Non-disassembly lead winding frequency response distribution parameter modeling method for converter transformer

Abstract

The invention discloses a non-disassembly lead winding frequency response distribution parameter modeling method for a converter transformer. The method comprises the following steps: establishing a circuit model of a winding; calculating electrical data before winding deformation according to actual parameters of each element of the converter transformer; setting simulation deformation and element parameter variation, and calculating electrical data after winding deformation; and performing simulation analysis to obtain a frequency response curve. The electrical parameters before and after winding deformation are calculated more accurately through vectors, a frequency response curve is obtained by using a winding distribution parameter model, and the accuracy of non-lead-disassembly detection of the converter transformer can be improved by combining the changes of inductance parameters and capacitance parameters, the detection efficiency of the converter transformer is improved, and safe and stable operation of a power grid is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of power transmission and distribution technology, and in particular to a method for modeling the frequency response distributed parameters of converter transformers without disconnecting lead windings. Background Technology

[0002] Converter transformers are a key piece of equipment in power systems, primarily functioning to achieve bidirectional conversion of electrical energy, thereby facilitating the efficient transfer of power between different voltages and frequencies. Simultaneously, by improving energy transmission efficiency and reducing energy loss, they are core equipment in ultra-high voltage direct current (UHVDC) transmission systems, directly impacting the safe and reliable operation of the entire DC transmission system. Therefore, the State Grid Corporation of China stipulates that converter transformers must undergo preventative testing during power outages according to regulations. As capacity gradually increases, converter transformer leads become thicker, resulting in a large workload for disconnecting and reconnecting leads. Furthermore, frequent disconnection and reconnection of leads can cause cumulative mechanical damage to the bushings themselves, bushing lead joints, and bushing riser mounts. Especially for UHV converter transformers, the top terminal block of the high-voltage side bushing is nearly 20 meters above the ground, requiring the use of aerial work platforms and cranes for lead disconnection and installation, presenting problems of high labor intensity, high operational risks, and long processing times.

[0003] In recent years, research on transformer testing without disconnecting leads has gradually increased, and the frequency response method is one of the commonly used testing techniques for converter transformers without disconnecting leads. In simulation studies using the frequency response method to detect winding deformation, it is usually assumed that the electric field is uniformly distributed and the magnetic field changes uniformly before and after deformation. Different types of deformation are simulated by simply adjusting the model parameters in the equivalent circuit, but this method has a large error.

[0004] Based on the above-mentioned technical problems, this application proposes a method for modeling the frequency response distributed parameters of converter transformer windings without disconnecting leads. Summary of the Invention

[0005] The purpose of this invention is to provide a method for modeling the frequency response distributed parameters of converter transformers without disconnecting lead windings, in order to solve the technical problems mentioned in the background art. This purpose is achieved through the following technical solution: A method for modeling the distributed parameters of the frequency response of a converter transformer without disconnecting the lead windings includes the following steps: Step S1: Establish the circuit model of the winding; Step S2: Calculate the electrical data of the winding before deformation based on the actual component parameters of the converter transformer and the parameters obtained through calculation; Step S3: Set the deformation mode for the circuit model of the winding, set the simulated deformation amount and the magnitude of component parameter changes, and calculate the electrical data after the winding deformation; Step S4: Construct a winding distributed parameter model based on the circuit model of the winding, substitute the electrical parameters before and after deformation into the winding distributed parameter model, perform simulation analysis, and obtain the frequency response curve; Step S5: Compare the frequency response curve obtained from the simulation with the measured data to evaluate the winding deformation state.

[0006] Furthermore, the electrical data mentioned in step S3 includes the capacitance parameter C, the inductance parameter L, and the resistance parameter r.

[0007] Furthermore, the capacitance parameter is the capacitance to ground, which is obtained based on the actual converter transformer.

[0008] Furthermore, the inductance parameters include self-inductance and mutual inductance when the current I flows only through the i-th turn of the winding: In the formula, Let the self-inductance of the i-th turn be... Let ω be the angular frequency, and Im be the symbol for the imaginary part. Let be the voltage on the i-th turn. For mutual intuition, Let be the induced voltage on the j-th turn.

[0009] Furthermore, the resistance parameter r is determined based on the model of the converter transformer itself.

[0010] Furthermore, the simulated deformation includes at least one of radial deformation, axial deformation, and inter-turn short circuit.

