A method for analyzing the remanence phase angle of a closing inrush protection

Abstract

The application discloses a closing inrush current protection residual magnetism phase angle analysis method, and belongs to the technical field of excitation inrush current limiting method.The application discloses a closing inrush current protection residual magnetism phase angle analysis method, which is based on the saturation characteristics of the magnetic flux linkage in the transformer closing process, combined with the transformer phase selection switching technology, analyzes the closing strategies of the single-phase transformer and the three-phase transformer under the conditions of no residual magnetism and residual magnetism, based on the closing strategies, further analyzes and proposes the closing strategy combining the direct current component dynamic compensation and the phase selection control, and further proposes the closing strategy combining the pre-excitation and the phase selection control; the simulation tool is used to simulate the closing strategies, the feasibility of each closing strategy is verified, and the purpose of limiting the closing excitation inrush current by controlling the closing phase angle is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of excitation inrush limiting method, and particularly relates to a residual magnetism phase angle analysis method for closing inrush protection. BACKGROUND

[0002] When a no-load transformer is operated, a high-amplitude excitation inrush current will be generated, and each harmonic will be injected into the power grid, causing current and voltage distortion, which may adversely affect the production and operation of the power grid, such as causing DC blocking or overvoltage phenomenon. Therefore, it is of great significance to explore measures to limit the transformer excitation inrush current for ensuring the reliable operation of the power grid and the safety of related power grid equipment.

[0003] The concept of phase control was first proposed in the 1970s, and since the 1990s, phase-controlled switches have been widely used abroad. The phase selection switching technology applied to transformers is to comprehensively consider the selection of the voltage phase at the moment of closing, avoid the saturation of the core magnetic flux when the transformer is put into operation, and thus achieve the purpose of reducing the excitation inrush current. Although the common transformer closing excitation inrush current suppression method or related device based on the phase selection switching technology on the market can suppress the size of the excitation inrush current, it cannot accurately and conveniently determine the residual magnetism size and the best closing phase angle in the suppression control process. Therefore, the present application provides a residual magnetism phase angle analysis method for closing inrush protection. SUMMARY

[0004] The present application aims to provide a residual magnetism phase angle analysis method for closing inrush protection to solve the problem that the prior art cannot accurately and conveniently determine the residual magnetism size and the best closing phase angle in the suppression control process.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A residual magnetism phase angle analysis method for closing inrush protection, comprising the following steps:

[0007] S1, according to the principle of transformer closing excitation inrush current, the transformer is connected to the loop in an angular connection mode, the closing bus voltage is represented by U m sin(ωt+α), and the flux of the transformer can be represented as:

[0008] ψ=-ψ m cos(ωt+α)+ψ m cos(α)+ψ r (1)

[0009] wherein, ψ m cos(ωt+α)+ψ r represents the free component of the flux;

[0010] S2. Based on the influence mechanism of the free component of magnetic flux in S1 on the degree of transformer saturation, and combined with the transformer phase selection switching technology, select an appropriate closing phase and analyze the phase selection closing strategy under the condition of no residual magnetism in the transformer.

[0011] S3. Based on the influence mechanism of the free component of magnetic flux in S1 on the degree of transformer saturation, and combined with the transformer phase selection switching technology, select an appropriate closing phase and analyze the phase selection closing strategy under the condition of residual magnetism in the transformer.

[0012] S4. The DC component compensation method is used to limit the first phase of the transformer. Combined with the closing strategy proposed in S2 to S3, the closing strategy combining DC component compensation and phase selection switching is further analyzed.

[0013] S5. Based on the DC component compensation method mentioned in S4, a certain amplitude of pre-excitation current is injected into the low-voltage side before closing the circuit to make the transformer flux reach a certain constant value. Then, combined with the closing strategy proposed in S2 to S3, the closing strategy combining pre-excitation and phase selection switching is analyzed.

[0014] S6. Use simulation tools to simulate the closing strategies proposed in S2 to S5, verify the feasibility of each closing strategy, and achieve the purpose of limiting the inrush current of closing excitation by controlling the closing phase angle.

[0015] Preferably, S2 specifically includes the following:

[0016] S2.1 Phase selection strategy for single-phase transformers under no-residual magnetism conditions: According to equation (1), under no-residual magnetism conditions, the free component of the flux linkage is ψ m cos(α), therefore when α=90°, that is, when the bus voltage peak point is closed, the free component of the magnetic flux is 0, and the inrush current is minimal at this time;

[0017] S2.2 Phase selection strategy for three-phase transformers without residual magnetism: the three phases are closed separately. The first phase to be closed operates at the voltage peak, which is consistent with the operation in S2.1 above. After the first phase is closed, the other two phases are closed when the closing time reaches 1 / 4 of the power frequency cycle.

[0018] Preferably, S3 specifically includes the following:

[0019] S3.1 Phase selection strategy under residual magnetism condition of single-phase transformer: According to equation (1), the free component of flux linkage ψ is calculated. m cos(α)+ψ r The optimal closing phase angle α is 0. When closing at this phase, the free component of the magnetic flux is 0, and the inrush current is minimized.

