Single-core phase-shifting transformer loop closing control and differential protection method and system based on single-voltage source excitation

Abstract

The application relates to a single-core phase-shifting transformer loop closing control and differential protection method and system based on single-voltage source excitation, which comprises a single-core phase-shifting transformer body and a module in communication connection with the same; the single-core phase-shifting transformer adopts a single-voltage source excitation topology, one end of a primary side of an excitation transformer is grounded, the other end is connected to a single-voltage source, a secondary side is regularly connected to a secondary side of a series transformer, and a primary side of the series transformer is connected to a power distribution network and leads out a loop closing output end. The method comprises the following steps: collecting real-time data of the power distribution network; through the establishment of a voltage-position mapping relationship, the actual access of the number of turns of a secondary side coil of the excitation transformer and the tap position are dynamically adjusted, amplitude-phase decoupling adjustment of voltages on both sides of a loop closing point is realized; based on double criteria of electric balance and magnetic balance, a tap self-adaptive current correction algorithm and a harmonic braking strategy are introduced to suppress unbalanced current interference; through real-time intercommunication of control and protection data, integrated collaborative response of loop closing adjustment and fault protection is realized. Compared with the prior art, the application realizes the collaborative response of transformer adjustment and protection.

Description

Technical Field

[0001] This invention relates to the field of flexible loop-connected power supply and transformer protection technology for 10kV distribution networks, and in particular to a method and system for loop-connected control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation. Background Technology

[0002] With rapid economic development, electricity users are increasingly demanding higher reliability and quality in power supply. As the direct power transmission link to users, the traditional closed-loop design and open-loop operation mode of the distribution network can no longer meet the needs of uninterrupted power supply. Live-loop operation has become a key means to improve power supply reliability. However, the distribution network structure is becoming increasingly complex. Differences in voltage amplitude, phase, and equivalent impedance on both sides of the loop closure point can easily trigger steady-state circulating currents and inrush currents, potentially causing relay protection malfunctions and resulting in power outages on non-faulty lines.

[0003] As the core equipment in loop-closing operations, the phase-shifting transformer's regulation performance and protection strategy directly affect the safety of loop closure. In existing technologies, single-core phase-shifting transformers generally suffer from problems such as coupled amplitude and phase regulation and poor adaptability to asymmetrical operating conditions. Furthermore, loop closure control and differential protection are often designed separately, leading to poor coordination between regulation and protection, and delayed response. In addition, when switching taps, the rated voltage parameters of the relay protection device cannot be adaptively adjusted in single-core phase-shifting transformers with tap changes, easily generating unbalanced currents, which in turn increases the risk of differential protection maloperation. While dual-core phase-shifting transformers offer some improvement in regulation range, their complex topology and higher cost make them unsuitable for widespread application in medium and low-voltage distribution networks.

[0004] Most existing differential protection methods are based on fixed ratio calculations, lack the ability to adaptively correct for changes in gear ratios, and do not fully consider the impact of dynamic changes in voltage and current on protection criteria during loop regulation.

[0005] Therefore, inventing an integrated technology that combines high-precision closed-loop regulation with high-reliability differential protection to achieve coordinated response of regulation and protection has become a key requirement for solving the safety hazards of closed-loop operation in distribution networks. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a method for loop control and differential protection of a single-core phase-shifting transformer based on single voltage source excitation.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for closed-loop control and differential protection of a single-core phase-shifting transformer based on single-voltage-source excitation, wherein the single-core phase-shifting transformer adopts a single-voltage-source excitation topology, including a series transformer bank and an excitation transformer bank, and the method includes: Collect real-time data of the distribution network, including voltage phasors on both sides of the loop closure point, phase currents flowing through the input and output terminals of the single-core phase-shifting transformer, excitation current of the excitation transformer, and the current tap position of the secondary side tap of the excitation transformer. Based on the voltage phasors on both sides of the loop closing point, the voltage amplitude and phase angle to be compensated are calculated, a voltage-taper mapping relationship is established, and the target number of turns connected to the secondary coil of the excitation transformer is calculated and mapped to the target tap position. Based on the Thevenin equivalent model, the loop closing impact current is predicted, and after safety verification, a tap position adjustment command is generated. Based on the current of each phase and the current tap position, calculate the electrical balance and magnetic balance differential current. Based on the tap position adaptive correction algorithm, correct the equivalent ratio and proportional balance coefficient of the current transformer according to the tap position change. Calculate the electrical balance differential current and magnetic balance differential current in parallel using the corrected differential current, and perform preliminary fault identification of the differential current by combining the ratio braking and harmonic braking criteria. While outputting the tap change adjustment command, a tap position change warning signal is sent. Based on the tap position change warning signal, the current correction parameters are updated in advance and the anti-disturbance logic is enabled. If the preliminary fault identification detects an internal fault and the differential current reaches the action threshold, a blocking command is sent and the circuit breaker is tripped, while all adjustment and loop closing operations are stopped. If the differential current does not reach the tripping threshold but the preliminary fault identification remains abnormal, the fault type is identified by combining voltage and current waveform characteristics. According to the fault type, a tap position fine-tuning operation is performed to eliminate the abnormality or enter the protection standby state and prepare for tripping.