[0011] Furthermore, methods for constructing winding distributed parameter models include: Step S41: Based on the actual physical structure of the converter transformer winding, electrically discretize it into N consecutive and identical π-type unit circuits. Step S42: Characterize each π-type unit circuit using a lumped π-type equivalent circuit; Step S43: Connect N π-type unit circuits in series and integrate lead wire models at the beginning and end, i.e., winding distributed parameter models.

[0012] Furthermore, the π-type unit circuit includes capacitors, inductors, and resistors, and several π-type unit circuits are connected in series to obtain the winding distributed parameter model.

[0013] The technical solutions provided in this application have at least the following technical effects or advantages:

[0014] By accurately calculating the electrical parameters of the winding before and after deformation using the vector method, and obtaining the frequency response curve using the winding distributed parameter model, combined with the changes in inductance and capacitance parameters, the accuracy of non-disconnection testing of converter transformers can be improved, the testing efficiency of converter transformers can be increased, and the safe and stable operation of the power grid can be ensured. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 This is a circuit model diagram of the winding in an embodiment of this application; Figure 2 This is a converter transformer winding model without disconnecting the leads, as described in the embodiments of this application. Figure 3 The time domain diagram (a) and frequency domain diagram (b) obtained when the input signal frequency is set to 200kHz in the embodiments of this application. Figure 4 The time domain diagram (a) and frequency domain diagram (b) obtained when the input signal frequency is set to 500kHz in the embodiments of this application. Figure 5 The time domain diagram (a) and frequency domain diagram (b) obtained when the input signal frequency is set to 900kHz in the embodiment of this application. Detailed Implementation

[0017] To better understand the above technical solutions, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, will illustrate the technical solutions in detail. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] A method for modeling the distributed parameters of the frequency response of a converter transformer without disconnecting the lead windings includes the following steps: Step S1: Establish a circuit model of the winding based on a converter transformer of model D-800 / 35. The specific parameters are shown in Table 1. The circuit model of the winding includes components such as capacitors, inductors, resistors, signal sources, and leads.

[0019] Table 1 Main parameters of converter transformer

[0020] Step S2: Based on the component parameters of the actual converter transformer and the electrical parameters obtained through calculation, calculate the electrical data of the winding before deformation. Obtain the capacitance parameters of the actual converter transformer, calculate the inductance through equations, and calculate the resistance parameters using its own model number, thereby obtaining the electrical data of the winding before deformation.

[0021] Step S3: Set the deformation mode for the circuit model of the winding, set the simulated deformation amount and the magnitude of component parameter changes, and calculate the electrical data of the winding after deformation. The simulated deformation amount includes radial deformation, axial deformation, and inter-turn short circuit. The parameters of each component are changed according to the magnitude of the deformation, and the electrical data of the winding after deformation is further calculated through equations.

[0022] In step S3, the electrical data includes the capacitance parameter C, the inductance parameter L, and the resistance parameter r.

[0023] The capacitance parameter is the capacitance to ground, which is obtained based on the actual converter transformer, as shown in Table 2.

[0024] Table 2. Capacitor parameters (pF) on three sides of the converter transformer

[0025] Inductance parameters include self-inductance and mutual inductance, when the current I flows through only the i-th turn of the winding: In the formula, Let the self-inductance of the i-th turn be... Let ω be the angular frequency, and Im be the symbol for the imaginary part. Let be the voltage on the i-th turn. For mutual intuition, Let be the induced voltage on the j-th turn. The calculated inductance parameters of the three sides are shown in Table 3.

[0026] Table 3. Inductance parameters (nH) of the three sides of the converter transformer

[0027] The resistance parameter r is determined based on the converter transformer's model. Given a rated capacity of 800kVA, a grid-side voltage of 30kV, a valve-side voltage of 10.5kV, and currents flowing through the valve-side winding (737A) and the grid-side winding (76.2A), the calculated grid-side winding resistance is 5.9Ω, the valve-side winding resistance is 0.73Ω, and the regulating-side winding resistance is 0.009Ω.

[0028] In step S3, the simulated deformation amount and the magnitude of component parameter changes are set. This method sets the radial deformation of the winding, i.e., the winding is concave. This deformation mainly changes the spatial distribution of the winding, as well as the degree of electromagnetic coupling and electric field distribution characteristics between the windings. The circuit model of the winding is designed as follows: In the RCL equivalent circuit, the component parameters corresponding to the regulating side, valve side, and grid side windings within the entire winding structure region are adjusted to simulate the changes in inductance and capacitance caused by radial deformation. The shortened inter-turn distance leads to enhanced electromagnetic coupling, increasing the inductance of the three winding sides by 10%; simultaneously, the narrowed insulation gap increases the capacitance by 15%. Regarding resistance parameters, although the winding structure changes, the conductor cross-sectional area and total current path length do not change significantly during deformation. Therefore, without considering secondary effects such as hotspot damage or contact degradation, this invention maintains a constant resistance value in the modeling.

