A method for determining the capacity of a converter transformer induction test power supply considering the superposition of capacitive loads

Abstract

The present application relates to a kind of commutation inductive test power supply fixed capacity method considering capacitive load superposition, belong to high voltage test and power equipment on-site maintenance technical field.First, by single commutation empty load inductive voltage rise experiment, the excitation current of valve side when network side reaches voltage standard value and basic voltage are measured.Second, based on the ratio calculation valve side standard input voltage, and according to this quantitative calculation valve tower ground stray capacitance current and network side coupling capacitor conversion to valve side equivalent capacitive current.Finally, the measured excitation current and double-side capacitive current component are directly superimposed to obtain total driving current, and the ratio correlation type dynamic compensation factor based on measured data regression is constructed, and finally the rated capacity of test power supply is determined.The present application solves the problem of complex load capacity estimation difficulty in few solution introduction condition and error amplification problem caused by high ratio by mixed strategy of measurement and calculation and ratio correlation correction mechanism, and provides a standard basis for test power supply selection.

Description

Technical Field

[0001] This invention belongs to the technical field of high voltage testing and on-site maintenance of power equipment. More specifically, it relates to a method for calibrating a converter transformer induction test power supply that takes into account capacitive load superposition. Background Technology

[0002] As a core component of DC transmission systems, the insulation performance of the grid-side bushings of converter transformers directly impacts operational safety. Traditional bushing pressure tests employ a full disconnection mode, requiring the complete removal of high-voltage leads and auxiliary components. This approach suffers from drawbacks such as lengthy operation times and significant risks associated with working at heights. Therefore, the minimal disconnection inductive pressure testing technology, which retains most electrical connections, has become a trend in maintenance development. However, when performing minimal disconnection pressure testing verification on a single converter transformer, the electrical topology of the test circuit undergoes a fundamental change. The load is no longer simply the transformer itself, but rather a complex parallel system encompassing the transformer's inductive excitation impedance and multiple external capacitive components.

[0003] In practical engineering, existing methods for estimating test power supply capacity often only focus on the excitation power requirements of the converter transformer itself, severely neglecting the stray capacitance to ground of the valve tower structure connected to the valve side, and the equivalent capacitive load of the coupling capacitors on the grid side that have not been removed, referred to the low-voltage side via the transformer ratio. Furthermore, traditional methods typically use fixed empirical margin coefficients when determining power supply capacity, failing to consider the amplification effect of the converter transformer ratio on the accuracy of the grid-side load. This calculation method easily leads to error accumulation under high transformer ratio conditions: either insufficient capacity prevents the grid-side induced voltage from reaching the preset standard, resulting in test failure; or, for safety, large-capacity equipment is blindly selected, resulting in bulky equipment that cannot meet the needs of portable on-site testing. Therefore, there is an urgent need for a power supply capacity calibration method that comprehensively considers the measured excitation of a single converter transformer, the superposition of capacitive loads on both sides, and the influence of transformer ratio correlation. Summary of the Invention

[0004] The purpose of this method is to propose a capacity determination method for the converter transformer induction test power supply that takes into account the superposition of capacitive loads, providing a standardized calculation basis and technical support for the selection, capacity optimization and lightweight design of the converter transformer field induction withstand voltage test power supply.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] S1: Build a basic test platform for induction voltage application of a single converter transformer. Under no-load conditions, with the converter transformer grid side and valve side bushing disconnected from external auxiliary facilities, apply excitation voltage to the valve side winding using power frequency power supply until the induced voltage of the grid side bushing reaches the preset test standard value. Measure and record the measured excitation current input to the valve side winding at this time.

[0007] S2: Based on the preset test standard value and the grid-valve side voltage ratio of the converter transformer, calculate the standard input voltage required for the valve side winding during the formal test. This voltage value is the quotient of the test standard value and the voltage ratio.

[0008] S3: Obtain the stray capacitance value of the valve tower to ground connected to the valve side bushing under actual field conditions. Based on the standard input voltage obtained in step S2, use the capacitance current calculation formula to obtain the valve side capacitive current component consumed by the stray capacitance of the valve tower to ground.

[0009] S4: Obtain the capacitance value of the coupling capacitor connected in parallel under the actual working conditions of the grid-side bushing, calculate the grid-side capacitor current based on the preset test standard value, and convert it to the valve-side circuit using the voltage ratio to obtain the grid-side converted capacitive current component corresponding to the grid-side coupling capacitor.

