Zero-sequence pilot frequency excitation method for double-circuit line in incomplete power failure environment

Abstract

The invention discloses a zero-sequence pilot-frequency excitation method for a double-circuit line in an incomplete power failure environment, which comprises the following steps of: applying zero-sequence pilot-frequency signal excitation on a power failure line by using a pilot-frequency power supply as an excitation signal source of a zero-sequence network of the double-circuit line, different-frequency induced current and voltage are measured at secondary sides of a current transformer and a voltage transformer at two sides of the operation line, and different-frequency zero-sequence voltage and different-frequency zero-sequence current in the double-circuit line zero-sequence network are obtained; simultaneously solving a zero-sequence network equation, and calculating mutual impedance between double circuits; performing frequency conversion to obtain the power frequency mutual impedance of the line; and finally, carrying out simulation verification by constructing a non-full-stop double-circuit line zero-sequence mutual inductance impedance measurement system. According to the method, the multi-path coupling caused by the existing power frequency interference method and the accuracy problem caused by the signal measurement error of the zero sequence increment method are solved, the test calculation can be accurately completed under the complex interference working condition, and the safety risk caused by the single-phase reclosing operation is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of power system relay protection, and in particular to a zero-sequence frequency-differential excitation method for a double-circuit line in a partial power outage environment. Background Art

[0002] As power grids expand and their structures optimize, there are increasingly instances of one circuit operating while another circuit is being constructed on the same tower or in parallel. This necessitates testing the mutual inductance parameters of both circuits without a complete power outage. Traditional measurement methods require a complete power outage of both circuits. However, a complete power outage reduces the number of channels in the power supply section, resulting in power loss. Furthermore, the change in operating mode reduces the grid's ability to withstand risk.

[0003] The zero-sequence mutual inductance of double-circuit lines for partial power outages was initially measured using a live line mutual inductance test. This test utilizes the zero-sequence current increment generated when a single-phase tripping occurs on the operating line and the zero-sequence induced voltage component generated on the adjacent infrastructure line to calculate the line mutual inductance. During the test, a program controller is connected to the operating line circuit breaker control circuit to open and close the circuit breaker for phases A, B, and C, respectively. However, existing methods present difficulties in analyzing transient zero-sequence current signals sampled from current transformers, resulting in significant errors in the calculated results. Furthermore, this test method carries the potential safety hazard of a three-phase tripping of the operating line due to a failure to reclose after a single-phase trip. This safety hazard cannot be avoided through technical means. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a zero-sequence frequency-differential excitation method for a double-circuit line in a partial power outage environment, mainly to solve the technical problems existing in the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the technical solution of the embodiment of the present invention is implemented as follows: a zero-sequence frequency-differential excitation method for a double-circuit line in a partial power outage environment comprises the following steps:

[0006] Step S1: using a different-frequency power supply as an excitation signal source for a double-circuit line zero-sequence network, applying a zero-sequence different-frequency signal excitation to the power outage line, wherein the zero-sequence different-frequency signal includes 45 Hz and 55 Hz;

[0007] Preferably, a different-frequency power supply is used as a test power supply to simulate two parallel lines including line 1 and line 2, so that line 1 is powered off, a different-frequency power supply is added to the head end, and the three-phase short circuit is grounded at the end; line 2 operates normally.

[0008] Step S2: simultaneously measuring the heterodyne induced current and voltage on the secondary sides of the current transformer and the voltage transformer on both sides of the operating line to obtain the heterodyne zero-sequence voltage and heterodyne zero-sequence current in the double-circuit line zero-sequence network;

[0009] Preferably, parameter measurements are performed at the head and end of the power outage line. Voltage and current lead wires are used at the head end of the line, the voltage measurement lead is connected close to the line side, and the current measurement lead is connected close to the output side of the measurement power supply. The resistance part of the measured impedance is subtracted from the resistance of the end measurement lead.

