GIC blocking method under geomagnetic disturbance based on transformer real-time reactive monitoring

Abstract

The invention discloses a GIC blocking method under geomagnetic disturbance based on real-time reactive monitoring of a transformer. The method comprises the following steps: judging whether an estimated GIC amplitude meets a first preset threshold condition or not; if so, taking the estimated GIC amplitude as a final GIC amplitude; if not, obtaining the equivalent inductance of the autotransformer, and based on an Lmef-Idc nonlinear curve established through a three-dimensional electromagnetic field-circuit coupling simulation technology, carrying out backstepping and obtaining a final GIC amplitude corresponding to the equivalent inductance at the moment; on the basis of a controllable resistance type dynamic blocking and closed-loop control strategy monitored and fed back in real time, whether the GIC amplitude meets a second preset threshold value condition or not is judged, and when the second preset threshold value condition is not met, an adjustable resistor in the GIC blocking device is adjusted till the obtained final GIC amplitude meets the second preset threshold value condition. According to the method, the problem that GIC blocking of the autotransformer under geomagnetic disturbance cannot be effectively achieved through an existing method is solved.

Description

Technical Field

[0001] This invention relates to the intersection of power grid disaster prevention and mitigation, electromagnetic compatibility, and autotransformer protection technologies, and particularly to a GIC blocking method under geomagnetic disturbances based on real-time reactive power monitoring of transformers. Background Technology

[0002] Intense geomagnetic disturbances induce quasi-DC GIC on the Earth's surface, which flows into the power grid through the neutral point of the autotransformer, causing half-wave saturation of the autotransformer core. This can lead to distortion of the autotransformer's excitation current, a surge in reactive power, and the generation of a large number of harmonics. It may also cause relay malfunctions, cascading failures, and ultimately result in widespread power outages.

[0003] Existing technologies for defending against geomagnetic induced currents mainly revolve around two aspects: "monitoring" and "blocking".

[0004] At the level of monitoring geomagnetic induced current, based on the structure and physical principles of autotransformers, and by analyzing the autotransformer saturation model, the equivalent excitation inductance and magnetic flux relationship of the autotransformer model under GIC intrusion are linearized. A fixed proportional coefficient is derived between the amplitude of geomagnetic induced current and the reactive power increment generated by the autotransformer. Then, by using synchronous phasor measurement units (PMUs) widely deployed in the power grid to measure reactive power in real time, the intensity of the GIC intrusion is deduced in reverse, providing a basis for subsequent defense decisions.

[0005] In terms of GIC blocking technology, the main approach is to connect a capacitor or resistor in series at the neutral point to increase the impedance of the geomagnetic induced current loop flowing into the autotransformer, thereby reducing the amplitude of GIC.

[0006] Although the aforementioned technologies have been applied in practice, this paper points out significant problems and risks: First, the monitoring and evaluation methods suffer from accuracy deficiencies. The traditional K-value method is based on a simplified linear magnetization model. However, the BH curve of the autotransformer core material is nonlinear, especially in the deep saturation region, where its equivalent inductance drops sharply. At this point, the ratio of GIC to reactive power increment changes significantly. This measurement result based on inaccurate estimation will lead to inaccurate GIC prediction, potentially resulting in insufficient or excessive protection, failing to effectively protect critical equipment, or adding extra burden to the system when unnecessary.

[0007] Secondly, there are negative impacts and secondary risks associated with traditional blocking techniques: While series fixed resistors can reduce GIC, they can affect the grounding configuration of the power system and the operating characteristics of relay protection, potentially leading to new safety hazards; series capacitor methods can alter the GIC distribution path of the entire power grid. Blockage at one node may cause GIC to flow to other nearby autotransformers or substations, resulting in a regional increase in GIC levels, or even more serious consequences. Summary of the Invention

