Method for measuring parameters of same-tower parallel double-circuit direct current transmission line in high induced voltage environment

Abstract

The invention discloses a method for measuring parameters of a same-tower parallel double-circuit direct-current transmission line in a high induced voltage environment, and the method comprises the steps: enabling the head ends of four polar leads to adopt a plurality of parallel combination modes, measuring series impedance when the tail ends of the four polar lines are grounded through impedance and short-circuit impedance when the tail ends are directly grounded under different parallel combination conditions under a certain non-power frequency; according to the line length, the series impedance when the tail ends of the four pole wires are grounded through impedance and the short-circuit impedance when the tail ends are directly grounded under different parallel combination conditions, characteristic impedance and propagation coefficients under different parallel combination conditions are calculated respectively, and then equivalent distribution impedance and equivalent distribution admittance are calculated; and according to the equivalent distribution impedance and the equivalent distribution admittance under different parallel combination conditions, obtaining each distribution parameter under the unit length of the line polar wire. According to the scheme, in an environment with high induced voltage, the induced voltage can be effectively suppressed, and line parameters can be accurately measured.

Description

Technical Field

[0001] The present application relates to the field of electrical engineering, and in particular to a method for measuring parameters of a double-circuit direct current transmission line mounted on the same tower in a high induced voltage environment. Background Art

[0002] The double-circuit DC transmission line on the same tower has four monopolar conductors. In addition to its own resistance, inductance, and capacitance to the ground, there are also coupling capacitance and coupling inductance between the pole conductors. The influence of these parameters makes the fault behavior of the double-circuit DC line extremely complex, which needs to be studied through theoretical calculation and simulation calculation. This requires measuring the electrical parameters of the double-circuit DC transmission line on the same tower, including the coupling parameters, when the double-circuit DC transmission line on the same tower is built.

[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 of the four pole conductors at the head end when the end of the double-circuit DC line is open-circuited. , and when the ends of the four pole conductors are open, the four pole conductors at the head end are combined into a two-phase positive sequence circuit, a total of 3 combined wiring modes for the two-phase positive sequence open circuit impedance (i=1,2,3). At the same time, it is also necessary to measure the zero-sequence short-circuit grounding impedance when the four pole conductors at the end are short-circuited and grounded, and the four pole conductors at the head end are connected in parallel. , and when the four pole conductors are short-circuited to the ground at the ends, the four pole conductors at the head end are combined into a two-phase positive sequence circuit in pairs, and the two-phase positive sequence short-circuit impedance under a total of 3 combinations (i=1,2,3). The open circuit impedance under the above four combinations (i=0,1,2,3) and short-circuit impedance Based on the measurement results of (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, since long-distance DC transmission lines are thousands of kilometers long, they are inevitably built in parallel with other ultra-high (UHV) AC and DC lines in the same line corridor. When the measured double-circuit DC lines on the same tower are open-circuited and unloaded, there will be an induced voltage of up to tens of thousands of volts. The induced voltage has both DC and AC components, which has been confirmed in actual measurements. Therefore, the above measurement method has many difficulties in actual operation, especially for reasons related to personal safety and measurement equipment safety. The excessively high induced voltage makes it almost impossible to measure the parameters of the double-circuit DC lines on the same tower. Summary of the invention

[0005] The content of this application is to solve the problem of how to effectively suppress the induced voltage on the measured line in a high voltage induction environment and safely and accurately measure the parameters of a double-circuit DC transmission line on the same tower.

[0006] The present application provides 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 on the same tower includes four pole conductors, which are arranged symmetrically with the tower as the axis, and the two pole conductors on the left and right sides are arranged equidistantly from top to bottom. The specific method includes:

[0007] Step A: Connect the first ends of the four polar conductors in parallel as the first combination mode, apply a single-phase power supply to the ground at the first end; under the condition that the ends of the four polar conductors are directly grounded, synchronously collect the single-phase voltage output by the power supply at the first end and current , and calculate the short-circuit impedance when the ends of the four pole conductors are short-circuited to the ground under the first combination mode according to formula (1): ; In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the single-phase voltage output by the head-end power supply is synchronously collected and current , and calculate the series impedance when the ends of the four polar conductors are grounded through impedance Z in the first combination mode according to formula (2) :

