Control system, method and device for a current limiting reactor at the neutral point of the medium voltage side of a transformer

Abstract

The application provides a control system, method and device for a current-limiting reactor of a neutral point of a medium-voltage side of a transformer, and belongs to the technical field of transformer fault control. The transformer control system comprises: a first current sensor for acquiring three-phase electric current; a second current sensor for acquiring neutral point current; a current-limiting reactor having one end connected to the neutral point of the medium-voltage side of the transformer and the other end connected to a grounding switch; and a fast switch connected in parallel across the current-limiting reactor. The method comprises: in a first control mode, controlling the fast switch to act according to the three-phase electric current and the neutral point current; and in a second control mode, controlling the fast switch to act according to a control signal sent by a relay protection controller and the neutral point current acquired by the second current sensor. In this embodiment, two flexible control modes are provided, so that the transformer control system can be quickly switched according to actual operating conditions, optimal performance of the system is ensured in various application scenarios, and therefore the reliability and stability of the system are improved.

Description

Technical Field

[0001] This application relates to the field of transformer fault control technology, and in particular to a control system, method and device for a neutral point current-limiting reactor on the medium voltage side of a transformer. Background Technology

[0002] In recent years, with economic development and the scaling up of industrial production, the demand for electricity resources has exploded. The expansion and upgrading of the power grid has become crucial to meeting this demand. However, with the continuous expansion of the medium-voltage power grid, the problem of unbalanced short-circuit faults on the medium-voltage side has become increasingly prominent. The short-circuit impedance of the medium-voltage windings is relatively low, and coupled with the zero-sequence current generated by unbalanced and nonlinear loads, the short-circuit current on the neutral grounding wire of the medium-voltage side increases sharply, sometimes even exceeding the amplitude of the three-phase short-circuit current on the low-voltage side.

[0003] For transformers already in operation, the failure to fully anticipate the current increase in short-circuit current during the initial design phase has resulted in insufficient short-circuit current withstand capability. Once a short-circuit fault occurs, the transformer windings will face the enormous challenge of rapid temperature rise and internal stress, which may not only cause fires but also lead to winding deformation or damage, seriously threatening the safe and stable operation of the power grid. Therefore, to ensure the safe, stable, and reliable power supply of the power grid and reduce the operating pressure on power equipment, controlling the short-circuit current on the neutral point grounding wire of the transformer's medium-voltage side has become an urgent problem to be solved.

[0004] One feasible solution is to install a fault current limiter on the neutral grounding wire of the transformer. By putting a current-limiting reactor into the neutral point, the asymmetrical short-circuit current can be effectively limited, thereby improving the transformer's ability to withstand short-circuit impacts and ensuring that the circuit breaker's breaking capacity can adapt to the system's short-circuit level.

[0005] However, the control strategy setting of the neutral point fault current limiter is crucial to its current limiting effect. Inappropriate settings may lead to fault handling errors or even exacerbate equipment damage. If fault identification is inaccurate, the fault current limiter may operate incorrectly. Similarly, if zero-crossing prediction is inaccurate, the fault current limiter may switch at an inappropriate time, causing the fast switch to have difficulty extinguishing the arc during opening, increasing the arcing time and shortening the switch's lifespan. Furthermore, if fault identification or zero-crossing prediction takes too long, the current-limiting reactor cannot be activated in time within the first current cycle, thus failing to provide timely current limiting protection for the transformer and increasing the risk of equipment damage.

[0006] Traditional fault current limiter control strategies typically rely on current signals at the installation point for fault diagnosis. However, under conditions such as heavy load switching, transformer tap changer adjustments, or changes in operating status, the three-phase unbalanced current that may appear on the neutral grounding wire can lead to misjudgments. Traditional fault diagnosis methods, such as those based on short-circuit current characteristics, Fourier analysis, or wavelet transform, are susceptible to the influence of the DC component of the short-circuit current, harmonics, and electromagnetic interference, resulting in insufficient accuracy and speed. Similarly, traditional zero-crossing prediction techniques, such as Fourier algorithms, BP neural networks, and least squares methods, struggle to achieve a balance between speed and accuracy. Therefore, a clear and effective solution remains lacking for the problem of how to rationally set the control strategy for the neutral point fault current limiter on the medium-voltage side of the transformer. Summary of the Invention

[0007] This invention provides a control system, method, and apparatus for a neutral point current-limiting reactor on the medium-voltage side of a transformer, in order to solve the problem of how to reasonably set the control strategy for the neutral point fault current-limiting reactor on the medium-voltage side of a transformer.

[0008] In a first aspect, embodiments of the present invention provide a transformer control system, comprising: a first current sensor, a second current sensor, a remote controller, a relay protection controller, a fast switch, a current-limiting reactor, and a grounding switch;

[0009] The first current sensor is installed at the input and output terminals of the transformer to acquire the three-phase current.

[0010] The second current sensor is installed on the neutral point grounding wire of the transformer to obtain the neutral point current;

[0011] One end of the current-limiting reactor is connected to the neutral point of the medium-voltage side of the transformer, and the other end is connected to the grounding switch; the other end of the grounding switch is grounded; the fast switch is connected in parallel across the current-limiting reactor.

[0012] The remote controller is configured to control the fast switch action in a first control mode based on the three-phase current and neutral point current obtained by the first current sensor and the second current sensor; and in a second control mode based on the control signal sent by the relay protection controller and the neutral point current obtained by the second current sensor.

[0013] In one possible implementation, the system also includes:

[0014] The circuit breaker is communicatively connected to the remote controller;

[0015] The remote controller is used to control the circuit breaker to operate when it is determined that a permanent short-circuit fault has occurred in the transformer control system.

[0016] In a second aspect, embodiments of the present invention provide a control method for a neutral point current-limiting reactor on the medium-voltage side of a transformer in a transformer control system as described in the first aspect or any embodiment of the first aspect, comprising:

[0017] In the first control mode, the fast switch is controlled to close, and the real-time three-phase current and real-time neutral point current are acquired. Based on the real-time three-phase current and real-time neutral point current, the fast switch is controlled to maintain the closed state or to operate.

