Phasor test method considering influence of adjacent line on empty charging current of ultra-high voltage line

Abstract

The invention relates to a phasor test method considering the influence of an adjacent line on the empty charging current of an ultra-high voltage line, and the method comprises the steps: obtaining an estimated value and a measured value of a secondary current in an empty charging state of the line, comparing the estimated value with the measured value, and obtaining a first comparison result; judging the erection form of the line, if the line is not erected on the same tower, judging the correctness of the phasor and the completeness of the secondary circuit based on the first comparison result, and completing the on-load phasor test; if the line is erected on the same tower, an induced current value of the line is calculated, the induced current value and the estimated value are superposed and then compared with the measured value, a second comparison result is obtained, the correctness of the phasor and the completeness of the secondary circuit are judged based on the first comparison result and the second comparison result, and the on-load phasor test is completed. According to the method, the problem of accurate estimation of the empty charging current under the condition that the ultrahigh-voltage lines are combined on the same tower can be solved, and the on-load test accuracy in the starting process of new equipment is improved.

Description

Technical Field

[0001] The invention relates to the technical field of parameter calculation of ultra-high voltage overhead transmission lines, and in particular to a phasor testing method that takes into account the influence of an ultra-high voltage line no-load current on an adjacent line. Background Art

[0002] The commissioning of new stations, CT replacement and protection transformation, etc., all require CT load phase measurement. The principle of CT load phase measurement test is that when the line is in the empty-charge state, the capacitance current of the ultra-high voltage line to the ground is estimated based on parameters such as line length, and the secondary current size and phase are compared after conversion to determine the correctness of the CT secondary circuit.

[0003] In engineering, the estimation method is generally used for the capacitance current of ultra-high voltage lines to the ground, and there is also an estimation method that directly converts the empty charging capacity by the line length. These methods generally simplify the three-phase line into a single phase and do not consider the impact of adjacent energized lines. The construction of transmission lines requires a large amount of land. Regions with a large demand for electricity generally have a high level of economic development, and land resources are tight. In order to improve the power transmission capacity per unit area and save the cost of line construction, ultra-high voltage lines generally adopt the construction form of the same tower and the same tower. In addition to the same tower for the same voltage level lines, in some special mountainous areas or areas with dense lines, ultra-high voltage lines will share the transmission corridor with distribution lines. The two are installed at different heights, but in the case of sharing the transmission corridor, the two will be very close to each other, minimizing the land occupation area. The same tower and the shared transmission line corridor further reduce the construction cost of transmission lines, but also bring new problems. Due to the self-inductance and mutual inductance between the lines, the line voltage and current are affected by the adjacent lines, which is different from the lines running alone. When the ultra-high voltage line is operating normally, the impact on the load current can be ignored, but in the case of empty charging of the line, the impact of the adjacent lines is large and cannot be ignored. Therefore, it is urgent to consider the phasor testing method of the UHV line no-charge current affected by adjacent lines. Summary of the invention

[0004] The purpose of the present invention is to provide a phasor testing method that takes into account the influence of the no-charge current of an ultra-high voltage line on adjacent lines, solve the problem of accurate estimation of the no-charge current when ultra-high voltage lines are installed on the same tower, and improve the accuracy of load testing during the startup of new equipment.

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

[0006] The phasor test method considering the influence of the UHV line no-charge current on the adjacent lines includes:

[0007] In an empty-charging state of the line, respectively obtaining an estimated value and a measured value of the secondary current, and comparing the estimated value with the measured value to obtain a first comparison result;

[0008] Determine the installation form of the line. If the line is not installed on the same tower, determine the phasor correctness and secondary circuit integrity based on the first comparison result, and complete the load phasor test;

[0009] If they are installed on the same tower, the induced current value of the line is calculated, the induced current value and the estimated value are superimposed and compared with the measured value to obtain a second comparison result, and the phasor correctness and secondary circuit integrity are judged based on the first comparison result and the second comparison result to complete the load phasor test.