[0008] Furthermore, the voltage phasors on both sides of the loop closure point are acquired by voltage transformers configured on the busbars on both sides of the loop closure point; the phase currents flowing through the input and output terminals of the single-core phase-shifting transformer and the excitation current of the excitation transformer are acquired by current transformers configured at the input and output terminals of the single-core phase-shifting transformer and the winding circuit of the excitation transformer.

[0009] Furthermore, the voltage-level mapping relationship is established based on the topology, winding parameters, and electromagnetic induction law of a single-core phase-shifting transformer with single-voltage source excitation.

[0010] Furthermore, an iterative optimization algorithm is used to determine the target number of turns connected to the secondary winding of the excitation transformer. The iterative optimization algorithm is either the Newton-Raphson method or the gradient descent method.

[0011] Furthermore, the Thevenin equivalent model is constructed based on the equivalent power supply and equivalent impedance of the system on both sides of the loop closing point; the judgment criteria for the safety verification are: the amplitude of the loop closing inrush current does not exceed the circuit breaker breaking capacity, and the bus voltage fluctuation caused by the loop closing operation does not exceed the set threshold.

[0012] Furthermore, the electrical balance differential current is calculated based on Kirchhoff's current law, and the magnetic balance differential current is calculated based on the ampere-turn balance relationship of electromagnetic induction.

[0013] Furthermore, the specific criteria for ratio braking and harmonic braking are as follows: Ratio braking criterion: in, For differential current, For braking current, Minimum operating current threshold, Where K is the inflection point current and K is the braking coefficient; Harmonic braking criterion: When the second harmonic content in the differential current exceeds a set ratio, the differential protection output is blocked; the set ratio ranges from 15% to 25%.

[0014] Furthermore, the process of identifying fault types by combining voltage and current waveform characteristics includes: extracting the distortion characteristics, amplitude variation patterns, and phase shift characteristics of voltage and current waveforms, and combining the characteristic information to distinguish between adjustable and eliminable operating condition anomalies and potential internal faults of the transformer.

[0015] A single-core phase-shifting transformer closed-loop control and differential protection system based on single-voltage-source excitation is disclosed. The single-core phase-shifting transformer adopts a single-voltage-source excitation topology, including a series transformer group and an excitation transformer group. The system includes: a data acquisition module, a closed-loop control module, a differential protection module, an integrated processing unit, and a fault diagnosis and recovery module, all communicatively connected to the single-core phase-shifting transformer. The primary winding of the series transformer group is directly connected to the lines on both sides of the loop point of the distribution network, and the secondary winding serves as the voltage compensation output winding; the primary winding of the excitation transformer group adopts a star connection, the neutral point is directly grounded, and the ungrounded terminals of each phase are respectively connected to the center tap of the corresponding phase primary winding of the series transformer, thereby obtaining single-phase excitation power from the system; the secondary side of the excitation transformer is an adjustable winding with multiple tap positions. The output terminal of the secondary winding of the excitation transformer is connected in series with the secondary winding of the series transformer according to a preset phase sequence rule, thereby injecting a compensation voltage with controllable amplitude and phase into the secondary side of the series transformer. This topology can change the vector of the injected compensation voltage by adjusting the tap position of the secondary winding of the excitation transformer, thereby achieving decoupling adjustment of the voltage amplitude and phase on both sides of the loop point. The data acquisition module is used to collect the voltage phasors on both sides of the distribution network loop point, the phase currents at the input and output terminals of the single-core phase-shifting transformer, the excitation current of the excitation transformer, and the current tap position of the secondary side tap of the excitation transformer in real time, and synchronize the collected data to the other modules. The loop-closing control module is used to calculate the voltage amplitude and phase angle to be compensated based on the voltage phasors on both sides of the loop-closing point, establish a voltage-taper mapping relationship, and solve for the target number of turns connected to the secondary coil of the excitation transformer, which is then mapped to the target tap position. Based on the Thevenin equivalent model, the loop-closing inrush current is predicted, and after safety verification, tap adjustment commands are generated and output. The differential protection module is used to calculate the electrical balance differential current and magnetic balance differential current based on the collected current and tap position information, correct the equivalent ratio and proportional balance coefficient of the current transformer based on the tap position change, and perform preliminary differential current fault identification by combining ratio braking and harmonic braking criteria. The integrated processing unit is used to simultaneously send a gear change warning signal when outputting tap adjustment command, update the current correction parameters in advance and enable anti-disturbance logic according to the warning signal; if the preliminary fault judgment detects an internal fault and the differential current reaches the action threshold, it sends a lockout command and triggers the circuit breaker to trip, while stopping all adjustment and loop closing operations. The fault diagnosis and recovery module is used to identify the fault type by combining voltage and current waveform characteristics when the differential current does not reach the trip threshold but continues to be abnormal; and selects to perform tap position fine-tuning operation to eliminate the abnormality or control the system to enter the protection standby state and prepare to trip according to the fault type.