[0020] S3.2 Phase selection strategy for three-phase transformers with residual magnetism: The three phases are closed separately. It is assumed that the residual magnetism of phase A is 0, the residual magnetism of phase B is less than 0, and the residual magnetism of phase C is greater than 0. If phase A reaches the ideal time point first, then phase A is closed at the voltage peak point. After the first phase is closed, the other two phases are closed when the closing time reaches 1 / 8 of the power frequency cycle.

[0021] Preferably, S4 specifically includes the following:

[0022] The DC compensation circuit is connected to the low-voltage side of each phase transformer in a delta connection. The DC component compensation method is used to limit the first phase of the transformer. When only the first phase is closed, the compensation circuit outputs DC current only on the first phase branch, while the other two phase branches are equivalent to open circuits. When the DC component of the excitation current decays to a low level, the other two phases are closed. The closing time is selected as the optimal closing point determined in S2 or S3.

[0023] Preferably, the simulation tool used in S6 is PSCAD / EMTDC.

[0024] Compared with the prior art, the present invention provides a method for analyzing the residual magnetism phase angle of inrush current protection, which has the following advantages:

[0025] This invention analyzes the closing strategies of single-phase and three-phase transformers under conditions of no and with residual magnetism, based on the saturation characteristics of magnetic flux during transformer closing and combined with transformer phase selection switching technology. Based on this closing strategy, a further analysis proposes a closing strategy combining dynamic DC component compensation and phase selection control. Specifically, the first closing phase uses dynamic DC component compensation control after closing to rapidly attenuate the inrush current in that phase; subsequent closing phases primarily reduce the inrush current amplitude through phase control, combined with DC component compensation control to accelerate its attenuation. Furthermore, a closing strategy combining pre-excitation and phase selection control is proposed. Before closing, a certain steady-state pre-excitation current is applied through a DC compensation circuit to pre-set the transformer's residual magnetism value, and phase control is used during closing to suppress the closing inrush current. In addition, simulations were performed on the above closing strategies to verify their feasibility and achieve the goal of limiting the closing excitation inrush current by controlling the closing phase angle. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the three-phase closing phase under the condition of no residual magnetism in Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the three-phase closing phase under residual magnetism conditions in Embodiment 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of the closing strategy combining DC component compensation and phase selection switching in Embodiment 1 of the present invention;

[0029] Figure 4 This is a schematic diagram of the closing strategy combining pre-excitation and phase selection switching in Embodiment 1 of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Example 1:

[0032] A method for analyzing the residual magnetism phase angle of inrush current protection includes the following steps:

[0033] S1. Based on the transformer closing excitation inrush current principle, the closing bus voltage is represented by U. m If sin(ωt+α) is used, then the flux linkage of the transformer can be expressed as:

[0034] ψ=-ψ m cos(ωt+α)+ψ m cos(α)+ψ r (1)

[0035] Where, ψ m cos(α)+ψ r This represents the free component of the magnetic flux, which has a significant impact on the transformer saturation level. By selecting an appropriate closing phase angle, reducing or even eliminating this free component can effectively reduce the inrush current.

[0036] S2. Based on the influence mechanism of the free component of magnetic flux on the transformer saturation degree in S1, and combined with the transformer phase selection switching technology, an appropriate closing phase is selected, and the phase selection closing strategy under the condition of no residual magnetism in the transformer is analyzed; specifically, the following content is included:

[0037] S2.1 Phase selection strategy for single-phase transformers under no-residual magnetism conditions: According to equation (1), under no-residual magnetism conditions, the free component of the flux linkage is ψ m cos(α), therefore when α=90°, that is, when the bus voltage peak point is closed, the free component of the magnetic flux is 0, and the transformer will not reach saturation. At this time, the inrush current is minimal.

[0038] S2.2 Phase selection strategy for three-phase transformers without residual magnetism: The three phases are closed separately. The first phase to be closed operates at voltage peak, consistent with the operation in S2.1 above. After the first phase closes, due to the coupling effect of the low-voltage angle-connected coil, the voltages of the subsequent two phases are equal, with their voltage amplitudes being 1 / 2 compared to the first phase, and their phases being exactly opposite. When the closing time reaches 1 / 4 of the power frequency cycle (e.g., ... Figure 1As shown in the figure, since the magnetic flux induced by phase A to phases B / C is equal to the forced magnetic flux generated by the bus voltage of phases B / C, the free component generated by phases B / C is 0, and the inrush current can be ignored. At this time, the other two phases are closed.

[0039] S3. Based on the influence mechanism of the free component of magnetic flux in S1 on the transformer saturation, and combined with transformer phase selection switching technology, this paper analyzes the phase selection closing strategy under the condition of residual magnetism in the transformer by selecting an appropriate closing phase. Specifically, this includes the following:

[0040] S3.1 Phase selection strategy under residual magnetism condition of single-phase transformer: According to equation (1), the free component of flux linkage ψ is calculated. m cos(α)+ψ r The optimal closing phase angle α is 0. When closing at this phase, the free component of the magnetic flux is 0, and the inrush current is minimized.

