Method for measuring parameters of double-circuit dc transmission line on same tower under high induced voltage environment

Abstract

The application discloses a method for measuring parameters of double-circuit DC transmission lines on the same tower in a high induced voltage environment, comprising the following steps: using multiple parallel combination modes for the first ends of four pole conductors, measuring the series impedance of the four pole line ends grounded through impedance and the short-circuit impedance of the four pole line ends directly grounded under different parallel combination conditions at a non-power frequency; according to the line length, and according to the series impedance of the four pole line ends grounded through impedance and the short-circuit impedance of the four pole line ends directly grounded under different parallel combination conditions, respectively calculating the characteristic impedance, the propagation coefficient under different parallel combination conditions, and then calculating the equivalent distributed impedance and the equivalent distributed admittance; according to the equivalent distributed impedance and the equivalent distributed admittance under different parallel combination conditions, obtaining each distribution parameter of the pole conductor unit length of the line. The scheme can realize effective suppression of induced voltage and accurate measurement of line parameters in a high induced voltage environment.

Description

Technical Field

[0001] This application relates to the field of electrical engineering technology, and in particular to a method for measuring the parameters of a double-circuit DC transmission line on the same tower under a high induced voltage environment. Background Technology

[0002] Double-circuit DC transmission lines mounted on the same tower have four single-pole conductors. In addition to their own resistance, inductance, and capacitance to ground, each conductor also has coupling capacitance and coupling inductance between the conductors. The influence of these parameters makes the fault behavior of double-circuit DC lines extremely complex, requiring theoretical calculations and simulations for study. This necessitates measuring all electrical parameters, including coupling parameters, of the double-circuit DC transmission line when it is constructed.

[0003] According to the power industry standard DL / T 1566-2016 "Guide for the Measurement of DC Transmission Line and Earth Electrode Line Parameters" and the American standard IEEE std. 1893-2015 "IEEE std.1893-2015, Guide for the Measurement of DC Transmission Line and Earth Electrode Line Parameters", when measuring the parameters of a double-circuit DC transmission line on the same tower, it is necessary to measure the zero-sequence open-circuit impedance when the four pole conductors at the beginning of the double-circuit DC line are connected in parallel with the end open-circuit. And when measuring the open circuit at the ends of the four pole conductors, the first four pole conductors are combined in pairs to form a two-phase positive sequence circuit, resulting in a total of three possible connection methods for measuring the two-phase positive sequence open circuit impedance. (i=1,2,3). It is also necessary to measure the zero-sequence short-circuit grounding impedance when the ends of the four conductors are short-circuited to ground, and when the four conductors at the beginning are connected in parallel. And when the ends of the four conductors are short-circuited to ground, the first four conductors are combined in pairs to form a two-phase positive sequence circuit, resulting in a total of three combinations of two-phase positive sequence short-circuit impedance. (i=1,2,3). Open-circuit impedance under the aforementioned four combinations. (i=0,1,2,3) and short-circuit impedance Based on the measurement results (i=0,1,2,3), the electrical parameters of the double-circuit transmission line on the same tower can be calculated according to theoretical analysis.

[0004] However, due to the length of long-distance DC transmission lines, which can reach thousands of kilometers, they inevitably run parallel to other ultra-high voltage AC and DC lines along the same corridor. When the double-circuit DC line on the same tower is open-circuited under no-load conditions, it can generate induced voltages as high as tens of thousands of volts. These induced voltages contain both DC and AC components, as confirmed in actual measurements. Therefore, the aforementioned measurement method presents many difficulties in practical operation, especially regarding personal safety and the safety of the measuring equipment. The excessively high induced voltage makes parameter measurements of double-circuit DC lines on the same tower almost impossible. Summary of the Invention

[0005] The purpose of this application is to solve a method for effectively suppressing induced voltage on the measured line under high voltage induced environment and for safely and accurately measuring the parameters of a double-circuit DC transmission line on the same tower.

