault is a PT disconnection or a short-circuit fault. This includes: taking a two-winding transformer as an example, obtaining the phase voltages on both sides of the low-frequency transformer; and determining a short-circuit fault in response to the voltage fluctuations on both sides of the low-frequency transformer.

[0012] Δu Mx >δ4&Δu Nx >δ4 (3)

[0013] Where, Δu Mx The voltage change on one phase of a low-frequency transformer, Δu Nx δ4 is the voltage change of one phase on the other side of the low-frequency transformer, where x = a, b, c represents any phase of the three-phase voltage, and δ4 is the threshold value for the voltage change of the phase.

[0014] In response to the detection that only one phase of the low-frequency transformer experiences a sudden voltage change, it is determined that the PT is disconnected, and the undervoltage protection is blocked:

[0015] Δu Mx >δ4&Δu Na,b,c <δ4 (4)

[0016] Where, Δu Na,b,c This refers to the voltage fluctuations of the three phases a, b, and c on the other side of a low-frequency transformer.

[0017] Furthermore, after a short-circuit fault occurs, undervoltage protection is activated, including: determining whether the voltage of any phase of the low-frequency transformer is less than the undervoltage setting; responding to the condition that the voltage of any phase is less than the undervoltage setting:

[0018] u x set (5)

[0019] Among them, u x Let x = a, b, c represent any phase voltage of the three-phase transformer, and u represent any phase voltage of the three-phase transformer. set This is the low voltage setting value in low voltage protection;

[0020] The condition is determined to meet the undervoltage protection requirements, and a delay t is set. set The low voltage protection activated.

[0021] ​Furthermore, in the case of current-initiated element startup, a time extension is applied to the PT disconnection criterion, wherein the extension time is adaptively adjusted based on the undervoltage protection output delay time, and the specific formula is as follows:

[0022] t I =t set +Δt (2)

[0023] Among them, t I For adaptive stretching time, t set The low voltage protection delay setting is Δt, which is taken as two electrical cycle times.

[0024] Secondly, a low-voltage protection system for low-frequency transformers is provided, comprising: a current-starting element identification module for determining whether the current-starting element is activated; a fault identification module for identifying whether a PT disconnection or a short-circuit fault has occurred based on the sudden changes in phase voltage on each side of the low-frequency transformer when the current-starting element is not activated; and a low-voltage protection module for performing low-voltage protection actions after a short-circuit fault occurs.

[0025] Furthermore, the process for determining whether the current-starting element has started is as follows: The current of each phase on each side of the low-frequency transformer is collected; the line current surge, negative sequence current, and zero sequence current are calculated based on the current of each phase on each side of the low-frequency transformer; if any phase of the current on any side satisfies any of the following formula, then it is determined that the current-starting element has started.

[0026]

[0027] Where ΔI is the line current mutation, I2 is the negative sequence current, I0 is the zero sequence current, δ1 is the line current mutation threshold, δ2 is the negative sequence current threshold, and δ3 is the zero sequence current threshold.

[0028] Furthermore, based on the voltage fluctuations on each phase of the low-frequency transformer, it is determined whether the fault is a PT disconnection or a short-circuit fault. This includes: taking a two-winding transformer as an example, obtaining the phase voltages on both sides of the low-frequency transformer; and determining a short-circuit fault in response to the voltage fluctuations on both sides of the low-frequency transformer.

[0029] Δu Mx >δ4&Δu Nx >δ4 (3)

[0030] Where, Δu Mx The voltage change on one phase of a low-frequency transformer, Δu Nx δ4 is the voltage change of one phase on the other side of the low-frequency transformer, where x = a, b, c represents any phase of the three-phase voltage, and δ4 is the threshold value for the voltage change of the phase.

[0031] In response to the detection that only one phase of the low-frequency transformer experiences a sudden voltage change, it is determined that the PT is disconnected, and the undervoltage protection is blocked:

[0032] Δu Mx >δ4&Δu Na,b,c <δ4 (4)

[0033] Where, Δu Na,b,c This refers to the voltage fluctuations of the three phases a, b, and c on the other side of a low-frequency transformer.