[0018] In the second control mode, the fast switch is controlled to close. If no asymmetrical short-circuit fault signal is received from the relay protection controller, the fast switch is controlled to remain closed; otherwise, the real-time neutral point current is acquired, and the fast switch is controlled to operate based on the real-time neutral point current.

[0019] In one possible implementation, controlling the fast switch to maintain its closed position or to operate based on the real-time three-phase current and the real-time neutral point current includes:

[0020] Calculate the load angle change of each phase based on the real-time three-phase current;

[0021] When the load angle change of each phase is less than or equal to the set change threshold, or when the load angle change of each phase is greater than the set change threshold, the fast switch is controlled to remain closed; otherwise, zero-crossing prediction is performed based on the real-time neutral point current.

[0022] Based on the prediction results, at the zero-crossing prediction time, the fast switch is controlled to open, and after the current limiting time is set, the instantaneous current value is monitored based on the real-time neutral point current.

[0023] If the instantaneous current value remains below a set threshold for the instantaneous value within a set detection time, a transient fault is determined to have occurred in the system, and the fast switch is controlled to close.

[0024] In one possible implementation, the calculation of the load angle change of each phase based on the real-time three-phase current includes:

[0025] Based on the real-time three-phase current, continuous sampling with a time interval Δ is performed to obtain the current sample value [i]. s1 i s2 i s3 i s4 ...i sN ]; where the current sampling value of any 3 consecutive sampling points is i k-2 i k-1 , and i k The expressions are as follows:

[0026]

[0027]

[0028] The difference between adjacent current sample values ​​is calculated using the following formula:

[0029] i k -i k-1 =I bm (sin(θ k )-sin(θ k -δ));

[0030] i k-1 -i k-2 =I bm (sin(θ k -δ)-sin(θ k -2δ));

[0031] make:

[0032]

[0033] Therefore, we can conclude that:

[0034]

[0035] From the expression for the current sampling value ik, we can obtain:

[0036]

[0037] If I bm >0, then

[0038]

[0039] otherwise

[0040]

[0041] Where Δ is the sampling time interval, ωΔ=δ; I bm The current amplitude before the fault occurred. This indicates the phase difference between voltage and current.

[0042] In one possible implementation, the sampling time interval is less than or equal to 2ms.

[0043] In one possible implementation, acquiring the real-time neutral point current and controlling the fast switching action based on the real-time neutral point current includes:

[0044] Zero-crossing prediction is performed based on the real-time neutral point current.

[0045] Based on the prediction results, at the zero-crossing prediction time, the fast switch is controlled to open, and after the current limiting time is set, the instantaneous current value is monitored based on the real-time neutral point current.

[0046] If the instantaneous current value remains below a set threshold for the instantaneous value within a set detection time, a transient fault is determined to have occurred in the system, and the fast switch is controlled to close.

[0047] One possible implementation also includes:

[0048] When the instantaneous current value is greater than or equal to a set threshold value, a permanent fault is determined to have occurred in the system. The circuit breaker is controlled to operate, and after a set delay interval, the fast switch is controlled to close to reset the system state.

[0049] In one possible implementation, the zero-crossing prediction based on the real-time neutral point current includes:

[0050] Based on the real-time neutral point current, continuous sampling is performed at time intervals of mΔ, and the root interval search is started from the time t1+(N-1)*Δ corresponding to the last neutral point current sample value;

[0051] If the equation has roots between T1 and T2, the root interval search ends, and the root calculation is performed based on Newton's method.

[0052] The process involves continuous sampling of the real-time neutral point current at time intervals of mΔ, starting from the time t1+(N-1)*Δ corresponding to the last neutral point current sample value, and includes:

[0053] set up

[0054]

[0055] Let T1=t1+(N-1)*Δ, T2=T1+m*Δ, f1=f(T1), f2=f(T2), q=f1*f2;

[0056] If q > 0, it means that there is no root of the equation between T1 and T2, so that the new T1 = T2 and the new T2 = T1 + m*Δ. Calculate f1, f2 and q again and compare them.

[0057] If q < 0, it means that there are roots of the equation between T1 and T2, and the search for the root interval ends.

[0058] The root-finding calculation based on Newton's method includes:

[0059] The numerical solution is obtained through the following iterative process:

[0060]

[0061] Here, f'(t) is the derivative of f(t).

[0062]

[0063] During the iteration process, when |T k+1 -T k The iteration stops when | < ε, where ε is a pre-set error.

[0064] Thirdly, embodiments of the present invention provide a control device for a neutral point current-limiting reactor on the medium-voltage side of a transformer, comprising:

[0065] The acquisition module is used to acquire real-time three-phase current and real-time neutral point current;

[0066] The control module is used to control the fast switch to close in the first control mode, and to control the fast switch to maintain its closed state or to operate the fast switch based on the real-time three-phase current and the real-time neutral point current; in the second control mode, it controls the fast switch to close, and if no asymmetrical short-circuit fault signal is received from the relay protection controller, it controls the fast switch to maintain its closed state; otherwise, it controls the fast switch to operate based on the real-time neutral point current.

[0067] This invention provides a control system, method, and apparatus for a neutral point current-limiting reactor on the medium-voltage side of a transformer. It acquires three-phase current data at the transformer's inlet and outlet terminals and neutral point current data on the neutral point grounding wire using a first current sensor and a second current sensor, respectively. This ensures that when performing relevant judgments based on three-phase current, it can effectively avoid three-phase unbalanced current caused by factors such as large load switching, transformer tap changer adjustments, or changes in operating status (e.g., parallel or standalone operation), thereby eliminating potential misjudgments. A remote controller and a relay protection controller provide two control modes and corresponding control strategies to meet the needs of different application scenarios. These two controllers can comprehensively analyze the data acquired by the first and second current sensors. The remote controller can flexibly switch between the two control modes to adapt to different changes in the zero-sequence network caused by the activation of the current-limiting reactor. In this embodiment, two flexible control modes are provided, enabling the transformer control system to quickly switch according to actual operating conditions, ensuring optimal performance in various application scenarios, thereby improving the system's reliability and stability. Attached Figure Description

[0068] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0069] Figure 1 This is a schematic diagram of the structure of the transformer control system provided in an embodiment of the present invention;

[0070] Figure 2 This is a flowchart illustrating the implementation of the control method for the neutral point current-limiting reactor on the medium voltage side of a transformer provided in this embodiment of the invention.

