Method for measuring and calculating parameters of single-circuit bipolar direct-current transmission line under high induced voltage

Abstract

The invention relates to a method for measuring and calculating parameters of a single-circuit bipolar direct current transmission line under high induced voltage. The method comprises the steps of obtaining two-phase zero-sequence impedance and two-phase positive-sequence series impedance of the bipolar direct-current line, and calculating various self-parameters and coupling parameters of the single-circuit bipolar direct-current transmission line by matching with results of two-phase zero-sequence short-circuit impedance and two-phase zero-sequence series impedance of the bipolar direct-current line. The method has the advantages that the threat to the safety of measuring personnel and measuring equipment due to the fact that the measured line is interfered by adjacent alternating-current and direct-current lines and the induced voltage is too high when the no-load zero-sequence open-circuit impedance and the no-load positive-sequence open-circuit impedance of the line are measured according to related guide rules in the past is overcome.

Description

Technical Field

[0001] The present invention relates to electrical engineering technology, and more particularly to a technology for safely and accurately measuring parameters of a single-circuit bipolar direct current transmission line under high induced voltage conditions. Background Art

[0002] A single-circuit bipolar DC transmission line has two monopolar conductors, which are symmetrically arranged on both sides of the tower. In addition to the resistance, inductance, and capacitance to ground of each conductor, there are also coupling capacitance and coupling inductance between the bipolar conductors. The mutual influence of these parameters makes the fault behavior of the bipolar DC line extremely complex, which needs to be studied through theoretical calculation and simulation analysis. This requires measuring and using various electrical parameters of the DC transmission line, including various coupling parameters.

[0003] According to the current 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", during the measurement of single-circuit bipolar DC transmission line parameters, the following parameters need to be measured: Figure 1 When the end of the bipolar DC line is open, the two pole conductors at the head end are connected in parallel and a single-phase power supply is applied to the ground. O,0 ; and press Figure 2 The positive-sequence open-circuit impedance Z when a two-phase positive-sequence voltage is applied between the two pole conductors at the head end is shown when the two pole conductors are open at the ends. O,1 .

[0004] However, it is found in practice that Figure 1 and Figure 2 When measuring the open-circuit impedance of a bipolar DC line, the DC induced voltage and AC induced voltage on the measured line are extremely high, far exceeding the insulation level of the measuring equipment, and pose a serious threat to the personal safety of the measuring personnel. As a result, the line parameters cannot be measured.

[0005] In order to make intensive use of land, modern AC transmission lines and DC transmission lines are basically concentrated along the same line corridor. Since the distance between the transmission lines on the same corridor is close and the parallel path is long, the induced voltage between the lines is high: when the unloaded DC line is open at both ends, the power frequency induced voltage on the line can be as high as tens of thousands of volts. Excessive line induced voltage requires the measuring instrument to have a corresponding withstand voltage level; at the same time, in order to meet the measurement accuracy requirements, the signal-to-noise ratio must be improved so that the output signal level of the measuring instrument reaches a specific level. This is bound to increase the manufacturing cost of the measuring instrument and increase the size and weight of the instrument. For the situation where there are multiple AC lines and multiple DC lines in the same corridor, there is not only an AC induced voltage on the measured DC line, but also an extremely high DC induced voltage through air conductivity and capacitance induction. Excessive induced voltage also poses a safety threat to measurement personnel.

[0006] The present invention is a method for measuring transmission line parameters safely and accurately under high induction power frequency voltage and direct current voltage. Summary of the invention

[0007] Based on this, it is necessary to find a method to safely measure and calculate the parameters of a single-circuit bipolar DC transmission line in a high induced voltage environment to address the above technical problems.

[0008] The present invention provides a method for measuring and calculating parameters of a single-circuit bipolar DC transmission line in a high induced voltage environment, characterized in that the single-circuit bipolar DC transmission line has two monopolar conductors, which are symmetrically arranged on both sides of the tower. Under a non-industrial frequency ω, the head end of the bipolar DC line is divided into two groups of different combination circuit modes for measurement. The method comprises:

[0009] Step A: Short-circuit the ends of the bipolar wires to ground, connect the first ends of the bipolar wires in parallel and apply a single-phase power supply to the ground, and simultaneously collect the single-phase voltage output by the first-end power supply and current , calculate the zero-sequence short-circuit impedance of the line according to formula (1) :

[0010] (1)

[0011] Step B: Ground the ends of the bipolar wires through impedance Z, connect the first ends of the bipolar wires 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 series impedance of the line according to formula (2) :

