CN105807140A - Ultrahigh-voltage overhead-cable hybrid power transmission line order parameter measurement method - Google Patents

Abstract

The invention relates to an ultrahigh-voltage overhead-cable hybrid power transmission line order parameter measurement method. Positive-order parameter measurement comprises the following steps: system trends change according to demands of a scheduling portion, three-phase voltage and current phasors of the two sides of a hybrid line are obtained through measurement before change and measurement after the change, and positive-order voltages and positive-order currents of the two sides are obtained through the measurement of the two times; T-type equivalent circuit positive-order impedance parameters of the whole hybrid line are solved; T-type equivalent circuit positive-order admittance parameters of an overhead line section and T-type equivalent circuit positive-order admittance parameters of a power cable section are solved; T-type equivalent circuit positive-order impedance parameters of the overhead line section and T-type equivalent circuit positive-order impedance parameters of the power cable section are solved; and positive-order impedance and positive-order admittance parameters of a unit length of an overhead line and a power cable are solved. The measurement method provided by the invention has quite high accuracy.

Description

Method for measuring sequence parameters of ultrahigh voltage overhead-cable hybrid transmission line

Technical Field

The invention relates to the technical field of power system measurement, in particular to a method for measuring sequence parameters of an ultrahigh voltage overhead-cable hybrid power transmission line.

Background

The ultrahigh voltage overhead-cable hybrid power transmission line has the advantages of economy, reliability and the like in the aspect of power transmission to urban load centers and across rivers and seas, so that the ultrahigh voltage overhead-cable hybrid power transmission line is generally applied and popularized in modern power construction and power grid transformation. Accurate line parameters are the basis for load flow calculation, relay protection setting, fault location and the like of the system. The factory parameters of the lines which are commonly used in engineering are calculated, so that large errors are inevitably caused. After the line is built, the parameters of the line can be changed along with the change of factors such as environmental temperature, climate and soil, and the parameters of the line are greatly changed compared with the parameters given when the line leaves a factory. Due to the difference of parameters of all sections of the hybrid power transmission line, the traditional single uniform line parameter calculation method cannot accurately calculate the parameters.

Disclosure of Invention

In view of the problems of parameter measurement of the ultrahigh voltage overhead line-cable hybrid line in the background art, the invention provides a method for measuring sequence parameters of an ultrahigh voltage overhead-cable hybrid transmission line. The invention provides an overhead line-cable hybrid line sequence parameter measuring method by adopting distributed parameters for calculation on the basis of fully considering the parameter characteristics of the hybrid line.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a method for measuring sequence parameters of an extra-high voltage overhead-cable hybrid line comprises the following steps of:

step A: when the hybrid line normally runs, the system power flow can change according to the requirements of a dispatching part, three-phase voltage and current phasors of M, N end points on two sides of the hybrid line are obtained through two measurements before and after the change, and positive sequence voltage and positive sequence current on two sides of M, N which are obtained through two measurements are respectively obtained through a symmetrical component method

And B: according to the circuit principle, the positive sequence impedance parameter Z of the T-shaped equivalent circuit of the whole line of the mixed line₁′、Z₂' and Z₃' obtaining the following

And C: the positive sequence capacitance of the whole line of the section of the power cable is k times of that of the whole line of the section of the overhead line, and the positive sequence admittance parameter Y of the T-shaped equivalent circuit of the section of the overhead line_OH1And T-shaped equivalent circuit positive sequence admittance parameter Y of power cable section_Cb1The following were obtained

Step D: order toAndt-shaped equivalent circuit positive sequence impedance parameter Z of overhead line section_OH1And positive sequence impedance parameter Z of T-shaped equivalent circuit of power cable section_Cb1Find out the following

Step E: positive sequence impedance z per unit length of overhead line and power cable_OH1、z_Cb1And a positive sequence admittance parameter y_OH1、y_Cb1The following were obtained

Wherein l_OHIndicating the length of the overhead line section,/_CbRepresenting the length of the power cable section, archonh (·) represents an inverse hyperbolic sinusoidal function.

Compared with the prior art, the invention has the beneficial effects that:

1. the parameter measurement method can realize the measurement of the parameters of the ultrahigh voltage overhead-cable mixed line, and has high accuracy by utilizing the distribution parameters to calculate;

2. the method is suitable for the on-line measurement of sequence parameter measurement of the overhead line section and the power cable section of the ultrahigh voltage hybrid line, and therefore, the method has higher practicability.

Drawings

FIG. 1 is a schematic diagram of a two-section hybrid circuit;

FIG. 2 is a positive sequence distributed parameter equivalent circuit of a hybrid line;

FIG. 3 is a positive sequence T-shaped equivalent circuit of a hybrid line segment;

FIG. 4 is an equivalent transformation circuit diagram of a hybrid line;

fig. 5 is a positive sequence T-type equivalent circuit diagram of the hybrid line.

