An improved BCTRAN simulation structure and method for three-phase three-column transformer considering core deep saturation characteristics

Abstract

The present invention discloses an improved BCTRAN simulation structure and method for a three-phase three-column transformer considering the deep saturation characteristics of the core. The method comprises the following steps: 1) establishing a BCTRAN matrix for a three-phase three-column transformer; 2) calculating the fundamental frequency component I of the current on the excitation side of the transformer; k And the fundamental frequency component of the voltage at the excitation side port U k ; 3) Calculate the input current I bctk ; 4) Calculate the deep saturation inductance L of the transformer port excitation branch satk ; 5) Calculate the deep saturation inductance of all ports of the transformer to obtain the complete excitation branch of the port. The structure includes a BCTRAN parameter module, an excitation branch, an ideal transformer and a winding resistance; The present invention adds an excitation branch that characterizes the difference in the spatial excitation characteristics of the core to the BCTRAN model port, establishes an improved BCTRAN model that considers the deep saturation characteristics of the core, and realizes the accurate characterization of the saturation characteristics of different ports of the transformer.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic transient research of transformer equipment, and in particular to an improved BCTRAN simulation structure and method for a three-phase three-column transformer taking into account core deep saturation characteristics. Background Art

[0002] The three-phase three-column transformer is one of the most important equipment in the power transmission and transformation link of the power system. Its operating status directly affects the safe and stable operation of the power system. Establishing a relatively accurate electromagnetic transient model of the three-phase three-column transformer is of great significance for analyzing the electromagnetic transient phenomena generated on the transformer and ensuring the safe operation of the power system.

[0003] The three-phase transformer models in the existing electromagnetic transient simulation software (EMTP) mainly include transformer saturation model, electromagnetic dual model, hybrid model, and BCTRAN model. The transformer saturation model requires that the number of windings is no more than three. When the number of windings is too large, numerical oscillation and other problems may occur. The electromagnetic dual model uses the electromagnetic dual principle to establish a model, which can reflect the corresponding relationship between the transformer magnetic circuit structure and the circuit elements. Each component of the model has actual physical meaning, but an accurate electromagnetic dual model requires detailed structural information inside the transformer and is complex to model. The hybrid model uses the admittance matrix to characterize the coupling relationship between windings and sets a virtual winding outside the model to connect the nonlinear excitation branch that characterizes the core topology structure. Like the electromagnetic dual model, an accurate hybrid model requires knowledge of the internal structure and size information of the transformer, which limits its application scope. The BCTRAN model uses a matrix form to characterize the coupling relationship of the leakage inductance between the windings. Although the model lacks physical meaning, the model is highly versatile and has high engineering simulation accuracy below 1kHz. It has excellent scalability for multi-winding transformers. However, the BCTRAN model is a linear model. When used for transient analysis involving core saturation, a nonlinear excitation branch can be added to the winding on the side of the transformer close to the core. The simulation error of this model is not large when the core is slightly saturated. When the transformer core enters deep saturation, the relative magnetic permeability of the core decreases, the excitation inductance value decreases sharply, the magnetic flux flowing into the air gap increases, and the saturation degree of the transformer core space shows significant differences. Studies have shown that when the core is deeply saturated, the simulation value of the excitation inrush current on the high-voltage winding side of the transformer is more accurate, while the simulation value of the excitation inrush current on the third winding side will have a large error. Therefore, in order to accurately characterize the saturation characteristics of the transformer port, it is necessary to accurately obtain the excitation characteristics of the excitation branches corresponding to each port of the transformer under the deep saturation state.

[0004] The rated operating point of power transformers is often designed near the knee point. The national standard stipulates that the no-load test should be carried out at 1.1 times the rated voltage. When the test voltage is further increased, the core gradually enters a deep saturation state, and the excitation current will increase rapidly, even equivalent to the rated current, causing the silicon steel sheet to produce a large magnetostrictive stress, causing the transformer body to vibrate and heat up seriously, and the noise increases. In addition, the test process also puts forward extremely stringent requirements on the capacity of the power supply. The research on the measurement method of the deep saturation inductance of the transformer has always been the focus and difficulty in the field of electromagnetic transient modeling. Summary of the invention

[0005] The object of the present invention is to provide an improved BCTRAN simulation method for a three-phase three-column transformer considering the core deep saturation characteristics, comprising the following steps:

[0006] 1) Obtain the positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance of the three-phase three-column transformer to be simulated, and establish the BCTRAN matrix of the three-phase three-column transformer, that is:

[0007]

[0008] In the formula, the elements in the three-phase three-column transformer BCTRAN matrix A include positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance.