[0010] Step S3: Solve the zero-sequence network equations simultaneously to calculate the mutual impedance between the double-circuit lines;

[0011] Preferably, a zero-sequence coupling model of parallel transmission lines is constructed, and the volt-ampere characteristics of the zero-sequence coupling model of parallel transmission lines can be expressed by the following equations:

[0012]

[0013] Among them, Z 11 , Z 12 , Z 22 It is the zero-sequence impedance parameter of the two circuits, that is, the zero-sequence impedance parameter of different frequencies. and is the zero-sequence current phasor, and is the zero-sequence voltage phasor, is the current phasor at the beginning and end of line 1, is the current phasor at the beginning and end of line 2, is the voltage phasor at the beginning and end of line 1, It is the voltage phasor at the beginning and end of line 2. All electrical quantities are zero-sequence phasors. The error caused by capacitive current is reduced by taking the average value of the current phasor at the beginning and end.

[0014] Preferably, the zero-sequence coupling model of the parallel transmission lines includes: equal zero-sequence self-parameters of the two circuits and unequal zero-sequence self-parameters of the two circuits.

[0015] As a preferred method, when the zero-sequence self parameters of the two circuits are equal: there are only two unknowns, and it is only necessary to obtain the power of the two lines under one operating mode to calculate the heterofrequency impedance parameters. The independent operation mode options of the two circuits when the zero-sequence self parameters are equal include: line 1 is powered off, the head end is added with a heterofrequency power supply, and the end is short-circuited to ground with three phases; line 2 is normally energized, and the heterofrequency zero-sequence impedance parameter Z is obtained by simulation modeling when the zero-sequence self parameters are equal. 11 , Z 12 , Z 22 The solution calculation formula is:

[0016]

[0017] Further, The calculation formula is:

[0018]

[0019] in, is the zero-sequence voltage phasor of line 1 and line 2 at different frequencies, is the zero-sequence current phasor of line 1, It is the heterofrequency zero-sequence current phasor of line 2, that is, each current and voltage is a heterofrequency zero-sequence phasor.

[0020] As a preferred method, when the zero-sequence impedance parameters of the two circuits are not equal: there are three unknowns. The power of the double-circuit lines under two independent operation modes is used to calculate the zero-sequence impedance parameter Z of the different frequency. 11 , Z 12 , Z 22 Calculation is performed, where the line independent operation mode selection when the zero-sequence parameters of the two circuits are not equal includes:

[0021] Independent operation mode 1: Line 1 is powered off, a different frequency power supply is added to the head end, and the three phases at the end are short-circuited and grounded; Line 2 operates normally with power on.

[0022] Independent operation mode 2: Line 1 operates normally with power; Line 2 is powered off, a different frequency power supply is added to the head end, and the three phases at the end are short-circuited and grounded;

[0023] From the above two independent operation modes, the zero-sequence impedance parameter Z can be obtained: 11 , Z 12 , Z 22 The calculation formula is:

[0024]

[0025]

[0026] Further, The calculation formula is:

[0027]

[0028] in, It is the zero-sequence current phasor of line 1 and line 2 in independent operation mode 1. is the zero-sequence current phasor of line 1 and line 2 in independent operation mode 2, is the zero-sequence voltage phasor of line 1 in independent operation mode 2, is the zero-sequence current phasor of line 1 in independent operation mode 2, It is the heterodyne zero-sequence current phasor of line 2 in independent operation mode 2.

[0029] Step S4: performing frequency conversion to obtain the power frequency mutual impedance of the line;

[0030] As a preferred method, the zero-sequence impedance at different frequencies is converted into the zero-sequence impedance at the power frequency using the following formula:

[0031]

[0032] Among them, f0, f1, and f2 are the frequencies of the different-frequency test power supply, f0 = 50 Hz, f1 = 45 Hz, and f2 = 55 Hz. R and X are the power frequency zero-sequence impedances.

[0033] Step S5: Synchronously construct a zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line and perform simulation verification.

[0034] The preferred zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line consists of a variable-frequency power supply unit, a synchronous measurement unit, and a handheld data terminal. The synchronous measurement unit at the headend of the outage line controls the variable-frequency power supply to inject heterodyne zero-sequence current into the line and simultaneously collects heterodyne voltage and current signals from the outage line. The synchronous measurement unit on the operating line collects heterodyne voltage and current signals from the PT and CT secondary circuits and transmits them via Bluetooth to the corresponding handheld data terminal. The handheld data terminal, connected via an IoT card, aggregates the synchronous data and solves the zero-sequence equation to obtain mutual inductance data.

