Phase selection switching-on method based on transformer residual magnetism measurement and calculation
By disassembling and equivalent transformer residual magnetic flux, a circuit of residual magnetic calculation test is established, which solves the problem that the residual magnetism cannot be accurately measured in the prior art, and realizes the effect of accurately measuring the residual magnetism before closing, selecting the appropriate gate time to suppress excitation surge current.
Patent Information
- Application Number
- CN202411830188.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-12
- Publication Date
- 2025-03-25
AI Technical Summary
The prior art cannot accurately measure the residual magnetism of the transformer, resulting in the inability to effectively select the appropriate phase selection and closing time to suppress the adverse effects of the excitation inrush current.
By disassembling the total magnetic flux in the equivalent circuit of the closing of the no-load transformer, the residual magnetic flux is obtained, and equivalent to an equivalent inductor with the initial magnetic flux, a residual magnetic calculation test equivalent circuit is established, the voltage loop equation and current loop equation are solved, and the value of the residual magnetic inductor is obtained and the voltage value equivalent to the energy on the residual magnetic inductor is obtained, and the optimal closing time is determined.
It realizes the accurate calculation of the residual magnetic condition of the transformer before closing, selects the appropriate closing time, effectively suppresses the generation of excitation surge current, and improves the operating stability of the power system and the power transmission efficiency.
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Figure CN119695771A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of closing control, and in particular to a phase selection closing method based on transformer residual magnetism measurement. Background Art
[0002] UHV large oil-filled equipment has outstanding characteristics such as high voltage level, large equipment capacity, complex insulation structure, and large oil filling volume. Once a high-energy discharge fault occurs inside, its short-circuit current and fault energy level will be significantly higher than those of conventional equipment. Among them, the excitation inrush current phenomenon of the transformer is when the transformer is put into operation again after no-load closing or external fault removal, due to the existence of residual magnetism and sudden changes in voltage, the magnetic field of the iron core is sharply enhanced. The rapid change of the magnetic field will push the iron core to saturation and produce an instantaneous current phenomenon. The excitation inrush current phenomenon will have an important impact on the operation of the power system and the malfunction of the protection device, such as causing the relay protection device to malfunction, resulting in the failure of the transformer to be put into operation, and may also cause local or large-scale power outages in the power grid; at the same time, a large number of harmonic components in the excitation inrush current will interfere with the normal transmission of electric energy and reduce the transmission efficiency and quality of electric power.
[0003] Therefore, it is necessary to use scientific means to measure the residual magnetism and then select the appropriate phase selection closing time. In the prior art, when the conventional transformer is closed at no-load, the strategy of suppressing the excitation inrush current usually relies on the precise measurement of the residual magnetism, and then determines the closing time, so that the pre-induced magnetic flux and the residual magnetism are offset, thereby reducing the inrush current. However, the accuracy of the residual magnetism measurement faces the following problems: ① When using sensors and other external measurements for the transformer as a whole, it will be affected by the core leakage and it is difficult to accurately measure the tiny flux changes inside the primary side core. ② When using external demagnetization and other methods for measurement, it is difficult to ensure that the measurement process has no effect on the residual magnetism. ③ After the measurement, it is difficult to ensure that the residual magnetism does not change for a long time due to interference such as temperature, electromagnetic interference, and mechanical vibration. Based on the above reasons, the residual magnetism measured is not accurate enough, and thus it is impossible to effectively control and reduce the adverse effects of the excitation inrush current. Summary of the invention
[0004] The present invention provides a phase selection and closing method based on transformer residual magnetism measurement to overcome the technical problem that the prior art cannot accurately measure residual magnetism, resulting in failure to accurately select a suitable phase selection and closing time to suppress excitation inrush current.