[0008] (1)

[0009] (2)

[0010] Step B: At the head end of the four pole conductors, the two pole conductors on the left side of the tower are connected in parallel, and the two pole conductors on the right side of the tower are connected in parallel as the second combination mode, and a two-phase positive sequence power supply is applied between the left pole conductor and the right pole conductor at the head end; under the condition that the ends of the four pole conductors are directly grounded, the two-phase voltage output of the head end power supply is synchronously collected , and current , , and calculate the short-circuit impedance when the ends of the four pole conductors are directly grounded under the second combination mode according to formula (3) In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the two-phase voltage output of the head-end power supply is synchronously collected. , and current , , and calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z in the second combination mode according to formula (4) :

[0011] (3)

[0012] (4)

[0013] Step C: At the head end of the four pole conductors, connect the two pole conductors above the pole tower in parallel, and connect the two pole conductors below the pole tower in parallel as the third combination mode, and apply a two-phase positive sequence power supply between the upper pole conductor and the lower pole conductor at the head end; under the condition that the ends of the four pole conductors are directly grounded, synchronously collect the two-phase voltage output of the head end power supply , and current , , and calculate the short-circuit impedance when the ends of the four pole conductors are directly grounded under the third combination mode according to formula (5) In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the two-phase voltage output of the head-end power supply is synchronously collected. , and current , , and calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z in the third combination mode according to formula (6) :

[0014] (5)

[0015] (6)

[0016] Step D: At the head end of the four pole conductors, the upper pole conductor on the left side of the tower is connected in parallel with the lower pole conductor on the right side, and the lower pole conductor on the left side of the tower is connected in parallel with the upper pole conductor on the right side as the fourth combination mode, and a two-phase positive sequence power supply is applied between the upper pole conductor on the left side and the upper pole conductor on the right side at the head end of the four pole conductors; under the condition that the ends of the four pole conductors are directly grounded, the two-phase voltage output of the head end power supply is synchronously collected , and current , , and calculate the short-circuit impedance when the ends of the four pole conductors are directly grounded under the fourth combination mode according to formula (7) In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the two-phase voltage output of the head-end power supply is synchronously collected. , and current , , and calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z in the fourth combination mode according to formula (8) :

[0017] (7)

[0018] (8)

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

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

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

[0022] Step F: The characteristic impedances of the four different combinations obtained in step E are and the propagation coefficient Substituting (i=0,1,2,3) into formulas (11) and (12) in pairs, we can 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: Equivalent distributed impedance under four different combinations in step F and equivalent distributed admittance (i=0,1,2,3), and calculate the distribution 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 of a single polar conductor to ground :

[0031] (15)

[0032] The calculation formula of the self-inductance of a single pole conductor and the mutual inductance between pole conductors per unit length is:

[0033] (16)

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

[0035] The calculation formula of the capacitance of a single pole conductor to ground and the coupling capacitance between pole conductors per unit length is:

[0036] (17)

[0037] in, is the capacitance per unit length of a single polar conductor to ground, It is the coupling capacitance per unit length between the upper pole conductor on the left side of the tower and the upper pole conductor on the right side (or the lower pole conductor on the left side of the tower and the lower pole conductor on the right side), It is the coupling capacitance per unit length between the upper pole conductor on the left side of the tower and the lower pole conductor on the left side (or the upper pole conductor on the right side of the tower and the lower pole conductor on the right side), It is the coupling capacitance per unit length between the upper pole conductor on the left side of the tower and the lower pole conductor on the right side (or the upper pole conductor on the right side of the tower and the lower pole conductor on the left side);

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

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

[0040] This application can suppress the induced voltage on the measured line within the safe permitted range by grounding the end of the measured pole conductor through impedance Z, while accurately measuring various parameters on the double-circuit DC transmission line on the same tower. This solution avoids the safety threat to measurement personnel and equipment when measuring by open-circuiting the end of the line. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0042] Figure 2 It is a measurement circuit for measuring the two-phase positive sequence open-circuit impedance of a double-circuit DC line on the same tower in existing regulations;