[0041] S3.2 Phase selection strategy for three-phase transformers with residual magnetism: The three phases are switched on separately, with phase A's residual magnetism set to 0, phase B's residual magnetism less than 0, and phase C's residual magnetism greater than 0. If phase A reaches the ideal time point first, then phase A is switched on at the voltage peak point. The flux evolution of phases B and C of the transformer at this time is as follows: Figure 2 As shown, Figure 2 M and N can be used as ideal closing points for phases B and C; however, point M is significantly less affected by the dispersion of closing time compared to point N. Therefore, point M is the best closing point for phases B and C. That is, after the first phase is closed, the other two phases will be closed when the closing time reaches 1 / 8 of the power frequency cycle.

[0042] S4. A DC component compensation method is used to limit the operation of the transformer's first phase. Combining this with the closing strategies proposed in S2-S3, a closing strategy integrating DC component compensation and phase selection switching is further analyzed. Please refer to [link to relevant documentation]. Figure 3 Specifically, it includes the following:

[0043] The DC component compensation method is used to limit the first phase of the transformer. When the DC component of the excitation current decays to a low level, the other two phases are closed. The closing time is selected as the optimal closing point determined in S2 or S3.

[0044] S5, please refer to Figure 4 Based on the DC component compensation method mentioned in S4, a certain amplitude of pre-excitation current is injected into the low-voltage side before closing in its circuit, so that the magnetic flux of the transformer reaches a certain constant value. Furthermore, combined with the closing strategy proposed in S2 to S3, the closing strategy combining pre-excitation and phase selection switching is analyzed.

[0045] S6. Use the simulation tool PSCAD / EMTDC to simulate the closing strategies proposed in S2 to S5, verify the feasibility of each closing strategy, and achieve the purpose of limiting the closing excitation inrush current by controlling the closing phase angle.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for analyzing the residual magnetism phase angle of inrush current protection, characterized in that, Includes the following steps: S1. Based on the principle of transformer inrush current during closing, the transformer is connected to the circuit in a delta connection manner, and the closing bus voltage is used... If we express this as an expression, then the flux linkage of the transformer can be represented as: （1） in, Represents the free component of the magnetic flux linkage; S2. Based on the influence mechanism of the free component of magnetic flux on the transformer saturation degree in S1, and combined with the transformer phase selection switching technology, an appropriate closing phase is selected, and the phase selection closing strategy under the condition of no residual magnetism in the transformer is analyzed; specifically, the following content is included: S2.1 Phase selection strategy for single-phase transformers under no-residual magnetism conditions: According to equation (1), under no-residual magnetism conditions, the free component of the flux linkage is , so when α When the angle is 90°, that is, when the bus voltage peak point is closed, the free component of the magnetic flux is 0, and the inrush current is minimal at this time. S2.2 Phase selection strategy for three-phase transformers without residual magnetism: The three phases are closed separately. The first phase to be closed operates at the voltage peak, which is the same as the operation in S2.1 above. After the first phase is closed, the other two phases are closed when the closing time reaches 1 / 4 of the power frequency cycle. S3. Based on the influence mechanism of the free component of magnetic flux in S1 on the transformer saturation, and combined with transformer phase selection switching technology, this paper analyzes the phase selection closing strategy under the condition of residual magnetism in the transformer by selecting an appropriate closing phase. Specifically, this includes the following: S3.1 Phase selection strategy under residual magnetism condition of single-phase transformer: According to equation (1), the free component of the flux linkage is calculated. The optimal closing phase angle is 0. α When the circuit is closed at this phase, the free component of the magnetic flux is 0, and the inrush current during closing is minimized. S3.2 Phase selection strategy for three-phase transformers with residual magnetism: The three phases are closed separately. It is assumed that the residual magnetism of phase A is 0, the residual magnetism of phase B is less than 0, and the residual magnetism of phase C is greater than 0. If phase A reaches the ideal time point first, then phase A is closed at the voltage peak point. After the first phase is closed, when the closing time reaches 1 / 8 of the power frequency cycle, the other two phases are closed. S4. The DC component compensation method is used to limit the first phase of the transformer. Combined with the closing strategy proposed in S2 to S3, the closing strategy combining DC component compensation and phase selection switching is further analyzed. S5. Based on the DC component compensation method mentioned in S4, a certain amplitude of pre-excitation current is injected into the low-voltage side before closing the circuit to make the transformer flux reach a certain constant value. Then, combined with the closing strategy proposed in S2 to S3, the closing strategy combining pre-excitation and phase selection switching is analyzed. S6. Use simulation tools to simulate the closing strategies proposed in S2 to S5, verify the feasibility of each closing strategy, and achieve the purpose of limiting the inrush current of closing excitation by controlling the closing phase angle.

2. The method for analyzing the residual magnetism phase angle of inrush current protection according to claim 1, characterized in that, S4 specifically includes the following: The DC component compensation method is used to limit the first phase of the transformer. When the DC component of the excitation current decays to a low level, the other two phases are closed. The closing time is selected as the optimal closing point determined in S2 or S3.

3. The method for analyzing the residual magnetism phase angle of inrush current protection according to claim 1, characterized in that, The simulation tool used in S6 is PSCAD / EMTDC.

Images