[0006] This application provides a method for measuring parameters of a double-circuit DC transmission line erected on the same tower under high induced voltage conditions. The double-circuit DC transmission line includes four pole conductors arranged symmetrically about the tower axis. The two pole conductors on the left and two pole conductors on the right are arranged at equal vertical intervals. The specific method includes:

[0007] Step A: Connect the beginning ends of the four conductors in parallel as the first combination, and apply a single-phase power supply to ground at the beginning ends; with the ends of all four conductors directly grounded, synchronously collect the single-phase voltage output from the power supply at the beginning ends. and current And calculate the short-circuit impedance when all four pole conductors are short-circuited to ground under the first combination mode according to formula (1). Furthermore, with the ends of the four conductors grounded via impedance Z, the single-phase voltage output from the power supply at the first end is simultaneously collected. and current And calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z under the first combination method according to formula (2). :

[0008] (1)

[0009] (2)

[0010] Step B: Connect the two pole conductors on the left side of the tower in parallel at the beginning of the four pole conductors, and connect the two pole conductors on the right side of the tower in parallel as a second combination. Apply a two-phase positive sequence power supply between the left and right pole conductors at the beginning. With all four pole conductors directly grounded at their ends, synchronously collect the two-phase voltage output from the power supply at the beginning. , and current , And calculate the short-circuit impedance when the ends of all four pole conductors are directly grounded under the second combination method according to formula (3). Furthermore, with the ends of the four conductors grounded via impedance Z, the two-phase voltages output from the power supply at the starting end are simultaneously acquired. , and current , And calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z under the second combination method according to formula (4). :

[0011] (3)

[0012] (4)

[0013] Step C: Connect the two upper pole conductors in parallel at the beginning of the four pole conductors, and connect the two lower pole conductors in parallel as a third combination. Apply a two-phase positive sequence power supply between the upper and lower pole conductors at the beginning. With all four pole conductors directly grounded at their ends, synchronously sample the two-phase voltage output from the power supply at the beginning. , and current , And calculate the short-circuit impedance when the ends of all four pole conductors are directly grounded under the third combination method according to formula (5). Furthermore, with the ends of the four conductors grounded via impedance Z, the two-phase voltages output from the power supply at the starting end are simultaneously acquired. , and current , And calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z under the third combination method according to formula (6). :

[0014] (5)

[0015] (6)

[0016] Step D: Connect the upper left pole conductor and the lower right pole conductor in parallel at the beginning of the four pole conductors, and connect the lower left pole conductor and the upper right pole conductor in parallel as the fourth combination. Apply a two-phase positive sequence power supply between the upper left pole conductor and the upper right pole conductor at the beginning of the four pole conductors. With all four pole conductors directly grounded at their ends, synchronously collect the two-phase voltage output from the power supply at the beginning. , and current , And calculate the short-circuit impedance when the ends of all four pole conductors are directly grounded under the fourth combination method according to formula (7). Furthermore, with the ends of the four conductors grounded via impedance Z, the two-phase voltages output from the power supply at the starting end are simultaneously acquired. , and current , And calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z under the fourth combination method according to formula (8). :

[0017] (7)

[0018] (8)

[0019] Step E: Based on the length D of the parallel double-circuit DC transmission line on the same tower, measure the short-circuit impedance under the four different combinations of conditions from Step A to Step D. and series impedance Substitute the pairs (i=0,1,2,3) into formulas (9) and (10) respectively to calculate the characteristic impedance under the four different combinations. and propagation coefficient (i=0,1,2,3):

[0020] (i=0,1,2,3)(9)

[0021] (i=0,1,2,3)(10)

[0022] Step F: Calculate the characteristic impedances obtained in Step E under the four different combinations. and propagation coefficient Substituting (i=0,1,2,3) into formulas (11) and (12) in pairs, we obtain the equivalent distributed impedance under four different combinations. and equivalent distributed admittance (i=0,1,2,3):

[0023] (11)

[0024] (12)

[0025] Step G: Based on the equivalent distributed impedance under the four different combinations in Step F and equivalent distributed admittance (i=0,1,2,3), calculate the various distributed parameters of the double-circuit DC transmission line on the same tower according to formulas (13)-(17):

[0026] Resistance per unit length of a single polar conductor :

[0027] (13)

[0028] Resistance per unit length of the earth loop :

[0029] (14)

[0030] Conductivity per unit length to ground of a single polar conductor :

[0031] (15)

[0032] Formulas for calculating the self-inductance of a single pole conductor per unit length and the mutual inductance between pole conductors:

[0033] (16)

[0034] Where ω is the non-power frequency angular frequency of the power supply. The self-inductance per unit length of a single polar conductor. The mutual inductance per unit length between the upper left polar conductor and the upper right polar conductor (or the lower left polar conductor and the lower right polar conductor) of the tower. The mutual inductance per unit length between the upper left polar conductor and the lower left polar conductor (or the upper right polar conductor and the lower right polar conductor) of the tower. The mutual inductance per unit length between the upper left polar conductor and the lower right polar conductor (or the upper right polar conductor and the lower left polar conductor) of the tower;

[0035] Formulas for calculating the capacitance to ground of a single pole conductor per unit length and the coupling capacitance between pole conductors:

[0036] (17)

[0037] in, This refers to the capacitance to ground per unit length of a single-pole conductor. The coupling capacitance per unit length between the upper left polar conductor and the upper right polar conductor (or the lower left polar conductor and the lower right polar conductor) of the tower. This refers to the coupling capacitance per unit length between the upper left polar conductor and the lower left polar conductor (or the upper right polar conductor and the lower right polar conductor) of the tower. The coupling capacitance per unit length between the upper left pole conductor and the lower right pole conductor (or the upper right pole conductor and the lower left pole conductor) of the tower.

[0038] In formulas (13)-(17), Re(*) represents taking the real part of the complex number, Im(*) represents taking the imaginary part of the complex number, and ω is the angular frequency of the power supply.

[0039] In one embodiment, during the measurement, the series impedance Z is measured in real time at the measurement frequency ω.

[0040] This application, by grounding the end of the conductor being measured via impedance Z, can suppress the induced voltage on the measured line within a safe range while accurately measuring various parameters on a double-circuit DC transmission line on the same tower. This solution avoids the safety threats to measurement personnel and equipment posed by using an open-circuit method at the end of the line for measurement. Attached Figure Description

[0041] Figure 1 It is the measuring circuit used in existing regulations for measuring the zero-sequence open-circuit impedance of a double-circuit DC line on the same tower;

[0042] Figure 2 It is the measuring circuit used in existing regulations to measure the positive sequence open-circuit impedance of a two-phase DC line with two circuits on the same tower.

[0043] Figure 3 This is a schematic diagram of the spatial arrangement of the four pole conductors of a double-circuit DC transmission line spanning the same tower.

[0044] Figure 4 This is a schematic diagram of the self-parameters and coupling parameters between the four pole conductors of a double-circuit DC transmission line erected on the same tower.

[0045] Figure 5 This is a schematic diagram of the short-circuit impedance measurement circuit when the ends of the four polar conductors are short-circuited to ground in the first combination mode of the present invention.

[0046] Figure 6 This is a schematic diagram of the series impedance measurement circuit when the ends of the four polar conductors are grounded through impedance Z in the first combination method of the present invention.

[0047] Figure 7 This is a schematic diagram of the short-circuit impedance measurement circuit when the ends of the four polar conductors are short-circuited to ground under the second combination method of the present invention;

[0048] Figure 8 This is a schematic diagram of the series impedance measurement circuit when the ends of the four polar conductors are grounded through impedance Z under the second combination method of the present invention;

[0049] Figure 9 This is a schematic diagram of the short-circuit impedance measurement circuit when the ends of the four polar conductors are short-circuited to ground under the third combination method of the present invention;

[0050] Figure 10This is a schematic diagram of the series impedance measurement circuit when the ends of the four polar conductors are grounded through impedance Z under the third combination method of the present invention;

[0051] Figure 11 This is a schematic diagram of the short-circuit impedance measurement circuit when the ends of the four polar conductors are short-circuited to ground under the fourth combination method of the present invention;

[0052] Figure 12 This is a schematic diagram of a series impedance series circuit when the ends of the four polar conductors are grounded through impedance Z under the fourth combination method of the present invention. Detailed Implementation

[0053] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the technical principles of this application will be further explained in detail below with reference to the accompanying drawings and specific embodiments.