[0043] Figure 3 It is a schematic diagram of the spatial arrangement of four pole conductors of a double-circuit DC transmission line erected on the same tower;

[0044] Figure 4 It 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 It is a schematic diagram of a short-circuit impedance measurement circuit when the ends of four polar conductors are short-circuited to the ground in the first combination mode of the present invention;

[0046] Figure 6 It is a schematic diagram of a series impedance measurement circuit when the ends of the four polar wires are grounded via impedance Z in the first combination mode of the present invention;

[0047] Figure 7 It is a schematic diagram of a short-circuit impedance measurement circuit when the ends of four polar conductors are short-circuited and grounded in the second combination mode of the present invention;

[0048] Figure 8 It is a schematic diagram of a series impedance measurement circuit when the ends of the four polar wires are grounded via impedance Z respectively under the second combination mode of measurement of the present invention;

[0049] Fig. 9 It is a schematic diagram of a short-circuit impedance measurement circuit when the ends of four polar conductors are short-circuited and grounded in the third combination mode of the present invention;

[0050] Fig.10It is a schematic diagram of a series impedance measurement circuit when the ends of four polar wires are grounded via impedance Z respectively under the third combination mode of measurement of the present invention;

[0051] Fig.11 It is a schematic diagram of a short-circuit impedance measurement circuit when the ends of four polar conductors are short-circuited and grounded in the fourth combination mode of the present invention;

[0052] Fig.12 It is a schematic diagram of a series impedance series circuit when the ends of the four polar wires are grounded via impedance Z respectively under the fourth combination mode of measurement of the present invention. DETAILED DESCRIPTION

[0053] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the technical principles of the present application are further explained in detail below in combination with the accompanying drawings and specific implementation methods.

[0054] 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, the following parameters need to be measured: Figure 1 When the end of the double-circuit DC line is open, the zero-sequence open-circuit impedance of the four pole conductors at the head end is connected in parallel ; and press Figure 2 When the ends of the four pole conductors are open, the four pole conductors at the head end are combined into two-phase positive sequence circuits, and the two-phase positive sequence open circuit impedance under a total of three combined wiring modes is shown in the figure. (i=1,2,3). At the same time, it is also necessary to measure the zero-sequence short-circuit grounding impedance when the four pole conductors at the end are short-circuited and grounded, and the four pole conductors at the head end are connected in parallel. When the four pole conductors are short-circuited to the ground at the ends, the four pole conductors at the head end are combined into a two-phase positive sequence circuit, and the two-phase positive sequence short-circuit impedance under three combinations is (i=1,2,3). The open circuit impedance under the above four combinations (i=0,1,2,3) and short-circuit impedance Based on the measurement results of (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, since long-distance DC transmission lines are thousands of kilometers long, they are inevitably built in parallel with other ultra-high voltage AC and DC lines in the same line corridor. When the double-circuit DC lines on the same tower are open-circuited and unloaded, there will be an induced voltage of up to tens of thousands of volts. The induced voltage contains both DC and AC components, which has been confirmed in actual measurements. Therefore, in actual operation, according to Figure 1 , Figure 2 When measuring the no-load zero-sequence open-circuit impedance and the two-phase positive-sequence open-circuit impedance in related combination modes using the measurement method, the excessively high induced voltage makes it almost impossible to measure the parameters of the double-circuit DC line on the same tower due to concerns about personal safety and the safety of measuring equipment.

[0056] Therefore, in order to solve the problem of difficulty in measuring line parameters of double-circuit DC transmission lines on the same tower, the present application proposes 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 the embodiment of the present application, the smoothing reactor at the end of the DC line in the converter station can be directly used as the impedance Z of the series grounding. Before the measurement, the impedance-frequency characteristics of the smoothing reactor are measured, and the measurement results are substituted into formulas (9) and (10) for calculation. The specific principles and steps are as follows:

[0058] Figure 3 It is a typical arrangement of extra-high voltage (UHV) double-circuit DC overhead transmission lines on the same tower, which adopts a single-circuit and single-side layout. A1 is the upper monopole conductor on the left, A2 is the lower monopole conductor on the left, B1 is the upper monopole conductor on the right, and B2 is the lower monopole conductor on the right. 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 the wires of each pole are of the same type, the self-impedance of each monopolar wire is and ground admittance The same; and, the double-circuit DC transmission lines erected on the same tower are arranged symmetrically with the tower as the axis, and the distance A1-B1 is equal to the distance A2-B2.