[0034] Furthermore, after a short-circuit fault occurs, undervoltage protection is activated, including: determining whether the voltage of any phase of the low-frequency transformer is less than the undervoltage setting; responding to the condition that the voltage of any phase is less than the undervoltage setting:

[0035] u x set (5)

[0036] Among them, u x Let x = a, b, c represent any phase voltage of the three-phase transformer, and u represent any phase voltage of the three-phase transformer. set This is the low voltage setting value in low voltage protection;

[0037] The condition is determined to meet the undervoltage protection requirements, and a delay t is set. set The low voltage protection activated.

[0038] Thirdly, a computer-readable storage medium is provided, the computer-readable storage medium including a stored computer program, wherein, when the computer program is executed by a processor, it controls the device in which the storage medium is located to perform the method described in the first aspect.

[0039] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention adds a voltage starting condition when the current starting element is not activated, and performs fault judgment based on the voltage change elements on each side of the transformer, thereby identifying whether it is a PT disconnection or a fault, which can accurately identify the fault and greatly improve the reliability and applicability of the low voltage protection of the low frequency transformer protection device in the low frequency transmission system. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the main process of a low-voltage protection method for a low-frequency transformer protection device in a low-frequency power transmission system, provided by an embodiment of the present invention.

[0041] Figure 2 This is an example diagram of a low-frequency power transmission system for which a low-voltage protection method for a low-frequency transformer protection device in a low-frequency power transmission system, as provided in an embodiment of the present invention, is applicable. Detailed Implementation

[0042] ​The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0043] Example 1:

[0044] like Figure 1 As shown, a low-voltage protection method for low-frequency transformers is applicable to low-frequency transformer protection devices in low-frequency transmission systems. The method includes: determining whether a current-initiating element has been activated; if the current-initiating element has not been activated, identifying whether the fault is a PT disconnection or a short-circuit fault based on the sudden changes in phase voltage on each side of the low-frequency transformer; and executing low-voltage protection actions after a short-circuit fault occurs.

[0045] This embodiment specifically includes the following steps.

[0046] Determine whether the current-starting element has started.

[0047] Step 1: Collect the phase current, phase voltage, and low voltage protection output delay setting value of each side of the transformer.

[0048] Step 2: Calculate the line current surge, negative sequence current and zero sequence current, phase voltage surge, and adaptive extension time of the current-starting element.

[0049] Step 3: If the current on either side satisfies any one of the following equations in any phase, then the current-starting element is determined to have started; otherwise, the current-starting element is determined to have not started.

[0050]

[0051] Where ΔI is the line current mutation, I2 is the negative sequence current, I0 is the zero sequence current, δ1 is the line current mutation threshold, δ2 is the negative sequence current threshold, and δ3 is the zero sequence current threshold.

[0052] Step 4: In response to the determination that the current-starting element has been started, adaptive expansion is performed, PT disconnection is blocked, and then it is determined whether the voltage of any phase is less than the low voltage setting value.

[0053] The widening time is adaptively adjusted based on the low-voltage protection output delay time, and the specific formula is as follows:

[0054] t I =t set +Δt (2)

[0055] Among them, t I For adaptive stretching time, t set The low voltage protection delay setting is Δt, which is taken as two electrical cycle times.

[0056] For normal power frequency power systems, current-initiating elements can generally be activated. Once the current is activated, the PT disconnection criterion is blocked, and the undervoltage protection is opened. However, for low-frequency transmission systems, when a fault occurs, the valve control device will quickly suppress the current to a steady-state value within one cycle, making it difficult to detect the sudden change in current. The current-initiating element may fail to activate, and it will be mistakenly judged as a PT disconnection, thus blocking the undervoltage protection. Therefore, this embodiment adds a voltage activation condition to distinguish between PT disconnection and various short-circuit faults to ensure accurate and error-free operation of the undervoltage protection.

[0057] If the current-starting element fails to start, the sudden changes in phase voltage on each side of the low-frequency transformer can be used to identify whether the PT is disconnected or a short-circuit fault has occurred.

[0058] Step 5: In response to the determination that the current-starting element has not started, determine the sudden change in voltage of each phase of the transformer; the process of determining the sudden change in voltage of each phase of the transformer is as follows:

[0059] Taking a two-winding transformer as an example, the phase voltages on both sides of the transformer are obtained. If the sudden changes in phase voltages on both sides of the low-frequency transformer are greater than the threshold value, a short-circuit fault is determined, and the undervoltage protection is activated.