[0071] Figure 3 This is a flowchart illustrating the implementation of the first control mode provided in an embodiment of the present invention;

[0072] Figure 4 This is a flowchart illustrating the implementation of the second control mode provided in an embodiment of the present invention;

[0073] Figure 5 This is a schematic diagram of the control device for the neutral point current-limiting reactor on the medium voltage side of the transformer provided in an embodiment of the present invention. Detailed Implementation

[0074] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0075] This application aims to address the increasing short-circuit current levels in modern power grids and the problem of insufficient short-circuit current withstand capability in transformer design. Without replacing the transformer, by installing a fault current limiter at the transformer neutral point and combining it with the control strategy proposed in this invention, the asymmetrical short-circuit current flowing through the transformer can be effectively and promptly limited, providing strong technical support for the economical and reliable operation of the equipment.

[0076] In one possible implementation, the transformer control system includes: a first current sensor, a second current sensor, a remote controller, a relay protection controller, a fast switch, a current-limiting reactor, and a grounding switch.

[0077] The first current sensor is installed at the input and output terminals of the transformer to acquire the three-phase current.

[0078] The second current sensor is installed on the neutral point grounding wire of the transformer to obtain the neutral point current;

[0079] One end of the current-limiting reactor is connected to the neutral point on the medium-voltage side of the transformer, and the other end is connected to the grounding switch; the other end of the grounding switch is grounded; a fast switch is connected in parallel across the current-limiting reactor.

[0080] The remote controller is used to control the fast switching action in a first control mode based on the three-phase current and neutral point current obtained by the first current sensor and the second current sensor; and in a second control mode, to control the fast switching action based on the control signal sent by the relay protection controller and the neutral point current obtained by the second current sensor.

[0081] Specifically, the data collected by the first and second current sensors are transmitted to the remote controller wirelessly or via a wired connection. When the sensors are connected to the remote controller via a wired connection, using an optical fiber connection ensures data transmission efficiency and stability. In some embodiments, the system includes a data acquisition module between the sensors and the remote controller to perform data sampling or signal conversion, thereby improving data sampling or processing efficiency.

[0082] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0083] Figure 1 This is a schematic diagram of the application scenario topology of the control method for the neutral point current-limiting reactor on the medium voltage side of the transformer provided in the embodiments of the present invention. Figure 1 The sensor and the remote controller are connected via a wired connection.

[0084] like Figure 1 As shown, the transformer control system consists of a first current sensor, a second current sensor, a data acquisition module, an optical fiber, a remote controller, a relay protection controller, a near-end controller, a fast switch, a current-limiting reactor, and a grounding switch.

[0085] The transformer control system is equipped with two sets of current sensors located at different positions to achieve accurate fault identification and zero-crossing prediction. For example... Figure 1 As shown, the first current sensor, namely the transformer input / output terminal sensor, is installed at the input and output terminals of the transformer and is responsible for monitoring the current at the input and output terminals, and is used to monitor the current of the three phases at this point in real time; the second current sensor, namely the neutral point grounding wire sensor, is arranged on the neutral point grounding wire of the transformer to capture the neutral point current.

[0086] The acquisition module is responsible for converting the electrical signals collected by the two sensors into optical signals and transmitting them to the remote controller via optical fiber, thereby enabling remote data processing and control.

[0087] The near-end controller is located at the installation site of the fault current limiter and serves as a manual control interface for emergency operation. The near-end controller is equipped with intuitive quick-switch status indicators, manual opening / closing buttons, and a reset function. In an emergency, by pressing the manual opening / closing button, the operator can directly manipulate the opening and closing action of the quick-switch, achieving immediate control of the fault current limiter.

[0088] During fault diagnosis, the system relies solely on data from the first current sensor, without considering the current information of the neutral grounding wire. This avoids potential misjudgments caused by three-phase unbalanced current due to heavy load switching, transformer tap changer adjustments, or changes in operating status (such as parallel or standalone operation). Furthermore, by analyzing the fault current data from the first current sensor, the system can also distinguish the fault type and determine whether it is a symmetrical or asymmetrical short circuit.

[0089] During the zero-crossing prediction process, the key data provided by the second current sensor ensures that the fast switch can operate accurately at the critical moment when the current crosses zero.

[0090] based on Figure 1 The system configuration shown allows the remote controller to implement two control modes. Control Mode 1: The remote controller, based on the current signals acquired by the first and second sensors transmitted by the acquisition module, sequentially performs fault judgment, zero-crossing prediction, and sends a signal to the fast switch when the current crosses zero, causing the fast switch to open and the current-limiting reactor to be connected in the circuit. Control Mode 2: The remote controller only accepts the opening and closing commands from the relay protection controller, and performs zero-crossing prediction according to the commands, and similarly switches the current-limiting reactor when the current crosses zero.

[0091] In control mode 1, since the current-limiting reactor can operate before the relay protection operates, the current-limiting reactor will change the zero-sequence network of the system. Therefore, the relevant relay protection needs to be checked and readjusted. Control mode 1 is suitable for application scenarios where the change in the zero-sequence network caused by the current-limiting reactor is small, the relay protection and system parameters that need to be reset are few, and the remote controller does not need to be connected to the relay protection controller. It can operate independently and make autonomous decisions on the switching of the current limiter.

[0092] In control mode 2, since the relay protection action is not affected by the current-limiting reactor's action, there is no need to adjust the relay protection. However, fault diagnosis still requires coordination with the relay protection controller. Control mode 2 is suitable for applications where the zero-sequence network changes significantly after the current-limiting reactor is activated, requiring resetting of the relay protection and numerous system parameters. It also requires an additional connection interface with the relay protection controller, and the remote controller needs to operate the activation and deactivation of the current-limiting reactor according to the instructions from the relay protection controller.