[0008] This invention provides a method for blocking GIC under geomagnetic disturbance based on real-time reactive power monitoring of transformers, in order to overcome the above-mentioned technical problems.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows: A method for blocking GIC under geomagnetic disturbances based on real-time reactive power monitoring of transformers specifically includes the following steps: S1: Under geomagnetic disturbance, a synchronous phasor measurement unit is used to monitor the reactive power disturbance on the high-voltage side of the autotransformer in the established GIC isolation device in real time, and use it as an indirect characterization of geomagnetic induced current intrusion. S2: Based on K The value method estimates the GIC amplitude of the intrusion into the autotransformer based on the reactive power disturbance by introducing a fixed proportional coefficient. ; S3: Determine the estimated GIC amplitude Does it meet the first preset threshold condition? If satisfied, the estimated GIC amplitude will be... As the final GIC amplitude ; If the conditions are not met, then obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. And based on the simulation technology established by three-dimensional electromagnetic field circuit coupling, L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude ; S4: Determine the final GIC amplitude Does the second preset threshold condition meet? If satisfied, proceed to step S5; otherwise, proceed to step S6. S5: Monitor and confirm in real time whether geomagnetic disturbances still exist; If so, then by continuously looping through steps S1 to S4, using reactive power disturbance feedback from the synchronous phasor measurement unit combined with the adjustment of the adjustable resistor, the final GIC amplitude is obtained. The second preset threshold condition is met to ensure that GIC is always suppressed, thereby achieving GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of autotransformer; otherwise, the loop ends. S6: Based on empirical values, adjust the adjustable resistor in the GIC blocking device and repeat S1 to S4.

[0010] Furthermore, the GIC blocking device described in S1 includes an autotransformer, a controllable switch, and a first disconnect switch. Adjustable resistor and second disconnect switch ; The high-voltage side of the autotransformer is connected to a synchronous phasor measurement unit; The low-voltage side terminals of the autotransformer, one end of the controllable switch, and the first disconnect switch One end is connected; the first disconnect switch The other end is connected to one end of the adjustable resistor, and the other end of the adjustable resistor is connected to the second disconnect switch. One end is connected to the second disconnect switch. The other end is grounded to the other end of the controllable switch.

[0011] Furthermore, in S2 based on K The value method estimates the GIC amplitude of the intrusion into the autotransformer based on the reactive power disturbance by introducing a fixed proportional coefficient. Its expression is: (1) In the formula: This represents the total reactive power loss of the autotransformer. This represents the reactive power loss of an autotransformer under normal conditions. This represents the reactive power consumed by the magnetizing inductance of the autotransformer under geomagnetic disturbance. Indicates the primary voltage of the autotransformer U 1. Peak voltage maintained during GIC intrusion; N Indicates the number of turns in the primary winding of the transformer; This represents the peak value of the sinusoidal AC magnetic flux corresponding to the autotransformer under rated operating conditions. This represents the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. This represents the saturation time duty cycle of an autotransformer within one power frequency cycle. K Indicates based on K The fixed proportionality coefficient introduced by the value method.

[0012] Furthermore, step S3 specifically includes the following steps: S31: Determine the estimated GIC amplitude Does it meet the first preset threshold condition? The first preset threshold condition is ,and (2) In the formula: This represents the inductance in the non-saturation region of an autotransformer; Indicates the magnetic flux at the knee point; This represents the AC magnetic flux of an autotransformer under normal operating conditions. This represents the critical current at which the autotransformer's operating point enters the saturation region. If satisfied, execute S32; otherwise, execute S33. S32: Estimate the GIC amplitude As the final GIC amplitude ; S33: Obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. And based on the simulation technology established by three-dimensional electromagnetic field circuit coupling, L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude .

[0013] Furthermore, step S33 specifically includes the following steps: S331: Obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. for: (3) In the formula: L ( t () represents the time-varying value of the magnetizing inductance of the transformer under geomagnetic disturbance; Indicates a time period; S332: Let the saturation time duty cycle of the autotransformer within one power frequency cycle be... Then the saturation angle is At this point, the magnetic flux relationship satisfies: ,in This represents the estimated GIC amplitude. The generated DC magnetic flux; S333: When the operating point of the autotransformer is in the core saturation region, combined with S332, the excitation current is... Defined as: (4) (5) In the formula: i n This represents the peak value of the rated excitation current, i.e. ; This represents the bias DC current component caused by DC magnetic flux. The excitation current portion representing the magnetic flux contribution in the saturation region; S334: Substitute equation (5) into equation (4) and adjust the excitation current. Performing Fourier decomposition yields: (6) S335: Based on three-dimensional electromagnetic field-circuit coupling simulation technology, equation (3) is rewritten as: (7) In the formula: h This indicates the simulation step size for the magnetic circuit coupling of the autotransformer; Represents the first [number]th ... k The instantaneous value of the inductance over a time step; Through simulation analysis under different DC current values, the equivalent inductance corresponding to different DC current values ​​is obtained by equation (7). This leads to the establishment of a system for characterizing equivalent inductance. With GIC amplitude Relationship L mef - I dc Nonlinear curves; S336: Based on the above L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude .

[0014] Beneficial effects: This invention provides a method for blocking GIC under geomagnetic disturbances based on real-time reactive power monitoring of transformers. By constructing a hierarchical evaluation strategy based on the coupling relationship between GIC, equivalent inductance, and reactive power under geomagnetic disturbances, it determines the estimated GIC amplitude. Does the first preset threshold condition meet? If so, then the estimated GIC amplitude will be... As the final GIC amplitude If not satisfied, obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. And based on the simulation technology established by three-dimensional electromagnetic field circuit coupling, L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude This significantly improves the accuracy of GIC monitoring and evaluation, thus avoiding misjudgments. A controllable resistive dynamic blocking and closed-loop control strategy based on real-time monitoring feedback was designed to determine the GIC amplitude. Whether the second preset threshold condition is met, and if not, adjusting the adjustable resistor in the GIC blocking device until the final GIC amplitude is obtained. It meets the second preset threshold condition; it can achieve precise and dynamic GIC suppression, avoiding the secondary risks of traditional blocking methods. This invention constructs a fusion protection system integrating "real-time monitoring, safety assessment, and dynamic control," and can ensure the operational safety of the power grid and equipment safety during geomagnetic disturbance events by clearly defining the safe range of transformer operating status, preventing voltage collapse caused by collective reactive power disturbances. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the GIC blocking method under geomagnetic disturbance based on real-time reactive power monitoring of autotransformer according to the present invention. Figure 2 This is a core block diagram of the method described in this embodiment; Figure 3 This is a schematic diagram of the GIC blocking device in this embodiment; Figure 4 This is a schematic diagram of the DC bias magnetization working state of the transformer core in this embodiment; Figure 5 This is a schematic diagram of the equivalent Γ-type model of the transformer in this embodiment; Figure 6 This is a schematic diagram of DC bias magnetization of the transformer core using a two-segment magnetization curve in this embodiment. Figure 7 This is a schematic diagram of the equivalent excitation branch of the transformer in this embodiment; Figure 8 This is a schematic diagram of the circuit model in this embodiment; Figure 9 This is a simulation diagram of the magnetic field model in this embodiment; Figure 10 This is a schematic diagram of a 1 / 4 finite element model in this embodiment; Figure 11 This is a finite element mesh diagram in this embodiment; Figure 12 This is the BH curve diagram for silicon steel sheet grade 27ZH095 in this embodiment; Figure 13 The diagram shows the excitation current and instantaneous inductance when the DC current is 5, 10, and 50A in this embodiment. Figure 14 This is a diagram showing the relationship between the transformer's equivalent inductance and DC current in this embodiment; Figure 15 This is a diagram showing the function relationships in this embodiment; Figure 16 This is a single-line diagram of the GIC-Benchmark power grid in this embodiment; Figure 17 This is a graph showing the experimental results of comparing the GIC (Eastward 1V / km GEF) of each substation before and after the blocking device was put into operation in this embodiment. Figure 18 This figure shows the experimental results of comparing the GIC (GEF) of each substation before and after the blocking device was put into operation in this embodiment (northbound 1V / km GEF). Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This embodiment provides a method for blocking GIC under geomagnetic disturbances based on real-time reactive power monitoring of transformers, such as... Figures 1 to 2 As shown, the specific steps include: S1: Under geomagnetic disturbance, a synchronous phasor measurement unit is used to monitor the reactive power disturbance on the high-voltage side of the autotransformer in the established GIC isolation device in real time, and this is used as an indirect characterization of geomagnetic induced current intrusion. Specifically, such as... Figure 3 As shown, the GIC blocking device includes an autotransformer, a controllable switch, and a first disconnect switch. Adjustable resistor and second disconnect switch The high-voltage side of the autotransformer is connected to a synchronous phasor measurement unit; the low-voltage side terminals of the autotransformer are connected to one end of a controllable switch and the first disconnect switch. One end is connected; the first disconnect switch The other end is connected to one end of the adjustable resistor, and the other end of the adjustable resistor is connected to the second disconnect switch. One end is connected to the second disconnect switch. The other end is grounded to the other end of the controllable switch.