[0016] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the single-core phase-shifting transformer loop-closing control and differential protection method based on single-voltage source excitation as described above.

[0017] Compared with the prior art, the beneficial effects of the present invention include: 1. This invention constructs an integrated collaborative architecture for closed-loop control and differential protection, deeply integrating voltage regulation and protection criteria. This solves the problems of response lag and miscoordination caused by the decoupled operation of control and protection in traditional solutions. It achieves precise regulation of voltage amplitude and phase decoupling at the closed-loop point and ensures safe and controllable closed-loop operation through pre-inrush current prediction and safety verification. It also realizes adaptive differential protection across all ranges, effectively suppressing unbalanced currents and protection maloperations caused by range adjustment and transient processes. Furthermore, through control-protection linkage and intelligent fault diagnosis and hierarchical handling, it achieves rapid fault identification, timely blocking, and reasonable handling. This completely solves the core pain points of control-protection separation, regulation coupling, and easy maloperation or failure to operate in traditional solutions, significantly improving the success rate, safety, and overall power supply reliability of 10kV distribution networks, and adapting to the actual operating needs of medium and low voltage distribution networks.

[0018] 2. This invention implements a tap-adaptive differential protection method by employing a tap-adaptive current correction algorithm, effectively solving the protection imbalance current problem caused by frequent tap adjustments of the excitation transformer. Based on real-time tap information, the equivalent ratio and balance coefficient of the current transformer are dynamically calculated, and the sampled current is corrected online, thereby eliminating differential current deviations caused by fixed parameter settings at different tap positions. Combining dual criteria of electrical and magnetic balance, ratio braking, and harmonic braking strategies, it can achieve highly sensitive and selective internal fault detection across the entire tap range, significantly reducing the risk of protection maloperation and failure to operate.

[0019] 3. This invention achieves improved accuracy and safety in closed-loop regulation by combining voltage-level mapping with the Thevenin equivalent prediction model. This method can predict inrush currents at different compensation levels and assess safety without actually performing closed-loop operations, thus mitigating risks in advance. This not only improves regulation accuracy and closed-loop success rate but also transforms safety assessment from "post-event response" to "pre-event prediction," enhancing the system's proactive fault prevention capabilities. 4. This invention constructs a two-way signal interaction link of feedforward warning and feedback interlocking. The control module adjusts the forward protection and sends a warning; when a protection fault occurs, it sends the highest priority interlocking command to the control module, solving the problems of information silos and response delays caused by the separation of control and protection in traditional systems. The feedforward mechanism allows the protection to adapt to parameter changes in advance, improving its anti-interference capability; the interlocking mechanism achieves fault isolation and adjustment termination within seconds, forming a safety control chain of adjustment as monitoring and fault interruption as blocking, greatly improving the overall system's rapid response capability and fault tolerance.

[0020] 5. The system proposed in this invention can be integrated into a single hardware platform, resulting in a compact system structure and efficient information exchange, reducing the interface complexity and communication latency issues caused by the separation of multiple devices. The solution has a clear principle and strong adaptability, applicable not only to typical single-core phase-shifting transformers with single-voltage source excitation, but also providing a reference for the design of other flexible loop-closing devices through its collaborative architecture and adaptive protection concept. It possesses high engineering promotion value and application prospects. 6. This invention adopts a single-core phase-shifting transformer structure based on single voltage source excitation to replace the traditional dual-core topology. While ensuring the same regulation performance, it significantly simplifies the physical structure, reduces manufacturing costs and maintenance difficulty, and makes it more suitable for the large-scale transformation and promotion needs of 10kV and below medium and low voltage distribution networks. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a topology diagram of the single-voltage-source excitation single-core phase-shifting transformer of the present invention; Figure 3This is a block diagram illustrating the internal logic and collaborative operation of the closed-loop control module of the present invention. Figure 4 for Figure 2 Schematic diagram of the voltage relationships in the middle; Figure 5 This is a block diagram of the integrated system hardware composition of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0023] Example 1 This embodiment discloses a single-core phase-shifting transformer closed-loop control and differential protection system based on single-voltage source excitation. The system includes a single-core phase-shifting transformer and a data acquisition module, a closed-loop control module, a differential protection module, an integrated processing unit, and a fault diagnosis and recovery module, all communicatively connected to the transformer body. The modules are interconnected via a high-speed data bus to achieve real-time information sharing and command coordination.