[0035] The beneficial effects of the present invention are as follows: the present invention extracts the heterofrequency zero-sequence voltage and heterofrequency zero-sequence current in the measurement signal, then calculates the heterofrequency zero-sequence impedance, and then performs frequency conversion to obtain the power frequency zero-sequence impedance of the line. Even under complex interference conditions, the test calculation can still be completed accurately. In a double-circuit line non-stop power supply environment, heterofrequency signal excitation is applied to the power-off line to measure the mutual impedance between the double-circuit lines, which solves the multi-path coupling caused by the existing power frequency interference method and the accuracy problem caused by the zero-sequence incremental method signal measurement error, while also avoiding the safety risks brought by single-phase reclosing operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of simulation modeling of parallel transmission lines in an embodiment of the present application;

[0037] Figure 2 Schematic diagram of zero-sequence coupling model of double-circuit lines with different frequency excitation in an embodiment of the present application;

[0038] Figure 3 This is a simulation modeling diagram when the zero-sequence self parameters are equal in the embodiment of the present application;

[0039] Figure 4 Schematic diagram of simulation modeling of independent operation mode 1 when zero-sequence self parameters are unequal in the embodiment of the present application;

[0040] Figure 5 This is a simulation modeling diagram of the second independent operation mode when the zero-sequence self parameters are unequal in the embodiment of the present application;

[0041] Figure 6 This is a schematic diagram of the composition of a dual-circuit line mutual impedance synchronous measurement system in an embodiment of the present application;

[0042] Figure 7 This is a wiring diagram for the verification test of the different-frequency excitation method in the embodiment of this application. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further elaborated in detail below in conjunction with the drawings and specific embodiments of the specification. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In the following description, reference is made to "some embodiments", which describes a subset of all possible embodiments, but it should be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments, and can be combined with each other without conflict.

[0044] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art are not described to avoid confusion with the present invention.

[0045] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments proposed herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. And the purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates another way. It should also be understood that the terms "comprising" and / or "comprising" when used in this specification determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0046] It should also be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "inner," "outer," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0047] In order to fully understand the present invention, a detailed structure will be provided in the following description to illustrate the technical solution proposed by the present invention. Optional embodiments of the present invention are described in detail below. However, in addition to these detailed descriptions, the present invention may also have other implementations.

[0048] Example 1

[0049] Please refer to the attached Figures 1 to 6 The present application provides a zero-sequence frequency-differential excitation method for a double-circuit line in a partial power outage environment, comprising the following steps:

[0050] Step S1: using a different-frequency power supply as an excitation signal source for a double-circuit line zero-sequence network, applying a zero-sequence different-frequency signal excitation to the power outage line, wherein the zero-sequence different-frequency signal includes 45 Hz and 55 Hz;

[0051] In this embodiment, a different frequency power supply is used instead of a power frequency power supply as the test power supply to avoid power frequency interference during the measurement process. Figure 1 The simulation is performed on two parallel lines including line 1 and line 2. Line 1 is powered off, a different frequency power supply is added to the head end, and the three phases are short-circuited and grounded at the end; line 2 operates normally.

[0052] For example, to meet the instrument identification accuracy requirements, the CT-measured frequency-induced current must be kept above 30 mA. Furthermore, the actual frequency-induced current that can be applied on the power outage side must not exceed 50 A. Therefore, using a 45 Hz zero-sequence frequency-induced signal, defining a line length of 20 km, a self-resistance of approximately 0.2, a self-reactance of approximately 1.0, and a mutual inductance coefficient of approximately 0.4, the following Tables 1-1 and 1-2 are obtained.