[0060] Figure 4 The coupling inductance and coupling capacitance between the pole conductors, as well as the self-parameters of a single conductor are indicated.

[0061] In a certain section of a double-circuit DC line on the same tower, if the currents passing through the four pole conductors are , 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 as:

[0064] (19)

[0065] (20)

[0066] (twenty one)

[0067] (twenty two)

[0068] (twenty three)

[0069] (twenty four)

[0070] (25)

[0071] (26)

[0072] There are four inductance and capacitance parameters in equations (19)-(26), and four linearly independent equations need to be solved simultaneously. To this end, the four polar conductors can be combined in pairs to form a zero-sequence circuit and three two-phase positive-sequence circuits to obtain Figure 4 The various self parameters and coupling parameters shown are analyzed and measured in four steps (or four circuit combinations) including combination 1, combination 2, combination 3 and combination 4.

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

[0074] Add equations (19) to (22) and equations (23) to (26) algebraically, and after merging similar terms, we have:

[0075] (27)

[0076] (28)

[0077] set up ,and , the normalized expressions of equations (27) and (28) are:

[0078] (29)

[0079] (30)

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

[0081] (31)

[0082] (32)

[0083] The two-port network equation of the zero-sequence circuit with a line length of D corresponding to formulas (29)-(30) is:

[0084] (33)

[0085] in and are the voltage and current at the beginning of the zero-sequence circuit, and is the voltage and current at the end of the zero-sequence circuit, and the characteristic impedance and the propagation coefficient Respectively expressed as:

[0086] (34)

[0087] (35)

[0088] The circuit that realizes the expression of formulas (29)-(30) is to connect the four pole conductors of the double-circuit DC in parallel, short-circuit the four pole conductors at the head end, and apply a single-phase power supply to the ground. This circuit connection method is referred to as combination method 1.

[0089] For this purpose refer to Figure 5 , short-circuit the ends of the four pole conductors to ground, connect the first end in parallel and apply a single-phase power supply to the ground, and synchronously collect the single-phase voltage output by the first end power supply 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 through smoothing reactors Z, the head ends are connected in parallel and a single-phase power supply is applied to the ground, and the single-phase voltage output by the head end power supply under this condition is synchronously collected and output current , calculate the zero-sequence series impedance under this combination mode 1 :

[0092] (37)

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

[0094] (38)

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

[0096] (39)

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

[0098] (40)

[0099] Therefore, the characteristic impedance of this zero-sequence circuit is and the propagation coefficient The zero-sequence series impedance and zero-sequence short-circuit impedance And the series impedance Z is calculated:

[0100] (41)

[0101] (42)

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

[0103] Formulas (19) to (26) are algebraically calculated as follows: ,at the same time After merging similar items and normalizing, we have:

[0104] (43)

[0105] (44)

[0106] Formula (43) and (44) are similar to the expressions of formula (27) and (28), which are a form of telegraph transmission equation. In order to realize the circuit form expressed by formula (43) and (44), A1 and A2 at the head end of the four pole conductors can be connected in parallel, B1 and B2 can be connected in parallel, and a two-phase positive sequence power supply can be applied between the head ends A1 and B1 (between A2 and B2). This circuit combination is called combination mode 2. Formula (43) and (44) also have two-port network equations with the same form as formula (33) but different parameters, and the positive sequence distributed impedance and distributed admittance of a single pole conductor under this mode are:

[0107] (45)

[0108] (46)

[0109] To do this, press Figure 7 The ends of the four pole conductors are directly short-circuited to ground, and a two-phase positive sequence power supply is applied between the head end A1 and B1 (between A2 and B2), and the two-phase voltage output of the head end power supply is synchronously collected. And two-phase current , , calculate the two-phase short-circuit impedance under this combination mode 2 :