[0005] In order to achieve the above object, the technical solution of the present invention is:
[0006] A phase selection and closing method based on transformer residual magnetism measurement, the specific steps include:
[0007] S1: Disassemble the total magnetic flux of the UHV converter transformer in the equivalent circuit of the no-load transformer closing to obtain the residual magnetic flux;
[0008] S2: Equivalent the residual magnetic flux to an equivalent inductance with an initial magnetic flux, namely, a residual magnetic inductance, to obtain an equivalent circuit for a residual magnetic measurement test;
[0009] S3: Establish voltage loop equation and current loop equation based on the equivalent circuit of residual magnetism measurement test;
[0010] S4: setting the voltage amplitude of the impulse voltage source of the residual magnetism measurement test equivalent circuit and measuring the current amplitude to solve the simultaneous equations formed by the voltage loop equation and the current loop equation to obtain the value of the residual magnetic inductance and the voltage value equivalent to the energy on the residual magnetic inductance;
[0011] S5: Substitute the solved residual magnetic inductance value and the voltage value equivalent to the energy on the residual magnetic inductance into the residual magnetic measurement test equivalent circuit to obtain the line current expression of the transformer no-load closing;
[0012] S6: Before each closing, the optimal closing time is determined based on the line current expression of the transformer no-load closing to suppress the excitation inrush current.
[0013] Furthermore, in S3, the voltage loop equation and the current loop equation established based on the equivalent circuit of the residual magnetism measurement test are respectively expressed as:
[0014]
[0015] Where, R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R m is the equivalent resistance of the excitation circuit, L r is the equivalent residual inductance; U is the impulse power supply voltage amplitude; I is the primary current of the transformer, I r is the current flowing through the residual magnetic inductance, and U0 is the voltage value equivalent to the energy on the residual magnetic inductance.
[0016] Furthermore, in S4, the simultaneous equations formed by the voltage loop equation and the current loop equation are expressed as:
[0017]
[0018] in:
[0019]
[0020] In the formula, △I is the measured primary current amplitude, and △t is the time of impulse power supply action;
[0021] Change the direction of the impulse power supply to obtain △I + and △I - , the two are the primary side current amplitudes corresponding to the positive and negative directions of the impulse power supply respectively;
[0022] △I +and △I - Substitute them into formula (3) respectively and solve the simultaneous equations to obtain the residual inductance L r The value of and the value of the voltage U0 equivalent to the energy on the residual magnetic inductance.
[0023] Furthermore, in S5, the solved residual magnetic inductance value and the voltage value equivalent to the energy on the residual magnetic inductance are substituted into the residual magnetic measurement test equivalent circuit, and the line current expression of the transformer no-load closing is obtained as follows:
[0024]
[0025] Where, R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R s , L s are the system equivalent resistance and equivalent inductance respectively; R m is the equivalent resistance of the excitation circuit; α is the closing phase angle; ω is the system voltage angular frequency; s is the time for phase selection and closing.
[0026] Furthermore, in S1, the total magnetic flux of the transformer in the equivalent circuit of the no-load transformer closing is disassembled to obtain the residual magnetic flux, which is expressed as:
[0027] Φ=Φ σ +Φ r
[0028] In the formula, Φ σ and Φ r They are leakage flux and residual flux respectively.
[0029] Beneficial effect: The present invention decomposes the total magnetic flux of the ultra-high voltage converter transformer in the equivalent circuit of no-load transformer closing into leakage magnetic flux and residual magnetic flux, and equates the residual magnetic flux to an equivalent inductance with initial magnetic flux, namely, residual magnetic inductance, to obtain a residual magnetic measurement test equivalent circuit. Based on the residual magnetic measurement test equivalent circuit, the line current expression of the transformer no-load closing is finally obtained, thereby determining the appropriate closing time before closing. The method is applicable to ultra-high voltage converter transformers, and can accurately measure the residual magnetic condition of the transformer before closing and then perform phase selection closing, thereby suppressing the excitation inrush current. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.