[0024] like Figure 2 As shown, the single-core phase-shifting transformer on which this system is based adopts a single voltage source excitation topology, and its main components are as follows: Series transformer group: Its primary winding is directly connected to the lines on both sides of the loop connection point of the distribution network, and the secondary winding is used as the voltage compensation output winding.

[0025] Excitation transformer group: Its primary winding adopts a star connection, the neutral point is directly grounded, and the ungrounded terminals of each phase are connected to the center tap of the corresponding phase primary winding of the series transformer, thereby obtaining single-phase excitation power from the system. The secondary side of the excitation transformer is an adjustable winding with multiple tap positions.

[0026] Electrical connection: The output terminal of the secondary winding of the excitation transformer is connected in series with the secondary winding of the series transformer according to the preset phase sequence rule, thereby injecting a compensation voltage with controllable amplitude and phase into the secondary side of the series transformer.

[0027] This topology can change the vector of the injected compensation voltage by adjusting the effective number of turns (i.e., the tap position) of the secondary winding of the excitation transformer, thereby achieving decoupling adjustment of the voltage amplitude and phase on both sides of the closing point.

[0028] The data acquisition module is used to collect the voltage phasors on both sides of the distribution network loop point, the phase currents at the input and output terminals of the single-core phase-shifting transformer, the excitation current of the excitation transformer, and the current tap position of the secondary side tap of the excitation transformer in real time, and synchronize the collected data to the other modules.

[0029] The loop closing control module is used to calculate the voltage amplitude and phase angle to be compensated based on the voltage phasors on both sides of the loop closing point, establish the voltage-taper mapping relationship, and solve for the target number of turns connected to the secondary coil of the excitation transformer, which is then mapped to the target tap position. Based on the Thevenin equivalent model, the loop closing inrush current is predicted, and after safety verification, the tap adjustment command is generated and output.

[0030] The core function of the loop-closing control module is to calculate and output the optimal tap adjustment command in real time to ensure smooth and safe loop-closing operation. Its internal logic is as follows: Figure 3 As shown, the specific implementation steps are as follows: 1. Real-time data acquisition and processing The amplitude (U) of the voltage on both sides of the busbar is collected in real time by voltage transformers (PTs) installed on both sides of the loop connection point. A U B ) and phase angle (θ) A , θ B ).

[0031] Current transformers (CTs) installed at the input / output terminals of the phase-shifting transformer series side and in the winding circuit of the excitation transformer are used to collect the phase current (I) in real time. in ,I out ) and excitation current (I e ).

[0032] Collect the current tap position status signal of the excitation transformer tap changer.

[0033] 2. Compensation voltage calculation and target range decision A voltage-taper mapping analytical model is established. Based on the principle of electromagnetic induction and the specific winding parameters of the transformer, this model accurately describes the number of turns (N) connected to the secondary side of the excitation transformer. eff The functional relationship between the output compensation voltage vector (ΔU) and the output compensation voltage vector is: ΔU = f(N) eff ).

[0034] The closed-loop control module calculates the required voltage difference ΔU to be compensated based on the acquired voltage phasors from both sides. req Subsequently, based on the voltage-gap mapping model, the Newton-Raphson iterative algorithm was used to solve for the compensation voltage that is closest to ΔU. req Target effective number of turns N traget And map it to a specific tap target gear.

[0035] 3. Loop Closure Security Verification Before issuing the gear adjustment command, the loop-closing control module initiates a safety verification process. First, based on the Thevenin equivalent circuit model of the systems on both sides of the loop-closing point (including equivalent power supply and equivalent impedance), and in conjunction with the target compensation voltage, the maximum inrush current that may be generated during the loop-closing operation is predicted.

[0036] The predicted inrush current value is compared with the circuit breaker's breaking capacity, and the fluctuation of the bus voltage after loop closure is assessed to see if it exceeds the allowable threshold (e.g., ±10%). Subsequent adjustment commands are only permitted to be executed if all safety constraints are met.

