Method and device for suppressing inrush current of main transformer of compressed air energy storage power station based on pre-magnetizing phase selection closing

Abstract

The application provides a compressed air energy storage power station main transformer inrush current suppression method and device based on pre-magnetizing phase selection closing technology, and the method comprises the following steps: solving a three-phase five-column transformer magnetic circuit model based on a simplified magnetic hysteresis loop model and considering residual magnetism uncertainty, obtaining pre-magnetizing current size and each phase optimal voltage closing phase, adopting a capacitor as a pre-magnetizing device of the compressed air energy storage power station main transformer pre-magnetizing and phase selection closing device, and designing related device parameters. The application also discloses a corresponding setting system, a computer readable storage medium and a terminal. Through the application, the problem of adjacent element zero sequence overcurrent protection misoperation during transformer air drop can be effectively solved without obtaining any electrical parameters of the transformer and adjacent elements, and meanwhile, the application has the characteristics of simplicity and reliability, easy operation and strong applicability.

Description

Technical Field

[0001] This invention belongs to the field of protection of main transformers in compressed air energy storage power stations, and more specifically, relates to a method and device for suppressing inrush current in main transformers of compressed air energy storage power stations based on pre-charged magnetic phase separation closing. Background Technology

[0002] Compressed air energy storage power stations can achieve "one charge and one discharge" within a day. Under full power conditions, it takes approximately 8 hours to complete energy storage and approximately 5 hours to generate and release energy. Therefore, the main transformer of a compressed air energy storage power station undergoes multiple closing and opening operations throughout the day. The inrush current generated by the energization of a large transformer is significant, which may cause malfunctions in related power grid protection systems and also affect the transformer's own safety. Built-in transformers are widely used in power grids due to their compact structure and low failure rate. Replacing the transformer with one that has a smaller inrush current on-site is costly and does not fundamentally solve the protection and safety problems caused by inrush current. A reliable inrush current suppression method is needed to ensure that compressed air energy storage power stations have higher operational efficiency.

[0003] Phase-selective closing technology is a widely used technique for inrush current suppression. Existing research has proposed several optimal phase-selective closing methods, but the inrush current suppression effect depends on the accurate acquisition of residual magnetism before closing. However, the operating conditions of transformers during shutdown are complex, and the variation law of residual magnetism is special. It is often difficult to accurately acquire the residual magnetism before transformer commissioning, which affects the effectiveness of the corresponding inrush current suppression methods.

[0004] Correspondingly, how to develop a simple, reliable and easy-to-operate method for suppressing inrush current in the main transformer of a compressed air energy storage power station has become one of the technical problems that urgently need to be solved in this field. Summary of the Invention

[0005] To address the aforementioned deficiencies or technical requirements of existing technologies, the present invention aims to provide a method and device for suppressing inrush current in the main transformer of a compressed air energy storage power station based on pre-magnetized phase-selective closing. The method utilizes a three-phase five-column magnetic circuit of the transformer, a simplified hysteresis loop model, and considers the uncertainty of residual magnetism to obtain the magnitude of the pre-magnetized current and the optimal voltage closing phase for each phase. A pre-magnetization method using capacitors as pre-magnetizing devices is proposed, and relevant equipment parameters are designed. In a scenario where the transformer can be closed in phases, an external DC current source is proposed to pre-magnetize the residual magnetism in the core to saturation, achieving controllable residual magnetism and closing phase. This allows for the suppression of inrush current with minimal inrush current through phase-separated and time-separated closing.

[0006] The traditional inrush current suppression method has been improved, and a pre-magnetizing device structure has been designed. Accordingly, the single-phase magnetic flux of the transformer can reach the saturation value through the pre-magnetizing device without obtaining the transformer's residual magnetism. This solves the protection maloperation and transformer operation problems caused by inrush current when large transformers are closed. At the same time, it has the characteristics of simplicity, reliability, easy operation, and strong applicability. Therefore, it is especially suitable for various high short-circuit impedance transformers in the grid system of compressed air energy storage power stations.

[0007] To achieve the above objectives, according to a first aspect of the present invention, a method for suppressing inrush current in a main transformer of a compressed air energy storage power station based on pre-charged magnetic phase separation closing is provided, the method comprising:

[0008] S101. Based on the basic parameters of the main transformer of the compressed air energy storage power station, starting from the magnetic circuit of the three-phase five-limb transformer, solve the three-phase magnetic flux under the condition of single-phase pre-magnetization when the transformer is not saturated. Calculate the required pre-magnetization current range for phases A and B of the transformer based on the critical saturation and the upper limit of the set magnetic flux.

[0009] S102. Select a suitable pre-magnetizing voltage, calculate the required pre-magnetizing circuit capacitance based on the pre-magnetizing current calculated in step S101, and build a pre-magnetizing and phase-selective closing device for the main transformer of the compressed air energy storage power station.

[0010] S103, the pre-magnetizing and phase-selective closing device of the main transformer of the compressed air energy storage power station injects DC current, which can be selected as 30 times the rated excitation current, into phase A through the pre-magnetizing circuit. dA This causes the magnetic flux of phase A to reach saturation, and then the current injection into the equipment is disconnected. The time t corresponds to the optimal closing phase of phase A, i.e., when the phase angle of phase A power supply is 180°. A Closing the circuit breaker;

[0011] S104. The pre-magnetizing and phase-selective closing device of the main transformer of the compressed air energy storage power station injects DC current, which can be selected as 30 times the rated excitation current, into phase B through the pre-magnetizing circuit at the optimal pre-magnetizing time, i.e., when the magnetic flux of phase A is at its maximum, corresponding to a phase angle of 60° of phase B power supply. dB This causes the magnetic flux of phase B to reach saturation, and then the current injection into the equipment is disconnected. At the optimal closing phase time, i.e., when the phase angle of phase B power supply is 180°, t... B Closing the circuit breaker;

[0012] S105, phase C closes with a delay of 1-2 cycles relative to phase B. When the phase of phase C power supply is 180°, t C Close the circuit breaker.