[0060] Δu Mx >δ4&Δu Nx >δ4 (3)

[0061] Where, Δu Mx The voltage change on one phase of a low-frequency transformer, Δu Nx δ4 is the voltage change of one phase on the other side of the low-frequency transformer, where x = a, b, c represents any phase of the three-phase voltage, and δ4 is the threshold value for the voltage change of the phase.

[0062] If the voltage surge on only one phase of the low-frequency transformer exceeds the threshold value, it is determined that a PT disconnection has occurred, and the undervoltage protection is blocked. The specific formula is as follows:

[0063] Δu Mx >δ4&Δu Na,b,c <δ4 (4)

[0064] Where, Δu Na,b,c This refers to the voltage fluctuations of the three phases a, b, and c on the other side of a low-frequency transformer.

[0065] After a short circuit fault occurs, the undervoltage protection action is executed.

[0066] Step 6: Determine if the voltage of any phase of the low-frequency transformer is less than the low-voltage setting; if the voltage of any phase is less than the low-voltage setting:

[0067] u x set (5) ​

[0068] Among them, u x Let x = a, b, c represent any phase voltage of the three-phase transformer, and u represent any phase voltage of the three-phase transformer. set This is the low voltage setting value in low voltage protection;

[0069] The condition is determined to meet the undervoltage protection requirements, and a delay t is set. set The low voltage protection activated.

[0070] Step 7: In response to the fact that the voltage of each phase of the low-frequency transformer is greater than or equal to the low voltage setting value, it is determined that the low voltage operation condition is not met, and the protection does not operate.

[0071] This invention adds a voltage-based starting condition when the current-initiating element is not activated. It uses voltage fluctuation indicators on each side of the transformer to determine whether the fault is a PT disconnection or a general fault, thus accurately identifying the fault and significantly improving the reliability and applicability of low-voltage protection for low-frequency transformers in low-frequency transmission systems. Figure 2 The diagram shown is an example of a low-frequency transmission system for which a low-voltage protection method for a low-frequency transformer protection device in a low-frequency transmission system, as provided in an embodiment of the present invention, is applicable.

[0072] The theoretical basis of this invention is as follows: When a PT (potential transformer) disconnects, only the phase voltage on the disconnected side changes, abruptly changing from a steady-state value to 0, while the phase voltage on the other side remains unaffected. Conversely, when a short-circuit fault occurs, the voltage of the faulty phase on the faulty side will definitely change, as the voltage on the other side of the transformer will also change. Based on the difference in phase voltage changes on both sides of the transformer, rapid and accurate identification of short-circuit faults and PT disconnections is achieved, improving the reliability and speed of low-voltage protection in low-frequency transformer protection devices in low-frequency transmission systems, thereby enhancing the safe operation level of transformers and the power grid.

[0073] Example 2:

[0074] Based on the low-voltage protection method for low-frequency transformers described in Embodiment 1, this embodiment provides a low-voltage protection system for low-frequency transformers, applicable to low-frequency transformer protection devices in low-frequency transmission systems. The system includes: a current-initiating element identification module for determining whether the current-initiating element is activated; a fault identification module for identifying whether a PT disconnection or a short-circuit fault occurs based on the voltage fluctuations of each phase of the low-frequency transformer when the current-initiating element is not activated; and a low-voltage protection module for performing low-voltage protection actions after a short-circuit fault occurs.

[0075] Example 3:

[0076] Based on the low-voltage protection method for a low-frequency transformer protection device in a low-frequency power transmission system described in Embodiment 1, this embodiment provides a computer-readable storage medium, which includes a stored computer program. When the computer program is run by a processor, it controls the device where the storage medium is located to execute the method described in Embodiment 1.