[0012] (2)

[0013] Step C: Short-circuit the ends of the bipolar wires to ground, apply two-phase positive sequence power between the bipolar wires at the head end, and synchronously collect the two-phase voltage output of the head end power supply. , and current , , and calculate the positive sequence short-circuit impedance of the line according to formula (3): :

[0014] (3)

[0015] Step D: Ground the ends of the bipolar conductors through impedance Z, apply a two-phase positive sequence power supply between the bipolar conductors at the head end, and synchronously collect the two-phase voltage output of the head end power supply. , and current , , calculate the positive sequence series impedance of the line according to formula (4) :

[0016] (4)

[0017] Step E: Zero-sequence short-circuit impedance obtained from steps A and B and zero-sequence series impedance , and the series impedance value Z, calculate the zero-sequence characteristic impedance of the line according to formulas (5) and (6) and the propagation coefficient :

[0018] (5)

[0019] (6)

[0020] Where D is the line length;

[0021] Step F: Positive sequence short-circuit impedance measured and calculated according to steps C and D and positive sequence series impedance , and the series impedance value Z, the positive sequence characteristic impedance of the line is calculated according to formula (7) (8) and the propagation coefficient :

[0022] (7)

[0023] (8)

[0024] Where D is the line length;

[0025] Step G: Positive sequence characteristic impedance obtained according to steps E and F and the propagation coefficient , and zero-sequence characteristic impedance and the propagation coefficient , calculate the positive sequence impedance per unit length of the line according to formulas (9)-(12) , Positive sequence admittance , zero sequence impedance , zero-sequence admittance :

[0026] (9)

[0027] (10)

[0028] (11)

[0029] (12)

[0030] Step H: The positive sequence impedance per unit length of the line obtained in step G , Positive sequence admittance , zero sequence impedance , zero-sequence admittance , the distributed parameters of the DC line are calculated according to formulas (13)-(19):

[0031] (1) Resistance r per unit length and conductivity g to ground of a monopolar conductor:

[0032] (13)

[0033] (14)

[0034] (2) Earth resistance per unit length :

[0035] (15)

[0036] (3) Self-inductance l and capacitance to ground per unit length of a monopolar conductor :

[0037] (16)

[0038] (17)

[0039] (4) Mutual inductance m and coupling capacitance per unit length between bipolar conductors :

[0040] (18)

[0041] (19)

[0042] In the above formula, Re (*) is the real part of the complex number, Im (*) is the imaginary part of the complex number; ω is the non-power frequency angular frequency of the power supply.

[0043] In one embodiment, the method further comprises:

[0044] Get the impedance value of the series impedance Z at the measurement frequency ω.

[0045] The above method for measuring and calculating the parameters of a single-circuit bipolar DC transmission line under a high induced voltage environment does not need to measure various open-circuit impedances of the line according to the current standards. Instead, the power frequency induced voltage of the line is suppressed within the safe permitted range by grounding the end of the bipolar conductor through impedance Z, thereby ensuring the safety of the measurement personnel and measurement equipment. At the same time, the accuracy of the measurement is ensured by measuring the series impedance of the line and combining the short-circuit impedance measurement results for parameter calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a measuring circuit for measuring the zero-sequence open-circuit impedance of a single-circuit DC line in existing regulations;

[0047] Figure 2 It is a measurement circuit for measuring the positive sequence open circuit impedance of a single-circuit DC line in existing regulations;

[0048] Figure 3 It is a schematic diagram of distributed parameters of a bipolar DC line;

[0049] Figure 4 It is a bipolar conductor zero-sequence short-circuit impedance measurement circuit in the present invention;

[0050] Figure 5 It is a circuit for obtaining zero-sequence series impedance when the ends of the bipolar conductors in the present invention are grounded via impedance Z;

[0051] Figure 6 It is a positive sequence short circuit impedance measurement circuit of a bipolar conductor in the present invention;

[0052] Figure 7 It is a circuit for obtaining positive sequence series impedance when the ends of the bipolar conductors of the present invention are respectively grounded via impedance Z. DETAILED DESCRIPTION

[0053] In order to facilitate the understanding of the above measurement and calculation methods, the bipolar DC line parameters are combined for analysis in principle.