[0031] Figure 1 It is a flow chart of a phase selection and closing method based on transformer residual magnetism measurement in the present invention;
[0032] Figure 2 is an equivalent circuit diagram of transformer no-load closing proposed in an embodiment of the present invention;
[0033] Figure 3 is a schematic diagram of synchronous closing of an unloaded transformer in an embodiment of the present invention;
[0034] Figure 4 is an equivalent circuit diagram for measuring residual magnetic inductance after adding an impulse voltage source in an embodiment of the present invention;
[0035] Figure 5 is a residual magnetic inductance equivalent circuit diagram in an embodiment of the present invention;
[0036] Figure 6 is a current waveform diagram of the closing option based on the method in an embodiment of the present invention;
[0037] Figure 7 3 is a current waveform diagram of random closing in an embodiment of the present invention. DETAILED DESCRIPTION
[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0039] In this embodiment, a single-phase transformer is taken as an example to analyze the transient process of closing the no-load transformer to illustrate the generation mechanism of the magnetizing inrush current of the no-load transformer. Figure 2 The equivalent circuit diagram of the no-load transformer closing is shown in the figure. s (t) is the system voltage; R s , L s are the system equivalent resistance and equivalent inductance respectively; K is the circuit breaker; R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R m is the equivalent resistance of the excitation circuit.
[0040] Assume that the system voltage is:
[0041] u s (t) = U sm sin(ωt+α) (1)
[0042] Among them, ω is the system voltage angular frequency, and α is the closing phase angle.
[0043] Assume i1 is the excitation current, N1 is the number of turns of the primary winding, according to Figure 2 The voltage equation of the no-load transformer closing circuit can be listed as:
[0044]
[0045] For the transformer core, the relationship between the total magnetic flux Φ and the excitation current i can be expressed as:
[0046]
[0047] Substituting formula (3) into formula (2) yields:
[0048]
[0049] Solving the differential equation yields:
[0050]
[0051] Due to the line impedance, Φ m is the steady-state flux amplitude, which can be expressed as:
[0052]
[0053] The initial value of transient magnetic flux Φ(t) is the residual magnetism of the core before the transformer is switched on. Assume that the residual magnetism of the core is Φ r , then
[0054] Φ(0)=-Φ m cosα+C=Φ r (7)
[0055] Therefore, the dynamic magnetic flux in the core during the closing transient process can be obtained as:
[0056]
[0057] From the analysis of formula (8), we can see that the dynamic flux in the closing process is composed of periodic steady-state flux and non-periodic transient flux, and the transient flux decays according to the time constant τ = R1 / L1. Further analysis shows that the transient flux is also composed of two parts. One part is the bias magnetic Φ generated at the moment of closing to resist the sudden change of flux. m cosα, the other part is the core remanence Φ r Due to the existence of transient magnetic flux, the core magnetic flux is very easy to saturate during the closing process. The essence of synchronously closing the no-load transformer to suppress the excitation inrush current is to control the circuit breaker to close at the moment when the residual magnetic flux of the core is equal to the pre-induced magnetic flux, so as to eliminate the transient component in equation (8) and avoid the core magnetic flux from entering saturation, thereby suppressing the generation of excitation inrush current from the root. The principle is as follows: Figure 3 shown.
[0058] Based on the above principle, this embodiment provides a phase selection and closing method based on transformer residual magnetism measurement. For the ultra-high voltage converter transformer, its residual magnetism can be effectively measured before its next closing, so that the circuit breaker can accurately select the phase for closing according to the residual magnetism, and control and reduce the adverse effects of the excitation inrush current. Figure 1 As shown, the specific steps include:
[0059] S1: Decompose the total magnetic flux of the UHV converter transformer in the equivalent circuit of no-load transformer closing into leakage magnetic flux and residual magnetic flux;
[0060] In a specific embodiment, in S1, it can be known from formula (3) that the magnitude of the excitation current i is affected by the transformer flux, the number of coil turns and the primary inductance of the transformer; in this embodiment, in order to separate the residual flux from the total flux and thus study the residual flux, the total flux of the UHV converter transformer in the equivalent circuit of the no-load transformer closing is split to obtain the leakage flux and the residual flux, which are expressed as:
[0061] Φ=Φ σ +Φ r (9)
[0062] Then we can get
[0063]
[0064] In the formula, Φ σ and Φ r They are leakage flux and residual flux respectively.