[0110] (47)

[0111] In accordance with Figure 8 The ends of the four pole conductors are grounded through smoothing reactors Z, and a two-phase positive sequence voltage is applied between the head end A1 and B1 (between A2 and B2). The two-phase voltage output of the power supply at the head end of the line is measured. Its two-phase current , , calculate the two-phase positive sequence series impedance under this combination mode 2 :

[0112] (48)

[0113] Accordingly, the characteristic impedance of combination mode 2 is and the propagation coefficient The positive sequence series impedance and positive sequence short-circuit impedance And the resistance value of the series impedance Z is calculated:

[0114] (49)

[0115] (50)

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

[0117] Formulas (19) to (26) are algebraically calculated as follows: ,at the same time After merging similar items and normalizing, we have:

[0118] (51)

[0119] (52)

[0120] Formula (51) and (52) are similar to the expressions of formula (27) and (28), which are another form of telegraph transmission equations. In order to realize the circuit form expressed by formula (51) and (52), A1 and B1 at the head end of the four polar conductors can be connected in parallel, A2 and B2 can be connected in parallel, and a two-phase positive sequence power supply can be applied between the head ends A1 and A2 (between B1 and B2). This combination is called combination method 3. Formula (51) and (52) also have two-port network equations with the same form as formula (33) but different parameters, and the positive sequence distributed impedance and distributed admittance of a single conductor under this method are:

[0121] (53)

[0122] (54)

[0123] To do this, press Fig. 9 The circuit wiring method is to short-circuit the wires at the end of the line to ground, connect the first ends A1 and B1 of the four wires in parallel, and A2 and B2 in parallel, apply a two-phase positive sequence power supply between the first ends A1 and A2 (between B1 and B2), and synchronously collect the two-phase voltage output of the power supply at the first end of the line at this time And two-phase current , , calculate the two-phase short-circuit impedance under this combination mode 3 :

[0124] (55)

[0125] Another press Fig.10 In this way, the pole conductors at the end of the line are grounded through the smoothing reactor Z, the head 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 head ends A1 and A2 (between B1 and B2), and the two-phase voltage output of the power supply at the head end of the line is synchronously collected. And two-phase current , , calculate the two-phase positive sequence series impedance under this combination mode 3 :

[0126] (56)

[0127] Similarly, the characteristic impedance of combination 3 is and the propagation coefficient The positive sequence series impedance and positive sequence short-circuit impedance And the series impedance Z is calculated:

[0128] (57)

[0129] (58)

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

[0131] Formulas (19) to (26) are algebraically calculated as follows: ,at the same time After merging similar items and normalizing, we have:

[0132] (59)

[0133] (60)

[0134] Formula (59) and (60) are similar to the expressions of formula (27) and (28), which are another form of telegraph transmission equations. In order to realize the circuit form expressed by formula (59) and (60), A1 and B2 at the head end of the four polar conductors can be connected in parallel, A2 and B1 can be connected in parallel, and a two-phase positive sequence power supply can be applied between the head ends A1 and A2 (between B2 and B1). This circuit connection method is called combination method 4. Formula (59) and (60) also have two-port network equations with the same form as formula (33) but different parameters, and the positive sequence distributed impedance and distributed admittance of a single conductor under this method are:

[0135] (61)

[0136] (62)

[0137] To do this, press Fig.11 The ends of the four pole conductors are short-circuited to ground, A1 and B2 at the head end of the four pole conductors are connected in parallel, A2 and B1 are connected in parallel, and a two-phase positive sequence power supply is applied between the head end A1 and A2 (between B2 and B1). The two-phase voltage output of the power supply at the head end of the line is synchronously collected. And two-phase current , , calculate the two-phase positive sequence short-circuit impedance under this combination mode 4 :

[0138] (63)