[0054] like Figure 3 As shown in the figure, the bipolar conductors of the DC transmission line with a length of D are arranged symmetrically with respect to the tower, so the self-impedance of the two monopolar conductors is and self-admittance There is also coupling capacitance between the bipolar wires and mutual inductance m. If the current in the bipolar conductor is unbalanced, part of the unbalanced current will pass through the earth resistance Return. According to Figure 3 , the voltage increment equation on the positive (subscript p) and negative (subscript n) wires is:

[0055] (20)

[0056] (twenty one)

[0057] The current increment equation for a bipolar conductor is:

[0058] (twenty two)

[0059] (twenty three)

[0060] (1) Differential equations and parameter measurement methods under zero-sequence power supply conditions

[0061] The voltage differential equations (20) (21) and current differential equations (22) (23) of the positive and negative wires are superimposed to obtain the following equations:

[0062] (twenty four)

[0063] (25)

[0064] To this end, the positive and negative poles of the bipolar conductor head end can be connected in parallel, and a single-phase voltage can be applied between the head end conductor and the ground of the converter station. , due to the symmetry of the bipolar conductor, and , the above equation can be rewritten as:

[0065] (26)

[0066] (27)

[0067] Formula (26) and (27) are a form of expression of the telegraph equation for long-distance transmission lines in circuit textbooks. Here, it is called the zero-sequence circuit equation for bipolar DC transmission lines. The corresponding zero-sequence impedance and admittance per unit length of HVDC lines are:

[0068] (28)

[0069] (29)

[0070] The solution of formula (26) (27) is the corresponding zero-sequence circuit two-port network equation:

[0071] , , (30)

[0072] To this end, Figure 4 As shown, when the ends of the bipolar wires are directly short-circuited to ground ( ), the zero-sequence short-circuit impedance measured at the head end of the line That is:

[0073] (31)

[0074] Another example Figure 5 As shown in the figure, when the ends of the bipolar conductors are grounded through the smoothing reactor Z at the ends of the converter station conductors, the voltage at the end of the line is:

[0075] (32)

[0076] At this time, the zero-sequence series impedance obtained at the head end of the line is for:

[0077] (33)

[0078] Will Substituting into the above formula, we get:

[0079] (34)

[0080] Therefore, the zero-sequence characteristic impedance is:

[0081] (35)

[0082] Zero sequence propagation coefficient:

[0083] (36)

[0084] (2) Differential equations and parameter measurement methods under positive sequence voltage conditions

[0085] Subtract the voltage differential equations (20), (21) and current differential equations (22), (23) of the positive and negative wires, respectively, to obtain the following equations:

[0086] (37)

[0087] (38)

[0088] For this purpose, Figure 6 , Figure 7As shown, a two-phase positive sequence voltage is applied between the positive and negative poles at the head end of the line. Under the condition of bipolar symmetry, the current difference of the bipolar line is , so equations (37) and (38) are simplified to:

[0089] (39)

[0090] (40)

[0091] Formula (39) (40) is another form of the telegraph equation for long-distance transmission lines in circuit textbooks. Here, it is called the positive sequence circuit equation for bipolar DC transmission lines. The corresponding positive sequence parameter per unit length of HVDC lines is:

[0092] (41)

[0093] (42)

[0094] The corresponding positive sequence circuit two-port network equation is:

[0095] , , (43)

[0096] For this purpose, Figure 6 As shown, when the ends of the bipolar wires are short-circuited to ground ( ), at this time, the bipolar positive sequence short-circuit impedance measured at the head end of the line is :

[0097] (44)

[0098] Another example Figure 7 As shown in the figure, when the end bipolar conductors are grounded through the smoothing reactor Z at the ends of the conductors in the converter station, the line end voltage is:

[0099] (45)

[0100] Under this condition, the bipolar positive sequence series impedance obtained at the first end is :

[0101] (46)

[0102] Substituting formula (44) into (46), we obtain:

[0103] (47)

[0104] Therefore, the bipolar positive sequence characteristic impedance is:

[0105] (48)

[0106] Bipolar positive sequence propagation coefficient:

[0107] (49)

[0108] (3) Calculation of distribution parameters per unit length

[0109] The positive sequence characteristic impedance is calculated based on the measurement results. and the propagation coefficient And zero sequence characteristic impedance and the propagation coefficient After that, the positive sequence impedance per unit length can be calculated respectively , Positive sequence admittance , zero sequence impedance , zero-sequence admittance :

[0110] (50)

[0111] (51)

[0112] (52)

[0113] (53)

[0114] In obtaining the positive sequence parameters per unit length of HVDC and zero sequence parameters Then, according to formulas (28), (29), (41), and (42), we can deduce Figure 3 The distribution parameters in .