[0009] 2) Calculate the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k ,Right now:

[0010] U k =N r (U Tk -I Tk R k ) / N k (2)

[0011] I k =N k I Tk / N r (3)

[0012] In the formula, R k Indicates the resistance of the kth phase. k=A,B,C,a,b,c. N r 、N k , U Tk ,I Tk They respectively represent the transformation ratio of the ideal transformer common turns side, the transformation ratio of the ideal transformer external port side, the ideal transformer external port voltage, and the ideal transformer common turns side voltage.

[0013] 3) Calculate the input current I bctk ,Right now:

[0014] I bctk =A(n,:)U (4)

[0015]

[0016] Where A(n,:) is a 1×6-order row vector, representing the nth row of the 6×6-order BCTRAN matrix. U is the fundamental frequency component of the voltage at the excitation side port, U k A 6×1 column vector.

[0017] 4) Calculate the deep saturation inductance L of the transformer terminal excitation branch satk ,Right now:

[0018]

[0019] Where ω is the angular frequency.

[0020] 5) Calculate the deep saturation inductance of all ports of the transformer and obtain the complete excitation branch of the port.

[0021] In calculating the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k Before the start of the test, an AC / DC mixed source excitation is applied to the current transformer port, and the other transformer ports are kept open, so as to monitor the voltage and current waveforms of the excitation side port and the voltage waveforms of other ports.

[0022] The invention discloses a structure of an improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics, comprising a BCTRAN parameter module, an excitation branch, an ideal transformer and a winding resistance.

[0023] The BCTRAN parameter module includes a BCTRAN parameter matrix that characterizes the coupling relationship between the windings of the transformer.

[0024] The excitation branch is used to characterize the difference in spatial excitation characteristics of the transformer core.

[0025] The ideal transformer is used to convert different voltage level sides of the transformer to the same voltage level.

[0026] The winding resistance is used to represent the resistance value of the transformer winding.

[0027] The BCTRAN parameter matrix includes positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence magnetizing inductance.

[0028] The excitation branch includes a parallel nonlinear inductor and a parallel resistor.

[0029] The excitation branch is added to each port of the BCTRAN model.

[0030] The technical effect of the present invention is unquestionable. The present invention adds an excitation branch that characterizes the difference in the spatial excitation characteristics of the core to the port of the BCTRAN model, establishes an improved BCTRAN model that takes into account the deep saturation characteristics of the core, and realizes the accurate characterization of the saturation characteristics of different ports of the transformer. At the same time, the excellent scalability of the BCTRAN model is effectively utilized to make the model easily adaptable to the electromagnetic transient simulation research of a multi-winding three-phase three-column transformer. The present invention has a simple and novel structure, excellent scalability, and strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of an improved BCTRAN model of a three-phase three-column transformer considering the core deep saturation characteristics of the present invention;

[0032] Figure 2 An improved BCTRAN model circuit diagram for a three-phase three-column transformer considering the core deep saturation characteristics;

[0033] Figure 3 (a) is a comparison diagram of transformer excitation inrush current test waveform and simulation waveform I; Figure 3 (b) is the comparison diagram II between the transformer excitation surge current test waveform and the simulation waveform. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0035] Embodiment 1:

[0036] See also Figures 1 to 3 , an improved BCTRAN simulation method for a three-phase three-column transformer considering the core deep saturation characteristics, comprising the following steps:

[0037] 1) Obtain the positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance of the three-phase three-column transformer to be simulated, and establish the BCTRAN matrix of the three-phase three-column transformer, that is:

[0038]

[0039] In the formula, the elements in the three-phase three-column transformer BCTRAN matrix A include positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance.

[0040] 2) Calculate the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k,Right now:

[0041] U k =N r (U Tk -I Tk R k ) / N k (2)

[0042] I k =N k I Tk / N r (3)

[0043] In the formula, R k Indicates the resistance of the kth phase. k=A,B,C,a,b,c. N r 、N k , U Tk ,I Tk They respectively represent the transformation ratio of the ideal transformer common turns side, the transformation ratio of the ideal transformer external port side, the ideal transformer external port voltage, and the ideal transformer common turns side voltage.

