Phase measurement method for no-load charging current of extra-high voltage line affected by adjacent lines

Abstract

The present invention relates to a phasor test method considering the influence of the no-load charging current of an extra-high voltage line on adjacent lines, including: under the no-load charging state of the line, respectively obtaining the estimated value and the measured value of the secondary current, and comparing the estimated value with the measured value to obtain a first comparison result; judging the erection form of the line, if it is not erected on the same tower, then judging the phasor correctness and the integrity of the secondary circuit based on the first comparison result to complete the load-bearing phasor test; if it is erected on the same tower, then calculating the induced current value of the line, adding the induced current value and the estimated value and comparing the result with the measured value to obtain a second comparison result, and judging the phasor correctness and the integrity of the secondary circuit based on the first comparison result and the second comparison result to complete the load-bearing phasor test. The present invention can solve the problem of accurate estimation of the no-load charging current in the case of double-circuit lines on the same tower of extra-high voltage lines, and improve the accuracy of the load-bearing test during the start-up process of newly installed equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of parameter calculation for extra-high voltage overhead transmission lines, and particularly to a phasor test method considering the influence of adjacent lines on the no-load charging current of extra-high voltage lines. Background Art

[0002] For works such as the commissioning of new substations, CT replacement, and protection renovation, phasor measurement with load for CT is required. The principle of the phasor measurement test with load for CT is that when the line is in a no-load charging state, the shunt capacitance current of the extra-high voltage line is estimated based on parameters such as the line length, and after conversion, the magnitude and phase of the measured secondary current are compared to judge the correctness of the CT secondary circuit.

[0003] In engineering, the shunt capacitance current of extra-high voltage lines is generally estimated by methods, and there is also an estimation method that directly converts the no-load capacity based on the line length. These methods generally simplify the three-phase line into a single-phase line and do not consider the influence of adjacent energized lines. The construction of transmission lines requires a large amount of land, and the regions with a large demand for electricity generally have a relatively high level of economic development, but the land resources are rather tense. In order to improve the power transmission capacity per unit area and save the line construction cost, extra-high voltage lines generally adopt the construction form of being erected on the same tower. In addition to the same-voltage-level lines being erected on the same tower, in some special mountainous areas or line-dense areas, extra-high voltage lines will share the transmission corridor with distribution lines. Although their erection heights are different, they will be very close in the case of sharing the transmission corridor, so as to minimize the land occupation area. The same-tower double-circuit lines and sharing the transmission corridor of transmission lines reduce the transmission line construction cost, but also bring new problems. Due to the self-inductance and mutual inductance between lines, the line voltage and current are affected by adjacent lines, which is different from the lines operating alone. When the extra-high voltage line is operating normally, the influence on the load current can be ignored, but in the case of no-load charging of the line, the influence of adjacent lines is relatively large and cannot be ignored. Therefore, there is an urgent need for a phasor test method considering the influence of adjacent lines on the no-load charging current of extra-high voltage lines. Summary of the Invention

[0004] The object of the present invention is to provide a phasor test method considering the influence of adjacent lines on the no-load charging current of extra-high voltage lines, solve the problem of accurate estimation of the no-load charging current in the case of the same-tower double-circuit of extra-high voltage lines, and improve the accuracy of the load test during the start-up process of newly installed equipment.

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

[0006] A phasor test method considering the influence of adjacent lines on the no-load charging current of extra-high voltage lines includes:

[0007] When the line is in a no-load charging state, the estimated value and the measured value of the secondary current are respectively obtained, and the estimated value is compared with the measured value to obtain a first comparison result;

[0008] Judge the erection form of the line. If it is not erected on the same tower, judge the phasor correctness and secondary circuit integrity based on the first comparison result, and complete the load-carrying phasor test.

[0009] If it is erected on the same tower, calculate the induced current value of the line, superimpose the induced current value and the estimated value, compare the result with the measured value to obtain a second comparison result, and judge the phasor correctness and secondary circuit integrity based on the first comparison result and the second comparison result, and complete the load-carrying phasor test.

[0010] Optionally, the estimated value includes a first estimated value and a second estimated value. Among them, the first estimated value is obtained by estimating with empirical constants, line voltage levels, and line lengths, and the second estimated value is obtained by converting the line length to the no-load capacity.