[0013] Furthermore, step S101 calculates the required pre-magnetizing current range for phases A and B of the transformer based on the transformer's basic parameters, specifically including:

[0014] Starting from the magnetic circuit of a three-phase five-limb transformer, the magnetic flux of each phase is solved under the condition that the transformer is unsaturated and there is residual magnetism in the three phases, and a pre-magnetizing current is applied to phase A.

[0015] Based on the expressions for the magnetic flux of each phase under unsaturated conditions, the maximum value of the pre-charging current when the magnetic flux of phase A reaches critical saturation under different remanence conditions is calculated, which is the minimum pre-charging current. Where R3 is the reluctance of the ABC three-phase core column, R2 is the reluctance of the main yoke, N is the number of turns on the primary side, and φ s It is the saturation flux;

[0016] With phase A already saturated, the magnetic flux of each phase is solved piecewise under the condition that there is residual magnetism in the three phases and a pre-magnetizing current is applied to phase A, based on the bi-segmented excitation characteristic curve.

[0017] Based on the expression for the magnetic flux of each phase under phase A saturation, an upper limit for the pre-magnetizing flux is set. The minimum value of the pre-magnetizing current when the phase A magnetic flux reaches the upper limit is calculated under different remanence conditions; this is the maximum pre-magnetizing current. Where R3 is the reluctance of the ABC three-phase core column, R2 is the reluctance of the main yoke, N is the number of turns on the primary side, and φ s is the saturation flux, and n is the multiple of the transformer flux after pre-magnetizing with the maximum pre-magnetizing current relative to the saturation flux;

[0018] Given the relevant parameters of the transformer, select an appropriate pre-magnetizing current based on the maximum and minimum pre-magnetizing currents and the actual engineering conditions.

[0019] In the absence of certain actual transformer parameters, the pre-magnetizing current is selected as 30 times the rated excitation current based on experience.

[0020] Furthermore, the specific steps of the pre-magnetizing and phase-selective closing device for the main transformer of the compressed air energy storage power station described in S103 and S104, which pre-magnetizes phases A and B through the pre-magnetizing circuit, are as follows: A charging capacitor and a diode are connected in parallel. Capacitor-inductor resonance is used to pre-magnetize the single-phase iron core. After 1 / 4 cycle of resonance, the capacitor voltage crosses zero. At the maximum pre-magnetizing current, the pre-magnetizing capacitor is naturally cut off through the anti-parallel diode, completing the pre-magnetizing process. The charging capacitor is designed as follows: Among them, I dAm U is the pre-magnetizing current, S is the transformer capacity, ω is the power frequency angular frequency, and U N I N These are the rated voltage, rated current, and I, respectively. m This is the rated excitation current of the transformer.

[0021] A surge current suppression device for the main transformer of a compressed air energy storage power station based on pre-charged magnetic phase separation closing technology, comprising:

[0022] The pre-magnetizing current range calculation module is used to calculate the required pre-magnetizing current range for phases A and B of the transformer based on the basic parameters of the main transformer of the compressed air energy storage power station, starting from the magnetic circuit of the three-phase five-limb transformer, and solving the three-phase magnetic flux under the condition of single-phase pre-magnetizing when the transformer is not saturated. Based on the critical saturation and the upper limit of the set magnetic flux, the module calculates the required pre-magnetizing current range for phases A and B of the transformer.

[0023] The module for building a pre-magnetizing and phase-selective closing device for the main transformer of a compressed air energy storage power station is used to select a suitable pre-magnetizing voltage, calculate the required pre-magnetizing circuit capacitance based on the calculated pre-magnetizing current, and build the pre-magnetizing and phase-selective closing device for the main transformer of the compressed air energy storage power station.

[0024] The pre-magnetizing and phase-selective closing device for the main transformer of the compressed air energy storage power station is used to inject DC current, selectable as 30 times the rated excitation current, into phase A through the pre-magnetizing circuit. dA This causes the magnetic flux of phase A to reach saturation, and then the current injection into the equipment is disconnected. The time t corresponds to the optimal closing phase of phase A, i.e., when the phase angle of phase A power supply is 180°. A Closing the circuit breaker;

[0025] The pre-magnetizing and phase-selective closing device for the main transformer of the compressed air energy storage power station is also used to inject a DC current of 30 times the rated excitation current into phase B through the pre-magnetizing circuit at the optimal pre-magnetizing time, i.e., when the magnetic flux of phase A is at its maximum, corresponding to a phase angle of 60° for phase B power. dB This causes the magnetic flux of phase B to reach saturation, and then the current injection into the equipment is disconnected. At the optimal closing phase time (i.e., when the phase angle of phase B power supply is 180°), t... B Closing the circuit breaker;

[0026] The pre-magnetization and phase-selective closing device for the main transformer of the compressed air energy storage power station is also used to delay the closing of phase C relative to phase B by 1-2 cycles, when the phase of phase C power supply is 180°. C Close the circuit breaker.

[0027] Furthermore, the pre-magnetizing current range calculation module calculates the required pre-magnetizing current range for phases A and B of the transformer, specifically including:

[0028] Starting from the magnetic circuit of a three-phase five-limb transformer, the magnetic flux of each phase is solved under the condition that the transformer is unsaturated and there is residual magnetism in the three phases, and a pre-magnetizing current is applied to phase A.

[0029] Based on the expressions for the magnetic flux of each phase under unsaturated conditions, the maximum value of the pre-charging current when the magnetic flux of phase A reaches critical saturation under different remanence conditions is calculated, which is the minimum pre-charging current. Where R3 is the reluctance of the ABC three-phase core column, R2 is the reluctance of the main yoke, N is the number of turns on the primary side, and φ s It is the saturation flux;

[0030] With phase A already saturated, the magnetic flux of each phase is solved piecewise under the condition that there is residual magnetism in the three phases and a pre-magnetizing current is applied to phase A, based on the bi-segmented excitation characteristic curve.