[0139] Another press Fig.12 The ends of the four pole conductors are grounded through smoothing reactors Z, A1 and B2 at the head end of the four lines are connected in parallel, A2 and B1 are connected in parallel, and two-phase positive sequence power is applied between the head end A1 and A2 (between B2 and B1). The two-phase voltage output of the power supply at the head end of the line is synchronously collected. And two-phase current , , calculate the two-phase positive sequence measurement impedance under this combination mode 4 :

[0140] (64)

[0141] Similarly, the characteristic impedance of combination 4 is and the propagation coefficient Positive sequence series impedance and positive sequence short-circuit impedance And the series impedance Z is calculated:

[0142] (65)

[0143] (66)

[0144] (5) Parameter calculation

[0145] The characteristic impedance of the four combinations obtained by the above measurement and calculation and propagation coefficient After that, 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, the calculation results of (67) and (68) are combined with formulas (31), (32), (45), (46), (53), (54), (61), (62) to finally calculate the self-parameters and coupling parameters of each pole conductor:

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

[0150] (69)

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

[0152] (70)

[0153] The conductivity of a monopolar conductor per unit length to ground :

[0154] (71)

[0155] The self-inductance per unit length of the four polar conductors and the mutual inductance between the monopolar conductors:

[0156] (72)

[0157] in, is the self-inductance of the monopolar conductor, is the mutual inductance between two polar conductors in the same horizontal plane, is the mutual inductance between two polar conductors in the same vertical plane, is the mutual inductance between the two polar conductors between the diagonals.

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

[0159] (73)

[0160] in, is the capacitance of the monopolar conductor to ground, is the coupling capacitance between two polar conductors on the same horizontal plane, is the coupling capacitance between two polar conductors in the same vertical plane, Arrange the coupling capacitors between the two polar conductors for diagonal lines.

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

[0162] In order to avoid the influence of residual power frequency induced voltage of the line, the measurement frequency in the embodiment of the present application can be any specified frequency except the power frequency.

[0163] The power frequency induced voltage of an unloaded line is very high, but after the end is short-circuited and grounded, the power frequency induced voltage measured at the head end can be reduced to a safe permitted range. Therefore, in this application, the impedance measurement is performed by replacing the open circuit method of the line end in the current regulations by grounding the line end through a smoothing reactor, which can greatly reduce the power frequency induced voltage on the line. In particular, after the line end is grounded through a smoothing reactor, the DC induced voltage at the line end can be suppressed to a zero potential level.