[0044] 3) Calculate the input current I bctk ,Right now:

[0045] I bctk =A(n,:)U (4)

[0046]

[0047] Where A(n,:) is a 1×6-order row vector, representing the nth row of the 6×6-order BCTRAN matrix. U is the fundamental frequency component of the voltage at the excitation side port, U k A 6×1 column vector.

[0048] 4) Calculate the deep saturation inductance L of the transformer terminal excitation branch satk ,Right now:

[0049]

[0050] Where ω is the angular frequency.

[0051] 5) Calculate the deep saturation inductance of all ports of the transformer and obtain the complete excitation branch of the port.

[0052] In calculating the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k Before the start of the test, an AC / DC mixed source excitation is applied to the current transformer port, and the other transformer ports are kept open, so as to monitor the voltage and current waveforms of the excitation side port and the voltage waveforms of other ports.

[0053] Embodiment 2:

[0054] The invention discloses a structure of an improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics, comprising a BCTRAN parameter module, an excitation branch, an ideal transformer and a winding resistance.

[0055] The BCTRAN parameter module includes a BCTRAN parameter matrix that characterizes the coupling relationship between the windings of the transformer.

[0056] The excitation branch is used to characterize the difference in spatial excitation characteristics of the transformer core.

[0057] The ideal transformer is used to convert different voltage level sides of the transformer to the same voltage level.

[0058] The winding resistance is used to represent the resistance value of the transformer winding.

[0059] The BCTRAN parameter matrix includes positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence magnetizing inductance.

[0060] The excitation branch includes a parallel nonlinear inductor and a parallel resistor.

[0061] The excitation branch is added to each port of the BCTRAN model.

[0062] Embodiment 3:

[0063] An improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics comprises the following steps:

[0064] 1) Obtain the positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance of the three-phase three-column transformer to be simulated, and establish the BCTRAN matrix of the three-phase three-column transformer, that is:

[0065]

[0066] In the formula, the elements in the three-phase three-column transformer BCTRAN matrix A include positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance.

[0067] 2) Calculate the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k ,Right now:

[0068] U k =N r (U Tk -I Tk R k ) / N k (2)

[0069] I k=N k I Tk / N r (3)

[0070] In the formula, R k Indicates the resistance of the kth phase. k=A,B,C,a,b,c. N r 、N k , U Tk ,I Tk They respectively represent the transformation ratio of the ideal transformer common turns side, the transformation ratio of the ideal transformer external port side, the ideal transformer external port voltage, and the ideal transformer common turns side voltage.

[0071] 3) Calculate the input current I bctk ,Right now:

[0072] I bctk =A(n,:)U (4)

[0073]

[0074] Where A(n,:) is a 1×6-order row vector, representing the nth row of the 6×6-order BCTRAN matrix. U is the fundamental frequency component of the voltage at the excitation side port, U k A 6×1 column vector.

[0075] 4) Calculate the deep saturation inductance L of the transformer terminal excitation branch satk ,Right now:

[0076]

[0077] Where ω is the angular frequency;

[0078] 5) Calculate the deep saturation inductance of all ports of the transformer and obtain the complete excitation branch of the port.

[0079] In calculating the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k Before the start of the test, an AC / DC mixed source excitation is applied to the current transformer port, and the other transformer ports are kept open, so as to monitor the voltage and current waveforms of the excitation side port and the voltage waveforms of other ports.

[0080] The invention discloses a structure of an improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics, comprising a BCTRAN parameter module, an excitation branch, an ideal transformer and a winding resistance.

[0081] The BCTRAN parameter module includes a BCTRAN parameter matrix that characterizes the coupling relationship between the windings of the transformer.

[0082] The excitation branch is used to characterize the difference in spatial excitation characteristics of the transformer core.

[0083] The ideal transformer is used to convert different voltage level sides of the transformer to the same voltage level.

[0084] The winding resistance is used to represent the resistance value of the transformer winding.

[0085] The BCTRAN parameter matrix includes positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence magnetizing inductance.

[0086] The excitation branch includes a parallel nonlinear inductor and a parallel resistor.

[0087] The excitation branch is added to each port of the BCTRAN model.

[0088] Embodiment 4:

[0089] An improved BCTRAN model of a three-phase three-column transformer considering the core deep saturation characteristics includes

[0090] BCTRAN parameter matrix, used to characterize the complex coupling relationship between transformer windings;

[0091] The excitation branch is used to characterize the differences in the spatial excitation characteristics of the transformer core;

[0092] Ideal transformer, used to convert different voltage level sides of transformer to the same voltage level to facilitate calculation;

[0093] Winding resistance is used to characterize the resistance value of transformer winding.