[0010] Optionally, the estimated value includes a first estimated value and a second estimated value, wherein the first estimated value is obtained by estimating an empirical constant, a line voltage level, and a line length, and the second estimated value is obtained by converting the line length into an empty charge capacity.

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

[0012] Constructing a mutual inductance equivalent circuit of lines erected on the same tower, wherein the mutual inductance equivalent circuit of lines erected on the same tower includes a running line and an empty charging line;

[0013] Based on the mutual inductance equivalent circuit of the lines erected on the same tower, a model of the induced current component and the voltage to the ground at any position on the empty charging line affected by the operating line is constructed;

[0014] The end induced current component and the end voltage of the empty-charging line are calculated based on the model, and the head-end induced current component of the empty-charging line, that is, the induced current value of the line, is solved based on the end induced current component and the end voltage.

[0015] Optionally, the model is:

[0016]

[0017] In the formula, is the voltage of phase a of the empty-charge circuit to ground, is the voltage at the beginning of phase a of the empty-charging line, l is the length of phase a of the empty-charging line, L a0 is the inductance per unit length of phase a of the empty-charge circuit to ground, is the induced current component of phase a of the empty-charge line, M Aa 、M Ba 、M Ca is the unit length inductance of the three phases of the running line to the phase a of the empty charging line, is the phase current of A, B, and C of the running line, C a0 is the capacitance per unit length of phase a of the empty-charge line to ground, C Aa , C Ba , C CaThe unit length capacitance of phase a of the three phases of the running line to the empty charging line is: is the phase voltage of A, B and C of the operating line, j is a unit imaginary number, and ω is the frequency.

[0018] Optionally, the terminal induced current component and the terminal voltage of the empty-charging circuit are calculated based on the model as follows:

[0019]

[0020] In the formula, is the terminal voltage of phase a of the empty-charge line, γ is the line propagation constant, is the inductive current component at the first end of phase a of the empty-charge line, Z C is the wave impedance, C is the capacitance simplification factor, M is the reactance simplification factor, It is the terminal current of phase a of the empty-charge circuit.

[0021] Optionally, the head-end induced current component of the empty-charging circuit is solved based on the terminal induced current component and the terminal voltage as follows:

[0022]

[0023] In the formula, It is the induced current component at the first end of phase a of the empty-charge line.

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

[0025] The method proposed in the present invention can calculate the impact of adjacent energized lines on the no-charge current of ultra-high voltage lines through electrostatic induction and electromagnetic induction analysis in two scenarios: ultra-high voltage lines are installed on the same tower and share a transmission corridor. The affected current component is superimposed with the no-charge current estimated by the existing method to obtain a more accurate no-charge current estimate, which can improve the accuracy of load testing of new equipment and better ensure the safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is a flow chart of a phasor testing method considering the influence of the no-charge current of an ultra-high voltage line on the adjacent lines according to an embodiment of the present invention;

[0028] Figure 2 This is an equivalent diagram of mutual inductance of lines installed in parallel on the same tower according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] This embodiment provides a phasor test method that considers the influence of the UHV line no-charge current on the adjacent lines, such as Figure 1 As shown, including:

[0032] In the line empty charging state, respectively obtaining an estimated value and a measured value of the secondary current, and comparing the estimated value with the measured value to obtain a first comparison result;

[0033] Determine the installation form of the line. If the line is not installed on the same tower, determine the phasor correctness and secondary circuit integrity based on the first comparison result and complete the load phasor test;

[0034] If they are installed on the same tower, the induced current value of the line is calculated, the induced current value and the estimated value are superimposed and compared with the measured value to obtain a second comparison result, and the phasor correctness and secondary circuit integrity are judged based on the first comparison result and the second comparison result to complete the load phasor test.

[0035] Furthermore, the estimated value includes a first estimated value and a second estimated value, wherein the first estimated value is obtained by estimating the empirical constant, the line voltage level, and the line length, and the second estimated value is obtained by converting the line length into the empty charge capacity.

[0036] In engineering, the estimation method is generally used for the capacitance current of ultra-high voltage lines to ground. Formula (1) estimates the first estimated value using empirical constants:

[0037] I0=k×V×L (1)

[0038] The empirical constant k is multiplied by the line voltage level and then by the line length. The result is applicable to the estimation of no-charge current of 500kV lines, but has large deviations for ultra-high voltage lines of other voltage levels.