[0037] The differential protection module is used to calculate the electrical balance differential current and magnetic balance differential current based on the collected current and tap position information, correct the equivalent ratio and proportional balance coefficient of the current transformer according to the tap position change, and perform preliminary fault identification of differential current by combining ratio braking and harmonic braking criteria.

[0038] The differential protection module receives real-time gear change warning signals from the closed-loop control module. Based on the target gear to be switched to, the module dynamically calculates the equivalent transformation ratio correction coefficient K of the current transformer (CT). corr .

[0039] The correction factor is applied to all relevant current sampling values ​​to correct changes in CT transmission characteristics caused by tap changes in real time, thereby suppressing unbalanced current at the source of differential current calculation. The balance factor is also adjusted synchronously with the tap position.

[0040] The differential protection module calculates two types of differential currents to form a dual main protection: Electrical balance differential protection: Based on Kirchhoff's current law (KCL), it sums the incoming and outgoing currents of each phase winding on the primary side of the series transformer (ΣI = I). in + I out In the absence of internal faults, ΣI should be approximately zero.

[0041] Magnetic balance differential protection: Based on the ampere-turn balance principle, a magnetomotive force balance equation is established between the series transformer and the excitation transformer. By comparing the current reflecting the magnetomotive force (such as the excitation current and the converted series side current), magnetic circuit imbalance faults, including inter-turn short circuits, are sensitively detected.

[0042] Ratio braking: A ratio braking equation with a piecewise linear characteristic is adopted. When the braking current (usually the maximum value of the current on each side) increases, the differential operating current threshold is raised to prevent false tripping caused by external faults or inrush current.

[0043] Harmonic braking: Real-time harmonic analysis is performed on the differential current. When the second harmonic content in the differential current exceeds the set threshold (preferably 20%), it is determined to be an inrush current, and the differential protection output is immediately blocked to prevent false tripping.

[0044] The harmonic braking criterion can be expressed as: ,in, This represents the effective value or amplitude of the fundamental component of the differential current. This represents the effective value or amplitude of the second harmonic component of the differential current. This is the harmonic braking ratio threshold.

[0045] The integrated processing unit is used to simultaneously send a tap change warning signal when outputting tap adjustment commands, update the current correction parameters in advance and enable anti-disturbance logic based on the warning signal; if the preliminary fault diagnosis detects an internal fault and the differential current reaches the action threshold, a blocking command is sent and the circuit breaker is triggered to trip, while all adjustment and loop closing operations are stopped.

[0046] The closed-loop control and differential protection modules form a closed-loop cooperative system through a bidirectional signal link, such as... Figure 1 and Figure 3 As shown: Feedforward coordination (control → protection): The closed-loop control module sends a warning signal to the differential protection module simultaneously with the gear adjustment command. Based on this, the protection module updates its correction parameters in advance and briefly activates anti-disturbance logic during the adjustment process to improve anti-interference capability and avoid maloperation of the protection due to switching transients.

[0047] Feedback Interlocking (Protection → Control): The differential protection module is assigned the highest priority. Once its internal fault criterion (electrical balance or magnetic balance) meets the operating conditions and harmonic braking has not been activated, it immediately sends an emergency interlocking command to the loop control module and simultaneously issues a trip command to the circuit breaker. Upon receiving the interlocking command, the control module immediately terminates any ongoing regulation processes.

[0048] Fault Diagnosis and Recovery: If the differential current remains abnormal but does not reach the trip threshold, the system initiates a diagnostic program to analyze waveform characteristics to identify the fault type (such as minor inter-turn faults, external interference, etc.). Based on the judgment results, a collaborative decision can be made for the control module to attempt fine-tuning to eliminate the abnormal operating condition, or for the protection module to prepare to execute a trip.

[0049] The fault diagnosis and recovery module is used to identify the fault type by combining voltage and current waveform characteristics when the differential current does not reach the trip threshold but continues to be abnormal; based on the fault type, it selects to perform tap position fine-tuning operation to eliminate the abnormality or the control system enters protection standby state and prepares to trip.

[0050] Specifically, fault diagnosis and recovery: If the differential current remains abnormal but does not reach the trip threshold, the system initiates a diagnostic program to analyze waveform characteristics to identify the fault type (such as minor inter-turn faults, external interference, etc.). Based on the judgment results, a collaborative decision can be made for the control module to attempt fine-tuning to eliminate the abnormal operating condition, or for the protection module to prepare to execute a trip.