[0010] S5: The measured excitation current obtained in step S1, the valve-side capacitive current component obtained in step S3, and the grid-side converted capacitive current component obtained in step S4 are algebraically superimposed to obtain the total drive current; at the same time, based on the regression analysis of a large amount of historical measured data, a transformer ratio-related dynamic compensation factor is constructed; finally, the total drive current, the valve-side standard input voltage, and the transformer ratio-related dynamic compensation factor are multiplied together to determine the rated capacity of the test power supply.

[0011] Preferably, in step S1, the preset test standard value of the induced voltage of the grid-side bushing is denoted as U. set In step S2, the grid-side to valve-side voltage transformation ratio of the converter transformer is denoted as K. Then, the valve-side standard input voltage U calculated in step S2... in Represented as formula (1):

[0012] (1).

[0013] Preferably, the calculation parameters involved in steps S3 and S4 are defined as follows: the stray capacitance of the valve tower to ground is denoted as C. valve The capacitance value of the coupling capacitor connected in parallel on the grid side is denoted as C. grid Let f be the frequency of the power supply, and let C be the parameter. valve and C grid All parameters are determined based on the nameplate parameters or measured data of the actual equipment on site.

[0014] Preferably, in step S3, the valve-side capacitive current component I consumed by the stray capacitance of the valve tower to ground is... C1 Calculated using formula (2), the equivalent capacitive current component I of the grid-side coupling capacitor referred to the valve side in step S4 is... C2 Calculated using formula (3):

[0015] (2);

[0016] (3);

[0017] In the formula, U in This is the standard input voltage on the valve side.

[0018] Preferably, in step S5, the rated capacity P of the test power supply is determined. 总 Described by formulas (4) and (5):

[0019] (4);

[0020] (5);

[0021] In the formula, I0 is the measured excitation current recorded in step S1; λ is the ratio-related dynamic compensation factor; K is the voltage ratio between the converter grid side and the valve side; α is the basic heat loss coefficient; and β is the ratio coupling gain coefficient.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention combines measured excitation data from a single converter transformer under no-load conditions with a theoretical conversion model for dual-sided capacitive loads, achieving for the first time accurate decoupling and quantification of power demand for mixed inductive-capacitive loads under conditions with limited decoupling. Specifically, addressing the problem of amplified errors in traditional estimation methods under high transformer ratio conditions, this invention constructs a nonlinear dynamic compensation model based on the statistical regression laws of multi-sample measured data and logarithmic saturation characteristics and load drift factors. This model effectively overcomes the problem of severely inflated capacity caused by linear extrapolation, achieving ultimate optimization and lightweight design of the test power supply capacity while ensuring coverage of capacitive voltage rise risks and line losses. This provides a standardized calculation basis for the scientific selection of power supplies for on-site induced withstand voltage tests of converter transformers. Attached Figure Description

[0024] Figure 1 This is a flowchart of the method of the present invention;

[0025] Figure 2 This is the equivalent circuit diagram of a capacitive load connected in parallel on both sides. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Further details of the technical solutions of the present invention will be described below.

[0027] Example 1

[0028] The present invention provides a method for calibrating a converter transformer inductive test power supply that takes into account capacitive load superposition, such as... Figure 1 As shown, the method includes the following steps:

[0029] S1. Build a basic test platform for induction voltage of a single converter transformer. Under no-load conditions, with the converter transformer grid side and valve side bushing disconnected from external auxiliary facilities, apply excitation voltage to the valve side winding using power frequency power supply until the induced voltage of the grid side bushing reaches the preset test standard value. Measure and record the measured excitation current input to the valve side winding at this time.