[0039] There is also an estimation method that directly converts the empty charge capacity by line length. Every 1km line length is equivalent to 1MVar empty charge capacity. The empty charge current is calculated as the second estimated value:

[0040]

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

[0042] Constructing a mutual inductance equivalent circuit of lines erected on the same tower, wherein the mutual inductance equivalent circuit of lines erected on the same tower includes an operating line and an empty charging line;

[0043] Based on the mutual inductance equivalent circuit of the lines erected on the same tower, the induced current component and ground voltage model affected by the operating line at any position on the empty charging line is constructed;

[0044] The end induced current component and the end voltage of the empty-charging line are calculated based on the model, and the head-end induced current component of the empty-charging line, that is, the induced current value of the line, is solved based on the end induced current component and the end voltage.

[0045] Specifically, for double-circuit lines on the same tower, there is electromagnetic induction between the lines. In particular, when one of the double-circuit lines is empty, the operating line generates an induced voltage and current on the capacitance of the empty line, which affects the current flowing through the empty line. Figure 2 As shown, an equivalent simplified analysis is performed on phase a of the empty-charging line. The currents of phases b and c of the empty-charging line are relatively small, and the mutual inductance between the phases of the empty-charging line is not considered for the time being.

[0046] Figure 2 middle, is the A, B, and C phase current of the running line, It is the voltage at the first end of the empty charging line and the induced current component at the first end. is the voltage at the end of the empty-charge line and the inductive current at the end, C Aa , C Ba , C Ca M is the unit length capacitance of phase a of the three phases of the running line to the empty charging line. Aa 、M Ba 、M Ca is the unit length inductance of the three phases of the running line to the empty charging line phase a, C a0 , L a0 is the capacitance and inductance per unit length of the empty-charge circuit a relative to the ground.

[0047] Construct the induced current component of the same tower line at any position on the empty charging line and voltage to ground The model is:

[0048]

[0049] Where ω is the system frequency. When the voltage and current at the end of the empty-charging line are calculated using equations (3) and (4), they can be simplified to equations (5) and (6):

[0050]

[0051] Where l is the line length, γ is the line propagation constant, and Z C is the wave impedance, C is the capacitance simplification factor, and M is the reactance simplification factor.

[0052]

[0053] In the empty charging line, only the first end circuit breaker is connected to the grid, and the end circuit breaker remains disconnected, and only the empty charging capacity current flows on the line. is the system voltage, the terminal current is 0, the inductive current component at the head end of the empty charging line can be solved

[0054]

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

[0056] The method proposed in this embodiment is specifically described below by taking a CT load phase measurement test after the secondary equipment of a 500kV ultra-high voltage line is modified as an example:

[0057] When the line is in the empty-charge state on this side, measure the CT secondary current. Since the line empty-charge current is a pure capacitive current, the measured voltage leads the current by about 90 degrees, which can determine that the CT polarity is correct. When the line is empty-charged, only one end is in operation. The line capacitance current amplitude is estimated by parameters such as line length and voltage level. When a double-circuit line is installed on the same tower, the induced current amplitude is calculated using formula (11). Since the double-circuit line on the same tower is derived from the same busbar and has the same phase, the calculated induced current amplitude is added to the original estimated result to obtain the estimated value of the line empty-charge current, verifying the correctness of the CT ratio and the integrity of the secondary circuit, and ensuring the correctness of the CT load phase measurement test results.

[0058] The line length is 190 km. According to the method of formula (1), the primary value of the no-charge current is 256.5 A, the CT ratio is 2500 / 1, and the secondary current is 102.6 mA. The calculation process is as shown in formula (12):

[0059]

[0060] According to the method of formula (2), the line length of 190km is equivalent to 190MVar empty charge capacity, the primary value of empty charge current is 219.4A, and the secondary current is 87.8mA. The calculation process is as shown in formula (13):

[0061]

[0062] The secondary current measured on site is 132.2 mA, which is significantly different from the estimated values ​​by the formula (1) and formula (2). The line is a double-circuit line on the same tower, and the induced current of the other circuit on the same tower is calculated by the formula (11).