Claims

1. A method for measuring parameters of a double-circuit DC transmission line on the same tower in a high induced voltage environment, wherein the double-circuit DC transmission line on the same tower comprises four pole conductors, which are arranged symmetrically with the tower as the axis, and the two pole conductors on the left and right sides are arranged equidistantly from top to bottom. The parameter measurement and calculation method is characterized by comprising: Step A: connecting the head ends of the four polar conductors in parallel as a first combination mode, and applying a single-phase power supply to the ground at the head ends; Under the condition that the ends of the four pole conductors are directly grounded, the single-phase voltage output by the head-end power supply is synchronously collected and current , calculate the short-circuit impedance when the ends of the four pole conductors are short-circuited to the ground under the first combination mode according to formula (1): ; In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the single-phase voltage output by the head-end power supply is synchronously collected and current , calculate the series impedance when the ends of the four polar conductors are grounded through impedance Z in the first combination mode according to formula (2): : （1） （2） Step B: At the head end of the four pole conductors, the two pole conductors on the left side of the tower are connected in parallel, and the two pole conductors on the right side of the tower are connected in parallel as the second combination mode, and a two-phase positive sequence power supply is applied between the left pole conductor and the right pole conductor at the head end; under the condition that the ends of the four pole conductors are directly grounded, the two-phase voltage output of the head end power supply is synchronously collected , and current , , calculate the short-circuit impedance when the ends of the four pole conductors are directly grounded in the second combination mode according to formula (3): In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the two-phase voltage output of the head-end power supply is synchronously collected. , and current , , calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z in the second combination mode according to formula (4): : （3） （4） Step C: At the head end of the four pole conductors, connect the two pole conductors above the pole tower in parallel, and connect the two pole conductors below the pole tower in parallel as the third combination mode, and apply a two-phase positive sequence power supply between the upper pole conductor and the lower pole conductor at the head end; under the condition that the ends of the four pole conductors are directly grounded, synchronously collect the two-phase voltage output of the head end power supply , and current , , and calculate the short-circuit impedance when the ends of the four pole conductors are directly grounded under the third combination mode according to formula (5) In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the two-phase voltage output of the head-end power supply is synchronously collected. , and current , , and calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z in the third combination mode according to formula (6) : （5） （6） Step D: At the head end of the four pole conductors, the upper pole conductor on the left side of the tower is connected in parallel with the lower pole conductor on the right side, and the lower pole conductor on the left side of the tower is connected in parallel with the upper pole conductor on the right side as the fourth combination mode, and a two-phase positive sequence power supply is applied between the upper pole conductor on the left side and the upper pole conductor on the right side at the head end of the four pole conductors; under the condition that the ends of the four pole conductors are directly grounded, the two-phase voltage output of the head end power supply is synchronously collected , and current , , and calculate the short-circuit impedance when the ends of the four pole conductors are directly grounded under the fourth combination mode according to formula (7) In addition, under the condition that the ends of the four polar conductors are grounded through impedance Z, the two-phase voltage output of the head-end power supply is synchronously collected. , and current , , and calculate the series impedance when the ends of the four pole conductors are grounded through impedance Z in the fourth combination mode according to formula (8) : （7） （8） Step E: According to the length D of the double-circuit DC transmission line on the same tower, the short-circuit impedance is measured in four different combinations of steps A to D. and series impedance Substitute (i=0,1,2,3) into formulas (9) and (10) in pairs to calculate the characteristic impedance of four different combinations: and the propagation coefficient (i=0,1,2,3): ，（i=0,1,2,3）（9） ，（i=0,1,2,3）（10） Step F: The characteristic impedances of the four different combinations obtained in step E are and the propagation coefficient Substituting (i=0,1,2,3) into formulas (11) and (12) in pairs, we can obtain the equivalent distributed impedance under four different combinations: and equivalent distributed admittance (i=0,1,2,3): （11） （12） Step G: Equivalent distributed impedance under four different combinations in step F and equivalent distributed admittance (i=0,1,2,3), and calculate the distribution 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 of a single polar conductor to ground : （15） The calculation formula of the self-inductance of a single pole conductor and the mutual inductance between pole conductors per unit length is: （16） in, is the non-power frequency angular frequency of the power supply, is the self-inductance per unit length of a single polar conductor, is the mutual inductance per unit length between the upper pole conductor on the left side of the tower and the upper pole conductor on the right side (or the lower pole conductor on the left side and the lower pole conductor on the right side), is the mutual inductance per unit length between the upper pole conductor on the left side of the tower and the lower pole conductor on the left side (or the upper pole conductor on the right side of the tower and the lower pole conductor on the right side), It is the mutual inductance per unit length between the upper pole conductor on the left side of the tower and the lower pole conductor on the right side (or the upper pole conductor on the right side of the tower and the lower pole conductor on the left side); The calculation formula of the capacitance of a single pole conductor to ground and the coupling capacitance between pole conductors per unit length is: （17） in, is the capacitance per unit length of a single polar conductor to ground, It is the coupling capacitance per unit length between the upper pole conductor on the left side of the tower and the upper pole conductor on the right side (or the lower pole conductor on the left side of the tower and the lower pole conductor on the right side), It is the coupling capacitance per unit length between the upper pole conductor on the left side of the tower and the lower pole conductor on the left side (or the upper pole conductor on the right tower side and the lower pole conductor on the right side), It is the coupling capacitance per unit length between the upper pole conductor on the left side of the tower and the lower pole conductor on the right side (or the upper pole conductor on the right side of the tower and the lower pole conductor on the left side); In formulas (13) to (17), Re(*) represents the real part of a complex number, Im(*) represents the imaginary part of a complex number, and ω is the angular frequency of the power supply.

2. The method according to claim 1, characterized in that The method further comprises: During the measurement, the impedance value of the series impedance Z at the measurement frequency ω is measured in real time.

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