[0031] Based on the expression for the magnetic flux of each phase under phase A saturation, an upper limit for the pre-magnetizing flux is set. The minimum value of the pre-magnetizing current when the phase A magnetic flux reaches the upper limit is calculated under different remanence conditions; this is the maximum pre-magnetizing current. Where R3 is the reluctance of the ABC three-phase core column, R2 is the reluctance of the main yoke, N is the number of turns on the primary side, and φ s is the saturation flux, and n is the multiple of the transformer flux after pre-magnetizing with the maximum pre-magnetizing current relative to the saturation flux;

[0032] Given the relevant parameters of the transformer, select an appropriate pre-magnetizing current based on the maximum and minimum pre-magnetizing currents and the actual engineering conditions.

[0033] In the absence of certain actual transformer parameters, the pre-magnetizing current is selected as 30 times the rated excitation current based on experience.

[0034] Furthermore, the specific steps of the pre-magnetizing and phase-selective closing device for the main transformer of the compressed air energy storage power station to pre-magnetize phases A and B through the pre-magnetizing circuit are as follows: A charging capacitor and a diode are connected in parallel. The single-phase iron core is pre-magnetized using capacitor-inductor resonance. After 1 / 4 cycle of resonance, the capacitor voltage crosses zero. At the maximum pre-magnetizing current, the pre-magnetizing capacitor is naturally cut off through the anti-parallel diode, completing the pre-magnetizing process. The charging capacitor is designed as follows: Among them, I dAm U is the pre-magnetizing current, S is the transformer capacity, ω is the power frequency angular frequency, and U N I N These are the rated voltage, rated current, and I, respectively. m This is the rated excitation current of the transformer.

[0035] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0036] (1) The present invention redesigns the inrush current suppression method of the main transformer of the compressed air energy storage power station. Instead of obtaining the residual magnetism, it uses pre-magnetization to suppress the inrush current. Accordingly, it can suppress the inrush current without obtaining the residual magnetism parameters of the large transformer, effectively solving the problem that the inrush current causes the protection to malfunction or affects the normal operation of the transformer when the transformer is energized.

[0037] (2) The inrush current suppression method of the main transformer of the compressed air energy storage power station according to the present invention can be applied to the main transformer of the compressed air energy storage power station with different parameters and core structure. It has the characteristics of reliability, easy operation and strong applicability. It also reduces the risk to safe and stable operation of the power grid system caused by the inrush current of such transformers. It is of great significance. Attached Figure Description

[0038] Figure 1 This is an overall flowchart of the inrush current suppression method for the main transformer of a compressed air energy storage power station based on pre-charged magnetic phase separation closing technology constructed in accordance with the present invention.

[0039] Figure 2 It is the excitation characteristic curve of the iron core and its simplified model;

[0040] Figure 3 It is a magnetic circuit model of a three-phase five-limb transformer;

[0041] Figure 4 It is the magnetic flux waveform of each phase after the A-phase core of the transformer is pre-magnetized;

[0042] Figure 5 This is a schematic diagram of a pre-magnetizing device constructed according to the present invention;

[0043] Figure 6 This is a schematic diagram of the transformer pre-magnetization process;

[0044] Figure 7 This refers to the magnetic flux waveforms of each phase after the A-phase core of the transformer is pre-magnetized and the A-phase is closed at the optimal closing time.

[0045] Figure 8 It is the magnetic flux waveform of each phase after pre-magnetizing phase B of the transformer under the most unfavorable initial magnetic flux conditions;

[0046] Figure 9 It is the magnetic flux waveform of each phase of the transformer B phase after pre-magnetization at different pre-magnetization times, taking into account the distributed nature of the circuit breaker.

[0047] Figure 10 This is a schematic diagram of the pre-charged magnetic separation phase closing strategy constructed according to the present invention over time;

[0048] Figure 11 This is a schematic diagram of the magnetic flux waveforms and inrush current of each phase during pre-charge magnetic phase separation closing of an actual transformer constructed according to the present invention. Detailed Implementation

[0049] 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, 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 are within the scope of protection of the present invention.

[0050] The electromagnetic equations of a single-phase transformer during the process of being energized with a sinusoidal voltage power supply are as follows:

[0051]

[0052] In the formula, φ is the magnetic flux in the transformer core, R is the winding current, and U is the sum of the system resistance and the transformer closing winding resistance. m α is the amplitude of the system power supply, and α is the initial phase angle of the power supply during the closing phase.

[0053] By solving equation (1), the expression for the magnetic flux φ can be obtained as follows:

[0054]

[0055] In the formula, L is the average inductance of the closing winding, and φ in The magnetic flux in the core of the transformer before it is switched on is called the initial magnetic flux.

[0056] In a three-phase five-limb transformer for compressed air energy storage power stations, the cores of each phase are interconnected, so the magnetic flux generated by the magnetomotive force of each phase will couple with each other. If R1 = R2 = ∞, and R3, R4, and R5 are the magnetic reluctances of the cores of each phase of a single-phase transformer bank, then the magnetic flux of each phase is determined by the magnetomotive force of that phase and is independent of other phases. In this case, the magnetic circuit is the same as that of a single-phase transformer bank. Figure 3 As shown. Therefore, the analysis of this patent is also applicable to single-phase transformers. It is only necessary to set R1=R2=∞ in the magnetic flux analysis of a three-phase five-limb transformer to analyze single-phase transformers.