[0019] S2: Based on K The value method estimates the GIC amplitude of the intrusion into the autotransformer based on the reactive power disturbance by introducing a fixed proportional coefficient. Specifically: This embodiment considers the GIC amplitude under geomagnetic disturbances. This will intrude into the autotransformer, causing the autotransformer core to saturate and the magnetizing inductance to decrease rapidly. At this point, the total reactive power loss of the autotransformer will decrease. Q Meeting It increases rapidly. Assume the primary voltage of the autotransformer... U 1. Maintain peak performance during GIC intrusion U m Given the rated power frequency AC voltage, neglecting core hysteresis and eddy current losses, the formula for calculating the reactive power loss of an autotransformer under DC bias is: (1) In the formula: U 1 indicates the effective value of the rated fundamental frequency voltage; I 1 represents the effective value of the fundamental frequency current obtained by Fourier decomposition of the waveform; according to Figure 6 As shown, it can convert the excitation current of the autotransformer Decompose the excitation current Divided into DC component, i.e., GIC amplitude RMS value of fundamental frequency component I 1. Two parts, then (2) Substituting equation (2) into equation (1), we can obtain the relationship between the reactive power loss of the autotransformer and the duty cycle as follows: (3) This embodiment, as shown in equation (3), can achieve the following: Q Decompose into reactive power loss under normal conditions Q 0 plus the reactive power consumed by the magnetizing inductance Its corresponding I 1 has two parts; at the same time, it can be known from equation (3) that the intrusion into the autotransformer under geomagnetic disturbance is The reactive power loss of an autotransformer is only related to the flux angle. θ The remaining parameters are constants. Therefore, if the intermediate function of the reactive power loss of the autotransformer can be obtained... use intermediate functions This means that it is possible to establish the relationship between reactive power and direct current. The relationships between them. For example... Figure 15 The function shown is... and The graph shows that the two curves are... θ The values ​​below a certain value exhibit almost identical trends, therefore it is assumed that a constant exists. Make the function The percentage of the maximum difference within a certain interval is less than or equal to And the length of the interval The larger the better, the specific mathematical expression is: (4) The parameters in this embodiment are obtained through calculation. n The optimal value is 1.9, at which point... =48.5°, that is, when When the angle is less than or equal to 48.5°, it can be considered that... Plot the relationship between each function and the magnetic flux angle, such as... Figure 15 As shown. Because it makes θ >48.5° The value is very large, and it rarely exists in reality, so I will not go into further detail here.

[0020] In this embodiment, the bias DC current component caused by DC magnetic flux is ignored. ,based on K The value method estimates the GIC amplitude of the intrusion into the autotransformer based on the reactive power disturbance by introducing a fixed proportional coefficient. Its expression is: (5) In the formula: This represents the total reactive power loss of the autotransformer. This represents the reactive power loss of an autotransformer under normal conditions. This represents the reactive power consumed by the magnetizing inductance of the autotransformer under geomagnetic disturbance. Indicates the primary voltage of the autotransformer U 1. Peak voltage maintained during GIC intrusion; N Indicates the number of turns in the primary winding of the transformer; This represents the peak value of the sinusoidal AC magnetic flux corresponding to the autotransformer under rated operating conditions. This represents the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. This represents the saturation time duty cycle of an autotransformer within one power frequency cycle. Indicates based on K The fixed proportionality coefficient introduced by the value method. In this embodiment, the constant 0.95 in equation (5) is the traditional K Fixed proportional coefficient in the value method K In simple calculations, it can be assumed that... and Q There is a linear relationship, and the results are calculated using this method. K Value compared to traditional K The value method uses different core structures to obtain more accurate empirical values.

[0021] S3: Determine the estimated GIC amplitude Does the first preset threshold condition meet? If so, then the estimated GIC amplitude will be... As the final GIC amplitude If not satisfied, obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. And based on the simulation technology established by three-dimensional electromagnetic field circuit coupling, L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude The specific steps include: Under geomagnetic disturbances, the induced current-induced current-carrying capacity (GIC) in the power grid flows into the autotransformer. Since the frequency of GIC (0.0001Hz-0.01Hz) is a low-frequency component compared to the power frequency, it can be assumed that GIC remains constant within each power frequency cycle, i.e., it is a direct current. . The generated DC magnetic flux AC magnetic flux superimposed on normal operating conditions Above, the total magnetic flux will exceed the knee point magnetic flux. The autotransformer operates in the saturation region of the nonlinear magnetization curve, leading to half-wave saturation of the core and distortion of the excitation current, resulting in a spiked wave. Simultaneously, the equivalent inductance dynamically changes with the instantaneous value of the magnetic flux within the period. When the transformer's operating point transitions to the saturation region, leakage flux closes through the oil tank and the air gap between the core and the oil tank, thus reducing the equivalent inductance. The equivalent inductance decreases significantly; when the operating point of the autotransformer returns to the core saturation region, the equivalent inductance recovers accordingly, such as... Figure 4 As shown.