[0065] S2: The residual magnetic flux is equivalent to the equivalent inductance with the initial magnetic flux, that is, the residual magnetic inductance L r , get the equivalent circuit of residual magnetism measurement test;
[0066] Specifically, analogous to a capacitor with an initial charge, the residual magnetic flux is equivalent to an equivalent inductance L with an initial magnetic flux. r , in circuit theory, L r It should be a nonlinear inductance that changes with the excitation current. However, considering that when analyzing the excitation inrush current suppression, the main focus is on the effect of the first cycle, its nonlinear characteristics are ignored in this embodiment, and L r Defined as a constant inductance with an initial energy.
[0067] S3: Establish voltage loop equation and current loop equation based on the equivalent circuit of residual magnetism measurement test;
[0068] In a specific embodiment, in S3, the voltage loop equation and the current loop equation established based on the equivalent circuit of the residual magnetism measurement test are respectively expressed as:
[0069]
[0070] Where, R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R m is the equivalent resistance of the excitation circuit, L r is the equivalent residual inductance; U is the impulse power supply voltage amplitude; I is the primary current of the transformer, I r is the current flowing through the residual magnetic inductance, and U0 is the voltage value equivalent to the energy on the residual magnetic inductance.
[0071] S4: Set the impulse voltage source voltage amplitude of the residual magnetism measurement test equivalent circuit and measure the current amplitude to solve the simultaneous equations formed by the voltage loop equation and the current loop equation to obtain the residual magnetism inductance L r The value of and the energy equivalent voltage U0 on the residual magnetic inductance;
[0072] Specifically, in this embodiment, an impulse voltage power supply is selected as the test power supply to ensure that the action time of the power supply is short, and thus the magnitude of the residual magnetism of the transformer will not be changed. The test equivalent circuit diagram is as follows: Figure 4 shown.
[0073] In a specific embodiment, in S4, the simultaneous equations formed by the voltage loop equation and the current loop equation are expressed as:
[0074]
[0075] Among them, since an impulse voltage power supply is used, it can be ensured that a relatively small effect is applied to the iron core. At the same time, since it is an impulse voltage power supply, the effect of the power supply can be understood as linear, that is:
[0076]
[0077] In the formula, △I is the measured primary current amplitude, and △t is the time of impulse power supply action;
[0078] Change the direction of the impulse power supply to obtain △I + and △I - , the two are the primary side current amplitudes corresponding to the positive and negative directions of the impulse power supply respectively;
[0079] △I + and △I - Substitute them into formula (13) respectively and solve the simultaneous equations to obtain the residual inductance L r The value of the voltage U0 equivalent to the energy on the residual magnetic inductance is then substituted into the new equivalent circuit parameters as follows: Figure 5 In the phase selection and closing circuit shown, equivalent residual magnetism parameters are used to replace the effect of residual magnetism.
[0080] S5: The residual magnetic inductance L to be solved r Substitute the value of and the value of the voltage U0 equivalent to the energy on the residual magnetic inductance into the equivalent circuit of the residual magnetic measurement test to obtain the line current expression of the transformer no-load closing;
[0081] In a specific embodiment, in S5, the residual magnetic inductance L r Substituting the voltage value U0 equivalent to the energy on the residual magnetic inductance into the equivalent circuit of the residual magnetic measurement test, the line current expression of the transformer no-load closing is obtained:
[0082]
[0083] Where, R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R s , L s are the system equivalent resistance and equivalent inductance respectively; R m is the equivalent resistance of the excitation circuit; α is the closing phase angle; ω is the system voltage angular frequency; s is the time for phase selection and closing.
[0084] S6: Before each closing, the optimal closing time is determined based on the line current expression of the transformer no-load closing to suppress the excitation inrush current.
[0085] Specifically, in this embodiment, two conditions need to be met to accurately measure the residual magnetism: (1) the measurement should be performed before each closing of the circuit breaker to avoid the influence of time and environment; and (2) the measurement method used should not affect the residual magnetism as much as possible.