Detailed Description

In order to overcome the defects of the prior measurement technology, the invention provides a method for measuring the sequence parameters of the ultra-high voltage overhead-cable hybrid transmission line, which is suitable for the online measurement of the positive sequence, negative sequence and zero sequence parameters of the overhead line section and the power cable section of the hybrid line, and the calculation is carried out by utilizing the distribution parameters, so that the method has higher accuracy and practicability.

In order to achieve the purpose of the invention, the invention adopts the following technical scheme:

the method for measuring the sequence parameters of the ultrahigh-voltage overhead-cable hybrid line comprises the steps of positive sequence parameters, negative sequence parameters and zero sequence parameters. Taking the measurement of the positive sequence parameter as an example, the specific derivation process of the scheme is as follows:

(1) overhead line segment length l_OHLength of power cable section of l_CbThe overhead-cable hybrid transmission line is shown in figure 1, the positive sequence distribution parameter equivalent circuit of the hybrid line is shown in figure 2, and the positive sequence impedance and the positive sequence admittance of the unit length of the overhead line are respectively z_OH1＝r_OH1+jωL_OH1，y_OH1＝g_OH1+jωC_OH1(ii) a Let the positive sequence impedance and the positive sequence admittance of the unit length of the power cable be z respectively_Cb1＝r_Cb1+jωL_Cb1，y_Cb1＝g_Cb1+jωC_Cb1. The conductance of the overhead line section and the power cable section of the extra-high voltage hybrid line is approximately 0, and the equivalent circuit of the sections is a T-shaped equivalent circuit shown in figure 3.

The parameters of the T-shaped equivalent circuit of the overhead line section are obtained as follows

Wherein,is the positive sequence propagation constant of the overhead line,for the positive sequence wave impedance of the overhead line, sh (-) represents a hyperbolic sine function, and ch (-) represents a hyperbolic cosine function.

The parameters of the T-shaped equivalent circuit of the power cable section are obtained as follows

Wherein,is the positive sequence propagation constant of the power cable,is the positive sequence wave impedance of the power cable.

(2) In step (1), the equivalent circuit of FIG. 3Y_OH1And Y_Cb1Forming a triangle, performing triangle-star equivalent transformation, and obtaining an equivalent transformation circuit shown in figure 4, wherein the line parameter Z₃、Z₄、Z₅The following were obtained

Wherein,

(3) in step (2), the line parameters Z are respectively merged₃AndZ₄andthe T-shaped equivalent circuit of the mixed line is obtained as shown in figure 5, and the line parameter Z₁′、Z₂′、Z₃′。

(4) When the hybrid line normally runs, the system power flow can change according to the requirements of a dispatching part, three-phase voltage and current phasors of M, N end points on two sides of the hybrid line are obtained through two measurements before and after the change, and positive sequence voltage and positive sequence current on two sides of M, N which are obtained through two measurements are respectively obtained through a symmetrical component method

(5) According to the circuit principle, the positive sequence impedance parameter Z of the T-shaped equivalent circuit of the whole line of the mixed line₁′、Z₂' and Z₃' obtaining the following

(6) The positive sequence capacitance of the whole line of the section of the power cable is k times of that of the whole line of the section of the overhead line, and the positive sequence admittance parameter Y of the T-shaped equivalent circuit of the section of the overhead line_OH1And T-shaped equivalent circuit positive sequence admittance parameter Y of power cable section_Cb1The following were obtained

(7) Order toAndt-shaped equivalent circuit positive sequence impedance parameter Z of overhead line section_OH1And positive sequence impedance parameter Z of T-shaped equivalent circuit of power cable section_Cb1Find out the following

(8) Positive sequence impedance z per unit length of overhead line and power cable_OH1、z_Cb1And a positive sequence admittance parameter y_OH1、y_Cb1The following were obtained

Wherein arcsin h (·) represents an inverse hyperbolic sine function.

The method for measuring the sequence parameters of the ultrahigh voltage overhead-cable hybrid transmission line is suitable for online measurement of positive sequence, negative sequence and zero sequence parameters of an overhead line section and a power cable section of the hybrid transmission line, and calculation is performed by using the distributed parameters, so that the method has higher accuracy and practicability.