[0053] Table 1-1

[0054]

[0055] Table 1-2

[0056]

[0057] Further defining the line length as 35km, the self-resistance as approximately 0.2, the self-reactance as approximately 1.0, and the mutual inductance coefficient K as approximately 0.4, we obtain the following Tables 1-3 to 1-4;

[0058] Table 1-3

[0059]

[0060]

[0061] Table 1-4

[0062]

[0063] Further defining the line length as 55km, the self-resistance as approximately 0.2, the self-reactance as approximately 1.0, and the mutual inductance coefficient K as approximately 0.4, we obtain the following Tables 1-5 to 1-6:

[0064] Table 1-5

[0065]

[0066] Table 1-3

[0067]

[0068]

[0069] For example, combining the data in Tables 1-1 to 1-6 above, we can obtain:

[0070] When l = 20km and the CT ratio is 600A / 5A, the voltage amplitude of the hybrid power supply can be selected from 0.15kV to 0.8kV; when the CT ratio is 1200A / 5A, the voltage amplitude of the hybrid power supply can be selected from 0.3kV to 0.8kV. The data in the above table are measured when the coupling coefficient K = 0.4. When the coupling coefficient is larger, such as K = 0.5 or 0.6, because the mutual inductance current is larger than when K = 0.4, the CT secondary side current will be greater than 30mA, which meets the requirements.

[0071] When l=35km and the CT ratio is 600A / 5A, the voltage amplitude of the frequency-differential power supply can be selected from 0.25kV to 1.4kV; when the CT ratio is 1200A / 5A, the voltage amplitude of the frequency-differential power supply can be selected from 0.5kV to 1.4kV;

[0072] When l=50km and the CT ratio is 600A / 5A, the voltage amplitude of the heterogeneous power supply can be selected from 0.34kV to 2kV; when the CT ratio is 1200A / 5A, the voltage amplitude of the heterogeneous power supply can be selected from 0.68kV to 2kV.

[0073] Therefore, by adopting the intersection of three cases of 45Hz zero-sequence frequency-different signals, the amplitude of the frequency-different power supply is selected to be 0.75kV, and the frequencies are selected to be 45Hz and 55Hz for simulation testing.

[0074] Step S2: simultaneously measuring the heterodyne induced current and voltage on the secondary sides of the current transformer and the voltage transformer on both sides of the operating line to obtain the heterodyne zero-sequence voltage and heterodyne zero-sequence current in the double-circuit line zero-sequence network;

[0075] In this embodiment, relevant parameter measurements are performed at the head and end of the power outage line. The voltage and current lead wires are used at the head end of the line. The voltage measurement lead is connected close to the line side, and the current measurement lead is connected close to the output side of the measurement power supply. The resistance part of the measured impedance is subtracted from the resistance of the end measurement lead.

[0076] Step S3: Solve the zero-sequence network equations simultaneously to calculate the mutual impedance between the double-circuit lines;

[0077] In this embodiment, combined with Figure 2 The volt-ampere characteristics of the zero-sequence coupling model of parallel transmission lines shown can be expressed by the following equations:

[0078]

[0079] Among them, Z 11 , Z 12 , Z 22 It is the zero-sequence impedance parameter of the two circuits, that is, the zero-sequence impedance parameter of different frequencies. and is the zero-sequence current phasor, and is the zero-sequence voltage phasor, is the current phasor at the beginning and end of line 1, is the current phasor at the beginning and end of line 2, is the voltage phasor at the beginning and end of line 1, It is the voltage phasor at the beginning and end of line 2. All electrical quantities are zero-sequence phasors. The error caused by capacitive current is reduced by taking the average value of the current phasor at the beginning and end.

[0080] For example, when the zero-sequence parameters of two circuits are equal, there are only two unknowns. Therefore, only the power of the two lines under one operation mode is needed to calculate the heterodyne impedance parameters. When the zero-sequence parameters of the two circuits are equal, the independent operation mode options of the lines include: Line 1 is powered off, a heterodyne power supply is added to the head end, and the three-phase short circuit is grounded at the end; Line 2 operates normally with power. Figure 3 As shown, the simulation modeling is performed when the zero-sequence self parameters are equal, and the zero-sequence impedance parameter Z 11 , Z 12 , Z 22 The solution calculation formula is:

[0081]

[0082] Further, The calculation formula is:

[0083]

[0084] in, is the zero-sequence voltage phasor of line 1 and line 2 at different frequencies, is the zero-sequence current phasor of line 1, It is the heterofrequency zero-sequence current phasor of line 2, that is, each current and voltage is a heterofrequency zero-sequence phasor.