[0077] Embodiments of this application may be provided as methods, systems, or computer program products. Therefore, this application may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application may take 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 code. The solutions in the embodiments of this application may be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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 undervoltage protection of low-frequency transformers, characterized in that, include: Determine whether the current-starting element has started; In the case where the current-starting element fails to activate, based on the sudden changes in phase voltage on each side of the low-frequency transformer, identify whether the fault is a PT disconnection or a short-circuit fault, including: Taking a two-winding transformer as an example, obtain the phase voltages on both sides of the low-frequency transformer; In response to the detection of a sudden change in phase voltage across the low-frequency transformer, a short-circuit fault is determined to have occurred: （3） in, This refers to the voltage change on one phase of a low-frequency transformer. Let x = a, b, c represent the voltage change of one phase on the other side of the low-frequency transformer, where x = a, b, c represents any one of the three phases. This is the threshold value for the sudden change in phase voltage; In response to the detection that only one phase of the low-frequency transformer experiences a sudden voltage change, it is determined that the PT is disconnected, and the undervoltage protection is blocked: （4） in, The voltage fluctuations of the three phases a, b, and c on the other side of the low-frequency transformer; After a short-circuit fault occurs, the undervoltage protection action is executed, including: Determine whether the voltage of any phase of the low-frequency transformer is less than the low-voltage setting. In response to any phase voltage being less than the low voltage setting: （5） in, Let x = a, b, and c represent any one of the three-phase voltages of the low-frequency transformer. This is the low voltage setting value in low voltage protection; The condition was determined to meet the undervoltage protection requirements, and a time delay was set. The low voltage protection activated.

2. The low-voltage protection method for low-frequency transformers according to claim 1, characterized in that, The process for determining whether a current-starting element has started is as follows: Collect phase currents on each side of the low-frequency transformer. Calculate the sudden change in line current, negative sequence current, and zero sequence current based on the phase currents on each side of the low-frequency transformer; If the current on either side satisfies any one of the following equations in either phase, then the current-initiating element is determined to have started. （1） in, This refers to the sudden change in line current. It is a negative sequence current. It is the zero-sequence current. This is the threshold value for sudden changes in line current. This is the negative sequence current threshold value. This is the zero-sequence current threshold value.

3. The low-voltage protection method for low-frequency transformers according to claim 1, characterized in that, When the current-initiating element is activated, the PT disconnection criterion is extended for a certain period of time. This extended period is adaptively adjusted based on the undervoltage protection output delay time, and the specific formula is as follows: （2） in, For adaptive stretching time, This is the delay setting for undervoltage protection. Take two electrical cycle times.

4. A low-voltage protection system for low-frequency transformers, characterized in that, include: The current-starting element identification module is used to determine whether the current-starting element is activated. The fault identification module is used to identify whether the fault is a PT open circuit or a short circuit fault based on the sudden changes in phase voltage on each side of the low-frequency transformer when the current-starting element fails to activate. This includes: Taking a two-winding transformer as an example, obtain the phase voltages on both sides of the low-frequency transformer; In response to the detection of a sudden change in phase voltage across the low-frequency transformer, a short-circuit fault is determined to have occurred: （3） in, This refers to the voltage change on one phase of a low-frequency transformer. Let x = a, b, c represent the voltage change of one phase on the other side of the low-frequency transformer, where x = a, b, c represents any one of the three phases. This is the threshold value for the sudden change in phase voltage; In response to the detection that only one phase of the low-frequency transformer experiences a sudden voltage change, it is determined that the PT is disconnected, and the undervoltage protection is blocked: （4） in, The voltage fluctuations of the three phases a, b, and c on the other side of the low-frequency transformer; The low-voltage protection module is used to perform low-voltage protection actions after a short-circuit fault occurs, including: Determine whether the voltage of any phase of the low-frequency transformer is less than the low-voltage setting. In response to any phase voltage being less than the low voltage setting: （5） in, Let x = a, b, and c represent any one of the three-phase voltages of the low-frequency transformer. This is the low voltage setting value in low voltage protection; The condition was determined to meet the undervoltage protection requirements, and a time delay was set. The low voltage protection activated.

5. The low-voltage protection system for low-frequency transformers according to claim 4, characterized in that, The process for determining whether a current-starting element has started is as follows: Collect phase currents on each side of the low-frequency transformer. Calculate the sudden change in line current, negative sequence current, and zero sequence current based on the phase currents on each side of the low-frequency transformer; If the current on either side satisfies any one of the following equations in either phase, then the current-initiating element is determined to have started. （1） in, This refers to the sudden change in line current. It is a negative sequence current. It is the zero-sequence current. This is the threshold value for sudden changes in line current. This is the negative sequence current threshold value. This is the zero-sequence current threshold value.

6. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, it controls the device in which the storage medium is located to perform the method according to any one of claims 1 to 3.

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