[0093] In this embodiment, the three-phase current at the transformer's input and output terminals and the neutral point current on the neutral point grounding wire are acquired using a first current sensor and a second current sensor, respectively. This ensures that when performing relevant judgments based on the three-phase current, it can effectively avoid three-phase unbalanced currents caused by factors such as large load switching, transformer tap changer adjustments, or changes in operating status (e.g., parallel or standalone operation), thereby eliminating potential misjudgments. The remote controller and relay protection controller provide two control modes and their corresponding control strategies to meet the needs of different application scenarios. These two controllers can comprehensively analyze the data acquired by the first and second current sensors. The remote controller can flexibly switch between the two control modes to adapt to different changes in the zero-sequence network caused by the activation of the current-limiting reactor. In this embodiment, two flexible control modes are provided, enabling the transformer control system to quickly switch according to actual operating conditions, ensuring that the system maintains optimal performance in various application scenarios, thereby improving the system's reliability and stability.

[0094] Based on the above system structure, this invention proposes control strategies for two control modes, so as to flexibly switch between the two control modes according to actual needs.

[0095] Figure 2 A flowchart illustrating the implementation of a control method for a neutral point current-limiting reactor on the medium-voltage side of a transformer control system, provided in this embodiment of the invention, includes the following steps:

[0096] S201, in the first control mode, controls the fast switch to close and obtains the real-time three-phase current and real-time neutral point current. Based on the real-time three-phase current and real-time neutral point current, controls the fast switch to maintain the closed state or controls the fast switch to operate.

[0097] The execution subject of the method provided in this application embodiment is the remote controller of the foregoing embodiments. Those skilled in the art will understand that using a controller as the execution subject is merely an exemplary description and should not be considered a limitation on the method provided in this application embodiment.

[0098] The first control mode is suitable for applications where the zero-sequence network changes little after the current-limiting reactor is put into operation, and where there are few relay protection and system parameters that need to be reset. The remote controller does not require an additional connection to the relay protection controller and can operate independently and make autonomous decisions on the switching of the current limiter.

[0099] In the first control mode, the control of the fast switch closing causes the current-limiting reactor to be short-circuited.

[0100] The system acquires real-time three-phase current and real-time neutral point current to determine faults based on the three-phase current. Specifically, it calculates the load angle change of each phase current and determines the fault type based on the load angle change.

[0101] In the specific implementation process, when the load angle change of all phases is less than the set threshold, it is determined that no short circuit fault has occurred, and the current limiting reactor does not need to operate; if the load angle change of any phase is greater than the set threshold, it is determined that a short circuit fault has occurred. Short circuit faults are further divided into three-phase symmetrical short circuit faults and asymmetrical short circuit faults.

[0102] If the load angle changes of all three phases exceed the set threshold, a three-phase symmetrical short-circuit fault is determined to have occurred, and the current-limiting reactor does not need to operate; otherwise, an asymmetrical short-circuit fault is determined to have occurred, and the current-limiting reactor should limit the current.

[0103] In the absence of a short circuit fault or in the event of a symmetrical short circuit fault, the fast switch is kept closed. In the event of an asymmetrical short circuit fault, the zero-crossing point is predicted based on the real-time neutral point current collected by the second current sensor. The fast switch is then controlled to open at the predicted zero-crossing point and to perform subsequent actions based on the zero-crossing point prediction result.

[0104] S202, in the second control mode, the fast switch is controlled to close. If no asymmetrical short-circuit fault signal is received from the relay protection controller, the fast switch is controlled to remain closed; otherwise, the real-time neutral point current is obtained, and the fast switch is controlled to operate based on the real-time neutral point current.

[0105] Control mode 2 is suitable for applications where the zero-sequence network changes significantly after the current-limiting reactor is put into operation, requiring the resetting of numerous relay protection and system parameters. The remote controller needs to operate the current-limiting reactor's activation and deactivation according to the instructions of the relay protection controller.

[0106] In the second control mode, the fast switch is closed, short-circuiting the current-limiting reactor. If no asymmetrical short-circuit fault signal is received from the relay protection controller, no short-circuit fault has occurred, or a symmetrical short-circuit fault has occurred, and the fast switch remains closed. If an asymmetrical short-circuit fault signal is received from the relay protection controller, zero-crossing prediction is performed based on the real-time neutral point current collected by the second current sensor. Based on the zero-crossing prediction result, the fast switch is controlled to open at the predicted zero-crossing point and perform subsequent actions.

[0107] In this embodiment, two control modes and corresponding control strategies are provided for the remote controller and the relay protection controller to meet the needs of different application scenarios. These two controllers can comprehensively analyze data acquired by the first and second current sensors. The remote controller can flexibly switch between the two control modes to adapt to different changes in the zero-sequence network caused by the activation of the current-limiting reactor. In the first control mode, the remote controller performs relevant judgments based on the three-phase currents at the transformer's input and output terminals, effectively avoiding three-phase unbalanced currents caused by factors such as large load switching, transformer tap changer adjustments, or changes in operating status (e.g., parallel or standalone operation), thereby eliminating potential misjudgments. In the second control mode, the remote controller works in conjunction with the relay protection controller to control the current-limiting reactor's connection status, improving the stability of the transformer system. In this embodiment, two flexible control modes are provided, enabling the transformer control system to quickly switch according to actual operating conditions, ensuring optimal performance in various application scenarios, thereby improving the system's reliability and stability.

[0108] In different embodiments, the way to control the fast switching state differs in the first control mode and the second control mode.

[0109] In one possible implementation, in the first control mode, based on the real-time three-phase current and the real-time neutral point current, the fast switch is controlled to maintain the closed state or to operate.

[0110] Calculate the load angle change of each phase based on the real-time three-phase current;

[0111] When the load angle change of each phase is less than or equal to the set change threshold, or when the load angle change of each phase is greater than the set change threshold, the fast switch is controlled to maintain the closed circuit; otherwise, zero-crossing prediction is performed based on the real-time neutral point current.

[0112] Based on the prediction results, at the zero-crossing prediction time, control the fast switch to open, and after the set current limiting time, monitor the instantaneous current value based on the real-time neutral point current.

[0113] If the instantaneous current value remains below the set threshold for the instantaneous value within the set detection time, a transient fault is determined to have occurred in the system, and the system controls the fast switch to close.