Claims (1)

1. A method for measuring sequence parameters of an extra-high voltage overhead-cable hybrid line comprises the following steps of:

step A: when the hybrid line normally runs, the system power flow can change according to the requirements of a dispatching part, three-phase voltage and current phasors of M, N end points on two sides of the hybrid line are obtained through two measurements before and after the change, and positive sequence voltage and positive sequence current on two sides of M, N which are obtained through two measurements are respectively obtained through a symmetrical component method

And B: according to the circuit principle, the positive sequence impedance parameter Z of the T-shaped equivalent circuit of the whole line of the mixed line₁′、Z₂' and Z₃' obtaining the following

$\left[\begin{array}{cc}{Z_1}^{\′}+{Z_3}^{\′}& {Z_3}^{\′}\\ {Z_3}^{\′}& {Z_2}^{\′}+{Z_3}^{\′}\end{array}\right]=\left[\begin{array}{cc}{\stackrel{\·}{U}}_{M1}& {\stackrel{\·}{U}}_{M1}^{\′}\\ {\stackrel{\·}{U}}_{N1}& {\stackrel{\·}{U}}_{N1}^{\′}\end{array}\right]{\left[\begin{array}{cc}{\stackrel{\·}{I}}_{M1}& {\stackrel{\·}{I}}_{M1}^{\′}\\ {\stackrel{\·}{I}}_{N1}& {\stackrel{\·}{I}}_{N1}^{\′}\end{array}\right]}^{-1}$

And C: the positive sequence capacitance of the whole line of the section of the power cable is k times of that of the whole line of the section of the overhead line, and the positive sequence admittance parameter Y of the T-shaped equivalent circuit of the section of the overhead line_OH1And T-shaped equivalent circuit positive sequence admittance parameter Y of power cable section_Cb1The following were obtained

$Y_{OH1}=1/\sqrt{\frac{{Z_3}^{\′}}{k}\[{Z_1}^{\′}+{Z_2}^{\′}+{Z_3}^{\′}(k+\frac{1}{k}+2)\]}$

$Y_{Cb1}=1/\sqrt{{{\mathrm{kZ}}_3}^{\′}\[{Z_1}^{\′}+{Z_2}^{\′}+{Z_3}^{\′}(k+\frac{1}{k}+2)\]}$

Step D: order toAndt-shaped equivalent circuit positive sequence impedance parameter Z of overhead line section_OH1And positive sequence impedance parameter Z of T-shaped equivalent circuit of power cable section_Cb1Find out the following

$Z_{OH1}=2{Z_1}^{\′}-2Z_{Y_{OH1}}+(2+\frac{2}{k}){Z_3}^{\′}$

$Z_{Cb1}=2{Z_2}^{\′}-2Z_{Y_{Cb1}}+(2k+2){Z_3}^{\′}$

Step E: positive sequence impedance z per unit length of overhead line and power cable_OH1、z_Cb1And a positive sequence admittance parameter y_OH1、y_Cb1The following were obtained

$z_{OH1}=\frac{ar\sinh (\sqrt{(Z_{OH1}^2+\sqrt{Z_{OH1}^4+4Z_{OH1}^2{Z}_{Y_{OH1}}^2})/2}/Z_{Y_{OH1}})}{l_{OH}}\sqrt{(Z_{OH1}^2+\sqrt{Z_{OH1}^4+4Z_{OH1}^2{Z}_{Y_{OH1}}^2})/2}$

$z_{Cb1}=\frac{ar\sinh (\sqrt{(Z_{Cb1}^2+\sqrt{Z_{Cb1}^4+4Z_{Cb1}^2{Z}_{Y_{Cb1}}^2})/2}/Z_{Y_{Cb1}})}{l_{Cb}}\sqrt{(Z_{Cb1}^2+\sqrt{Z_{Cb1}^4+4Z_{Cb1}^2{Z}_{Y_{Cb1}}^2})/2}$

$y_{OH1}=\frac{ar\sinh (\sqrt{(Z_{OH1}^2+\sqrt{Z_{OH1}^4+4Z_{OH1}^2{Z}_{Y_{OH1}}^2})/2}/Z_{Y_{OH1}})}{l_{OH}\sqrt{(Z_{OH1}^2+\sqrt{Z_{OH1}^4+4Z_{OH1}^2{Z}_{Y_{OH1}}^2})/2}}$

$y_{Cb1}=\frac{ar\sinh (\sqrt{(Z_{Cb1}^2+\sqrt{Z_{Cb1}^4+4Z_{Cb1}^2{Z}_{Y_{Cb1}}^2})/2}/Z_{Y_{Cb1}})}{l_{Cb}\sqrt{(Z_{Cb1}^2+\sqrt{Z_{Cb1}^4+4Z_{Cb1}^2{Z}_{Y_{Cb1}}^2})/2}}$

Wherein l_OHRepresenting sections of overhead linesLength,. l_CbRepresenting the length of the power cable section, archonh (·) represents an inverse hyperbolic sinusoidal function.