[0022] In other words, the magnetizing inductance of a transformer under geomagnetic disturbance is not a constant value, but a time-varying value. L ( t The equivalent inductance of a transformer over one cycle for: (6) set up Equivalent inductance The corresponding transformer magnetizing susceptance is then represented by the transformer equivalent Γ-type model as follows: Figure 5 As shown, this allows for the further calculation of the reactive power increment of the transformer under geomagnetic disturbances. The equivalent inductance of the transformer is then established. With GIC amplitude The quantitative correspondence between them is the key to calculating the reactive power disturbance of autotransformers and monitoring and maintaining the stable operation of the power grid under geomagnetic disturbances.

[0023] This embodiment aims to facilitate a quick and easy calculation of the transformer's equivalent inductance. A relatively simple method is to [the transformer core]. The curves are linearized, and the magnetization curves before and after core saturation are represented by two straight lines, such as... Figure 6 As shown. In Figure 6 In the middle, the magnetic flux of the iron core The peak value under rated operating conditions is sinusoidal alternating magnetic flux and DC current The generated DC magnetic flux The superposition, that is ,in The angular frequency is the power frequency. Ignoring leakage inductance, the slopes of the straight lines at both ends represent the inductance in the unsaturated region of the transformer. and saturation region inductance L s Under geomagnetic disturbances, the excitation inductance exhibits the following changes: In the absence of geomagnetic disturbances or when the GIC amplitude is very small, if the peak value of the superimposed magnetic flux... The magnetic flux does not exceed the knee point, the iron core is unsaturated, and the transformer inductance remains constant before this point. The critical DC for: (7) In the formula: This represents the inductance in the non-saturation region of an autotransformer; Indicates the magnetic flux at the knee point; This represents the AC magnetic flux of an autotransformer under normal operating conditions. This represents the critical current at which the autotransformer's operating point enters the saturation region. S31: Determine the estimated GIC amplitude Does it meet the first preset threshold condition? Specifically, safety assessment and status classification: based on the obtained... The operating state of the autotransformer is divided into three zones: the safe zone ( < ): The autotransformer is not saturated and no intervention is required; Warning / Action Zone ( ≤ ≤ 1.5 ): Entering the saturation zone, triggering an early warning and preparing for intervention; Danger / Execution Zone ( >1.5 ): Deep saturation, immediately execute autotransformer blocking operation; In this embodiment, the first preset threshold condition is defined as: ; If satisfied, execute S32; otherwise, execute S33. S32: Estimate the GIC amplitude As the final GIC amplitude ; S33: Obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. And based on the simulation technology established by three-dimensional electromagnetic field circuit coupling, L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude The specific steps include: S331: Obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance. for: (8) In the formula: L ( t () represents the time-varying value of the magnetizing inductance of the transformer under geomagnetic disturbance; Indicates a time period; S332: Direct current, i.e., GIC amplitude. Exceed Afterwards, the autotransformer's operating point enters the saturation region. Let the saturation time duty cycle of the autotransformer within one power frequency cycle be... Then the saturation angle is At this point, the magnetic flux relationship satisfies: ,in This represents the estimated GIC amplitude. The generated DC magnetic flux can be derived from equation (8): (9) Therefore, the equivalent inductance of the transformer under geomagnetic disturbance can be calculated. That is, the analytical expression of the equivalent inductance of an autotransformer under the simplified analytical method; S333: According to Figure 6 When the operating point of the autotransformer is in the core saturation region, the excitation current can be controlled by combining the magnetic flux relationship in S332. Defined as: (10) (11) In the formula: i n This represents the peak value of the rated excitation current, i.e. ; This represents the bias DC current component caused by DC magnetic flux. The excitation current portion representing the magnetic flux contribution in the saturation region; In this embodiment, the autotransformer excitation branch under geomagnetic disturbance can be regarded as such as Figure 7 The circuit shown: When < The autotransformer operates in the unsaturated region. Φ < The switch is off. L m = That is, the magnetizing inductance of the transformer is equal to the core inductance; when ≥ The autotransformer operates in the saturation region. Φ ≥ When the switch is closed, it can... See as and L s The parallel value is ; S334: Substitute equation (11) into equation (10) and adjust the excitation current. Performing Fourier decomposition yields: (12) For precise calculations The quantitative relationship between them requires different methods. The DC bias simulation of the transformer is performed by substituting the current calculated from the circuit model into a preset magnetic field model as excitation. Based on the principle of energy perturbation, the instantaneous inductance value at that moment is calculated and then substituted back into the circuit model to solve for the current at the next moment. In this embodiment, the ultra-high voltage transformer, which is most susceptible to geomagnetic disturbances, is selected as the research object. The ultra-high voltage transformer is a single-phase four-column structure. Figures 8 to 9 These represent the transformer's no-load circuit model and magnetic field model, respectively, established based on its structure. The circuit model contains... It is a DC voltage source. To shorten the series resistance during the transition process, r 1. r 2 represents the resistance of the high- and medium-voltage windings. u m , u 1. u 2 represents the power frequency AC voltage source, the primary voltage of the transformer, and the secondary voltage, respectively. Since the low-voltage winding is unloaded and has no electrical connection with the high- and medium-voltage windings, the low-voltage winding is ignored in the circuit model. L 1. L 2. M 12 These represent the self-inductance of the high-voltage and medium-voltage windings, the mutual inductance of the high-voltage and medium-voltage windings, and the total inductance of the transformer. L T = L 1+ L 2+2M 12 The solution of the differential equations of the circuit model is implemented through self-programming. A magnetic field model is established based on commercial finite element software. Since the ultra-high voltage transformer has a symmetrical structure, it can be simplified by setting appropriate boundary conditions to improve calculation speed. The 1 / 4 finite element model established in this embodiment is as follows: Figure 10 As shown. The finite element model is meshed. It is worth noting that the transformer windings need to be modeled using the edge-finite element method, as shown below. Figure 11 As shown, the method reduces the error caused by severe leakage flux under the saturated state of the iron core, and its effectiveness and accuracy have been verified.