[0114] Based on the above embodiments, the methods for calculating the load angle change of each phase according to the real-time three-phase current, the method for zero-crossing prediction according to the real-time neutral point current, the setting of change threshold, and the setting of instantaneous value threshold differ in different embodiments.

[0115] In one possible implementation, in the second control mode, the real-time neutral point current is acquired, and the fast switching action is controlled based on the real-time neutral point current, including:

[0116] Zero-crossing prediction is performed based on the real-time neutral point current.

[0117] Based on the prediction results, at the zero-crossing prediction time, control the fast switch to open, and after the set current limiting time, monitor the instantaneous current value based on the real-time neutral point current.

[0118] If the instantaneous current value remains below the set threshold for the instantaneous value within the set detection time, a transient fault is determined to have occurred in the system, and the system controls the fast switch to close.

[0119] Based on the above embodiments, the zero-crossing prediction method based on the real-time neutral point current, the setting of the change threshold, and the setting of the instantaneous value threshold are different in different embodiments.

[0120] The following focuses on a detailed description of the embodiments of this application, which calculate the load angle change of each phase based on the real-time three-phase current and perform zero-crossing prediction based on the real-time neutral point current.

[0121] In this embodiment, fault diagnosis is based on the load angle mutation method, which can determine the fault within a very short time and with a small number of sampling points. This method is unaffected by harmonics and electromagnetic interference, has a simple principle, and does not require setting appropriate initial values ​​to ensure convergence, thus ensuring the speed, accuracy, and reliability of fault diagnosis.

[0122] Taking the zero-crossing time of the voltage under normal system conditions as the phase reference point, the load current of the system is typically:

[0123]

[0124] Among them, I bm The current amplitude before the fault occurred. This indicates the phase difference between voltage and current.

[0125] In one possible implementation, the load angle change of each phase is calculated based on the real-time three-phase current, including:

[0126] Based on the real-time three-phase current, continuous sampling with a time interval Δ is performed to obtain the current sample value [i]. s1 i s2 i s3 i s4 ...i sN ]; where the current sampling value of any 3 consecutive sampling points is i k-2 i k-1 , and i k The expressions are as follows:

[0127]

[0128]

[0129]

[0130] The difference between adjacent current sample values ​​is calculated using the following formula:

[0131] i k -i k-1 =I bm (sin(θ k )-sin(θ k -δ));

[0132] i k-1 -i k-2 =I bm (sin(θ k -δ)-sin(θ k -2δ));

[0133] make:

[0134]

[0135] Therefore, we can conclude that:

[0136]

[0137] From the current sampling value i k The expression yields:

[0138]

[0139] If I bm >0, then

[0140]

[0141] otherwise

[0142]

[0143] Where Δ is the sampling time interval, ωΔ=δ; I bm The current amplitude before the fault occurred. This indicates the phase difference between voltage and current.

[0144] In actual testing, the time required for fault identification mainly depends on the sampling rate; a higher sampling rate results in less computation time. In one possible implementation, the sampling time interval is less than or equal to 2ms.

[0145] The acquisition of data from three consecutive sampling points requires at least two sampling time intervals Δ. To ensure that the fault detection time is less than 2ms, the sampling rate of the current transformer involved in this control method should be 1kHz or higher.

[0146] Under normal system conditions, load angle It is a relatively small and slowly changing positive value (corresponding to an inductive load), however, when an asymmetrical short-circuit fault occurs in the system, the load angle... This will approach π / 2, meaning the load angle will undergo a sudden change. This can be used to detect the timing of short-circuit faults in the system.

[0147] In this embodiment, zero-crossing prediction is based on the dichotomy-Newton method. Zero-crossing prediction is performed using the dichotomy-Newton method and the real-time neutral point current on the transformer neutral point grounding wire, thus balancing accuracy and speed.

[0148] Based on the basic principles of circuits, from t d At time 10, the short-circuit current of the line is:

[0149]

[0150] The above equation illustrates the characteristics of short-circuit current, which consists of a steady-state component following a sinusoidal law and a transient component following a negative exponential law. The first zero-crossing point of the short-circuit current plays a crucial role in the process of a fast-switching switch interrupting the short-circuit current. Although the arc of a fast-switching switch usually extinguishes naturally at the moment the current crosses zero, the breaking efficiency of the fast-switching switch is also affected by the arc burning time (i.e., arcing time). A longer arcing time reduces the breaking performance of the fast-switching switch, and vice versa. Therefore, shortening the arcing time is crucial for improving the breaking capacity of the fast-switching switch and ensuring that it reliably interrupts the short-circuit current. Clearly, implementing a controllable fast-switching switch operation and precisely controlling the separation of its contacts at the optimal moment before the short-circuit current crosses zero is an effective strategy for optimizing circuit breaker performance. To achieve this strategy, accurately predicting the specific moment of the short-circuit current's zero-crossing point becomes particularly critical. Calculating the first zero-crossing time of the short-circuit current is essentially solving the first root of the following equation.

[0151]

[0152] Clearly, this equation is a transcendental equation, typically requiring numerical methods to solve. Among conventional numerical methods, the bisection method, while reliably finding a solution, is slow. Newton's method and Chebyshev's method converge faster, but carry the risk of non-convergence, and Chebyshev's method is computationally intensive. Therefore, this invention employs the bisection-Newton method, combining the stability of the bisection method with the speed of Newton's method to optimize the solution process and more efficiently address the problem of solving this equation.

[0153] In one possible implementation, zero-crossing prediction is performed based on the real-time neutral point current, including:

[0154] According to the principle of the bisection method, the real-time neutral point current is continuously sampled at time intervals of mΔ (i.e., m times the sampling interval Δ). The root interval search is started from the time t1+(N-1)*Δ corresponding to the last neutral point current sample value to determine the interval where the root of the equation is located.

[0155] If the equation has roots between T1 and T2, the root interval search ends, and the root calculation is performed based on Newton's method.

[0156] The process involves continuous sampling of the real-time neutral point current at time intervals of mΔ, starting from the time t1+(N-1)*Δ corresponding to the last neutral point current sample value, and includes:

[0157] set up

[0158]

[0159] Let T1=t1+(N-1)*Δ, T2=T1+m*Δ, f1=f(T1), f2=f(T2), q=f1*f2;

[0160] If q > 0, it means that there is no root of the equation between T1 and T2, so that the new T1 = T2 and the new T2 = T1 + m*Δ. Calculate f1, f2 and q again and compare them.