[0054] According to the power industry standard DL / T 1566-2016 "Guidelines for the Measurement of DC Transmission Line and Earth Electrode Line Parameters" and the American standard IEEE std. 1893-2015 "IEEE std.1893-2015, Guide for the Measurement of DC Transmission Line and Earth Electrode Line Parameters", when measuring the parameters of a double-circuit DC transmission line on the same tower, the following parameters need to be measured: Figure 1 The zero-sequence open-circuit impedance of the four pole conductors at the beginning of the double-circuit DC line when the end is open-circuited is shown. ; and according to Figure 2 The measurement shows the two-phase positive sequence open-circuit impedance under three different connection methods: when the ends of the four pole conductors are open-circuited, the four pole conductors at the beginning are combined in pairs to form a two-phase positive sequence circuit. (i=1,2,3). It is also necessary to measure the zero-sequence short-circuit grounding impedance when the ends of the four conductors are short-circuited to ground, and when the four conductors at the beginning are connected in parallel. ; and when the ends of the four conductors are grounded and short-circuited, the four conductors at the beginning are combined in pairs to form a two-phase positive sequence circuit, resulting in a total of three combinations of two-phase positive sequence short-circuit impedances. (i=1,2,3). Open-circuit impedance under the aforementioned four combinations. (i=0,1,2,3) and short-circuit impedance Based on the measurement results (i=0,1,2,3), the electrical parameters of the double-circuit transmission line on the same tower can be calculated according to theoretical analysis.

[0055] However, due to the length of long-distance DC transmission lines, which can reach thousands of kilometers, they inevitably run parallel to other ultra-high voltage AC and DC lines along the same corridor. When the double-circuit DC line on the same tower is open-circuited under no-load conditions, it can generate induced voltages of up to tens of thousands of volts. These induced voltages contain both DC and AC components, as confirmed in actual measurements. Therefore, in practical operation, according to... Figure 1 , Figure 2 When measuring the open-circuit impedance under no-load zero-sequence and related combinations, the excessively high induced voltage makes it almost impossible to measure the parameters of a double-circuit DC line on the same tower due to personal safety and the safety of the measuring equipment.

[0056] Therefore, this application addresses the difficulty in measuring the line parameters of double-circuit DC transmission lines on the same tower by proposing a method that can effectively suppress the induced voltage on the measured line and accurately measure the parameters of double-circuit DC transmission lines on the same tower under high induced voltage conditions.

[0057] In this embodiment, the smoothing reactor at the end of the DC line in the converter station can be directly used as the impedance Z for series grounding. Before measurement, the impedance-frequency characteristic of the smoothing reactor is measured, and the measurement results are substituted into formulas (9) and (10) for calculation. The specific principle and steps are as follows:

[0058] Figure 3 This is a typical arrangement of ultra-high voltage (UHV) double-circuit DC overhead transmission lines on the same tower. It adopts a single-circuit single-sided arrangement. Let A1 be the upper left single-pole conductor, A2 be the lower left single-pole conductor, B1 be the upper right single-pole conductor, and B2 be the lower right single-pole conductor. Let A1 and A2 represent the bipolar conductors of the first DC circuit, and B1 and B2 represent the bipolar conductors of the second DC circuit.

[0059] It should be noted that, since all pole conductors use the same type of conductor, the self-impedance of each single pole conductor is... and Earth-guided The same; and, the double-circuit DC transmission lines on the same tower are arranged symmetrically on the left and right with the tower as the axis, and the distance between A1 and B1 is equal to the distance between A2 and B2.

[0060] Figure 4 The coupling inductance and coupling capacitance between each pole wire are indicated, as well as the self-parameters of each individual wire.

[0061] At a certain cross-section of a double-circuit DC transmission line on the same tower, if the currents passing through the four conductors are respectively Then through the earth resistance r g The returned current is:

[0062] (18)

[0063] Reference Figure 4 The differential equations for the voltage and current of the four polar conductors can be written:

[0064] (19)

[0065] (20)

[0066] (twenty one)

[0067] (twenty two)

[0068] (twenty three)

[0069] (twenty four)

[0070] (25)

[0071] (26)

[0072] The inductance and capacitance parameters in equations (19)-(26) each have four values, requiring four linearly independent equations to solve simultaneously. This can be achieved by combining the four polar conductors in pairs to form one zero-sequence circuit and three two-phase positive-sequence circuits, thus obtaining the required values. Figure 4 The various self-parameters and coupling parameters are shown. The following analysis and measurement will be carried out in four steps (or four circuit combination methods) according to combination method 1, combination method 2, combination method 3 and combination method 4.