[0024] In this embodiment, the autotransformer core is made of Nippon Steel's 27ZH095 silicon steel sheet. Figure 12 The silicon steel sheet is given. B - H Curves and equivalent inductance curves, saturation magnetic flux density along the rolling direction of silicon steel sheets The value is 1.75T. Under geomagnetic disturbance, the core hysteresis of the autotransformer may cause asymmetry in the dynamic change waveform of the excitation inductance, but the effect is very small and can be ignored.

[0025] Based on the finite element model of the UHV transformer established in this embodiment, a time-domain simulation of the DC bias magnetic field circuit coupling is performed, and the following is selected: =5, 10, 50 A represent the GIC intrusion into the transformer under different geomagnetic disturbance intensities. The simulation results of the transformer's DC bias magnetization are shown below, illustrating the changes in excitation current and instantaneous inductance over one cycle. Figure 13 As shown. In the first half-cycle, the degree of distortion of the excitation current increases with... The amplitude increased, but even Even a small amplitude of the excitation current will cause the transformer core to enter the deep saturation region, resulting in a very small instantaneous inductance. In the second half-cycle, the excitation current reaches a negative peak, which will also cause a certain degree of decrease in the transformer's equivalent inductance.

[0026] S335: To determine and Based on the three-dimensional electromagnetic field circuit coupling simulation technology, the correspondence between them can be rewritten as follows: (8) In the formula: h This represents the simulation step size for the magnetic circuit coupling of the autotransformer, which is set to (0.02 / 2000) s here; Represents the first [number]th ... k The instantaneous inductance values ​​at each time step are used to calculate the DC current values ​​at 5, 10, and 50 A. The values ​​were 18.91, 11.49, and 5.68H, respectively. This embodiment obtains the equivalent inductance corresponding to different DC currents through simulation analysis under different DC currents using equation (8). This leads to the establishment of a system for characterizing equivalent inductance. With GIC amplitude Relationship L mef - I dc Nonlinear curves, such as Figure 14 As shown; S336: Based on the above L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude ; S4: Determine the GIC amplitude Does it meet the second preset threshold condition? The second preset threshold condition is... ; If satisfied, proceed to step S5; otherwise, proceed to step S6. S5: Monitor and confirm in real time whether geomagnetic disturbances still exist; If so, then by continuously looping through steps S1 to S4, using reactive power disturbance feedback from the synchronous phasor measurement unit combined with the adjustment of the adjustable resistor, the final GIC amplitude is obtained. The second preset threshold condition is met to ensure that GIC is always suppressed, thereby achieving GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of autotransformer; otherwise, the loop ends. S6: Based on empirical values, adjust the adjustable resistor in the GIC blocking device and repeat S1 to S4.