[0161] If q < 0, it means that there are roots of the equation between T1 and T2, and the search for the root interval ends.

[0162] Root-finding calculations based on Newton's method include:

[0163] The numerical solution is obtained through the following iterative process:

[0164]

[0165] Here, f'(t) is the derivative of f(t).

[0166]

[0167] During the iteration process, when |T k+1 -T k The iteration stops when | < ε, where ε is a pre-set error.

[0168] T1 is determined by searching the root interval, and T2 is calculated using relevant formulas. Then, it is verified whether the error is within an acceptable range. If the error meets the preset conditions, the iteration ends and an approximate value of the root is obtained; if not, T3 is calculated using T2, and so on, until the error meets the requirements, thereby accurately determining the time when the short-circuit current first crosses zero.

[0169] In this embodiment, a balance between computational efficiency and solution accuracy is fully considered. The load angle catastrophe method and the binary-Newton method are employed to ensure that computational resources are rationally allocated and concentrated on critical computational tasks, effectively reducing redundant calculations. The computational flow of the binary-Newton method and the load angle catastrophe method is simple, making fault detection and response strategies more intuitive and easy to understand. Furthermore, based on the accurate prediction of the zero-crossing point of the short-circuit current using the binary-Newton method, the timing of fast switching is optimized, thereby improving the system's response speed and safety. This enables accurate triggering of protection mechanisms at critical moments, ensuring the stable operation of equipment and the system.

[0170] In the aforementioned embodiments, the control scheme for fast switching when the transformer system has no fault, a three-phase asymmetrical short circuit fault, or a symmetrical short circuit fault is mainly introduced. In the actual implementation process, there are also cases where permanent faults occur. Accordingly, a control scheme needs to be set up to improve the system's operational stability.

[0171] One possible implementation also includes:

[0172] When the instantaneous current value is greater than or equal to the instantaneous value set threshold, a permanent fault is determined in the system. The circuit breaker is controlled to operate, and after a set delay interval, the fast switch is controlled to close to reset the system state.

[0173] The foregoing embodiments describe the calculation of load angle change, zero-crossing prediction, and fast switching control strategies when different faults occur. The following describes the complete first control mode and second control mode in conjunction with specific embodiments.

[0174] Depend on Figure 3 As shown, the control flow steps for remote controller control mode 1 are as follows:

[0175] (1) Initially, the fast switch closes and the current-limiting reactor is short-circuited.

[0176] (2) The remote controller receives the three-phase current data of the transformer input and output terminals detected by the first current sensor installed on the transformer output terminal in real time, and calculates the load angle change of each phase current.

[0177] (3) When the load angle change of all phases is less than the set threshold, it is determined that no short circuit fault has occurred and the current limiting reactor does not need to operate; if the load angle change of any phase is greater than the set threshold, it is determined that a short circuit fault has occurred.

[0178] (4) Determine whether the load angle change of the three phases exceeds the set threshold. If so, it is determined that a three-phase symmetrical short circuit fault has occurred, and the current limiting reactor does not need to operate. Otherwise, it is determined that an asymmetrical short circuit fault has occurred, and the current limiting reactor should limit the current.

[0179] (5) The remote controller receives the neutral point grounding wire current data detected by the second current sensor installed on the neutral point grounding wire of the transformer in real time, and performs zero-crossing prediction based on the binary-Newton method.

[0180] (6) When the current crosses zero, the fast switch is opened and the current-limiting reactor is connected to the neutral point grounding wire for current limiting.

[0181] (7) After current limiting for 3 seconds, the remote controller will monitor the instantaneous current value based on the data provided by the second current sensor. If the instantaneous current value remains below the preset threshold for 20 consecutive milliseconds, the system will determine this as a transient short-circuit fault and immediately instruct the fast switch to close, reconnecting the current-limiting reactor to the circuit. Conversely, if the instantaneous current value exceeds the threshold, the system will determine this as a permanent short-circuit fault and immediately send an action signal to the circuit breaker. After the circuit breaker operates, the system will wait for a 1-second delay before the fast switch closes again to reset the system state.

[0182] In this embodiment, during fault diagnosis, the system relies solely on data from the first current sensor, without considering the current information of the neutral grounding wire. This avoids potential misjudgments caused by three-phase unbalanced currents resulting from heavy load switching, transformer tap changer adjustments, or changes in operating status (such as parallel or standalone operation). By combining the stability of the bisection method with the speed of Newton's method, the efficiency and accuracy of zero-crossing prediction are improved. This first control mode enhances the safety and stability of the power system, reduces operating costs, and provides a solid technical guarantee for the safe operation of transformers.

[0183] Depend on Figure 4 As shown, the control flow steps for remote controller control mode 2 are as follows:

[0184] (1) Initially, the fast switch closes and the current-limiting reactor is short-circuited.

[0185] (2) If the remote controller receives a command from the relay protection controller, it determines that an asymmetrical short circuit fault has occurred and the current-limiting reactor should limit the current; otherwise, it determines that no asymmetrical short circuit fault has occurred.

[0186] (3) The remote controller receives the neutral point grounding wire current data detected by the second current sensor installed on the neutral point grounding wire of the transformer in real time, and performs zero-crossing prediction based on the binary-Newton method.

[0187] (4) When the current crosses zero, the fast switch is opened and the current-limiting reactor is connected to the neutral point grounding wire for current limiting.

[0188] (5) After current limiting for 3 seconds, the remote controller will monitor the instantaneous current value based on the data provided by the second current sensor. If the instantaneous current value remains below the preset threshold for 20 consecutive milliseconds, the system will determine this as a transient short-circuit fault and immediately instruct the fast switch to close, reconnecting the current-limiting reactor to the circuit. Conversely, if the instantaneous current value exceeds the threshold, the system will determine this as a permanent short-circuit fault and immediately send an action signal to the circuit breaker. After the circuit breaker operates, the system will wait for a 1-second delay before the fast switch closes again to reset the system state.