[0030] In this embodiment of the invention, at the converter transformer de-energization maintenance site, the connection between the grid-side bushing and the GIS pipeline and coupling capacitor is first disconnected, and the electrical connection between the valve-side bushing and the internal components of the valve tower is also disconnected, so that the converter transformer is in an "unloaded" state with only the main body remaining. A general-purpose power frequency test power supply is connected to the valve-side winding of the converter transformer. The power output is adjusted to gradually increase the induced voltage of the grid-side bushing until it reaches the preset test standard value U. set (In this embodiment, U) set (Set to 10kV). At this time, measure and record the current value at the input terminal of the valve-side winding, and record it as the measured excitation current I0. This step aims to accurately obtain the inductive excitation requirement of the converter transformer under a specific voltage through actual measurement, eliminating the error caused by the magnetic circuit saturation characteristics calculated theoretically;

[0031] S2, Calculate the standard input voltage required for the valve side winding during the formal test based on the preset test standard value and the grid-side-valve-side voltage ratio of the converter transformer;

[0032] In this embodiment of the invention, according to the preset net-side test standard value U set Using the nameplate parameters of the converter transformer—the grid-side / valve-side voltage ratio K—calculate the standard input voltage U required for the valve-side winding during formal testing. in The calculation formula is:

[0033] (1).

[0034] S3, obtain the stray capacitance value of the valve tower to ground connected to the valve side bushing under actual working conditions on site, and calculate the valve side capacitive current component consumed by the stray capacitance of the valve tower to ground.

[0035] In this embodiment of the invention, the stray capacitance C of the valve tower structure connected to the valve side sleeve to ground is obtained under actual field conditions. valve (Typically, the value is about 25nF). This capacitor is connected directly in parallel to the power supply output in the experiment. Based on the standard input voltage obtained in step S2, the capacitive current is calculated using formula (2):

[0036] (2);

[0037] In the formula, f is the power frequency, which is taken as 50Hz.

[0038] S4, obtain the capacitance value of the coupling capacitor connected in parallel with the grid-side bushing under actual field conditions, and calculate the grid-side converted capacitive current component corresponding to the grid-side coupling capacitor;

[0039] In this embodiment of the invention, the capacitance value C of the coupling capacitor connected in parallel with the grid-side bushing is obtained. grid (Typically, the value is approximately 5nF). This load is located on the high-voltage side of the transformer, and its current needs to be coupled to the low-voltage side through the transformer. This step uses the turns ratio K to convert the grid-side capacitive current to the valve side. The calculation formula is:

[0040] (3);

[0041] S5. Construct a dynamic compensation factor based on the ratio correlation of measured data regression, and multiply it by the total drive current and the valve-side standard input voltage to determine the rated capacity of the test power supply.

[0042] In embodiments of the present invention, such as Figure 2 The equivalent circuit diagram of the dual-side parallel connection of the decapacitive load shown requires the test power supply to provide not only the excitation current I0 of the converter transformer body, but also the local stray capacitance current I on the valve side. C1 And the grid-side capacitor current I derived from the transformer magnetic circuit coupling. C2 First, set I0 and I... C1 I C2 The total drive current is obtained by algebraic superposition. Then, in order to achieve scientific calibration of the power supply capacity, this invention abandons the traditional fixed empirical coefficients and innovatively constructs a transformation ratio-related dynamic compensation factor λ.

[0043] In this embodiment, the calculation model for the variable ratio-related dynamic compensation factor λ is not based on a single theoretical assumption, but rather on an empirical formula derived from statistical regression analysis of multiple sample measured data. Its construction process and the physical meaning of each parameter are as follows:

[0044] To determine the mathematical relationship between the converter transformer turns ratio K and the risk of power supply capacity error, measured data from induced withstand voltage tests of dozens of converter transformers with different voltage levels (covering ±500kV, ±800kV to ±1100kV) and different turns ratio ranges in past projects were collected. Comparative analysis revealed that while linear models showed acceptable accuracy in the low turns ratio range, the calculated recommended capacity far exceeded actual requirements under high turns ratio (K>2.5) conditions, resulting in a severely inflated power supply selection. Measured data showed that although the conversion error caused by leakage reactance voltage drop increased with increasing turns ratio K, its growth rate gradually slowed, exhibiting a clear "saturation convergence" characteristic. Curve fitting of discrete data points revealed that the natural logarithm function most accurately describes this physical law.

[0045] Based on the above data fitting results, this invention finally established a nonlinear empirical formula containing the ln(K) term as the calibration basis.

[0046] The λ calculation model used in this embodiment is:

[0047] (4);

[0048] The physical meanings of each parameter are as follows:

[0049] α is the basic heat loss coefficient, which is preferably set to 1.2 in this embodiment. This coefficient is used to cover the inherent power loss of the system that is independent of the sample ratio parameters, and consists of two parts:

[0050] First, considering the heat dissipation characteristics of portable power supplies during long-term continuous operation in the field, and in accordance with the thermal design specifications for power electronic equipment, a power margin of approximately 15% is reserved. Second, considering the long test leads and contact resistance in the field, which typically result in approximately 5% power loss. Taking both factors into account, the value of α is approximately 1.2.