[0057] According to Kirchhoff's current law, the equation with magnetic flux as the solution variable can be written using branch analysis:

[0058] GF=Φ (3)

[0059] Where G is the nodal admittance matrix of the magnetoresistance, Φ is the magnetic flux injected into each node, F is the magnetomotive force of each node, and are the variables to be solved. The magnetic flux of the three-phase iron core is then:

[0060]

[0061] Furthermore, because the leakage inductance on the secondary side of the transformer is small, the secondary winding is almost in a short-circuit state, resulting in a large induced current that almost cancels out the zero-sequence magnetic flux on the primary side. Therefore, the following equation can be considered valid:

[0062] φ A +φ B +φ C =0 (5)

[0063] In reality, the excitation characteristics (φ-i) of ferromagnetic materials exhibit nonlinear characteristics of saturation and hysteresis, requiring a hysteresis loop model for description. The equivalent magnetic circuit actually contains multiple nonlinear elements, and equation (3) is a set of nonlinear equations. If the hysteresis loop model is used for precise consideration, obtaining the analytical expression of the magnetic flux in each phase and conducting theoretical analysis is quite difficult. If only the numerical solution of the magnetic flux is obtained, it is not conducive to understanding the magnetic flux change law during pre-magnetization and closing processes. Therefore, it is necessary to obtain the most accurate analytical expression of the magnetic flux as possible. To reduce the difficulty of magnetic flux analysis, based on the IEC's method for describing the excitation characteristics of the iron core, the hysteresis loop model is simplified to a bi-segmented model, such as... Figure 2 As shown by the solid line, to reflect the remanence of the core, the hysteresis characteristics of the core need to be considered. The double-broken line is shifted left and right respectively, so that the unsaturated segment of the broken line passes through the remanence point (0, ±φ). r ),Right now Figure 2 The left dashed curve 1 and the right dashed curve 2, after being translated, form the simplified hysteresis loop model of the excitation characteristic curve.

[0064] When the residual magnetism of the iron core is positive, the excitation characteristic of the iron core is curve 1. The corresponding characteristic equation is:

[0065]

[0066] When the remanence of the iron core is negative, the excitation characteristic of the iron core is curve 2. The corresponding characteristic equation is:

[0067]

[0068] In the formula, φ s R is the saturation flux of the iron core, and R is the magnetic reluctance when unsaturated. s When the reluctance is at saturation, we have R s =u r R. When unsaturated, the relative permeability is very large, and u r ≈5000-8000. The cores of the side yoke and main yoke are also described using the simplified excitation characteristics described above. After this simplification, the analytical solution of equation (3) can be obtained.

[0069] Iron core magnetic circuit such as Figure 3 As shown, the residual magnetism of each part before pre-magnetization of phase A is: the residual magnetism of the three-phase core is φ Arφ Br φ Cr The remanence of the side yoke and the main yoke are φ respectively. 01r φ 12r φ 23r φ 34r φ 45r φ 50r The subscript number represents the magnetic circuit node number.

[0070] Assume that phase A is pre-magnetized at time 0, and the pre-magnetizing current is I. dA Then F A =NI dA F B =F C =0. Assume the pre-charge current is in the form of:

[0071]

[0072] According to this formula, the time constant of the pre-magnetizing current is τ, and the amplitude of the pre-magnetizing current is I. dAm .

[0073] When the iron core is unsaturated, solving equations (3) and (5) simultaneously yields the analytical expression for the three-phase magnetic flux:

[0074]

[0075] in:

[0076]

[0077]

[0078] σ5=R2+3R3

[0079]

[0080]

[0081] A preliminary analysis of the magnetic flux equation shows that the magnetic flux of phase A is related to the pre-charge current, the unsaturated magnetic reluctance of the iron core, and the magnitude of the residual magnetism of the three-phase iron core, but is independent of the magnitude of the residual magnetism of the side yoke and the main yoke.

[0082] It should be noted that the expressions for the magnetic flux of each phase do not contain integral terms, even during the pre-magnetizing process φ. A +φ B +φ C =0 is not true, or the pre-magnetizing current can vary arbitrarily, as long as the expression for the pre-magnetizing current is determined after the pre-magnetizing is completed, and φ is satisfied. A +φ B +φ C=0, and the final magnetic flux of each phase is of the form of equation (9).

[0083] Please see Figure 1 This invention provides a method for suppressing inrush current in the main transformer of a compressed air energy storage power station based on pre-charged magnetic phase separation closing technology. The method includes:

[0084] S101. Calculate the pre-magnetizing currents of phases A and B.

[0085] The closing process of the main transformer in a compressed air energy storage power station is analyzed. For ease of analysis, phase A is taken as the first closing phase. According to equation (9), the key factors affecting the magnetic flux characteristics of phase A during pre-magnetization and closing are residual magnetism, pre-magnetization current, and closing phase. Since the opening angle may not be obtainable, and the residual magnetism of ferromagnetic materials has attenuation characteristics, the magnitude of residual magnetism cannot be accurately obtained. Therefore, the parameters of pre-magnetization current and closing phase need to be designed. In order to ensure that the core of phase A can be pre-magnetized to saturation under various residual magnetism magnitudes and modes, the pre-magnetization current must have a lower limit, denoted as I. dAmL This is called the reference current. However, pre-magnetizing should not cause excessive saturation of the iron core; otherwise, a large inrush current will still be generated after closing the circuit. That is, there is an upper limit to the pre-magnetizing current, denoted as I. dAmH After pre-magnetization is completed, σ1 can be considered as 0. According to equation (9), we have:

[0086]

[0087] in σ9=(R2+2R3) 2 , σ 10 = 3R² + 8R³. To ensure pre-magnetization to saturation flux under any remanence mode, the lower limit of the pre-magnetizing current should be I. dAm The maximum value.