[0027] During geomagnetic disturbances, transformers subjected to excessively high amplitude GIC (Geomagnetic Intrusion) may suffer equipment damage and trigger collective reactive power interference, thereby impairing grid voltage stability. To address this issue, this embodiment analyzes and simplifies the operating state of the transformer core under DC bias, establishes a method for calculating the equivalent inductance of the transformer during geomagnetic disturbance events, and further determines the correspondence between the equivalent inductance and reactive power increment of the transformer under DC bias and GIC. This is verified through three-dimensional finite element simulation and experimental methods. This series of works shows that: 1) the traditional K-value method has errors in calculating the reactive power increment of the transformer under GIC, especially when the GIC amplitude is large; 2) the correspondence between the GIC amplitude and the reactive power increment of the transformer can be obtained more accurately through transformer core parameters; 3) during geomagnetic disturbances, the GIC amplitude flowing into the transformer can be derived by reverse calculation of the transformer reactive power measured by the PMU (Power Management Unit). Based on this, this embodiment proposes a real-time GIC blocking method based on PMU measurement. This method can effectively avoid the secondary risks caused by traditional neutral point series capacitors or resistors, realize real-time and accurate adjustment of GIC flowing into the power grid, effectively reduce voltage fluctuations caused by reactive power increments derived from transformers, and ensure the safety of equipment and power grid under geomagnetic disturbances.

[0028] To verify the effectiveness and accuracy of the method described in this embodiment, the GIC amplitude after the new device is deployed is calculated using the GIC-Benchmark standard example. For example... Figure 16 As shown, the GIC-Benchmark power grid consists of 20 busbars, 15 lines, 7 substations, 1 switching station, and 15 transformers. The blue portion represents high-voltage (345kV) transmission lines, and the red portion represents ultra-high-voltage (500kV) transmission lines. It is evident that the GIC-Benchmark includes various scenarios such as different winding connection methods, different transformer combinations, and single (double) circuit transmission lines, making it suitable for verifying the effectiveness of this novel GIC suppression measure. For ease of comparison, except for T1, it is assumed that all remaining 14 transformers have this GIC blocking device installed at their neutral points. The GIC amplitude at each node in the east direction (1V / km) before and after applying the method described in this embodiment is compared with the GIC amplitude at each node in the north direction (1V / km) before and after applying the method described in this embodiment. Figures 17 to 18 As shown, it can be observed that after applying this GIC blocking device, the GIC amplitude flowing through each substation has decreased significantly, which will not have a serious impact on the safe operation of the transformer. Furthermore, the GIC distribution in each substation is relatively balanced, and it will not pose any additional risks to the system.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of transformer, characterized in that, Specifically comprising the following steps: S1: Real-time monitoring of the reactive power disturbance of the high-voltage side of the autotransformer in the established GIC blocking device under geomagnetic disturbance by using a synchronous phasor measurement unit, and taking it as an indirect representation of geomagnetic induced current intrusion; S2: based on K The value method estimates the GIC amplitude of the self-coupling transformer according to the reactive power disturbance by introducing a fixed proportion coefficient ; S3: judging the estimated GIC amplitude whether the first preset threshold condition is met; If satisfied, the estimated GIC amplitude as the final GIC amplitude ; If not, the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance is obtained , and based on the three-dimensional electromagnetic field coupling simulation technology established L mef - I dc The nonlinear curve is deduced and the final GIC amplitude corresponding to the equivalent inductance at this time is obtained ;​ S4: judging the final GIC amplitude whether the second preset threshold condition is met; If yes, S5 is executed; if no, S6 is executed; S5: Real-time monitoring and confirmation of whether the geomagnetic disturbance still exists; If yes, then through the continuous cycle of steps S1 to S4, through the combination of the reactive power disturbance feedback of the synchronous phasor measurement unit and the adjustment of the adjustable resistance, until the final GIC amplitude is obtained The second preset threshold condition is met to ensure that the GIC is always suppressed, thereby realizing the GIC blocking under the geomagnetic disturbance based on the real-time reactive monitoring of the autotransformer; if not, the cycle is ended; S6: Adjusting the adjustable resistor in the GIC blocking device based on the empirical value, and repeatedly executing S1 to S4.