[0073] (1) Combination method 1 (zero sequence circuit)

[0074] Adding equations (19)-(22) and (23)-(26) algebraically, and after merging like terms, we have:

[0075] (27)

[0076] (28)

[0077] set up ,and Equations (27) and (28) after normalization are expressed as follows:

[0078] (29)

[0079] (30)

[0080] Formulas (29)-(30) are called the zero-sequence propagation equations for a double-circuit DC line on the same tower, and are a form of the telegraph equations in textbooks. The distributed impedance and distributed admittance under this zero-sequence circuit combination are as follows:

[0081] (31)

[0082] (32)

[0083] The corresponding equations for the two-port network of a zero-sequence circuit with a line length of D, corresponding to formulas (29)-(30), are as follows:

[0084] (33)

[0085] in and These represent the voltage and current at the beginning of the zero-sequence circuit. and The voltage and current at the end of the zero-sequence circuit, and the characteristic impedance. and propagation coefficient They are represented as follows:

[0086] (34)

[0087] (35)

[0088] The circuit that realizes the expression of formula (29)-(30) is to connect the four pole wires of the double-circuit DC in parallel, and short-circuit the four pole wires at the beginning and apply a single-phase power supply to ground. Here, the circuit connection method is called combination method 1.

[0089] Therefore, refer to Figure 5 The ends of the four conductors are short-circuited to ground, and the beginning ends are connected in parallel with a single-phase power supply applied to ground. The single-phase voltage output from the beginning power supply is collected synchronously. and current Calculate the zero-sequence short-circuit impedance under this combination mode 1. :

[0090] (36)

[0091] See also Figure 6 The ends of the four pole conductors are grounded via smoothing reactor Z, and the beginning ends are connected in parallel with a single-phase power supply applied to ground. The single-phase voltage output from the beginning end power supply under this condition is collected synchronously. and output current Calculate the zero-sequence series impedance under this combination method 1. :

[0092] (37)

[0093] After the line ends are grounded via impedance Z, the voltage at the end of each pole is:

[0094] (38)

[0095] According to formula (33), the zero-sequence series impedance at the beginning of the monopole conductor under this condition There is another form of expression:

[0096] (39)

[0097] Substituting formula (36) into formula (39), we get:

[0098] (40)

[0099] Therefore, the characteristic impedance under this zero-sequence circuit mode and propagation coefficient It can be achieved through zero-sequence series impedance and zero-sequence short-circuit impedance The series impedance Z is calculated as follows:

[0100] (41)

[0101] (42)

[0102] (2) Combination method 2 (two-phase positive sequence circuit method 1)

[0103] Perform the following algebraic calculations on formulas (19) to (26): ,at the same time After merging like terms and normalizing, we have:

[0104] (43)

[0105] (44)

[0106] Equations (43) and (44) are similar to expressions (27) and (28), representing a form of telegraph transmission equations. To realize the circuit form represented by equations (43) and (44), the ends A1 and A2 of the four pole conductors can be connected in parallel, and B1 and B2 can be connected in parallel, with a two-phase positive-sequence power supply applied between the ends A1 and B1 (and between A2 and B2). This circuit combination is referred to as combination mode 2. Equations (43) and (44) also have the same form as equation (33) but with different parameters, and the positive-sequence distributed impedance and distributed admittance of a single pole conductor under this mode are respectively:

[0107] (45)

[0108] (46)

[0109] Therefore, it can be done according to Figure 7 The method involves directly short-circuiting and grounding the ends of the four conductors, applying a two-phase positive-sequence power supply between A1 and B1 (between A2 and B2), and simultaneously acquiring the two-phase voltage output from the power supply at the beginning of the circuit. and two-phase current , Calculate the two-phase short-circuit impedance under this combination mode 2. :

[0110] (47)

[0111] According to Figure 8 In this method, the ends of the four pole conductors are grounded via smoothing reactor Z. Two-phase positive sequence voltages are applied between the beginning terminals A1 and B1 (and between A2 and B2), and the two-phase voltages output from the power supply at the beginning of the line are measured. and its two-phase current , Calculate the two-phase positive sequence series impedance under this combination mode 2. :