[0029] Step S4: Construct a winding distributed parameter model based on the circuit model of the winding, substitute the electrical parameters before and after deformation into the winding distributed parameter model, perform simulation analysis, and obtain the frequency response curve; The methods for constructing the winding distributed parameter model include: Step S41: Based on the actual physical structure of the converter transformer winding, the actual physical structure is electrically discretized into N consecutive and identical π-type unit circuits. The determination of the number of units N needs to be balanced between model accuracy and computational complexity. It is usually determined based on the physical length of the winding and the wavelength corresponding to the highest frequency of interest, ensuring that the electrical size of each unit is much smaller than the minimum wavelength. Step S42: Characterize each π-type unit circuit using a lumped π-type equivalent circuit; the equivalent circuit includes series branches and parallel branches. The series branches include the unit's self-inductance, DC resistance, and AC resistance characterizing high-frequency losses; the parallel branches include the unit's capacitance to ground and the inter-turn (or inter-pane) capacitance between units. Step S43: Connect N π-type unit circuits in series and integrate lead wire models at the beginning and end to form a complete distributed parameter model of the converter transformer without disconnecting the lead wire windings. Step S5: Compare the frequency response curve obtained from the simulation with the measured data to evaluate the winding deformation state.

[0030] Specifically, such as Figure 1As shown, a distributed parameter model of the winding is established using electromagnetic transient simulation software. This model consists of multiple π-type unit circuits connected in series, each integrating electrical components such as capacitors, resistors, and inductors. By treating the winding as a collection of distributed parameter chains, the parameters of each chain segment can be calculated separately, thus integrating them into a more complex and realistic distributed parameter model of the converter transformer winding. In this model, the determination of component parameters depends on the geometry of the converter transformer, the electrical characteristics of the materials used, and the winding layout. The valve-side winding can be modeled as a series-parallel circuit with equivalent capacitance and inductance, where the equivalent capacitance represents the inter-winding capacitance and the capacitive parameters inherent in the winding itself. Although the actual valve-side winding is not a pure capacitor, this distributed parameter model is sufficient to effectively simulate actual electrical behavior.

[0031] like Figure 2 As shown, two leads were placed at the break points on the grid side and valve side of the winding distributed parameter model to obtain a non-disassembled converter transformer winding circuit model.

[0032] As shown in Table 4, the frequency response curve was obtained by setting the waveform parameters of the pulse power signal using electromagnetic transient simulation software. In the parameter settings, Peak represents the simulated peak value, and Freq represents the simulated frequency.

[0033] Table 4 Excitation signal source parameters

[0034] 1) Low-frequency waveform comparison analysis The time domain plot (a) and frequency domain plot (b) obtained when the input signal frequency is set to 200kHz are as follows: Figure 3 As shown in the diagram, in the time domain, after the lead was removed, the waveform exhibited irregular fluctuations between -11 and 13 dB for the first 30 µs, with a period of approximately 1 µs. After 30 µs, the fluctuations gradually decreased and became more regular. In contrast, the waveform without the lead remained within a range of -10 to 10 dB, exhibiting a more regular fluctuation with a period of approximately 2 µs. Its waveform was slightly smaller before 20 µs, and thereafter maintained a period of approximately 2 µs. In the frequency domain, the waveforms obtained by both methods showed almost identical trends. Both waveforms showed a significant increase in amplitude at 450 kHz, followed by a rapid decrease, then a sustained increase until around 900 kHz when they began to decline. Except for 180 kHz, the waveform with the lead removed exhibited higher amplitudes at other frequencies.

[0035] 2) Comparative analysis of intermediate frequency waveforms The time domain plot (a) and frequency domain plot (b) obtained when the input signal frequency is set to 500kHz are as follows: Figure 4As shown in the time domain plot, the waveform at the intermediate frequency (IF) with the leads intact overlaps more closely with the waveform at the lower frequencies with the leads completely removed. Both waveforms exhibit amplitude oscillations within the range of -12 to 12 dB, gradually decreasing and becoming more regular after 25 µs. The frequency domain plot also demonstrates their high similarity; the amplitudes of both experimental methods increase uniformly before 800 kHz, reaching their maximum value at 900 kHz. At 950 kHz, the waveform with the leads removed experiences a greater drop, resulting in a higher final amplitude for the waveform with the leads intact compared to the one with the leads removed.