[0085] For example, when the zero-sequence impedance parameters of two circuits are not equal, there are three unknowns. The power of the double-circuit lines under two independent operation modes is required to calculate the zero-sequence impedance parameter Z 11 , Z 12 , Z 22 Calculate and combine Figure 4 and Figure 5 As shown in the figure, the independent operation modes of the two lines when the zero-sequence parameters are not equal include:

[0086] Independent operation mode 1: Line 1 is powered off, a different frequency power supply is added to the head end, and the three phases at the end are short-circuited and grounded; Line 2 operates normally with power on.

[0087] Independent operation mode 2: Line 1 operates normally with power; Line 2 is powered off, a different frequency power supply is added to the head end, and the three phases at the end are short-circuited and grounded;

[0088] From the above two independent operation modes, the zero-sequence impedance parameter Z can be obtained: 11 , Z 12 , Z 22 The calculation formula is:

[0089]

[0090] Further, The calculation formula is:

[0091]

[0092] in, It is the zero-sequence current phasor of line 1 and line 2 in independent operation mode 1. is the zero-sequence current phasor of line 1 and line 2 in independent operation mode 2, is the zero-sequence voltage phasor of line 1 in independent operation mode 2, is the zero-sequence current phasor of line 1 in independent operation mode 2, It is the heterodyne zero-sequence current phasor of line 2 in independent operation mode 2.

[0093] Step S4: performing frequency conversion to obtain the power frequency mutual impedance of the line;

[0094] In this embodiment, after solving the zero-sequence impedance obtained under the heterodyne working condition according to the above formula, the heterodyne zero-sequence impedance is converted into the working frequency zero-sequence impedance, and the formula is as follows:

[0095]

[0096] Among them, f0, f1, and f2 are the frequencies of the different-frequency test power supply, f0 = 50 Hz, f1 = 45 Hz, and f2 = 55 Hz. R and X are the power frequency zero-sequence impedances.

[0097] Step S5: Synchronously construct a zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line and perform simulation verification.

[0098] In this embodiment, combined with Figure 6 As shown, a zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line is constructed, consisting of a variable-frequency power supply unit, a synchronous measurement unit, and a handheld data terminal. The synchronous measurement unit at the headend of the shut-down line controls the variable-frequency power supply to inject heterodyne zero-sequence current into the line and simultaneously collects heterodyne voltage and current signals from the shut-down line. The synchronous measurement unit on the operating line collects heterodyne voltage and current signals from the PT and CT secondary circuits and transmits them via Bluetooth to the corresponding handheld data terminal. The handheld data terminal, connected via an IoT card, aggregates the synchronous data and solves the zero-sequence equations to obtain mutual inductance data.

[0099] For example, the variable frequency power supply unit consists of a frequency converter module including voltage and current acquisition, and an isolation transformer. The maximum output current of the variable frequency power supply unit is 100A, the maximum output voltage is 1000V, and the frequency converter and isolation transformer capacity is 100kW. The output frequency of the variable frequency power supply unit is 45Hz and 55Hz. The variable frequency power supply unit has a GPRS communication interface, receives control commands from the test software APP, and returns the output voltage and current values.

[0100] The synchronized phasor measurement unit (SMU) simultaneously collects three voltage and three current channels, using the GPS clock signal as the sampling synchronization signal. The voltage sensor is selected to have a 0.01-level accuracy, and the current sampling uses a clamp-on current sensor with a level 1 accuracy. The SMU samples the 3U0 and 3I0 signals on the secondary sides of the PTs and CTs. If sampling the 3U0 or 3I0 signals is unavailable, the three-phase voltage and current signals are collected, and the zero-sequence voltage and current phasors are numerically calculated. Each SMU exports the measured data to a handheld data terminal via GPRS for data combination and simultaneous equation solution to obtain the mutual impedance parameters.