2. The method for GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of transformer according to claim 1, characterized in that, The GIC blocking device in S1 comprises a self-coupling transformer, a controllable switch, a first knife switch , an adjustable resistance and a second knife switch ; The high-voltage side of the autotransformer is connected with a synchronous phasor measurement unit; The end point of the low-voltage side of the autotransformer is connected with one end of the controllable switch and one end of the first knife switch ; the other end of the first knife switch is connected with one end of the adjustable resistance, the other end of the adjustable resistance is connected with one end of the second knife switch , and the other end of the second knife switch is grounded with the other end of the controllable switch.

3. The method for GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of transformer according to claim 2, characterized in that, In S2, based on K The value method estimates the GIC amplitude of the self-coupling transformer according to the reactive power disturbance by introducing a fixed proportion coefficient The expression is: （1） wherein: represents the total reactive power loss of the autotransformer; represents the reactive power loss of the autotransformer in normal state; represents the reactive power loss of the excitation inductance of the autotransformer under geomagnetic disturbance; represents the primary side voltage of the autotransformer U 1 peak voltage maintained during GIC intrusion; N represents the number of turns of the primary winding of the transformer; represents the peak value of the autotransformer under rated operating condition corresponding to sinusoidal alternating magnetic flux; represents the equivalent inductance of the autotransformer in one cycle of the current geomagnetic disturbance; represents the saturation time duty ratio of the autotransformer in one power frequency cycle; K represents a fixed scaling factor introduced based on K a value method.

4. The method for GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of transformer according to claim 3, characterized in that, S3 specifically comprises the following steps: S31: judging the estimated GIC amplitude whether the first preset threshold condition is met; The first preset threshold condition is that , and （2） In the formula: represents the unsaturated region inductance of the autotransformer; represents the knee point magnetic flux; represents the alternating magnetic flux of the autotransformer under normal working conditions; represents the critical current at which the working point of the autotransformer enters the saturation region; If yes, S32 is executed; if no, S33 is executed; S32: estimating the GIC amplitude as the final GIC amplitude ; S33: Obtain the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance , and based on the three-dimensional electromagnetic field coupling simulation technology established L mef - I dc Nonlinear curve, backstepping and obtaining the final GIC amplitude corresponding to the equivalent inductance at this time .​ 5. The method for GIC blocking under geomagnetic disturbance based on real-time reactive power monitoring of transformer according to claim 4, characterized in that, S33 specifically comprises the following steps: S331: obtaining the equivalent inductance of the autotransformer within one cycle of the current geomagnetic disturbance is: （3） wherein: L t represents the time-varying value of the magnetizing inductance of the transformer under geomagnetic disturbance; represents the time period;​ S332: the duty ratio of the saturation time of the autotransformer in one power frequency cycle is , the saturation angle is , at this time the magnetic flux relationship satisfies: ; wherein, represents the estimated GIC amplitude generated by the direct-current magnetic flux; S333: the operating point of the autotransformer is in the core saturation region, in combination with S332 the excitation current is defined as: （4） （5） wherein: i n denotes the rated excitation current peak value, i.e. ; denotes the bias DC current component caused by the DC magnetic flux; denotes the excitation current portion of the saturation region magnetic flux contribution; S334: Substituting formula (5) into formula (4) and performing Fourier decomposition on the excitation current can be obtained. （6） S335: Based on three-dimensional electromagnetic field coupling simulation technology, formula (3) is rewritten as: （7） In the formula: h represents the simulation step of the magnetic circuit coupling of the autotransformer; represents the instantaneous value of the inductance at the time step k in a power frequency cycle; Through the simulation analysis under different direct current, the equivalent inductance corresponding to different direct current is obtained through formula (7) , and the nonlinear curve for representing the correlation between the equivalent inductance and the GIC amplitude is established L mef - I dc Nonlinear curve; S336: Based on the above L mef - I dc The nonlinear curve is used to inversely deduce and obtain the corresponding equivalent inductance at this point. The final GIC amplitude .

Images