[0088] The saturation magnetic flux density is approximately (1.15~1.25B). m Here we take 1.15B. m，即

[0089] φ s =1.15φ m (11)

[0090] Under normal circumstances, due to the decay of remanence, the remanence φ of the iron core decreases. r It will not exceed 0.85φ m Meanwhile, the residual magnetism of the three-phase core of the transformer is not necessarily generated by the circuit breaker tripping; an asymmetry may occur, such as after a DC resistance test. Therefore, based on the relationship between the magnitudes of the reluctance, when φ... Ar =-0.85φ m , φ Br =φCr =0.85φ m At that time, I dAm The maximum value is the lower limit I of the pre-magnetizing current. dAmL :

[0091]

[0092] Next, we analyze the upper limit of the pre-magnetizing current. The final magnetic flux after pre-magnetizing with the upper limit current is... Let n = 1.05.

[0093] In the worst-case scenario, when the magnetic flux of phase A is most likely to saturate, the value is: φ Ar =0.85φ m , φ Br =φ Cr =-0.85φ m Without applying a pre-charge current, φ A as follows

[0094] In most cases, it has exceeded φ s =1.15φ m The iron core has entered saturation. When unsaturated, the relative permeability is very high, with u0. r ≈5000-8000.

[0095] When the iron core is saturated, R3' = u r Since R3 >> R2, the magnetic reluctance of phase A is much greater than that of phases B and C. Under the influence of residual magnetism, the magnetic flux of phase A approximately no longer increases. The magnetic flux of phase A is charged to the target value by the pre-charging current. Therefore:

[0096]

[0097] Due to u r ≈5000-8000, approximately yielding:

[0098]

[0099] There is I dAmH >>I dAmL Approximately 200 times the minimum pre-charge current.

[0100] Taking a 220kV compressed air energy storage power station three-phase five-limb transformer as an example, the control parameters are designed and parameter margin analysis is performed. The core material is 0.3mm thick silicon steel sheet of model 30Z120 produced by Nippon Steel Corporation of Japan. The basic dimensional parameters are shown in Table 1.

[0101] Table 1 Dimensions of 220kV Three-Phase Five-Column Iron Core

[0102]

[0103]

[0104] The rated operating magnetic flux density of the iron core is 1.70T, and the saturation magnetic flux density is approximately (1.15~1.25B). m Here we take 1.15 B. m That is, 1.96T. Substituting the actual parameters, we can solve for:

[0105] I dAmL =12.2A (15)

[0106] Calculations show that the minimum pre-magnetizing current, or reference current, is about 1.93% of the rated current, which is close to the rated excitation current but much smaller than the rated current.

[0107] As can be seen from the above examples, when the transformer core parameters are known, the current range required for pre-magnetization can be accurately calculated, and the pre-magnetization equipment parameters can be selected according to the actual situation. If the core parameters cannot be accurately obtained, since the reference current and the excitation current are relatively close, and the feasible pre-magnetization current range is relatively large, the middle value in the range, i.e., 30 times the rated excitation current, can be selected. This method of selecting the pre-magnetization current is highly adaptable.

[0108] When the residual magnetism of phase A is at its worst, a value of I is used. dAmL The reference current, which takes 5ms to reach steady state, is used to pre-magnetize phase A of the transformer with two different core structures. Substituting this into equation (9), the magnitude of the three-phase magnetic flux density B can be obtained. Figure 4 As shown.

[0109] It is evident that for transformers with different core structures, even when the transformer is in the worst residual magnetism state, the magnetic flux of phase A can reach the saturation value after the reference current is applied to phase A winding, which is consistent with the theoretical analysis and verifies the correctness of the pre-magnetization parameter design.

[0110] The three phases of the transformer have the same core characteristics. Therefore, when pre-magnetizing phase B of the transformer, we choose the same pre-magnetizing current as phase A.

[0111] S102, Pre-magnetization device setup

[0112] This invention proposes an engineering implementation method for the pre-magnetization strategy of the main transformer in a compressed air energy storage power station, which uses capacitors and diodes to construct a pre-magnetization device and suppresses inrush current based on DC pre-magnetization technology. The method also designs the pre-magnetization voltage U of the charging capacitor. cm The capacitance value is C. A schematic diagram of the pre-magnetizing device is shown below. Figure 5 As shown.

[0113] Its basic principle is to use an external power source to charge the voltage of the charging capacitor to Uc, then close the circuit breaker DL to pre-magnetize the transformer winding, and the diode will naturally withdraw from the charging capacitor. At the same time, it prevents the winding magnetic flux from decreasing. After the pre-magnetization is completed, the pre-magnetization device will be withdrawn.

[0114] After the pre-magnetizing equipment is put into operation, a resonance phenomenon occurs between the charging capacitor of the pre-magnetizing equipment and the excitation inductance of the transformer. When the switch is closed, the voltage of the transformer pre-magnetizing winding increases to the capacitor voltage, and then the capacitor pre-magnetizes the transformer, causing the magnetic flux of the transformer pre-magnetized phase core to continuously increase. During this process:

[0115]

[0116] Among them U c Let ω0 be the initial voltage of the capacitor discharge and ω0 be the resonant frequency of the circuit. L m The unsaturated magnetizing inductance of the transformer can be calculated using the following formula:

[0117]

[0118] Among them, U N I is the rated voltage of the transformer. m % represents the per-unit value of the rated excitation current, and S represents the transformer capacity.

[0119] After a quarter-resonant cycle of pre-magnetization, the polarity of the capacitor voltage reverses, the protection diode connected in parallel turns on, the capacitor is removed from the circuit, and the diode maintains the pre-magnetization current.

[0120] Based on previous theoretical analysis, when the provided pre-magnetizing current is I dAm At that time, it can transfer the transformer's magnetic flux from the residual magnetism φ r Pre-magnetized to saturation flux φ s Therefore, when pre-magnetizing the winding by discharging the capacitor, the magnetic flux must reach saturation flux at one-quarter of the resonance period. According to equation (16), substituting t = T0 / 4, we can obtain:

[0121]

[0122] A schematic diagram of the magnetization process during pre-magnetization is shown below. Figure 6 As shown:

[0123] During the pre-magnetization process, the iron core is almost unsaturated, so the following equation holds true:

[0124]

[0125] Among them, I m φ is the rated excitation current of the transformer. sThis represents saturation flux. The transformer is rated to operate in a slightly saturated state, therefore:

[0126]

[0127] Where T is the power frequency period and ω is the power frequency angular frequency. Combining (17) and (20), we can derive:

[0128]

[0129] Among them, U N I N These are the rated voltage and rated current, respectively.