[0101] The handheld data terminal uses a tablet computer and is loaded with a measurement software APP. The measurement software APP sends a boost control command to the variable frequency power supply unit via GPRS, receives the output voltage and current data sent back by the variable frequency power supply unit, and controls the test current output size; the measurement software APP sends a start sampling command to the synchronous phasor measurement unit via GPRS. After receiving the sampling start command, each synchronous measurement unit starts collecting data according to the GPS synchronized clock signal. After the measurement is completed, the voltage and current phasor data are sent back to the handheld data terminal; the APP completes the calculation of the mutual impedance parameters.

[0102] For example, combined Figure 7 As shown, the operating method of the zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line includes the following steps:

[0103] Step S51: Connect a grounded power supply (frequency 45Hz and 55Hz) to the primary tap 1 of the isolation transformer. The primary tap 2 of the isolation transformer is directly grounded. Use the voltage transmission unit 1 to measure the voltage U of the primary tap 1. 11 , use current unit 1 to measure the primary tap 1 current I 11 ;

[0104] Step S52: Connect a 50Hz power supply with one end grounded to the secondary tap 1 of the isolation transformer. The secondary tap 2 of the isolation transformer is grounded through the current limiting resistor R1. Use the voltage unit 2 to measure the voltage U of the secondary tap 1. 12 , use current unit 2 to measure the secondary tap 1 current I 12 , use voltage unit 3 to measure the secondary tap 2 voltage U 12p ;

[0105] Step S53: The power frequency power supply output voltage is set to 220V, simulating the operation of the transmission line 2;

[0106] Step S54: The output voltage of the heterodyne AC power source is set to 100V at 45Hz and 55Hz, and the readings of each meter are measured and recorded. The zero-sequence impedance of transmission line 1 and the zero-sequence impedance of transmission line 2 at 45Hz and 55Hz, and the mutual inductance impedance between transmission line 1 and transmission line 2 are calculated, and the results are converted to 50Hz.

[0107] Step S55: Compare the experimental results with the simulation data and output the verified simulation results.

[0108] Example 2

[0109] In this embodiment, the feasibility verification test scheme is used to verify the feasibility and accuracy of the power frequency interference method and the different-frequency excitation method in testing the zero-sequence impedance of two mutual inductance lines. By comparing the test results and simulation results, the measurement error of the two methods adopted and their impact on the zero-sequence impedance measurement results are verified to evaluate their reliability in practical application. At the same time, the experiments conducted through this test scheme can also further explore the application prospects and limitations of the power frequency interference method and the different-frequency excitation method in actual engineering, providing a reference for the accurate measurement of the zero-sequence impedance of the mutual inductance line.

[0110] This verification test uses an isolation transformer to simulate two transmission lines, where the primary side of the transformer simulates "transmission line 1" and the secondary side of the transformer simulates "transmission line 2". Grounding points are set at the beginning and end of the two lines (i.e., the primary and secondary taps of the isolation transformer). The transformers of the simulated lines are as follows: Figure 1 shown.

[0111] Use a 50Hz industrial frequency power supply, applied to the secondary side of the isolation transformer, simulate "transmission line 2" as a line that operates without power outages, and use a single-phase voltage regulator for the industrial frequency power supply, such as Figure 2 shown.

[0112] A power transmission line power frequency parameter test system is used to collect voltage and current signals of different frequency power sources. The test system has GPS timing function and can realize multi-point current and voltage synchronous testing. The measuring device is as follows: Figure 3 shown.

[0113] By collecting the voltage and current signals at each point, the zero-sequence impedance and mutual inductance impedance of the line are calculated to verify the simulation results of the different-frequency excitation method.

[0114] The basic principle of verification test is based on theoretical analysis and simulation model, but factors such as actual line conditions, performance differences of actual electrical equipment, and environmental influences may affect the accuracy of test results. Therefore, verification test needs to fully consider these factors and conduct sufficient data processing and error analysis to ensure the reliability of test results.