[0189] In this embodiment, the remote controller and the relay protection controller cooperate with each other. The remote controller operates the switching on and off of the current-limiting reactor according to the instructions of the relay protection controller. The relay protection controller performs fault diagnosis, while the remote controller performs zero-crossing prediction and fast switching control based on the binary-Newton method, reducing the computational burden on the remote controller and improving the efficiency and accuracy of zero-crossing prediction.

[0190] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0191] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0192] Figure 5 This diagram illustrates the structure of a control device for a neutral point current-limiting reactor on the medium-voltage side of a transformer, as provided in an embodiment of the present invention. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown, and are detailed below: Figure 5 As shown, the control device for the neutral point current-limiting reactor on the medium-voltage side of the transformer includes:

[0193] The acquisition module 501 is used to acquire real-time three-phase current and real-time neutral point current;

[0194] The control module 502 is used to control the fast switch to close in the first control mode, and to control the fast switch to maintain its closed state or to operate the fast switch based on the real-time three-phase current and the real-time neutral point current; in the second control mode, it controls the fast switch to close, and if no asymmetrical short-circuit fault signal is received from the relay protection controller, it controls the fast switch to maintain its closed state; otherwise, it controls the fast switch to operate based on the real-time neutral point current.

[0195] In one possible implementation, the control module 502 is specifically used for:

[0196] Calculate the load angle change of each phase based on the real-time three-phase current;

[0197] When the load angle change of each phase is less than or equal to the set change threshold, or when the load angle change of each phase is greater than the set change threshold, the fast switch is controlled to maintain the closed circuit; otherwise, zero-crossing prediction is performed based on the real-time neutral point current.

[0198] Based on the prediction results, at the zero-crossing prediction time, control the fast switch to open, and after the set current limiting time, monitor the instantaneous current value based on the real-time neutral point current.

[0199] If the instantaneous current value remains below the set threshold for the instantaneous value within the set detection time, a transient fault is determined to have occurred in the system, and the system controls the fast switch to close.

[0200] In one possible implementation, the control module 502 is specifically used for:

[0201] Based on the real-time three-phase current, continuous sampling with a time interval Δ is performed to obtain the current sample value [i]. s1 i s2 i s3 i s4 ...i sN ]; where the current sampling value of any 3 consecutive sampling points is i k-2 i k-1 , and i k The expressions are as follows:

[0202]

[0203]

[0204]

[0205] The difference between adjacent current sample values ​​is calculated using the following formula:

[0206] i k -i k-1 =I bm (sin(θ k)-sin(θ k -δ));

[0207] i k-1 -i k-2 =I bm (sin(θ k -δ)-sin(θ k -2δ));

[0208] make:

[0209]

[0210] Therefore, we can conclude that:

[0211]

[0212] From the expression for the current sampling value ik, we can obtain:

[0213]

[0214] If I bm >0, then

[0215]

[0216] otherwise

[0217]

[0218] Where Δ is the sampling time interval, ωΔ=δ; I bm The current amplitude before the fault occurred. This indicates the phase difference between voltage and current.

[0219] In one possible implementation, the sampling time interval is less than or equal to 2ms.

[0220] In one possible implementation, the control module 502 is specifically used for:

[0221] Zero-crossing prediction is performed based on the real-time neutral point current.

[0222] Based on the prediction results, at the zero-crossing prediction time, control the fast switch to open, and after the set current limiting time, monitor the instantaneous current value based on the real-time neutral point current.

[0223] If the instantaneous current value remains below the set threshold for the instantaneous value within the set detection time, a transient fault is determined to have occurred in the system, and the system controls the fast switch to close.

[0224] In one possible implementation, the control module 502 is further configured to:

[0225] When the instantaneous current value is greater than or equal to the instantaneous value set threshold, a permanent fault is determined in the system. The circuit breaker is controlled to operate, and after a set delay interval, the fast switch is controlled to close to reset the system state.

[0226] In one possible implementation, the control module 502 is specifically used for:

[0227] Based on the real-time neutral point current, continuous sampling is performed at time intervals of mΔ, and the root interval search is started from the time t1+(N-1)*Δ corresponding to the last neutral point current sample value;

[0228] If the equation has roots between T1 and T2, the root interval search ends, and the root calculation is performed based on Newton's method.

[0229] The process involves continuous sampling of the real-time neutral point current at time intervals of mΔ, starting from the time t1+(N-1)*Δ corresponding to the last neutral point current sample value, and includes:

[0230] set up

[0231]

[0232] Let T1=t1+(N-1)*Δ, T2=T1+m*Δ, f1=f(T1), f2=f(T2), q=f1*f2;

[0233] If q > 0, it means that there is no root of the equation between T1 and T2, so that the new T1 = T2 and the new T2 = T1 + m*Δ. Calculate f1, f2 and q again and compare them.

[0234] If q < 0, it means that there are roots of the equation between T1 and T2, and the search for the root interval ends.

[0235] Root-finding calculations based on Newton's method include:

[0236] The numerical solution is obtained through the following iterative process:

[0237]

[0238] Here, f'(t) is the derivative of f(t).

[0239]

[0240] During the iteration process, when |T k+1 -T k The iteration stops when | < ε, where ε is a pre-set error.

[0241] In this embodiment, two control modes and their corresponding control strategies are provided to meet the needs of different application scenarios. Data acquired by the first and second current sensors are comprehensively analyzed. The control device flexibly switches between the two control modes to adapt to different changes in the zero-sequence network caused by the activation of the current-limiting reactor. In the first control mode, the control device performs relevant judgments based on the three-phase currents at the transformer's input and output terminals, effectively avoiding three-phase unbalanced currents caused by factors such as large load switching, transformer tap changer adjustments, or changes in operating status (e.g., parallel or standalone operation), thereby eliminating potential misjudgments. In the second control mode, the control device works in conjunction with the relay protection controller to control the current-limiting reactor's connection status, improving the stability of the transformer system. In this embodiment, two flexible control modes are provided, enabling the transformer control system to quickly switch according to actual operating conditions, ensuring optimal performance in various application scenarios, thereby improving the system's reliability and stability.