[0011] Optionally, calculating the induced current value of the line includes:

[0012] Construct an equivalent mutual inductance circuit for the lines erected on the same tower, where the equivalent mutual inductance circuit for the lines erected on the same tower includes an operating line and a no-load line.

[0013] Based on the equivalent mutual inductance circuit for the lines erected on the same tower, construct an induced current component and ground voltage model at any position on the no-load line affected by the operating line.

[0014] Based on the model, calculate the induced current component and terminal voltage at the end of the no-load line, and solve the induced current component at the head end of the no-load line based on the induced current component and terminal voltage at the end, that is, the induced current value of the line.

[0015] Optionally, the model is:

[0016]

[0017] In the formula, is the ground voltage of phase a of the no-load line, is the head-end voltage of phase a of the no-load line, l is the length of phase a of the no-load line, L a0 is the inductance per unit length to the ground of phase a of the no-load line, is the induced current component of phase a of the no-load line, M Aa 、M Ba 、M Ca are the inductances per unit length of the three phases of the operating line to phase a of the no-load line respectively, are the currents of phases A, B, and C of the operating line, C a0 is the capacitance per unit length to the ground of phase a of the no-load line, C Aa 、C Ba 、C Cais the capacitance per unit length of the three phases of the operating line with respect to the a-phase of the line being charged into the air, are the voltages of phases A, B, and C of the operating line, j is the unit imaginary number, and ω is the frequency.

[0018] Optionally, based on the model, the induced current component and the terminal voltage at the end of the line being charged into the air are calculated as:

[0019]

[0020] In the formula, is the terminal voltage of the a-phase of the line being charged into the air, γ is the line propagation constant, is the induced current component at the head end of the a-phase of the line being charged into the air, Z C is the wave impedance, C is the capacitance simplification coefficient, and M is the reactance simplification coefficient, is the current at the end of the a-phase of the line being charged into the air.

[0021] Optionally, based on the induced current component and the terminal voltage at the end, the induced current component at the head end of the line being charged into the air is solved as:

[0022]

[0023] In the formula, is the induced current component at the head end of the a-phase of the line being charged into the air.

[0024] The beneficial effects of the present invention are:

[0025] The method proposed by the present invention can, in two scenarios of double-circuit lines on the same tower and shared transmission corridors for extra-high voltage lines, calculate the influence of adjacent energized lines on the no-load current of extra-high voltage lines through electrostatic induction and electromagnetic induction analysis, superimpose the affected current components with the no-load current estimated by the existing method to obtain a more accurate estimated value of the no-load current, improve the accuracy of the load test for newly installed equipment, and better ensure the safety and stability of the operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0027] Figure 1 is the flowchart of the phasor test method for considering the influence of adjacent lines on the no-load current of extra-high voltage lines in the embodiment of the present invention;

[0028] Figure 2 is the mutual inductance equivalent diagram of double-circuit lines on the same tower in the embodiment of the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the drawings and specific implementation manners.

[0031] This embodiment provides a phasor test method considering the influence of the no-load charging current of an extra-high voltage line on the adjacent line, as Figure 1 shown, including:

[0032] Under the no-load charging state of the line, the estimated value and the measured value of the secondary current are respectively obtained, and the estimated value is compared with the measured value to obtain the first comparison result;

[0033] Judge the erection form of the line. If it is not erected on the same tower, then judge the phasor correctness and the integrity of the secondary circuit based on the first comparison result to complete the load-bearing phasor test;

[0034] If it is erected on the same tower, then calculate the induced current value of the line, superimpose the induced current value and the estimated value and compare them with the measured value to obtain the second comparison result, and judge the phasor correctness and the integrity of the secondary circuit based on the first comparison result and the second comparison result to complete the load-bearing phasor test.

[0035] Furthermore, the estimated value includes a first estimated value and a second estimated value. Among them, the first estimated value is obtained by estimating with an empirical constant, the line voltage level, and the line length, and the second estimated value is obtained by converting the no-load charging capacity according to the line length.

[0036] In engineering, the method of estimating the capacitance current of an extra-high voltage line to the ground is generally used. Equation (1) estimates the first estimated value with an empirical constant:

[0037] I0 = k × V × L (1)

[0038] The result of multiplying the empirical constant k by the line voltage level and then by the line length is applicable to the estimation of the no-load charging current of a 500 kV line, and there are relatively large deviations for extra-high voltage lines of other voltage levels.