[0115] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. The scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A zero-sequence frequency-differential excitation method for double-circuit lines under a partial power outage environment, characterized in that: The following steps are involved: Step S1: using a different-frequency power supply as an excitation signal source for a double-circuit line zero-sequence network, applying a zero-sequence different-frequency signal excitation to the power outage line, wherein the zero-sequence different-frequency signal includes 45 Hz and 55 Hz; Step S2: simultaneously measuring the heterodyne induced current and voltage on the secondary sides of the current transformer and the voltage transformer on both sides of the operating line to obtain the heterodyne zero-sequence voltage and heterodyne zero-sequence current in the double-circuit line zero-sequence network; Step S3: Solve the zero-sequence network equations simultaneously to calculate the mutual impedance between the double-circuit lines; Step S4: performing frequency conversion to obtain the power frequency mutual impedance of the line; Step S5: Synchronously construct a zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line and perform simulation verification.

2. The zero-sequence frequency-different excitation method for a double-circuit line under a partial power outage environment according to claim 1 is characterized in that: The method of applying zero-sequence heterofrequency signal excitation to the power-off line specifically includes: using a heterofrequency power supply as a test power supply, simulating two parallel lines including line 1 and line 2, causing line 1 to be powered off, adding a heterofrequency power supply at the head end, and short-circuiting the three phases at the end to ground; and line 2 operates normally.

3. The zero-sequence frequency-different excitation method for a double-circuit line under a partial power outage environment according to claim 1 is characterized in that: The measurement of the heterodyne induced current and voltage includes: performing parameter measurements at the head end and the end end of the power outage line, using voltage and current lead wires at the head end of the line, with the voltage measurement lead connected close to the line side and the current measurement lead connected close to the output side of the measurement power supply, and subtracting the resistance of the end measurement lead from the resistance part of the measured impedance.

4. The zero-sequence frequency-different excitation method for a double-circuit line under a partial power outage environment according to claim 1 is characterized in that: The calculation of the mutual impedance between the double-circuit lines includes: constructing a zero-sequence coupling model of the parallel transmission lines. The volt-ampere characteristics of the zero-sequence coupling model of the parallel transmission lines can be expressed by the following equations: Among them, Z 11 , Z 12 , Z 22 It is the zero-sequence impedance parameter of the two circuits, that is, the zero-sequence impedance parameter of different frequencies. and is the zero-sequence current phasor, and is the zero-sequence voltage phasor, is the current phasor at the beginning and end of line 1, is the current phasor at the beginning and end of line 2, is the voltage phasor at the beginning and end of line 1, It is the voltage phasor at the beginning and end of line 2. All electrical quantities are zero-sequence phasors. The error caused by capacitive current is reduced by taking the average value of the current phasor at the beginning and end.

5. The zero-sequence frequency-different excitation method for a double-circuit line under a partial power outage environment according to claim 4 is characterized in that: The parallel transmission line zero-sequence coupling model includes: equal zero-sequence self-parameters of the two circuits and unequal zero-sequence self-parameters of the two circuits.

6. The zero-sequence frequency-different excitation method for double-circuit lines under a partial power outage environment according to claim 5, characterized in that: When the zero-sequence self-parameters of the two circuits are equal: there are only two unknowns, and it is only necessary to obtain the electrical quantity of the two circuits under one operating mode to calculate the heterofrequency impedance parameters. The independent operation mode selection of the two circuits when the zero-sequence self-parameters are equal includes: line 1 is powered off, a heterofrequency power supply is added to the head end, and the three-phase short circuit is grounded at the end; line 2 is normally energized, and the heterofrequency zero-sequence impedance parameter Z is obtained by simulation modeling when the zero-sequence self-parameters are equal. 11 , Z 12 , Z 22 The solution calculation formula is: Further, The calculation formula is: in, is the zero-sequence voltage phasor of line 1 and line 2 at different frequencies, is the zero-sequence current phasor of line 1, It is the heterofrequency zero-sequence current phasor of line 2, that is, each current and voltage is a heterofrequency zero-sequence phasor.