[0086] In order to verify the effectiveness of this embodiment, simulation is performed in Simulink software, and the transformer voltage is set to 10kV, the capacity is 800kVA, the no-load current is 0.8%, the no-load loss is 1.4kW, the load loss is 7.5kW, the short-circuit impedance is 4.5%, the ratio is 10 / 0.4, the frequency is 50Hz, the initial residual magnetism is 0.6pu, and an impulse voltage simulation loop is built. According to the impulse voltage test results, the theoretical closing time is calculated and the closing experiment is carried out to obtain the following results. Figure 6 As shown in the figure, the results of random closing are compared with Figure 7 As shown in the figure, it can be seen that by adopting the random closing method, the primary side current can reach 77pu, and by using the method proposed in this embodiment to calculate the optimal closing time and then perform phase selection closing, the primary side current is only 0.13pu, which shows that this method can effectively suppress the excitation inrush current.
[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 phase selection and closing method based on transformer residual magnetism measurement, characterized in that: The specific steps include: S1: Disassemble the total magnetic flux of the UHV converter transformer in the equivalent circuit of the no-load transformer closing to obtain the residual magnetic flux; S2: Equivalent the residual magnetic flux to an equivalent inductance with an initial magnetic flux, namely, a residual magnetic inductance, to obtain an equivalent circuit for a residual magnetic measurement test; S3: Establish voltage loop equation and current loop equation based on the equivalent circuit of residual magnetism measurement test; S4: setting the voltage amplitude of the impulse voltage source of the residual magnetism measurement test equivalent circuit and measuring the current amplitude to solve the simultaneous equations formed by the voltage loop equation and the current loop equation to obtain the value of the residual magnetism inductance and the voltage value equivalent to the energy on the residual magnetism inductance; S5: Substitute the solved residual magnetic inductance value and the voltage value equivalent to the energy on the residual magnetic inductance into the residual magnetic measurement test equivalent circuit to obtain the line current expression of the transformer no-load closing; S6: Before each closing, the optimal closing time is determined based on the line current expression of the transformer no-load closing to suppress the excitation inrush current.
2. The phase selection and closing method based on transformer residual magnetism measurement according to claim 1 is characterized in that: In S3, the voltage loop equation and current loop equation established based on the equivalent circuit of the residual magnetism measurement test are expressed as follows: Where, R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R m is the equivalent resistance of the excitation circuit, L r is the equivalent residual magnetic inductance; U is the impulse power supply voltage amplitude; I is the primary current of the transformer, I r is the current flowing through the residual magnetic inductance, and U0 is the voltage value equivalent to the energy on the residual magnetic inductance.
3. The phase selection and closing method based on transformer residual magnetism measurement according to claim 2 is characterized in that: In S4, the simultaneous equations formed by the voltage loop equation and the current loop equation are expressed as: in: In the formula, △I is the measured primary current amplitude, and △t is the time of impulse power supply action; Change the direction of the impulse power supply to obtain △I + and △I - , the two are the primary current amplitudes corresponding to the positive and negative directions of the impulse power supply respectively; △I + and △I - Substitute them into formula (3) respectively and solve the simultaneous equations to obtain the residual inductance L r The value of and the value of the voltage U0 equivalent to the energy on the residual magnetic inductance.
4. The phase selection and closing method based on transformer residual magnetism measurement according to claim 3 is characterized in that: In S5, the solved residual magnetic inductance value and the voltage value equivalent to the energy on the residual magnetic inductance are substituted into the residual magnetic measurement test equivalent circuit, and the line current expression of the transformer no-load closing is obtained as follows: Where, R1 and L1 are the leakage resistance and leakage inductance of the primary winding of the transformer respectively; R s , L s are the system equivalent resistance and equivalent inductance respectively; R m is the equivalent resistance of the excitation circuit; α is the closing phase angle; ω is the system voltage angular frequency; s is the time for phase selection and closing.
5. The phase selection and closing method based on transformer residual magnetism measurement according to claim 4 is characterized in that: In S1, the total magnetic flux of the transformer in the equivalent circuit of the no-load transformer closing is disassembled to obtain the residual magnetic flux, which is expressed as: F=F σ +F r In the formula, Φ σ and Φ r They are leakage flux and residual flux respectively.