[0130] S103, Phase A closing phase

[0131] The closing phase of phase A is analyzed. After the pre-magnetization of phase A reaches the saturation value, according to equation (2), the phase of the power supply of phase A is selected to close the circuit when the phase is 180°, and the magnetic flux of phase A after closing is calculated as follows:

[0132]

[0133] As can be seen from the formula, after phase A is closed, the magnetic flux will not exceed the saturation value, and therefore no inrush current will be generated in phase A. This verifies that the optimal closing angle for phase A is 180°.

[0134] In reality, the closing time of a circuit breaker is variable, making precise closing impossible. However, under normal circumstances, the time deviation caused by the variable closing time of the circuit breaker does not exceed ±1ms.

[0135] After the pre-magnetizing current pre-charges phase A to saturation, assume the offset angle of phase A closing is δ1. From equation (2), the aperiodic component of the magnetic flux caused by this angular offset is given by equation (23):

[0136]

[0137] The maximum magnetic flux after closing the switch is:

[0138] φ max =φ m +φ s -φ m cos(δ1) (24)

[0139] To satisfy φ max ≤1.17φ s Calculations show that -36°≤δ1≤36°. Therefore, when the circuit breaker offset time is within ±2ms, the magnetic flux can be controlled within 1.17 times the saturation flux range, preventing large inrush current. This indicates that the dispersion of circuit breaker closing has little impact on the inrush current suppression effect of the pre-magnetized transformer proposed in this invention.

[0140] S104, Phase B closing phase

[0141] After phase A of the main transformer in the compressed air energy storage power station is closed, phases B and C will generate induced magnetic flux due to their connection with phase A in the magnetic circuit. Let's assume that phase B will then be pre-magnetized and closed. The magnetic flux characteristics during the pre-magnetization and closing process of phase B are mainly affected by factors such as the magnetic flux of phase A, the magnitude of the pre-magnetization current of phase B, and the phase of pre-magnetization and closing.

[0142] Next, the pre-magnetizing timing and current of phase B will be designed. The magnetic flux of each phase after phase A pre-magnetization and closing of the three-phase five-limb transformer is as follows: Figure 7 Observations revealed that when the magnetic flux of phase A decreases, the magnetic flux of phase B increases. Therefore, pre-magnetizing phase B when the magnetic flux of phase A is at its positive peak, combined with the interphase magnetic flux coupling, makes it easier for phase B to reach saturation flux. Thus, the optimal pre-magnetizing time is chosen as the moment when the magnetic flux of phase A is at its maximum, corresponding to a phase angle of 60° for phase B.

[0143] The three-phase core characteristics of the transformer are identical. Therefore, when pre-magnetizing phase B of the transformer, we choose the same pre-magnetizing current as phase A. The pre-magnetizing process is relatively short, and we do not consider magnetic flux attenuation for now. The analytical expression for the three-phase magnetic flux is:

[0144]

[0145] in, It is a constant. φ FB The magnetic flux generated by the pre-charge current of phase B.

[0146] Because of the residual magnetism of phase BC φ Br2 With φ Cr2 All are uncertain values, and it is necessary to ensure that the B-phase magnetic flux can reach saturation through pre-magnetization under any residual magnetism condition. Analyzing from equation (25), when φ Cr2 At its maximum, phase B has the slowest pre-magnetization speed and is least prone to saturation. Also, because φ... Br2 ≥-0.85φ s And the sum of the three-phase magnetic flux is 0, so at φ Ar2 When φ = 0, Cr2 The maximum value is 0.85φ s Substituting the core parameters and pre-magnetization parameters, the three-phase magnetic flux can be obtained as shown in Figure 8.

[0147] It is evident that even under the most unfavorable initial residual magnetism, the B-phase flux can be pre-magnetized to saturation value within 5ms, and then maintained in a saturated state for approximately 10ms. This alternating state of saturation and unsaturation cycles repeats within each cycle. The optimal closing phase corresponding to B (B-phase voltage phase angle 180°) falls precisely within the saturation range of that phase. Therefore, at t B2 At this point, closing the B-phase power supply will achieve the same effect as closing the A-phase power supply; the B-phase will hardly generate inrush current. Figure 9 As shown.

[0148] Next, the dispersion margin at the pre-magnetization time of phase B is analyzed. Simulations of the magnetic flux and voltage of each phase are performed in the range of -60°≤δ≤60°, and the results are as follows: Figure 9 .

[0149] It can be seen that when the pre-magnetization angle offset range is -60°≤δ≤60°, at the moment when the phase angle of the B-phase power supply is 180° (t′ in the figure), B2 t″ B2 t″′ B2 The magnetic flux saturation of phase B is within the range. Therefore, even with a large error in the pre-magnetization timing, there is still an optimal closing angle for phase B closing.

[0150] Since the magnetic flux state when phase B is closed and the optimal closing time are exactly the same as those of phase A, the influence of the distributed nature of the phase B circuit breaker on the magnetic flux is exactly the same as that of phase A, and will not be elaborated further.

[0151] If we use the magnetic circuit parameters corresponding to the transformer group, and analyze the magnetic flux during the pre-magnetization and closing process of the transformer's B phase, we find that the pre-magnetization current and the pre-magnetization timing of the B phase have a good effect on the magnetic flux control of this structure. This shows that the method is adaptable to transformers of different structures, which will not be elaborated here.