[0115] The resistance r and the conductance g to ground per unit length of a monopolar conductor are:

[0116] (54)

[0117] (55)

[0118] The earth resistance takes effect when zero-sequence current passes through the bipolar line. The earth resistance per unit length is for:

[0119] (56)

[0120] The self-inductance l and capacitance to ground per unit length of a monopolar conductor They are:

[0121] (57)

[0122] (58)

[0123] Mutual inductance m and coupling capacitance per unit length between bipolar conductors They are:

[0124] (59)

[0125] (60)

[0126] In the above formula, Re (*) is the real part of the complex number, Im (*) is the imaginary part of the complex number. ω is the angular frequency of the power supply (not the power frequency).

[0127] The premise for the derivation and application of all formulas in this manual is any frequency other than the power frequency. This is because the residual power frequency induced voltage or induced current on the line will affect the zero-sequence impedance. and positive sequence impedance The measurement introduces errors.

[0128] In order to measure the parameters of HVDC transmission lines at AC power frequency without being disturbed by the induced voltage and induced current of adjacent power frequency lines, it is usually selected to measure the parameters of HVDC transmission lines at AC power frequency. Nearby frequencies and The parameters at the power frequency are then calculated by interpolation.

[0129] In this application example, the smoothing reactor of the converter station is directly used to replace the series impedance Z. Therefore, the impedance frequency characteristic of the smoothing reactor should be measured during the parameter measurement process, and the impedance measurement value Z at the corresponding frequency point ω should be substituted into the corresponding formula for calculation.

Claims

1. A method for measuring and calculating parameters of a single-circuit bipolar DC transmission line under a high induced voltage environment, characterized in that: The single-circuit bipolar DC transmission line has two monopolar conductors, which are symmetrically arranged on both sides of the tower. At a non-power frequency ω, the head end of the bipolar DC line is divided into two groups of different combination circuit modes for measurement and calculation. The method includes: Step A: Short-circuit the ends of the bipolar wires to ground, connect the first ends of the bipolar wires in parallel and apply a single-phase power supply to the ground, and simultaneously collect the single-phase voltage output by the first-end power supply and current , calculate the zero-sequence short-circuit impedance of the line according to formula (1) : （1） Step B: Ground the ends of the bipolar wires through impedance Z, connect the first ends of the bipolar wires 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 series impedance of the line according to formula (2) : （2） Step C: Short-circuit the ends of the bipolar wires to ground, apply two-phase positive sequence power between the bipolar wires at the head end, and synchronously collect the two-phase voltage output of the head end power supply. , and current , , and calculate the positive sequence short-circuit impedance of the line according to formula (3): : （3） Step D: Ground the ends of the bipolar conductors through impedance Z, apply a two-phase positive sequence power supply between the bipolar conductors at the head end, and synchronously collect the two-phase voltage output of the head end power supply. , and current , , calculate the positive sequence series impedance of the line according to formula (4) : （4） Step E: Zero-sequence short-circuit impedance obtained from steps A and B and zero-sequence series impedance , and the series impedance value Z, calculate the zero-sequence characteristic impedance of the line according to formulas (5) and (6) and the propagation coefficient : （5） （6） Where D is the line length; Step F: Positive sequence short-circuit impedance measured and calculated according to steps C and D and positive sequence series impedance , and the series impedance value Z, the positive sequence characteristic impedance of the line is calculated according to formula (7) (8) and the propagation coefficient : （7） （8） Where D is the line length; Step G: Positive sequence characteristic impedance obtained according to steps E and F and the propagation coefficient , and zero-sequence characteristic impedance and the propagation coefficient , calculate the positive sequence impedance per unit length of the line according to formulas (9)-(12) , Positive sequence admittance , zero sequence impedance , zero-sequence admittance : （9） （10） （11） （12） Step H: The positive sequence impedance per unit length of the line obtained in step G , Positive sequence admittance , zero sequence impedance , zero-sequence admittance , the distributed parameters of the DC line are calculated according to formulas (13)-(19): (1) Resistance r per unit length and conductivity g to ground of a monopolar conductor: (13) (14) (2) Earth resistance per unit length : （15） (3) Self-inductance l and capacitance to ground per unit length of a monopolar conductor : (16) (17) (4) Mutual inductance m and coupling capacitance per unit length between bipolar conductors : (18) (19) In the above formula, Re (*) is the real part of the complex number, Im (*) is the imaginary part of the complex number; ω is the non-power frequency angular frequency of the power supply.

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

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