[0112] (48)

[0113] Correspondingly, the characteristic impedance under this combination mode 2 and propagation coefficient It can be passed through positive sequence series impedance and positive sequence short-circuit impedance The resistance value of the series impedance Z is calculated as follows:

[0114] (49)

[0115] (50)

[0116] (3) Combination method 3 (two-phase positive sequence circuit method 2)

[0117] Perform the following algebraic calculations on formulas (19) to (26): ,at the same time After merging like terms and normalizing, we have:

[0118] (51)

[0119] (52)

[0120] Equations (51) and (52) are similar to expressions (27) and (28), representing another form of the telegraph transmission equation. To realize the circuit form represented by equations (51) and (52), the ends A1 and B1 of the four pole conductors can be connected in parallel, and A2 and B2 can be connected in parallel. A two-phase positive-sequence power supply is applied between the ends A1 and A2 (between B1 and B2). This combination is referred to as combination method 3. Equations (51) and (52) also have the same form as equation (33) but with different parameters. The positive-sequence distributed impedance and distributed admittance of a single conductor under this method are as follows:

[0121] (53)

[0122] (54)

[0123] Therefore, according to Figure 9 The circuit wiring method involves short-circuiting and grounding the conductors at the ends of the line, connecting the first ends A1 and B1 in parallel, and A2 and B2 in parallel, and applying a two-phase positive-sequence power supply between the first ends A1 and A2 (and between B1 and B2), while simultaneously acquiring the two-phase voltage output from the power supply at the first end of the line. and two-phase current , Calculate the two-phase short-circuit impedance under this combination mode 3. :

[0124] (55)

[0125] Press again Figure 10 In this method, each pole conductor at the end of the line is grounded via a smoothing reactor Z. The starting ends A1 and B1 of the four pole conductors are connected in parallel, and A2 and B2 are connected in parallel. A two-phase positive sequence power supply is applied between the starting ends A1 and A2 (and between B1 and B2), and the two-phase voltage output from the power supply at the starting end of the line is collected synchronously. and two-phase current , Calculate the two-phase positive-sequence series impedance under this combination mode 3. :

[0126] (56)

[0127] Similarly, the characteristic impedance under this combination method 3 and propagation coefficient It can be passed through positive sequence series impedance and positive sequence short-circuit impedance The series impedance Z is calculated as follows:

[0128] (57)

[0129] (58)

[0130] (4) Combination method 4 (two-phase positive sequence circuit method 3)

[0131] Perform the following algebraic calculations on formulas (19) to (26): ,at the same time After merging like terms and normalizing, we have:

[0132] (59)

[0133] (60)

[0134] Equations (59) and (60) are similar to expressions (27) and (28), representing another form of the telegraph transmission equation. To realize the circuit form represented by equations (59) and (60), A1 and B2 at the beginning of the four pole conductors can be connected in parallel, and A2 and B1 can be connected in parallel. A two-phase positive-sequence power supply is applied between the beginnings A1 and A2 (between B2 and B1). This circuit connection method is referred to as combination method 4. Equations (59) and (60) also have the same form as equation (33) but with different parameters. The positive-sequence distributed impedance and distributed admittance of a single conductor under this method are as follows:

[0135] (61)

[0136] (62)

[0137] Therefore, according to Figure 11 The four conductors are short-circuited to ground at their ends. The first ends A1 and B2 of the four conductors are connected in parallel, and A2 and B1 are connected in parallel. A two-phase positive-sequence power supply is applied between the first ends A1 and A2 (and between B2 and B1). The two-phase voltage output from the power supply at the first end of the line is simultaneously acquired. and two-phase current , Calculate the two-phase positive sequence short-circuit impedance under this combination mode 4. :

[0138] (63)

[0139] Press again Figure 12 The ends of the four conductors are grounded via smoothing reactor Z. A1 and B2 at the beginning of the four lines are connected in parallel, and A2 and B1 are connected in parallel. A two-phase positive-sequence power supply is applied between A1 and A2 (and between B2 and B1) at the beginning of the lines. The two-phase voltage output from the power supply at the beginning of the lines is simultaneously acquired. and two-phase current , Calculate the two-phase positive sequence measurement impedance under this combination mode 4. :