[0063]

[0064] The induced current calculated by formula (14) is superimposed with formula (12) and formula (13) respectively, and the current values ​​obtained by the two estimation methods of formula (1) and formula (2) are corrected to obtain the no-charge current of 144.8mA and 130mA respectively, which are close to the actual measured secondary current of 132.2mA on site, thus improving the accuracy of the CT load phase measurement test.

[0065] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A phasor test method considering the influence of the UHV line no-charge current on the adjacent lines, characterized in that: include: In an empty-charging state of the line, respectively obtaining an estimated value and a measured value of the secondary current, and comparing the estimated value with the measured value to obtain a first comparison result; Determine the installation form of the line. If the line is not installed on the same tower, determine the phasor correctness and secondary circuit integrity based on the first comparison result, and complete the load phasor test; If they are installed on the same tower, the induced current value of the line is calculated, the induced current value and the estimated value are superimposed and compared with the measured value to obtain a second comparison result, and the phasor correctness and secondary circuit integrity are judged based on the first comparison result and the second comparison result to complete the load phasor test.

2. The phasor test method considering the influence of the no-charge current of the ultra-high voltage line on the adjacent lines according to claim 1 is characterized in that: The estimated value includes a first estimated value and a second estimated value, wherein the first estimated value is obtained by estimating an empirical constant, a line voltage level, and a line length, and the second estimated value is obtained by converting the line length into an empty charge capacity.

3. The phasor test method considering the influence of the no-charge current of the ultra-high voltage line on the adjacent lines according to claim 1 is characterized in that: Calculating the induced current value of the line includes: Constructing a mutual inductance equivalent circuit of lines erected on the same tower, wherein the mutual inductance equivalent circuit of lines erected on the same tower includes a running line and an empty charging line; Based on the mutual inductance equivalent circuit of the lines erected on the same tower, a model of the induced current component and the voltage to the ground at any position on the empty charging line affected by the operating line is constructed; The end induced current component and the end voltage of the empty-charging line are calculated based on the model, and the head-end induced current component of the empty-charging line, that is, the induced current value of the line, is solved based on the end induced current component and the end voltage.

4. The phasor test method considering the influence of the no-charge current of the ultra-high voltage line on the adjacent lines according to claim 3 is characterized in that: The model is: In the formula, is the voltage of phase a of the empty-charge circuit to ground, is the voltage at the beginning of phase a of the empty-charging line, l is the length of phase a of the empty-charging line, L a0 is the inductance per unit length of phase a of the empty-charge circuit to ground, is the induced current component of phase a of the empty-charge line, M Aa 、M Ba 、M Ca is the unit length inductance of the three phases of the running line to the phase a of the empty charging line, is the phase current of A, B, and C of the running line, C a0 is the capacitance per unit length of phase a of the empty-charge line to ground, C Aa , C Ba , C Ca The unit length capacitance of phase a of the three phases of the running line to the empty charging line is: is the phase voltage of A, B and C of the operating line, j is a unit imaginary number, and ω is the frequency.

5. The phasor test method considering the influence of the no-charge current of the ultra-high voltage line on the adjacent lines according to claim 4 is characterized in that: Based on the model, the terminal inductive current component and the terminal voltage of the empty-charging circuit are calculated as follows: In the formula, is the terminal voltage of phase a of the empty-charge line, γ is the line propagation constant, is the inductive current component at the first end of phase a of the empty-charge line, Z C is the wave impedance, C is the capacitance simplification factor, M is the reactance simplification factor, It is the terminal current of phase a of the empty-charge circuit.

6. The phasor test method considering the influence of the no-charge current of the ultra-high voltage line on the adjacent lines according to claim 5 is characterized in that: Based on the terminal induced current component and the terminal voltage, the first-end induced current component of the empty-charging circuit is solved as follows: In the formula, It is the induced current component at the first end of phase a of the empty-charge line.

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