[0152] S105, C phase closing phase

[0153] The magnetic fluxes after phases A and B are closed are respectively: φ A =φ m cos(ωt)+φ s -φ m , φ B =φ m cos(ωt-120°)+φ s -φ m The three-phase magnetic flux is balanced, therefore the C-phase magnetic flux is:

[0154] φ C =φ m cos(ωt+120°)+2φ m -2φ s (26)

[0155] If φ s =1.15φ m Then the maximum amplitude of the magnetic flux in phase C is 1.13φ. s Slight saturation will occur. According to equation (26), it can be seen that the induced voltage of phase C corresponding to the magnetic flux before phase C closing is exactly equal to the power supply voltage of phase C. Therefore, it is not necessary to pre-magnetize phase C, and closing can be performed directly. When selecting the actual closing time of phase C, the closing time t of phase C is... C The closing time is delayed by 1-2 cycles relative to phase B, and the closing time is when the phase of phase C power supply is 180°.

[0156] Based on the above analysis of the pre-magnetization and closing flux of each phase of the transformer, a pre-magnetization and closing strategy was designed for inrush current suppression, summarized as follows: Figure 10 As shown.

[0157] Simulation verification

[0158] The above-mentioned pre-magnetization equipment parameter design method is verified by simulation.

[0159] Select the physical model of the main transformer of the compressed air energy storage power station, and combine it with (12) and (14) to select the required pre-magnetizing current I. dAm =0.4A. Select transformer pre-magnetizing voltage U c =100V, substituting into (21), we get C=163uF. Considering the capacitor specifications, we can choose a specification slightly larger than the calculated capacitance value. The capacitor selected here is: U c =100V, C=180uF. Selecting the worst-case residual magnetism (-0.8, 0.4, 0.4pu), and based on the previously proposed inrush current suppression strategy, the pre-magnetizing time of the pre-magnetizing equipment and the closing phase of the three-phase circuit breaker are obtained. Simulation is performed, and the results are as follows: Figure 11 As shown.

[0160] It is evident that even under the worst residual magnetism conditions, the pre-magnetizing equipment calculated and configured according to this patented method can charge the magnetic flux of each phase of the transformer to near saturation. Combined with the phase-selective closing strategy, the three-phase magnetic flux can be controlled within the saturation range throughout the entire pre-magnetizing closing process. The maximum three-phase inrush current is 8A, approximately 0.5I. N The inrush current is relatively small, indicating that the design parameters of the pre-magnetizing device are reasonable.

[0161] In summary, the present invention can effectively solve the problem of large inrush current during transformer energization, which leads to maloperation of related protection and unstable operation of transformer, by using the technology of pre-charging the three-phase core for phase selection and closing without obtaining the residual magnetism of the main transformer of the compressed air energy storage power station. Moreover, it has the characteristics of reliability, ease of operation and strong applicability, and is therefore particularly suitable for the application of various high short-circuit impedance transformers in power grid systems.

[0162] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for suppressing inrush current of a main transformer of a compressed air energy storage power station based on pre-magnetizing phase selection closing technology, characterized in that, The method comprises the following steps: S101, according to the basic parameters of the compressed air energy storage power station main transformer, starting from the magnetic circuit of the three-phase five-column transformer, solving the three-phase magnetic flux under the condition of single-phase pre-magnetization of the unsaturated transformer, calculating the pre-magnetization current range required by the transformer A and B phases according to reaching the critical saturation and reaching the set upper limit of magnetic flux; S102, selecting a suitable pre-magnetization voltage, calculating the required pre-magnetization circuit capacitance according to the pre-magnetization current calculated in step S101, and building a compressed air energy storage power station main transformer pre-magnetization and phase selection closing device; S103, the compressed air energy storage power station main transformer pre-magnetization and phase selection closing device injects a direct current IdA of 30 times the rated excitation current into the A phase through the pre-magnetization circuit, so that the A phase magnetic flux reaches the saturation value, then the current injection device is disconnected, and the A phase is closed at the optimal closing phase, that is, the A phase power phase angle is 180° at the corresponding time tA; S104, the compressed air energy storage power station main transformer pre-magnetization and phase selection closing device injects a direct current IdB of 30 times the rated excitation current into the B phase through the pre-magnetization circuit at the optimal pre-magnetization time, that is, the maximum A phase magnetic flux time, corresponding to the B phase power phase angle 60°, so that the B phase magnetic flux reaches the saturation value, then the current injection device is disconnected, and the B phase is closed at the optimal closing phase, that is, the B phase power phase angle is 180° at the corresponding time tB; S105, the C phase is closed at the relative B phase closing delay 1-2 cycles, at the C phase power phase 180°, tC; The specific steps of the pre-magnetizing and phase selection closing device of the compressed air energy storage power station main transformer in S103 and S104 pre-magnetizing A phase and B phase through a pre-magnetizing circuit are as follows: connecting a charging capacitor and a diode in parallel, pre-magnetizing a single-phase iron core by using a capacitor inductance resonance, cutting off the pre-magnetizing capacitor by a reverse diode naturally at the maximum pre-magnetizing current when the capacitor voltage is zero after 1 / 4 of a resonance period, completing pre-magnetizing, and designing the charging capacitor as wherein, I dAm is a pre-magnetizing current, S is a transformer capacity, ω is a power frequency angular frequency, U N , I N are a rated voltage and a rated current respectively, and I m is a transformer rated excitation current.