[0051] System hardware integration details are as follows Figure 5 As shown, the functions of the aforementioned closed-loop control module and differential protection module can be integrated into a single integrated processing unit. The core of this unit includes a high-performance multi-core processor, a high-speed ADC sampling circuit, a digital signal processor (DSP), and a programmable logic device (FPGA). All data acquisition, model calculation, and logical judgment are completed within the unit, greatly reducing communication latency and interface complexity between traditional discrete devices, and improving system response speed and reliability.

[0052] In summary, this embodiment deeply integrates precise loop-closing adjustment and adaptive differential protection at the information, logic, and hardware levels to construct a fast-responding, safe, and reliable closed-loop control system. It not only solves the problem of control and protection disconnection during the loop-closing process of traditional phase-shifting transformers, but also effectively overcomes the impact of tap change on protection reliability through tap position adaptive correction, providing a complete and high-performance solution for flexible loop-closing operation in distribution networks.

[0053] Example 2 This embodiment is based on the above embodiment 1 and discloses a loop control and differential protection method for a single-core phase-shifting transformer based on single voltage source excitation. The single-core phase-shifting transformer adopts a single voltage source excitation topology, including a series transformer group and an excitation transformer group.

[0054] The topology of a single-core phase-shifting transformer based on single-voltage source excitation is a series-coupled structure. It includes a series transformer bank and an excitation transformer bank. The primary winding of the excitation transformer is star-connected, with its neutral point directly grounded. The ungrounded terminals of each phase winding on its primary side are directly connected to the center taps of the corresponding phase primary windings of the series transformers to obtain the excitation source from the system phase voltage. The secondary side of the excitation transformer is a tapped winding, and its output terminals are connected to the secondary windings of the series transformers according to a specific phase sequence.

[0055] Single-core phase-shifting transformers need to be equipped with magnetic balance differential protection. This protection is based on the principle of ampere-turn balance and magnetomotive force balance between the series transformer and the excitation transformer. It is used to sensitively detect magnetic circuit imbalance faults, including inter-turn short circuits in the windings.

[0056] The electrical balance differential protection, based on the principle of current balance at the nodes of the primary winding of the series transformer, is used to quickly disconnect grounding and phase-to-phase faults in its windings and leads. The magnetic balance differential protection, based on the principle of magnetomotive force balance between the series transformer and the excitation transformer, is used to sensitively detect magnetic circuit imbalance faults, including inter-turn short circuits in the windings. Together, they constitute the main protection criteria of the differential protection module in the integrated method.

[0057] The methods specifically include: Step S1: Collect real-time data of the distribution network, including voltage phasors on both sides of the loop closure point, phase currents flowing through the input and output terminals of the single-core phase-shifting transformer, excitation current of the excitation transformer, and the current tap position of the secondary side tap of the excitation transformer.

[0058] The voltage phasors on both sides of the loop closure point are collected by voltage transformers configured on the busbars on both sides of the loop closure point; the phase currents flowing through the input and output terminals of the single-core phase-shifting transformer and the excitation current of the excitation transformer are collected by current transformers configured at the input and output terminals of the single-core phase-shifting transformer and the winding circuit of the excitation transformer.

[0059] Step S2: Based on the voltage phasors on both sides of the loop closing point, calculate the voltage amplitude and phase angle that need to be compensated, establish the voltage-taper mapping relationship, calculate the target number of turns connected to the secondary coil of the excitation transformer, map it to the target tap position, predict the loop closing impact current based on the Thevenin equivalent model, and generate the tap position adjustment command after safety verification.

[0060] The voltage-taper mapping relationship specifically refers to the deterministic correspondence established in the closed-loop control module between the number of turns or taps connected to the secondary side of the excitation transformer and the compensation voltage vector output by the single-core phase-shifting transformer. This mapping relationship is established based on the specific topology of a single-core phase-shifting transformer with single-voltage source excitation and the law of electromagnetic induction.

[0061] The target number of turns connected to the secondary coil of the excitation transformer is determined by an iterative optimization algorithm, which can be either the Newton-Raphson method or the gradient descent method.

[0062] The Thevenin equivalent model is constructed based on the equivalent power supply and equivalent impedance of the system on both sides of the loop closing point; the criteria for safety verification are: the amplitude of the loop closing inrush current does not exceed the circuit breaker breaking capacity, and the bus voltage fluctuation caused by the loop closing operation does not exceed the set threshold.

[0063] Step S3: Based on the current of each phase and the current tap position, calculate the electrical balance and magnetic balance differential current. Based on the tap position adaptive correction algorithm, correct the equivalent ratio and proportional balance coefficient of the current transformer according to the tap position change. Calculate the electrical balance differential current and magnetic balance differential current in parallel using the corrected differential current, and perform preliminary fault identification of the differential current by combining the ratio braking and harmonic braking criteria.