[0051] β is the transformer ratio coupling gain coefficient, which is preferably set to 0.15 in this embodiment. This combined term β×ln(K) characterizes the nonlinear saturation characteristic of the transformer grid-valve voltage ratio K on the amplification of the referred error. Traditional methods assume that the referred error increases linearly with the transformer ratio K. However, this invention reveals that, constrained by the transformer core window height and the geometric dimensions of the leakage flux path, the error growth rate caused by the leakage reactance voltage drop actually exhibits diminishing marginal returns as the transformer ratio K increases, rather than an infinitely linear divergence. Therefore, the natural logarithm function ln(K) is introduced to soften the error amplification trend, and combined with the gain coefficient β, capacity design optimization is achieved while ensuring safety.

[0052] This is the load characteristic drift factor. It is used to dynamically quantify the degree of drift of the tested system from inductive to capacitive dominance and to compensate for the resulting capacitive voltage rise effect. The capacitive-inductance current ratio directly reflects the proportion of capacitive load current in the total current. When the ratio is small, the system is inductive, and voltage transmission is stable; when the ratio increases significantly, a large capacitive current flows through the transformer leakage reactance, generating an electromotive force opposite to the inductive voltage drop, leading to an abnormal rise in the actual grid-side voltage. This voltage distortion forces the power supply to output more reactive power to maintain magnetomotive force balance.

[0053] Finally, the rated capacity P of the test power supply 总 Determined as:

[0054] (5);

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calibrating a converter transformer inductive test power supply considering superimposed capacitive loads, characterized in that, Includes the following steps: S1: Build a basic test platform for induction voltage application of a single converter transformer. Under no-load conditions, with the converter transformer grid side and valve side bushing disconnected from external auxiliary facilities, apply excitation voltage to the valve side winding using power frequency power supply until the induced voltage of the grid side bushing reaches the preset test standard value. Measure and record the measured excitation current input to the valve side winding at this time. S2: Calculate the standard input voltage required for the valve side winding during the formal test based on the preset test standard value and the grid-side-valve-side voltage ratio of the converter transformer; S3: Obtain the stray capacitance value of the valve tower to ground connected to the valve side bushing under actual field conditions, and calculate the valve side capacitive current component consumed by the stray capacitance of the valve tower to ground. S4: Obtain the capacitance value of the coupling capacitor connected in parallel with the grid-side bushing under actual field conditions, and calculate the grid-side converted capacitive current component corresponding to the grid-side coupling capacitor; S5: Construct a dynamic compensation factor based on the ratio correlation of measured data regression, multiply it by the total drive current and the valve-side standard input voltage, and determine the rated capacity of the test power supply.

2. The method according to claim 1, characterized in that: In step S1, the preset test standard value of the induced voltage of the grid-side bushing is denoted as U. set In step S2, the grid-side to valve-side voltage transformation ratio of the converter transformer is denoted as K. Then, the valve-side standard input voltage U calculated in step S2... in Represented as formula (1): （1）。 3. The method according to claim 1, characterized in that: The calculation parameters involved in steps S3 and S4 are defined as follows: the stray capacitance of the valve tower to ground is denoted as C. valve The capacitance value of the coupling capacitor connected in parallel on the grid side is denoted as C. grid Let f be the frequency of the power supply, and let C be the parameter. valve and C grid Determined based on the nameplate parameters or measured data of the actual equipment on site.

4. The method according to claim 1, characterized in that: In step S3, the valve-side capacitive current component I consumed by the stray capacitance of the valve tower to ground C1 Calculated using formula (2), the equivalent capacitive current component I of the grid-side coupling capacitor referred to the valve side in step S4 is... C2 Calculated using formula (3): （2）； （3）； In the formula, U in This is the standard input voltage on the valve side.

5. The method according to claim 1, characterized in that: In step S5, the rated capacity P of the test power supply is determined. 总 Described by formulas (4) and (5): （4）； （5）； In the formula, I0 is the measured excitation current recorded in step S1; λ is the ratio-related dynamic compensation factor; K is the voltage ratio between the converter grid side and the valve side; α is the basic heat loss coefficient; and β is the ratio coupling gain coefficient.

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