2. The pre-magnetizing phase selection closing technology based compressed air energy storage power station main transformer inrush current suppression method according to claim 1, characterized in that, Step S101 calculates the pre-magnetization current range required by the transformer A and B phases according to the basic parameters of the transformer, specifically including: Starting from the magnetic circuit of the three-phase five-column transformer, solving the three-phase magnetic flux under the condition of single-phase pre-magnetization of the unsaturated transformer; According to the expression of each phase magnetic flux under unsaturated condition, the maximum pre-magnetizing current when the A-phase magnetic flux reaches critical saturation under different residual magnetism is solved, which is the minimum pre-magnetizing current wherein is the magnetic resistance of the ABC three-phase core, is the main yoke magnetic resistance, N is the number of turns of the primary side, is the saturation magnetic flux; In the case that the A phase has been saturated, according to the double-fold line excitation characteristic curve, the three-phase magnetic flux under the condition of pre-magnetization current in the A phase is solved by segmentation; According to the expression of each phase magnetic flux under the saturation condition of phase A, an upper limit of pre-magnetizing magnetic flux is set, and the minimum value of pre-magnetizing current when the magnetic flux of phase A reaches the upper limit of pre-magnetizing magnetic flux under different residual magnetic conditions is solved, that is, the maximum pre-magnetizing current wherein is the magnetic resistance of the ABC three-phase core, is the main yoke magnetic resistance, N is the number of turns on the primary side, is the saturation magnetic flux, n is the multiple of the transformer magnetic flux relative to the saturation magnetic flux after pre-magnetizing using the maximum pre-magnetizing current In the case that the transformer related parameters are known, the appropriate pre-magnetization current is selected according to the maximum pre-magnetization current and the minimum pre-magnetization current and the actual engineering condition; In the case that the actual transformer parameters are uncertain, the pre-magnetization current is selected as 30 times the rated excitation current according to experience.

3. A compressed air energy storage power station main transformer inrush current suppression device based on pre-magnetizing phase selection closing technology, characterized in that, It comprises: A pre-magnetization current range calculation module for calculating the pre-magnetization current range required by the transformer A and B phases according to the basic parameters of the compressed air energy storage power station main transformer, starting from the magnetic circuit of the three-phase five-column transformer, solving the three-phase magnetic flux under the condition of single-phase pre-magnetization of the unsaturated transformer, and calculating the pre-magnetization current range required by the transformer A and B phases according to reaching the critical saturation and reaching the set upper limit of magnetic flux; A compressed air energy storage power station main transformer pre-magnetization and phase selection closing device building module for selecting a suitable pre-magnetization voltage, calculating the required pre-magnetization circuit capacitance according to the calculated pre-magnetization current, and building a compressed air energy storage power station main transformer pre-magnetization and phase selection closing device; The compressed air energy storage power station main transformer pre-magnetization and phase selection closing device is used for injecting 30 times rated excitation current direct current IdA of A phase through the pre-magnetization circuit, so that the A phase magnetic flux reaches the saturation value, then the current injection equipment is disconnected, and the A phase is closed at the optimal closing phase, that is, the A phase power phase angle is 180° at the corresponding time tA; The compressed air energy storage power station main transformer pre-magnetization and phase selection closing device is also used for injecting 30 times rated excitation current direct current IdB of B phase through the pre-magnetization circuit at the optimal pre-magnetization time, that is, the A phase magnetic flux maximum time, corresponding to the B phase power phase angle 60°, so that the B phase magnetic flux reaches the saturation value, then the current injection equipment is disconnected, and the B phase is closed at the optimal closing phase, that is, the B phase power phase angle is 180° at the corresponding time tB; The compressed air energy storage power station main transformer pre-magnetization and phase selection closing device is also used for C phase to be closed at the relative B phase closing delay 1-2 cycles, that is, the C phase power phase is 180° at the time tC; The pre-magnetizing and phase selection closing device of the compressed air energy storage power station main transformer pre-magnetizes A phase and B phase through a pre-magnetizing circuit, and the specific steps are as follows: connecting a charging capacitor and a diode in parallel, pre-magnetizing a single-phase iron core by using a capacitor inductance resonance, cutting off the pre-magnetizing capacitor by a reverse diode naturally at a maximum pre-magnetizing current when the capacitor voltage is zero after a resonance of 1 / 4 cycle, and completing the pre-magnetizing, wherein the charging capacitor is designed as wherein, I dAm is a pre-magnetizing current, S is a transformer capacity, ω is a power frequency angular frequency, U N , I N are a rated voltage and a rated current respectively, and I m is a transformer rated excitation current.

4. The compressed air energy storage power plant main transformer inrush current suppression device based on the pre-magnetizing phase selection closing technology according to claim 3, characterized in that, The pre-magnetization current range calculation module calculates the pre-magnetization current range required by the transformer A and B phases, and specifically includes: Starting from the magnetic circuit of the three-phase five-column transformer, the magnetic flux of each phase under the condition that there is residual magnetism in three phases and the pre-magnetization current is passed through the A phase is solved under the condition that the transformer is not saturated; According to the expression of each phase magnetic flux under unsaturated condition, the maximum pre-magnetizing current when the A-phase magnetic flux reaches critical saturation under different residual magnetism is solved, which is the minimum pre-magnetizing current wherein is the magnetic resistance of the ABC three-phase core, is the main yoke magnetic resistance, N is the number of turns of the primary side, is the saturation magnetic flux; Under the condition that the A phase has been saturated, according to the double-fold line excitation characteristic curve, the magnetic flux of each phase under the condition that there is residual magnetism in three phases and the pre-magnetization current is passed through the A phase is solved by segmentation; According to the expression of each phase magnetic flux under the saturation condition of phase A, an upper limit of pre-magnetizing magnetic flux is set, and the minimum value of pre-magnetizing current when the magnetic flux of phase A reaches the upper limit of pre-magnetizing magnetic flux under different residual magnetic conditions is solved, that is, the maximum pre-magnetizing current wherein is the magnetic resistance of the ABC three-phase core, is the main yoke magnetic resistance, N is the number of turns on the primary side, is the saturation magnetic flux, n is the multiple of the transformer magnetic flux after pre-magnetizing using the maximum pre-magnetizing current relative to the saturation magnetic flux; Under the condition that the related parameters of the transformer are known, according to the maximum pre-magnetization current and the minimum pre-magnetization current and the actual engineering condition, the appropriate pre-magnetization current is selected; Under the condition that the actual transformer parameters are uncertain, the pre-magnetization current is selected as 30 times the rated excitation current according to experience.

Images