CN102621388A - Electric transmission line lumped parameter on-line determination method based on synchronous time domain signals - Google Patents

Abstract

The invention relates to an online determination method for centralized parameters of transmission lines based on synchronous time-domain signals, which uses current and voltage synchronous time-domain signals on both sides of the transmission line to calculate the centralized parameters of the transmission line. In the equivalent circuit diagram of concentrated parameters of the transmission line, according to Kirchhoff’s first law KCL and Kirchhoff’s second law KVL, the differential equations are listed, and the expressions about the line parameters resistance R, inductance L, and capacitance C are obtained. The specific parameters can be obtained by substituting the voltage and current time domain signals on both sides of the line into the expression. The calculation accuracy of the transmission line centralized parameter determination method involved in the present invention is not affected by the attenuation of direct current and attenuation of high-frequency signals, the data window required for calculation is short, not only has high precision, but also has fast response speed.

Description

On-line Determination Method of Concentrated Parameters of Transmission Lines Based on Synchronous Time Domain Signals

technical field

The invention relates to an online determination method for transmission line parameters in a power system, in particular to an online determination method for centralized transmission line parameters based on synchronous time domain signals.

Background technique

With the rapid and steady progress of my country's smart grid construction, the requirements for the safe and stable operation of the power grid are getting higher and higher. The rapid increase in the physical complexity of the power grid makes the safe and stable operation of the power grid face severe challenges. As the scale of the power grid becomes larger and the network structure becomes more and more complex, the control of the characteristics of the power grid by dispatchers and operators is increasingly dependent on the accuracy of the parameters of the power grid model. Line parameters are an important basis for operating technicians to obtain the grid structure, generate node admittance matrix and impedance matrix required for power flow calculations, perform short-circuit current calculations, and set relay protection devices. Improving the accuracy, reliability, and real-time performance of power grid parameter calculations is a basic requirement for building a smart grid, and is of great significance to the safe and stable operation of the power grid.

Current operating experience shows that: in some power grids, there will be certain errors between the calculated values and the measured values of the links such as state estimation, power flow calculation, and protection setting. In some cases, the error is large, and even affects the system. Normal and stable operation. Through a lot of analysis, it is found that the main reason for the error is that the line parameters are not accurate enough, that is, the theoretical parameter values of the line used in the analysis and calculation are quite different from the actual parameter values. At present, most of the line parameter values used in the field are empirical values or off-line measurement values given by the manufacturer, rather than the actual operation parameters of the line. There will inevitably be errors between the two, which will affect the accuracy and precision of power system analysis and calculation. . Strictly speaking, there will be differences in line parameters at different times and under different operating conditions. If more accurate calculations are made, these differences cannot be ignored. If the parameter value of the transmission line can be calculated online through the real-time operation of the power grid, and the analysis and calculation of the power system based on the real-time transmission line parameters will certainly improve the accuracy of the analysis and calculation, thereby improving the safety and stability of the power grid.

The time domain signal refers to the signal that changes with time, and when it is reflected in the power system, it is the analog sampling value of the current and voltage signals. These signals are only the signals after time-discretization processing of current and voltage, and do not need to go through calculation links such as digital filtering and Fourier transform, so it can avoid the influence of DC components, harmonics and algorithm selection on the calculation results, and has Faster calculation speed, better application prospects.

Chinese patent application 201110024996 discloses a method for identifying and estimating power line parameters based on PMU measurement data. The method uses a computer to input the basic data of the line to be identified and estimated through a program, and then firstly identifies the wrong parameters of the line according to the PMU measurement data of multiple periods at both ends of the line, and then estimates the correct parameters of the line. Estimates of the correct parameters for the line are obtained. The invention is based on PMU measurement data, and the wrong parameters of the line must be identified first. The selection of the identification method will affect the estimation of the correct parameters of the line, and it is only for medium-length high-voltage and ultra-high-voltage transmission lines equipped with PMU devices.

Chinese patent application 200910107854 discloses an online measurement method of transmission line parameters based on fault recording. This method uses the GPS clock of the wave recording device to start on the hour, obtains the positive sequence voltage and current at both ends of the line, and saves them in the wave recording devices at both ends in the form of wave recording files, and then the central dispatching computer reads the positive sequence at both ends. Voltage, current value and zero sequence voltage, current value, measure the positive sequence parameters and zero sequence parameters of the line. This invention enables the wave recording device to be used for on-line measurement of transmission line parameters, and makes up for the defects that the existing online measuring device is not synchronized when measuring positive sequence parameters and has no zero-sequence power supply when measuring zero-sequence parameters, but it relies too much on the wave recording device. There are certain limitations.