[0094] The BCTRAN parameter matrix is ​​composed of positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence magnetizing inductance parameters.

[0095] The excitation branch is composed of a nonlinear inductor and a resistor in parallel.

[0096] The excitation branch is added to each port of the BCTRAN model.

[0097] The inductance of the deep saturation section of the excitation branch is different and needs to be determined by experiment, including

[0098] Change the winding connection method. The side with star-connected windings can remain unchanged, while the side with delta-connected windings needs to open the internal connection and change the same-named ends to star connection.

[0099] In the deep saturation test, AC / DC mixed source excitation is applied to one of the ports while keeping the other ports open. The voltage and current waveforms of the port on the excitation side and the voltage waveforms of the other ports are recorded. The deep saturation test is performed on all ports in turn and the test data is recorded.

[0100] Deep saturation inductance calculation, using one of the port deep saturation test obtained port voltage and current data and BCTRAN parameter matrix to calculate the deep saturation inductance value, the calculation steps are as follows:

[0101] 1) Three-phase three-column transformer BCTRAN matrix:

[0102]

[0103] 2) Calculate the fundamental frequency component of the excitation side current and the fundamental frequency component of the excitation side port voltage. The calculation method is as follows:

[0104] U k =N r (U Tk -I Tk R k ) / N k (8)

[0105] I k =N k I Tk / N r (9)

[0106] 3) Current I flowing into the BCTRAN matrix bctk The calculation formula is as follows (k=A,B,C,a,b,c):

[0107] I bctk =A(n,:)U (10)

[0108]

[0109] Where A(n,:) is a 1×6 row vector representing the nth row of a 6×6 BCTRAN matrix, and U is the calculated U k A 6×1 column vector.

[0110] 4) The calculation method of deep saturation inductance of the port excitation branch is:

[0111]

[0112] 5) Use the deep saturation inductance as the slope to extend the deep saturation section of the original excitation branch, and perform a deep saturation inductance acquisition test on each port of the transformer to obtain the complete excitation branch of each port.

[0113] Embodiment 5:

[0114] The improved BCTRAN model of the three-phase three-column transformer considering the core deep saturation characteristics of this embodiment includes:

[0115] The BCTRAN parameter matrix A is used to characterize the complex coupling relationship between the transformer windings. Its matrix elements are composed of positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance. It is used to characterize the complex coupling relationship between the transformer windings. Its matrix parameters are as follows:

[0116]

[0117] The excitation branch parameters corresponding to each phase core are obtained through the test, and the deep saturation test is carried out on the secondary port of phase A of the transformer. The voltage data of each phase port and the current data of the excitation side are recorded synchronously. The complex form of the voltage vector of each port and the complex form of the current vector of the excitation side are as follows:

[0118]

[0119] I 1 =0.7463+j0.0360A (15)

[0120] The calculated deep saturation inductance of the excitation branch of the secondary port of phase A is 9.85mH.

[0121] A deep saturation test was performed on each port of the transformer to obtain the deep saturation inductance of the excitation branch of the corresponding port. The primary deep saturation inductance of phase A was 10.72mH, the primary deep saturation inductance of phase B was 16.23mH, the secondary deep saturation inductance of phase B was 15.54mH, the primary deep saturation inductance of phase C was 10.57mH, and the secondary deep saturation inductance of phase C was 9.89mH. The deep saturation inductance was used as the slope to extend the last point of the excitation branch of each port to obtain a complete excitation curve.

[0122] See also Figure 2 The present invention also discloses an improved BCTRAN model circuit diagram of a three-phase three-column transformer considering the core deep saturation characteristics, comprising the following steps:

[0123] 1) In the ATP-EMTP simulation software, the BCTRAN module is used to combine the corresponding transformer positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance to establish the BCTRNA model to characterize the coupling relationship between transformer windings;

[0124] 2) Use a splitter outside the BCTRAN module to separate the three-phase line and add the corresponding phase excitation branch, where the excitation branch is composed of a nonlinear inductor and a resistor in parallel, and the nonlinear inductor uses a single-value magnetization curve to describe the excitation characteristics;

[0125] 3) Ideal transformers are used at both ends of the model for isolation, which is used to convert different voltage levels into the same voltage level for easy calculation;

[0126] 4) Add winding resistance on the outside of the ideal transformer to characterize the resistance value of the transformer winding.