[0039] There is also an estimation method of directly converting the no-load charging capacity according to the line length. Each 1 km of line length is approximately equivalent to 1 MVar of no-load charging capacity, and the no-load charging current is calculated as the second estimated value:

[0040]

[0041] Furthermore, calculating the induced current value of the line includes:

[0042] Construct an equivalent mutual inductance circuit for the lines erected on the same tower, where the equivalent mutual inductance circuit for the lines erected on the same tower includes the operating line and the idle-charging line;

[0043] Based on the equivalent mutual inductance circuit for the lines erected on the same tower, construct a model for the induced current component and the ground voltage at any position on the idle-charging line affected by the operating line;

[0044] Based on the model, calculate the induced current component and the terminal voltage at the end of the idle-charging line, and solve for the induced current component at the head end of the idle-charging line based on the induced current component and the terminal voltage at the end, which is the induced current value of the line.

[0045] Specifically, for the double-circuit lines erected on the same tower, there is an electromagnetic induction phenomenon between the lines. Especially when one of the double-circuit lines is idle-charging, the operating line generates an induced voltage and current on the capacitance of the idle-charging line, affecting the magnitude of the current flowing through the idle-charging line. The mutual inductance of the double-circuit lines erected on the same tower is equivalent as Figure 2 shown. Conduct an equivalent simplification analysis on phase a of the idle-charging line. The currents in phases b and c of the idle-charging line are relatively small, and the mutual inductance influence between the phases of the idle-charging line is not considered temporarily.

[0046] Figure 2 In are the currents of phases A, B, and C of the operating line, are the head-end voltage and the head-end induced current component of the idle-charging line, are the terminal voltage and the terminal induced current component of the idle-charging line, C Aa 、C Ba 、C Ca are the capacitance per unit length of the three phases of the operating line to phase a of the idle-charging line, M Aa 、M Ba 、M Ca are the inductance per unit length of the three phases of the operating line to phase a of the idle-charging line, C a0 、L a0 are the capacitance and inductance per unit length of phase a of the idle-charging line to the ground.

[0047] Construct a model for the induced current component and the ground voltage at any position on the idle-charging line affected by the lines on the same tower as:

[0048]

[0049] where ω is the system frequency. When calculating the terminal voltage and current of the idle-charging line using equations (3) and (4), it can be simplified to equations (5) and (6):

[0050]

[0051] where \(l\) is the line length, \(\gamma\) is the line propagation constant, \(Z\) C is the wave impedance, \(C\) is the capacitance reduction coefficient, and \(M\) is the reactance reduction coefficient.

[0052]

[0053] For an unloaded line, only the circuit breaker at the head end is connected to the power grid, and the circuit breaker at the tail end remains open. There is only unloaded charging capacitive current on the line. Therefore, the head-end voltage is the system voltage, and the tail-end current is 0. The induced current component at the head end of the unloaded line can be solved

[0054]

[0055] As can be seen from Equation (11), when one of the double-circuit lines on the same tower is in operation and the other is unloaded, the induced current at the head end of the unloaded line is related to the line voltage, length, and mutual inductance between the lines.

[0056] The following takes the phasor measurement test of CT with load after the transformation of the secondary equipment of a certain 500 kV EHV line as an example to specifically illustrate the method proposed in this embodiment:

[0057] When the line is in the unloaded state on this side, measure the secondary current of the CT. Since the unloaded line current is a purely capacitive current, the measured voltage leads the current by about 90 degrees, and the CT polarity can be judged to be correct. When the line is unloaded, it operates only at one end. Estimate the amplitude of the line capacitive current based on parameters such as the line length and voltage level. When encountering a double-circuit line on the same tower, calculate the amplitude of the induced current using Equation (11). Since the double-circuit lines on the same tower are led out from the same bus and have the same phase, add the calculated amplitude of the induced current to the original estimated result to obtain the estimated value of the unloaded line current, verify the CT transformation ratio correctness and the integrity of the secondary circuit, and ensure the correctness of the phasor measurement test result of the CT with load.