Chinese patent application 200810079455 discloses a method for measuring positive sequence parameters of high voltage transmission lines. The invention uses a single-phase test power supply to apply positive-phase voltage and reverse-phase voltage to the line to be tested, and uses the voltage, current, and power values measured before and after the reverse phase, combined with the interference voltage measured before the voltage is applied to the line, to eliminate the interference voltage through calculation The influence of the phase-to-phase impedance is obtained; then the other two phases are measured to obtain the phase-to-phase impedance, and the positive sequence parameters of the high-voltage transmission line are obtained after calculation. This invention can accurately measure the positive sequence parameters of the high-voltage transmission line in the environment of strong electromagnetic interference, especially in the case of different three-phase interference voltages, but the application of single-phase test power will affect the normal operation of the line .

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, and provide an online method for determining centralized parameters of transmission lines based on synchronous time-domain signals. The error between the centralized parameters of transmission lines calculated by this method and the actual parameters is very small , has very high accuracy, and the calculation accuracy of this method is not affected by the attenuation of DC and attenuation of high-frequency signals, the data window required for calculation is very short, and it has a faster response speed.

To achieve the above object, the present invention adopts the following technical solutions:

A method for online determination of concentrated parameters of transmission lines based on synchronous time-domain signals, comprising the following steps:

The first step: the transmission line is equivalent to a π-type lumped parameter model, and the differential equation of the π-type circuit is listed according to Kirchhoff's first law KCL and Kirchhoff's second law KVL;

Step 2: Simplify and combine the differential equations to obtain a set of differential equations about the centralized parameters resistance R, inductance L, and capacitance C of the transmission line;

Step 3: Bring the voltage and current synchronous time-domain signals on both sides of the transmission line into the differential equations, and use the least square method to solve the specific values of the line parameters resistance R, inductance L, and capacitance C.

The writing method of the differential equation in the first step is as follows: first, the transmission line is equivalent to a π-type equivalent circuit, and the KCL and KVL differential equations are written according to the structure of the π-type equivalent circuit.

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="i"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">i</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="i\; c"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">i</figure-callout></span><figure-callout\; id="1"\; label="i\; c"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="i\; c"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">i</figure-callout></span><figure-callout\; id="2"\; label="i\; c"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="i"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">i</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">C</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">C</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}\frac{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right.$

The differential equations obtained after simplification and merging in the second step are:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Ri</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; RC</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; LC</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="dt"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">dt</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\end{array}\right.$

Among them, u ₁ , u ₂ , i ₁ , and i ₂ are the voltage and current synchronous time-domain signals at both ends of the transmission line respectively, i _c1 and i _c2 are the time-domain signals of the current flowing through the distributed capacitance on both sides, the resistance R and the inductance L , Capacitance C is the line parameter after the transmission line is equivalent to a π-type circuit.

The solution method in the third step is: collect synchronous voltage and current time-domain signals at both ends of the line, and obtain the first-order derivative and second-order derivative for the time-domain signal, and substitute them into the differential equations in the second step. The least squares method is used to solve the equations to obtain the specific values of the line parameters resistance R, inductance L, and capacitance C.

The present invention uses synchronous time-domain signals to perform on-line calculation of centralized parameters of transmission lines, and has the following advantages compared with existing similar technologies:

1. The time domain signal refers to the signal that changes with time, which is reflected in the power system, which is the analog sampling value of the current and voltage signals. These signals are only signals after time-discretization processing of current and voltage, without digital filtering, Fourier transform and other calculation links, which can greatly simplify the calculation process and have a faster calculation response speed;

2. Calculating centralized parameters of transmission lines based on synchronous time-domain signals can avoid the impact of DC components and attenuated harmonics on the accuracy of calculation results;

3. The online calculation method of centralized parameters of the transmission line proposed by the present invention is not affected by the operation state of the line, and can perform parameter calculation no matter in the normal operation state or in the fault state, and can provide real-time and accurate power grid parameters.

Description of drawings

Figure 1 is a schematic structural diagram of the power system model with two-terminal power supply;

Fig. 2 is a schematic diagram of a π-type lumped parameter equivalent circuit;

Figure 3 is a diagram of the transmission line parameters calculated under the normal operating state of the system;

Fig. 4 is a diagram of transmission line parameters calculated under a fault state;

Detailed ways

The present invention will be further described below in conjunction with accompanying drawings and examples.

In order to illustrate that the method proposed in the present invention can accurately determine line parameters in various operating states of the power system, two different operating states are designed, which are normal operating state and fault state.

1. Calculation of transmission line parameters under normal operating conditions

In the double-ended power supply power system model shown in Figure 1, its π-type equivalent circuit is shown in Figure 2.