[0140] (64)

[0141] Similarly, the characteristic impedance under this combination method 4 and propagation coefficient Through positive sequence series impedance and positive sequence short-circuit impedance The series impedance Z is calculated as follows:

[0142] (65)

[0143] (66)

[0144] (5) Parameter calculation

[0145] The characteristic impedances under the four combinations obtained from the above measurements and calculations are... and propagation coefficient Then, the impedance per unit length under various circuit combinations can be calculated. (0,1,2,3) and admittance (i=0,1,2,3):

[0146] (i=0,1,2,3)(67)

[0147] (i=0,1,2,3)(68)

[0148] Furthermore, by combining the calculation results of (67) and (68) with formulas (31), (32), (45), (46), (53), (54), (61), and (62), the self-parameters and coupling parameters of each polar conductor are finally calculated:

[0149] Resistance per unit length of a unipolar conductor :

[0150] (69)

[0151] Resistance per unit length of the ground return circuit :

[0152] (70)

[0153] Conductivity to ground per unit length of a single-pole conductor :

[0154] (71)

[0155] Self-inductance per unit length of four polar conductors and mutual inductance between each individual conductor:

[0156] (72)

[0157] in, For the self-inductance of a unipolar conductor, The mutual inductance between two polar conductors on the same horizontal plane. The mutual inductance between two polar conductors in the same vertical plane. It represents the mutual inductance between the two polar conductors on the diagonal.

[0158] The capacitance to ground per unit length of the four conductors and the coupling capacitance between each conductor:

[0159] (73)

[0160] in, The capacitance to ground of a single-pole conductor. This refers to the coupling capacitance between two polarized wires on the same horizontal plane. This refers to the coupling capacitance between two polar conductors on the same vertical plane. The coupling capacitor between the two polar conductors is arranged diagonally.

[0161] In the above formula, Re(*) represents taking the real part of the complex number, Im(*) represents taking the imaginary part of the complex number, and ω is the angular frequency of the power supply.

[0162] To avoid the influence of residual power frequency induced voltage on the line, the measurement frequency in this embodiment can be any specified frequency other than the power frequency.

[0163] The power frequency induced voltage of an unloaded line is very high, but by short-circuiting and grounding the end, the power frequency induced voltage measured at the beginning can be reduced to a safe range. Therefore, this application replaces the current procedure of opening the line end for impedance measurement by grounding the line end through a smoothing reactor, which can greatly reduce the power frequency induced voltage on the line. In particular, grounding the line end through a smoothing reactor can suppress the DC induced voltage at the line end to a zero potential level.