[0058] For a line length of 190 km, estimated by the method of Equation (1), the primary value of the unloaded current is 256.5 A, the CT transformation ratio is 2500 / 1, and the converted secondary current is 102.6 mA. The calculation process is as shown in Equation (12):

[0059]

[0060] Estimated by the method of Equation (2), a line length of 190 km is equivalent to an unloaded capacity of about 190 MVar, the primary value of the unloaded current is 219.4 A, and the converted secondary current is 87.8 mA. The calculation process is as shown in Equation (13):

[0061]

[0062] The measured secondary current on site is 132.2 mA, which has a large gap from the estimated values of the methods in Equation (1) and Equation (2). This line is in the form of double-circuit on the same tower, and the induced current of the other circuit on the same tower is calculated by the method in Equation (11).

[0063]

[0064] The induced current obtained through the calculation of Equation (14) is respectively superimposed with Equation (12) and Equation (13) to correct the current values obtained by the two estimation methods of Equation (1) and Equation (2). The no-load charging currents are respectively obtained as 144.8 mA and 130 mA, which are close to the measured secondary current of 132.2 mA on site, improving the accuracy of the CT load-bearing phase measurement test.

[0065] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A phasor test method for considering the influence of adjacent lines on the no-load charging current of ultra-high voltage lines, characterized in that Including: Under the line no-load charging state, respectively obtain the estimated value and the measured value of the secondary current, and compare the estimated value with the measured value to obtain a first comparison result; Judge the erection form of the line. If it is not erected on the same tower, then judge the phasor correctness and the integrity of the secondary circuit based on the first comparison result to complete the load-carrying phasor test; If it is erected on the same tower, then calculate the induced current value of the line, add the induced current value and the estimated value and compare the result with the measured value to obtain a second comparison result, and judge the phasor correctness and the integrity of the secondary circuit based on the first comparison result and the second comparison result to complete the load-carrying phasor test; Calculating the induced current value of the line includes: Construct an equivalent mutual inductance circuit for the same-tower erected line, where the equivalent mutual inductance circuit for the same-tower erected line includes an operating line and a no-load charging line; Based on the equivalent mutual inductance circuit for the same-tower erected line, construct an induced current component and a ground voltage model at any position on the no-load charging line affected by the operating line; Based on the model, calculate the induced current component and the terminal voltage at the end of the no-load charging line, and based on the induced current component and the terminal voltage at the end, solve the induced current component at the head end of the no-load charging line, that is, the induced current value of the line.

2. The phasor test method for considering the influence of the no-load charging current of an extra-high voltage line on an adjacent line according to claim 1, wherein The estimated value includes a first estimated value and a second estimated value, where the first estimated value is obtained by estimating with an empirical constant, the line voltage level, and the line length, and the second estimated value is obtained by converting the no-load charging capacity according to the line length.

3. The phasor test method for considering the influence of the no-load charging current of the extra-high voltage line on the adjacent line according to claim 1, wherein The model is: Wherein, is the voltage to ground of phase a of the no-load energized line, is the voltage at the head end of phase a of the no-load energized line, l is the length of phase a of the no-load energized line, L a0 is the inductance per unit length of phase a of the no-load energized line to ground, is the induced current component of phase a of the no-load energized line, M Aa 、M Ba 、M Ca are the inductances per unit length of the three phases of the operating line with respect to phase a of the no-load energized line, are the currents of phases A, B, and C of the operating line, C a0 is the capacitance per unit length of phase a of the no-load energized line to ground, C Aa 、C Ba 、C Ca are the capacitances per unit length of the three phases of the operating line with respect to phase a of the no-load energized line, are the voltages of phases A, B, and C of the operating line, j is the unit imaginary number, and ω is the frequency.

4. The phasor test method for considering the influence of the no-load charging current of an extra-high voltage line on adjacent lines according to claim 3, characterized in that Based on the model, calculating the induced current component and the terminal voltage at the end of the no-load charging line is: Wherein, is the terminal voltage of phase a of the no-load line, γ is the line propagation constant, is the initial end induced current component of phase a of the no-load line, Z C is the wave impedance, C is the capacitance simplification coefficient, M is the reactance simplification coefficient, is the terminal current of phase a of the no-load line.

5. The phasor test method for considering the influence of the no-load charging current of an extra-high voltage line on adjacent lines according to claim 4, characterized in that Based on the induced current component and the terminal voltage at the end, solving the induced current component at the head end of the no-load charging line is: In the formula, is the leading-end induced current component of phase a of the empty-charged line.

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