7. The zero-sequence frequency-different excitation method for double-circuit lines under a partial power outage environment according to claim 5, characterized in that: When the zero-sequence impedance parameters of the two circuits are not equal, there are three unknowns. The power of the double-circuit circuit under two independent operation modes is used to calculate the zero-sequence impedance parameter Z 11 , Z 12 , Z 22 Calculation is performed, where the line independent operation mode selection when the zero-sequence parameters of the two circuits are not equal includes: Independent operation mode 1: Line 1 is powered off, a different frequency power supply is added to the head end, and the three phases at the end are short-circuited and grounded; Line 2 operates normally with power on. Independent operation mode 2: Line 1 operates normally with power; Line 2 is powered off, a different frequency power supply is added to the head end, and the three phases at the end are short-circuited and grounded; From the above two independent operation modes, the zero-sequence impedance parameter Z can be obtained: 11 , Z 12 , Z 22 The calculation formula is: Further, The calculation formula is: in, It is the zero-sequence current phasor of line 1 and line 2 in independent operation mode 1. is the zero-sequence current phasor of line 1 and line 2 in independent operation mode 2, is the zero-sequence voltage phasor of line 1 in independent operation mode 2, is the zero-sequence current phasor of line 1 in independent operation mode 2, It is the heterodyne zero-sequence current phasor of line 2 in independent operation mode 2.

8. The zero-sequence frequency-different excitation method for double-circuit lines under a partial power outage environment according to claim 1, characterized in that: Obtaining the power frequency mutual impedance of the line includes converting the different-frequency zero-sequence impedance into the power frequency zero-sequence impedance, and the formula is as follows: Among them, f0, f1, and f2 are the frequencies of the different-frequency test power supply, f0 = 50 Hz, f1 = 45 Hz, and f2 = 55 Hz. R and X are the power frequency zero-sequence impedances.

9. The zero-sequence frequency-different excitation method for double-circuit lines under a partial power outage environment according to claim 1, characterized in that: The zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line includes the following functional units: a variable-frequency power supply unit, a synchronous measurement unit, and a handheld data terminal. The variable-frequency power supply unit is composed of a frequency converter module including voltage and current acquisition and an isolation transformer, and is used to receive control commands from a test software APP and return output voltage and current values. The synchronous measurement unit is used to use a 3-channel voltage and 3-channel current simultaneous acquisition mode, using a GPS clock signal as a sampling synchronization signal, and deriving measurement data. The handheld data terminal is used to send control commands to control the test current output size and receive output voltage and current data transmitted back by the variable-frequency power supply unit.

10. The zero-sequence frequency-different excitation method for double-circuit lines in a partial power outage environment according to claim 9, characterized in that: The operating method of the zero-sequence mutual inductance impedance measurement system for a partially shut-down double-circuit line comprises the following steps: Step S51: Connect the 45Hz and 55Hz frequency power supplies with one end grounded to the primary tap 1 of the isolation transformer, and the primary tap 2 of the isolation transformer is directly grounded. Use the voltage transmission unit 1 to measure the voltage U of the primary tap 1. 11 , use current unit 1 to measure the primary tap 1 current I 11 ; Step S52: Connect a 50 Hz power supply with one end grounded to the secondary tap 1 of the isolation transformer. The secondary tap 2 of the isolation transformer is grounded through the current limiting resistor R1. Use the voltage unit 2 to measure the voltage U of the secondary tap 1. 12 , use current unit 2 to measure the secondary tap 1 current I 12 , use voltage unit 3 to measure the secondary tap 2 voltage U 12p ; Step S53: The power frequency power supply output voltage is set to 220V, simulating the operation of the transmission line 2; Step S54: The output voltage of the heterodyne AC power source is set to 100V at 45Hz and 55Hz, and the readings of each meter are measured and recorded. The zero-sequence impedance of transmission line 1 and the zero-sequence impedance of transmission line 2 at 45Hz and 55Hz, and the mutual inductance impedance between transmission line 1 and transmission line 2 are calculated, and the results are converted to 50Hz. Step S55: Compare the experimental results with the simulation data and output the verified simulation results.

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