[0036] 3) High-frequency waveform comparison and analysis The time-domain plot (a) and frequency-domain plot (b) obtained when the input signal frequency is set to 900kHz are as follows: Figure 5 As shown in the time domain graph, the waveform without disconnected leads oscillates only within the range of -7 to 7 dB before 20 µs, which is half the waveform with all leads disconnected. However, the amplitude patterns of the two waveforms are consistent, with periods of approximately 1 µs, and they gradually stabilize after 40 µs. The frequency domain graph also shows that the curve without disconnected leads is smaller than that with all leads disconnected before reaching 900 kHz, but the changes in the curves are roughly the same. The amplitude of both curves drops sharply at 840 kHz, then increases again, and finally gradually decreases at 880 kHz.

[0037] After describing and comparing the two test methods at three frequencies, it can be found that the waveforms with no leads removed and with all leads removed (i.e., with and without the mesh-side leads removed) have the highest similarity at the intermediate frequency. This indicates that when we choose the method of not removing the leads at all to replace the traditional method of removing the leads, it is best to conduct the test when the intermediate frequency (500kHz) signal is input.

[0038] The technical solutions provided in this application have at least the following technical effects or advantages: The vector method can accurately calculate the electrical data before and after winding deformation, and obtain the frequency response curve using the winding circuit model. Combined with the changes in inductance and capacitance parameters, it can improve the accuracy of non-disconnection testing of converter transformers, improve the testing efficiency of converter transformers, and ensure the safe and stable operation of the power grid.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., 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 frequency response distribution parameter modeling of a leadless winding of a converter transformer, comprising the following steps: Step S1, establishing a circuit model of the winding; Step S2, calculating electrical data before deformation of the winding according to element parameters of an actual converter transformer and parameters obtained through calculation; Step S3, setting a deformation mode for the circuit model of the winding, setting a simulated deformation amount and a variation size of element parameters, and calculating electrical data after deformation of the winding; Step S4, constructing a winding distribution parameter model based on the circuit model of the winding, substituting the electrical parameters before and after deformation into the winding distribution parameter model, performing simulation analysis, and obtaining a frequency response curve; Step S5, comparing the frequency response curve obtained through simulation with measured data, and evaluating a deformation state of the winding.

2. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 1, characterized in that, The electrical data in step S3 includes a capacitance parameter C, an inductance parameter L, and a resistance parameter r.

3. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 2, characterized in that, The capacitance parameter is a ground capacitance, which is obtained according to an actual converter transformer.

4. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 2, characterized in that, The inductance parameter includes self-inductance and mutual inductance, when a current I only flows through an i-th turn of the winding: wherein is the self-induction of the ith turn, is the angular frequency, Im is the imaginary unit, is the voltage over the ith turn, is the mutual inductance, is the induced voltage over the jth turn.

5. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 2, characterized in that, The resistance parameter r is determined according to a model of the converter transformer.

6. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 1, characterized in that, The simulated deformation amount includes at least one of radial deformation, axial deformation, and inter-turn short circuit.

7. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 1, characterized in that, The method for constructing the winding distribution parameter model includes: Step S41, discretely dividing the winding of the converter transformer into N continuous and identical π-type unit circuits in an electrical aspect according to an actual physical structure of the winding; Step S42, characterizing each π-type unit circuit with a lumped π-type equivalent circuit; Step S43, connecting the N π-type unit circuits in series, and integrating a lead model at the first and last ends, i.e., the winding distribution parameter model.

8. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 1, characterized in that, The π-type unit circuit includes a capacitance, an inductance, and a resistance, and a plurality of the π-type unit circuits are connected in series to obtain the winding distribution parameter model.

9. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 1, characterized in that, In step S3, radial deformation of the winding, i.e., a concave mode of the winding, is set.

10. The method for frequency response distributed parameter modeling of a leadless winding of a converter transformer according to claim 1, characterized in that, In the winding distribution parameter model, the valve-side winding is modeled as a series-parallel circuit with equivalent capacitance and inductance, wherein the equivalent capacitance represents inter-winding capacitance and capacitive parameters of the winding itself.

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