In the figure, u ₁ , u ₂ , i ₁ , and i ₂ are the synchronous time-domain signals of the voltage and current at both ends of the line, respectively, and i _c1 and i _c2 are the time-domain signals of the current flowing through the distributed capacitance on both sides. According to Kirchhoff's first law KCL, write the differential equation as follows:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="i"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">i</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">C</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">C</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="i"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">i</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Simplify to get the expression of capacitance C:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}}$

As long as the synchronous time-domain signals u ₁ , u ₂ , i ₁ , and i ₂ of the voltage and current on both sides of the line are obtained, and the first-order derivative of the voltage time-domain signal is obtained, the parameter of the distributed capacitance C of the line can be obtained by substituting the above formula .

For Figure 2, the differential equation can also be written according to Kirchhoff’s second law KVL as follows:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}\frac{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}$

将其代入上式，最终得到关于线路参数电阻R、电感L的表达式为：A known

Substituting it into the above formula, the expressions about the line parameters resistance R and inductance L are finally obtained as follows:

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="u"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Ri</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="RC"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">RC</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; L</span>}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; LC</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="u"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">u</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="dt"\; filenames="HDA0000153067710000014.png"\; state="\{\{state\}\}">dt</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

The above formula contains two unknowns, namely the resistance R and the inductance L, which can be solved by using multiple sets of synchronous time-domain signals based on the least squares method to obtain the final parameter values of the resistance R and inductance L. Figure 3 is the calculation under normal operating conditions The obtained transmission line parameter curve.

2. Calculation of transmission line parameters under fault conditions

Assume that the fault occurs at point F1 shown in Figure 1, and the fault type is a metal-to-ground short circuit of phase A, and the calculation adopts the voltage and current time domain signals on both sides of the transmission line under the fault state, obtained according to the calculation method proposed in the present invention The lumped parameter resistance, inductance and capacitance curves are shown in Fig. 4. Compared with Fig. 3, it can be seen that the calculated transmission line parameter values under the two operating states are almost equal, indicating that the calculation method proposed by the present invention has the advantage of not being affected by the operating state of the line, and has higher calculation accuracy.

Claims (3)

1. the online definite method of the transmission line of electricity lumped parameter based on the synchronous time domain signal is characterized in that, may further comprise the steps:

The first step: with the transmission line of electricity equivalence is π type lumped parameter model, lists the differential equation of pi-network according to Kirchhoff's first law KCL and Kirchhoff's second law KVL;

Second step: differential equation abbreviation is merged, obtain differential equation group about transmission line of electricity lumped parameter resistance R, inductance L, capacitor C;

The 3rd step: synchronizing voltage and the electric current time-domain signal of gathering the circuit two ends; And time-domain signal asked for first order derivative and second derivative; In the differential equation group in second step of substitution, adopt least square method solving equation group, obtain the occurrence of line parameter circuit value resistance R, inductance L, capacitor C.

2. the online definite method of the transmission line of electricity lumped parameter based on the synchronous time domain signal as claimed in claim 1; It is characterized in that; The row write method of the differential equation in the said first step is: be π type equivalent circuit with the transmission line of electricity equivalence at first, write out KCL, the KVL differential equation according to the structure of π type equivalent circuit;

$\left\{\begin{array}{c}{i}_1=i_{c1}+i_{c2}+i_2=\frac{C}{2}\frac{{\mathrm{du}}_1}{\mathrm{dt}}+\frac{C}{2}\frac{{\mathrm{du}}_2}{\mathrm{dt}}+i_2\\ u_1-[R(i_1-i_{c1})+L\frac{d(i_1-i_{c1})}{\mathrm{dt}}]=u_2\end{array}\right.$

Wherein, u ₁, u ₂, i ₁, i ₂Be respectively voltage, the electric current synchronous time domain signal at transmission line of electricity two ends, i _C1, i _C2For flowing through the electric current time-domain signal of both sides distributed capacitance, resistance R, inductance L, capacitor C are that the transmission line of electricity equivalence is the line parameter circuit value behind the pi-network.

3. the online definite method of the transmission line of electricity lumped parameter based on the synchronous time domain signal as claimed in claim 1 is characterized in that, the differential equation group that abbreviation obtains after merging in described second step is:

$\left\{\begin{array}{c}C=2(i_1-i_2)/(\frac{{\mathrm{du}}_1}{\mathrm{dt}}+\frac{{\mathrm{du}}_2}{\mathrm{dt}})\\ u_1-u_2={\mathrm{Ri}}_1-\frac{\mathrm{RC}}{2}\frac{{\mathrm{du}}_1}{\mathrm{dt}}+L\frac{{\mathrm{di}}_1}{\mathrm{dt}}-\frac{\mathrm{LC}}{2}\frac{d^2{u}_1}{{\mathrm{dt}}^2}\end{array}\right.$

Wherein, u ₁, u ₂, i ₁, i ₂Be respectively voltage, the electric current synchronous time domain signal at transmission line of electricity two ends, resistance R, inductance L, capacitor C are that transmission line of electricity equivalence is the line parameter circuit value behind the pi-network.

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