Claims

1. A method for measuring parameters of a double-circuit DC transmission line on the same tower under high induced voltage conditions, wherein the double-circuit DC transmission line comprises four pole conductors arranged symmetrically about the tower as the axis, with the two pole conductors on the left and two pole conductors on the right arranged equidistantly vertically, and the method for measuring and calculating its parameters is characterized by comprising: Step A: Connect the beginning ends of the four polar conductors in parallel as the first combination, and apply a single-phase power supply to ground at the beginning ends; With all four conductors directly grounded at their ends, the single-phase voltage output from the power supply at the first end is simultaneously collected. and current Calculate the short-circuit impedance when all four pole conductors are short-circuited to ground under the first combination method according to formula (1). Furthermore, with the ends of the four conductors grounded via impedance Z, the single-phase voltage output from the power supply at the first end is simultaneously collected. and current Calculate the series impedance of the four pole conductors under the first combination method when their ends are grounded through impedance Z according to formula (2). : （1） （2） Step B: Connect the two pole conductors on the left side of the tower in parallel at the beginning of the four pole conductors, and connect the two pole conductors on the right side of the tower in parallel as a second combination. Apply a two-phase positive sequence power supply between the left and right pole conductors at the beginning. With all four pole conductors directly grounded at their ends, synchronously collect the two-phase voltage output from the power supply at the beginning. , and current , Calculate the short-circuit impedance when all four pole conductors are directly grounded at the end under the second combination method according to formula (3). Furthermore, with the ends of the four conductors grounded via impedance Z, the two-phase voltages output from the power supply at the starting end are simultaneously acquired. , and current , Calculate the series impedance of the four pole conductors under the second combination method when their ends are grounded through impedance Z according to formula (4). : （3） （4） Step C: Connect the two upper pole conductors in parallel at the beginning of the four pole conductors, and connect the two lower pole conductors in parallel as a third combination. Apply a two-phase positive sequence power supply between the upper and lower pole conductors at the beginning. With all four pole conductors directly grounded at their ends, synchronously sample the two-phase voltage output from the power supply at the beginning. , and current , And calculate the short-circuit impedance when the ends of all four pole conductors are directly grounded under the third combination method according to formula (5). Furthermore, with the ends of the four conductors grounded via impedance Z, the two-phase voltages output from the power supply at the starting end are simultaneously acquired. , and current , And calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z under the third combination method according to formula (6). : （5） （6） Step D: Connect the upper left pole conductor and the lower right pole conductor in parallel at the beginning of the four pole conductors, and connect the lower left pole conductor and the upper right pole conductor in parallel as the fourth combination. Apply a two-phase positive sequence power supply between the upper left pole conductor and the upper right pole conductor at the beginning of the four pole conductors. With all four pole conductors directly grounded at their ends, synchronously collect the two-phase voltage output from the power supply at the beginning. , and current , And calculate the short-circuit impedance when the ends of all four pole conductors are directly grounded under the fourth combination method according to formula (7). Furthermore, with the ends of the four conductors grounded via impedance Z, the two-phase voltages output from the power supply at the starting end are simultaneously acquired. , and current , And calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z under the fourth combination method according to formula (8). : （7） （8） Step E: Based on the length D of the parallel double-circuit DC transmission line on the same tower, measure the short-circuit impedance under the four different combinations of steps A to D. and series impedance , i=0,1,2,3, respectively, substitute into formulas (9) and (10) to calculate the characteristic impedance under four different combinations. and propagation coefficient i=0,1,2,3: ，i=0,1,2,3（9） ，i=0,1,2,3（10） Step F: Calculate the characteristic impedances obtained in Step E under the four different combinations. and propagation coefficient Substituting i=0,1,2,3 into formulas (11) and (12) in pairs, we obtain the equivalent distributed impedance under four different combinations. and equivalent distributed admittance i=0,1,2,3: （11） （12） Step G: Based on the equivalent distributed impedance under the four different combinations in Step F and equivalent distributed admittance , i=0,1,2,3, and calculate the various distributed parameters of the double-circuit DC transmission line on the same tower according to formulas (13)-(17): Resistance per unit length of a single polar conductor : （13） Resistance per unit length of the earth loop : （14） Conductivity per unit length to ground of a single polar conductor : （15） Formulas for calculating the self-inductance of a single pole conductor per unit length and the mutual inductance between pole conductors: （16） in, It is the non-power frequency angular frequency of the power supply. The self-inductance per unit length of a single polar conductor. The mutual inductance per unit length between the upper left and upper right polar conductors, or the lower left and lower right polar conductors, of the pole. The mutual inductance per unit length between the upper left polar conductor and the lower left polar conductor of the tower, or between the upper right polar conductor and the lower right polar conductor of the tower. The mutual inductance per unit length between the upper left polar conductor and the lower right polar conductor of the tower, or between the upper right polar conductor and the lower left polar conductor of the tower. Formulas for calculating the capacitance to ground of a single pole conductor per unit length and the coupling capacitance between pole conductors: （17） in, This refers to the capacitance to ground per unit length of a single-pole conductor. This refers to the coupling capacitance per unit length between the upper left and upper right pole conductors, or the lower left and lower right pole conductors, of the pole. This refers to the coupling capacitance per unit length between the upper left pole conductor and the lower left pole conductor of the tower, or between the upper right pole conductor and the lower right pole conductor of the tower. The coupling capacitance per unit length between the upper left polar conductor and the lower right polar conductor of the tower, or between the upper right polar conductor and the lower left polar conductor of the tower. In formulas (13)-(17), Re(*) represents taking the real part of the complex number, Im(*) represents taking the imaginary part of the complex number, and ω is the non-power frequency angular frequency of the power supply.

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