[0242] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0243] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0244] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of the control method embodiments for the neutral point current-limiting reactor on the medium-voltage side of the above-described transformers. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0245] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A transformer control system, characterized in that, include: First current sensor, second current sensor, remote controller, relay protection controller, fast switch, current limiting reactor and grounding switch; The first current sensor is installed at the input and output terminals of the transformer to acquire the three-phase current. The second current sensor is installed on the neutral point grounding wire of the transformer to obtain the neutral point current; One end of the current-limiting reactor is connected to the neutral point of the medium-voltage side of the transformer, and the other end is connected to the grounding switch; the other end of the grounding switch is grounded; the fast switch is connected in parallel across the current-limiting reactor. The remote controller is configured to control the fast switch action in a first control mode based on the three-phase current and neutral point current obtained by the first current sensor and the second current sensor; and in a second control mode based on the control signal sent by the relay protection controller and the neutral point current obtained by the second current sensor.

2. The transformer control system according to claim 1, characterized in that, Also includes: The circuit breaker is communicatively connected to the remote controller; The remote controller is used to control the circuit breaker to operate when it is determined that a permanent short-circuit fault has occurred in the transformer control system.

3. A control method for a neutral point current-limiting reactor on the medium-voltage side of a transformer used in the transformer control system of claim 1 or 2, characterized in that, include: In the first control mode, the fast switch is controlled to close, and the real-time three-phase current and real-time neutral point current are acquired. Based on the real-time three-phase current and real-time neutral point current, the fast switch is controlled to maintain the closed state or to operate. In the second control mode, the fast switch is controlled to close. If no asymmetrical short-circuit fault signal is received from the relay protection controller, the fast switch is controlled to remain closed. Otherwise, the real-time neutral point current is acquired, and the fast switching action is controlled based on the real-time neutral point current.

4. The control method for the neutral point current-limiting reactor on the medium-voltage side of the transformer according to claim 3, characterized in that, The step of controlling the fast switch to maintain its closed position or to operate based on the real-time three-phase current and the real-time neutral point current includes: Calculate the load angle change of each phase based on the real-time three-phase current; When the load angle change of each phase is less than or equal to the set change threshold, or when the load angle change of each phase is greater than the set change threshold, the fast switch is controlled to remain closed; otherwise, zero-crossing prediction is performed based on the real-time neutral point current. Based on the prediction results, at the zero-crossing prediction time, the fast switch is controlled to open, and after the current limiting time is set, the instantaneous current value is monitored based on the real-time neutral point current. If the instantaneous current value remains below a set threshold for the instantaneous value within a set detection time, a transient fault is determined to have occurred in the system, and the fast switch is controlled to close.

5. The control method for the neutral point current-limiting reactor on the medium-voltage side of the transformer according to claim 4, characterized in that, The calculation of the load angle change of each phase based on the real-time three-phase current includes: The current sample values ​​are obtained by continuously sampling the real-time three-phase current at time intervals Δ. i s1 , i s2 , i s3 , i s4 ... i sN ]; where the current sampling value of any 3 consecutive sampling points is i k-2 , i k-1 ,and i k The expressions are as follows: ； The difference between adjacent current sample values ​​is calculated using the following formula: ； ； make: Therefore, we can conclude that: From the expression for the current sampling value ik, we can obtain: if I bm >0, then otherwise Where Δ is the sampling time interval. ω Δ= δ ; I bm The current amplitude before the fault occurred. φ 0 indicates the phase difference between voltage and current.

6. The control method for the neutral point current-limiting reactor on the medium-voltage side of the transformer according to claim 5, characterized in that, The sampling time interval is less than or equal to 2ms.

7. The control method for the neutral point current-limiting reactor on the medium-voltage side of a transformer according to claim 5, characterized in that, The step of acquiring the real-time neutral point current and controlling the fast switching action based on the real-time neutral point current includes: Zero-crossing prediction is performed based on the real-time neutral point current. Based on the prediction results, at the zero-crossing prediction time, the fast switch is controlled to open, and after the current limiting time is set, the instantaneous current value is monitored based on the real-time neutral point current. If the instantaneous current value remains below a set threshold for the instantaneous value within a set detection time, a transient fault is determined to have occurred in the system, and the fast switch is controlled to close.

8. The control method for the neutral point current-limiting reactor on the medium-voltage side of the transformer according to claim 4 or 7, characterized in that, Also includes: When the instantaneous current value is greater than or equal to a set threshold value, a permanent fault is determined to have occurred in the system. The circuit breaker is controlled to operate, and after a set delay interval, the fast switch is controlled to close to reset the system state.

9. The control method for the neutral point current-limiting reactor on the medium-voltage side of a transformer according to claim 7, characterized in that, The zero-crossing prediction based on the real-time neutral point current includes: Based on the real-time neutral point current, continuous sampling is performed at time intervals of mΔ, starting from the time corresponding to the last neutral point current sample value. Begin root interval search; exist T 1 and T If the equation has roots, the root interval search ends and the root calculation is performed based on Newton's method. Specifically, continuous sampling with time intervals of mΔ is performed based on the real-time neutral point current, starting from the time corresponding to the last neutral point current sample value. Begin the root interval search, including: set up make , , , , ; If q > 0, then it means T 1 and T There are no roots of the equation between 2, which makes the new T 1= T 2, and the new Calculate again , and And compare them; If q < 0, then it means T 1 and T If there are roots of the equation in 2, then the search for the root interval ends; The root-finding calculation based on Newton's method includes: The numerical solution is obtained through the following iterative process: in, for The derivative function; During the iteration process, when When ε is reached, the iteration stops, where ε is a pre-set error.

10. A control device for a neutral point current-limiting reactor on the medium-voltage side of a transformer in a transformer control system as described in claim 1 or 2, characterized in that, include: The acquisition module is used to acquire real-time three-phase current and real-time neutral point current; The control module is used to control the fast switch to close in the first control mode, and to control the fast switch to maintain its closed state or to control the fast switch to operate based on the real-time three-phase current and the real-time neutral point current; in the second control mode, if the fast switch is not closed and no asymmetrical short-circuit fault signal is received from the relay protection controller, the fast switch is controlled to maintain its closed state. Otherwise, the fast switching action is controlled based on the real-time neutral point current.

Images