[0127] The actual three-phase three-column transformer and the three-phase three-column transformer finite element model were subjected to port excitation inrush current test, and the improved BCTRAN model of the three-phase three-column transformer considering the core deep saturation characteristics of the present embodiment was used for simulation. When the excitation was applied to the rated voltage, the transformer produced an excitation inrush current phenomenon when the switch was closed. The actual transformer B phase first peak measured current was 12.42A, the current first peak value simulated in the present embodiment was 11.73A, and the current first peak value simulated by the traditional model was 10.65A, and the error was reduced from 14.3% to 5.6%. The excitation inrush current test was carried out on the finite element model of the three-phase three-column transformer. The finite element model C phase simulated current first peak value was 35.79A, the current first peak value simulated in the present embodiment was 32.59A, and the current first peak value simulated by the traditional model was 22.94A, and the error was reduced from 35.9% to 9.1%. Therefore, the present invention is more accurate in characterizing the port saturation characteristics of the transformer and has stronger applicability.

Claims

1. An improved BCTRAN simulation method for a three-phase three-column transformer considering the core deep saturation characteristics, characterized in that: The following steps are involved: 1) Obtain the positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance of the three-phase three-column transformer to be simulated, and establish the BCTRAN matrix of the three-phase three-column transformer; 2) Calculate the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k ,Right now: U k =N r (U Tk -I Tk R k ) / N k (1) I k =N k I Tk / N r (2) In the formula, R k Indicates the resistance of the kth phase; k = A, B, C, a, b, c; N r 、N k , U Tk ,I Tk They represent the transformation ratio of the ideal transformer common turns side, the transformation ratio of the ideal transformer external port side, the ideal transformer external port voltage, and the ideal transformer common turns side voltage respectively; 3) Calculate the input current I bctk ,Right now: I bctk =A(n,:)U (3) U=[U A IN a IN B IN b IN C IN c ] T (4) Where A(n,:) is a 1×6-order row vector, representing the nth row of the 6×6-order BCTRAN matrix; U is the fundamental frequency component of the voltage at the excitation side port, U k A 6×1-order column vector composed of; 4) Calculate the deep saturation inductance L of the transformer terminal excitation branch satk ,Right now: Where ω is the angular frequency; 5) Calculate the deep saturation inductance of all ports of the transformer and obtain the complete excitation branch of the port.

2. The improved BCTRAN simulation method for a three-phase three-column transformer considering the core deep saturation characteristics according to claim 1 is characterized in that: In calculating the fundamental frequency component I of the transformer excitation side current k And the fundamental frequency component of the voltage at the excitation side port U k Before the start of the test, an AC / DC mixed source excitation is applied to the current transformer port, and the other transformer ports are kept open, so as to monitor the voltage and current waveforms of the excitation side port and the voltage waveforms of other ports.

3. The improved BCTRAN simulation method for a three-phase three-column transformer considering the core deep saturation characteristics according to claim 1 is characterized in that: The BCTRAN matrix of a three-phase three-column transformer is shown below: In the formula, the elements in the three-phase three-column transformer BCTRAN matrix A include positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence excitation inductance.

4. A structure for improving the BCTRAN simulation method of a three-phase three-column transformer considering the core deep saturation characteristics as claimed in any one of claims 1 to 3, characterized in that: Includes BCTRAN parameter module, excitation branch, ideal transformer and winding resistance; The BCTRAN parameter module includes a BCTRAN parameter matrix that characterizes the coupling relationship between each winding of the transformer; The excitation branch is used to characterize the difference in spatial excitation characteristics of the transformer core; The ideal transformer is used to convert different voltage level sides of the transformer to the same voltage level; The winding resistance is used to represent the resistance value of the transformer winding.

5. The structure of the improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics according to claim 4, characterized in that: The BCTRAN parameter matrix includes positive-sequence short-circuit inductance, zero-sequence short-circuit inductance, and zero-sequence magnetizing inductance.

6. The structure of the improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics according to claim 4, characterized in that: The excitation branch includes a parallel nonlinear inductor and a parallel resistor.

7. The structure of the improved BCTRAN simulation method for a three-phase three-column transformer considering core deep saturation characteristics according to claim 4, characterized in that: The excitation branch is added to each port of the BCTRAN model.

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