[0064] The electrical balance differential current is calculated based on Kirchhoff's current law, while the magnetic balance differential current is calculated based on the ampere-turn balance relationship of electromagnetic induction.

[0065] The specific criteria for ratio braking and harmonic braking are as follows: Ratio braking criterion: in, For differential current, For braking current, Minimum operating current threshold, Where K is the inflection point current and K is the braking coefficient; Harmonic braking criterion: When the second harmonic content in the differential current exceeds the set ratio, the differential protection output is blocked; the set ratio range is 15% to 25%.

[0066] Step S4: While outputting the tap change adjustment command, send a gear change warning signal. Based on the gear change warning signal, update the current correction parameters in advance and enable the anti-disturbance logic. If the preliminary fault judgment detects an internal fault and the differential current reaches the action threshold, send a blocking command and trigger the circuit breaker to trip, while stopping all adjustment and loop closing operations.

[0067] Step S5: If the differential current does not reach the trip threshold but the initial fault judgment is still abnormal, the fault type is identified by combining the voltage and current waveform characteristics; according to the fault type, the tap position fine-tuning operation is performed to eliminate the abnormality or enter the protection standby state and prepare for tripping.

[0068] The process of identifying fault types by combining voltage and current waveform characteristics includes: extracting the distortion characteristics, amplitude variation patterns, and phase shift characteristics of voltage and current waveforms, and combining the characteristic information to distinguish between adjustable and eliminable abnormal operating conditions and potential internal faults of the transformer.

[0069] Example 3 Based on Embodiment 1, this embodiment provides an electronic device, including: one or more processors and a memory, wherein the memory stores one or more programs, the one or more programs including instructions for executing the aforementioned method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation.

[0070] At the hardware level, the electronic device includes a processor, internal bus, network interface, memory, and non-volatile memory, and may also include other hardware required for business operations. The processor reads the corresponding computer program from the non-volatile memory into memory and then runs it to implement the above-mentioned method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation. Of course, in addition to software implementation, this invention does not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to individual logic units, but can also be hardware or logic devices.

[0071] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0072] Computer-readable media include both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for closed-loop control and differential protection of a single-core phase-shifting transformer based on single-voltage-source excitation, wherein the single-core phase-shifting transformer adopts a single-voltage-source excitation topology, including a series transformer bank and an excitation transformer bank, characterized in that, The method includes: Collect real-time data of the distribution network, including voltage phasors on both sides of the loop closure point, phase currents flowing through the input and output terminals of the single-core phase-shifting transformer, excitation current of the excitation transformer, and the current tap position of the secondary side tap of the excitation transformer. Based on the voltage phasors on both sides of the loop closing point, the voltage amplitude and phase angle to be compensated are calculated, a voltage-taper mapping relationship is established, and the target number of turns connected to the secondary coil of the excitation transformer is calculated and mapped to the target tap position. Based on the Thevenin equivalent model, the loop closing impact current is predicted, and after safety verification, a tap position adjustment command is generated. Based on the current of each phase and the current tap position, calculate the electrical balance and magnetic balance differential current. Based on the tap position adaptive correction algorithm, correct the equivalent ratio and proportional balance coefficient of the current transformer according to the tap position change. Calculate the electrical balance differential current and magnetic balance differential current in parallel using the corrected differential current, and perform preliminary fault identification of the differential current by combining the ratio braking and harmonic braking criteria. While outputting the tap change adjustment command, a tap position change warning signal is sent. Based on the tap position change warning signal, the current correction parameters are updated in advance and the anti-disturbance logic is enabled. If the preliminary fault identification detects an internal fault and the differential current reaches the action threshold, a blocking command is sent and the circuit breaker is tripped, while all adjustment and loop closing operations are stopped. If the differential current does not reach the tripping threshold but the preliminary fault identification remains abnormal, the fault type is identified by combining voltage and current waveform characteristics. According to the fault type, a tap position fine-tuning operation is performed to eliminate the abnormality or enter the protection standby state and prepare for tripping.

2. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The voltage phasors on both sides of the loop closure point are collected by voltage transformers configured on the busbars on both sides of the loop closure point; the phase currents flowing through the input and output terminals of the single-core phase-shifting transformer and the excitation current of the excitation transformer are collected by current transformers configured at the input and output terminals of the single-core phase-shifting transformer and the winding circuit of the excitation transformer.

3. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The voltage-level mapping relationship is established based on the topology, winding parameters, and electromagnetic induction law of a single-core phase-shifting transformer with single-voltage source excitation.

4. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The target number of turns connected to the secondary coil of the excitation transformer is determined by an iterative optimization algorithm, which may be the Newton-Raphson method or the gradient descent method.

5. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The Thevenin equivalent model is constructed based on the equivalent power supply and equivalent impedance of the system on both sides of the loop closing point; the judgment criteria for the safety verification are: the amplitude of the loop closing inrush current does not exceed the circuit breaker breaking capacity, and the bus voltage fluctuation caused by the loop closing operation does not exceed the set threshold.

6. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The electrical balance differential current is calculated based on Kirchhoff's current law, and the magnetic balance differential current is calculated based on the ampere-turn balance relationship of electromagnetic induction.

7. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The specific criteria for ratio braking and harmonic braking are as follows: Ratio braking criterion: in, For differential current, For braking current, Minimum operating current threshold, Where K is the inflection point current and K is the braking coefficient; Harmonic braking criterion: When the second harmonic content in the differential current exceeds a set ratio, the differential protection output is blocked; the set ratio ranges from 15% to 25%.

8. The method for loop control and differential protection of a single-core phase-shifting transformer based on single-voltage source excitation according to claim 1, characterized in that, The process of identifying fault types by combining voltage and current waveform characteristics includes: extracting the distortion characteristics, amplitude variation patterns, and phase shift characteristics of voltage and current waveforms, and combining the characteristic information to distinguish between adjustable and eliminable abnormal operating conditions and potential internal faults of the transformer.

9. A loop control and differential protection system for a single-core phase-shifting transformer based on single-voltage-source excitation, wherein the single-core phase-shifting transformer adopts a single-voltage-source excitation topology, including a series transformer bank and an excitation transformer bank, characterized in that, The system includes: a data acquisition module, a loop control module, a differential protection module, an integrated processing unit, and a fault diagnosis and recovery module, all communicatively connected to the single-core phase-shifting transformer; wherein... The primary winding of the series transformer group is directly connected to the lines on both sides of the loop point of the distribution network, and the secondary winding serves as the voltage compensation output winding; the primary winding of the excitation transformer group adopts a star connection, the neutral point is directly grounded, and the ungrounded terminals of each phase are respectively connected to the center tap of the corresponding phase primary winding of the series transformer, thereby obtaining single-phase excitation power from the system; the secondary side of the excitation transformer is an adjustable winding with multiple tap positions. The output terminal of the secondary winding of the excitation transformer is connected in series with the secondary winding of the series transformer according to a preset phase sequence rule, thereby injecting a compensation voltage with controllable amplitude and phase into the secondary side of the series transformer; the topology can change the vector of the injected compensation voltage by adjusting the tap position of the secondary winding of the excitation transformer, thereby achieving decoupling adjustment of the voltage amplitude and phase on both sides of the loop point. The data acquisition module is used to collect the voltage phasors on both sides of the distribution network loop point, the phase currents at the input and output terminals of the single-core phase-shifting transformer, the excitation current of the excitation transformer, and the current tap position of the secondary side tap of the excitation transformer in real time, and synchronize the collected data to the other modules. The loop-closing control module is used to calculate the voltage amplitude and phase angle to be compensated based on the voltage phasors on both sides of the loop-closing point, establish a voltage-taper mapping relationship, and solve for the target number of turns connected to the secondary coil of the excitation transformer, which is then mapped to the target tap position. Based on the Thevenin equivalent model, the loop-closing inrush current is predicted, and after safety verification, tap adjustment commands are generated and output. The differential protection module is used to calculate the electrical balance differential current and magnetic balance differential current based on the collected current and tap position information, correct the equivalent ratio and proportional balance coefficient of the current transformer based on the tap position change, and perform preliminary differential current fault identification by combining ratio braking and harmonic braking criteria. The integrated processing unit is used to simultaneously send a gear change warning signal when outputting tap adjustment command, update the current correction parameters in advance and enable anti-disturbance logic according to the warning signal; if the preliminary fault judgment detects an internal fault and the differential current reaches the action threshold, it sends a lockout command and triggers the circuit breaker to trip, while stopping all adjustment and loop closing operations. The fault diagnosis and recovery module is used to identify the fault type by combining voltage and current waveform characteristics when the differential current does not reach the trip threshold but continues to be abnormal; and selects to perform tap position fine-tuning operation to eliminate the abnormality or control the system to enter the protection standby state and prepare to trip according to the fault type.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the single-core phase-shifting transformer loop-closing control and differential protection method based on single voltage source excitation as described in any one of claims 1-8.

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