CN107329022B - Method for analyzing thermal load capacity of power transmission line - Google Patents
Method for analyzing thermal load capacity of power transmission line Download PDFInfo
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- CN107329022B CN107329022B CN201710672251.8A CN201710672251A CN107329022B CN 107329022 B CN107329022 B CN 107329022B CN 201710672251 A CN201710672251 A CN 201710672251A CN 107329022 B CN107329022 B CN 107329022B
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Abstract
The invention provides a method for analyzing the heat load capacity of a power transmission line. The method comprises the steps of segmenting the power transmission line according to environmental meteorological conditions along the power transmission line, and calculating impedance parameters of each segment of the power transmission line. And carrying out power grid power flow analysis through the impedance parameters of the power transmission line to obtain a power flow analysis result comprising the current-carrying capacity of the power transmission line. And calculating the actual operating temperature of the power transmission line by utilizing an IEEE standard thermal balance equation of the overhead power transmission line according to the tidal current analysis result and the meteorological parameters of the environment along the power transmission line to obtain the heat load margin of the power transmission line. The method combines the actual operating temperature of the power transmission line, the meteorological parameters of the environment along the line and the IEEE standard thermal balance equation, so that the power grid operating state of the power grid flow analysis is closer to the actual operating state of the power grid, and the heat load capacity of the power transmission line is comprehensively and accurately evaluated. The heat load capacity can more accurately determine the active loss and the reactive loss of the power grid, and more accurately calculate the current load flow and the active load flow distribution.
Description
Technical Field
The invention relates to the technical field of power transmission, in particular to a method for analyzing the heat load capacity of a power transmission line.
Background
In order to meet the requirements of people on power quality and power safety, power energy is continuously developed, and power transmission is mainly realized through a power transmission line. Therefore, the load capacity of the transmission line determines whether the power can be safely, stably and economically transmitted. Factors influencing the load capacity of the power transmission line include the maximum allowable operation temperature limit of the power transmission line, the static power angle stability during the operation of the power grid system and the node voltage level limit. However, with the application of technologies such as flexible alternating current transmission and the like, the maximum allowable operating temperature limit of the transmission line itself gradually becomes a key factor for limiting the load capacity of the transmission line, that is, the thermal load capacity of the transmission line limits the load capacity of the transmission line.
At present, power transmission lines generally include overhead power transmission lines and underground cables. The overhead transmission line is an outdoor overhead line. The operating temperature of the overhead transmission line is easily influenced by external environments such as wind speed, wind direction, sunlight intensity and ambient temperature, and the influence is large. The external environment has a large influence on the operation temperature of the overhead transmission line, so that the external environment has a large influence on the heat load capacity of the overhead transmission line. Underground cables are power lines buried in underground portions. Because the underground cable is deeply buried underground, the influence of external environments such as wind speed, wind direction, sunlight intensity, environment temperature and the like on the running temperature of the underground cable is small, and further the influence on the heat load capacity of the underground cable is small. Therefore, the thermal load capacity of a transmission line is mainly determined by the thermal load capacity of an overhead transmission line, and is further determined by the operating temperature of the overhead transmission line. The operating temperature of the overhead transmission line is related to not only the physical parameters of the conductor itself of the electric line and the environment along the electric line, but also the current-carrying capacity of the overhead transmission line (the maximum current which can be continuously carried by the conductor without causing the stable temperature of the conductor to exceed a specified value under a specified condition of the current-carrying capacity), and therefore, the operating temperature of the overhead transmission line continuously changes along with the change of the current-carrying capacity and the change of the environment condition along the line.
In order to analyze the influence of the operating temperature of the overhead transmission line on the transmission line, a transmission line model is generally required to be established, and then the operating state of the power grid is calculated through power flow analysis of the power system. The currently used power transmission line model is mostly a pi-type or T-type equivalent circuit model with centralized parameters. In order to reduce the calculation amount of power flow analysis and calculation of the power system, a transmission line model with centralized parameters is mostly used in systems such as a state estimator and energy management. Because the parameters of the power transmission line are related to the operating temperature of the overhead power transmission line, and the operating temperature of the overhead power transmission line continuously changes along with the change of the current-carrying capacity and the change of the environmental conditions along the line, the difference exists between the power grid operating state result of the power grid power flow analysis and the actual operating state, and the heat load capacity of the power transmission line cannot be effectively evaluated.
Disclosure of Invention
The invention provides a method for analyzing the heat load capacity of a power transmission line, which aims to solve the problem that the heat load capacity of the power transmission line cannot be effectively evaluated by the existing analysis method.
The invention provides a method for analyzing the heat load capacity of a power transmission line, which comprises the following steps:
s01: preliminarily setting the ambient temperature along the power transmission line as the preset operating temperature of the power transmission line;
s02: calculating the impedance of a conductor in the power transmission line;
s03: carrying out load flow analysis on the power grid according to the impedance to obtain a load flow calculation result, wherein the load flow calculation result comprises the current-carrying capacity of the power transmission line;
s04: calculating the operating temperature of the power transmission line according to the current-carrying capacity, the environmental meteorological parameters of the power transmission line and an IEEE standard thermal balance equation;
s05: judging whether the absolute value of the difference between the operating temperature and the preset operating temperature is smaller than the preset temperature precision or not;
s06: if the absolute value is greater than or equal to the preset temperature precision, resetting the calculated operation temperature as the preset operation temperature of the power transmission line, and repeating the steps S02-S05 until the absolute value is less than the preset temperature precision;
s07: if the absolute value is smaller than the preset temperature precision, the operation temperature of the power transmission line is the actual operation temperature; and judging the heat load margin of the power transmission line according to the actual operation temperature and the critical operation temperature of the conductor of the power transmission line.
Preferably, the preliminarily setting the ambient temperature along the power transmission line before the preset operating temperature of the power transmission line includes:
segmenting the power transmission line according to the ambient temperature along the power transmission line;
calculating the average ambient temperature of the ambient temperature along the power transmission line of each section;
and setting the average environment temperature as the preset operation temperature of each section of the power transmission line.
Preferably, the calculating the impedance of the conductor in the power transmission line includes: and respectively calculating the impedance of the conductor in each section of the power transmission line according to the sections of the power transmission line.
Preferably, the calculating the impedance of the conductor in the power transmission line includes:
the calculation formula of the resistance of the conductor in the power transmission line is as follows: r (T) ═ r (T)0)×[1+α(T-T0)]；
The calculation formula of the reactance of the conductor in the power transmission line is as follows: x is the number ofL(ω,T)＝xL(ω,T0)×[1+β(T-T0)]；
The impedance of the conductor in the power transmission line is calculated according to the formula of z (T) ═ r (T) + i × xL(ω,T)。
Preferably, the preset temperature precision is 0.0001.
Preferably, the ambient meteorological parameters include ambient temperature, wind speed, wind direction and solar intensity.
Preferably, the determining the heat load margin of the power transmission line according to the actual operating temperature and the critical operating temperature of the conductor of the power transmission line includes:
if the difference between the critical operating temperature of the conductor of the power transmission line and the actual operating temperature is less than or equal to the temperature threshold, the power transmission line has smaller heat load margin;
and if the difference between the critical operation temperature of the conductor of the power transmission line and the actual operation temperature is greater than the temperature threshold value, the power transmission line has larger heat load margin.
Preferably, the temperature threshold is 5-10 ℃.
The technical scheme provided by the embodiment of the invention can have the following beneficial effects:
the invention provides a method for analyzing the heat load capacity of a power transmission line. Because the operating temperature of the power transmission line has more influence factors, the ambient temperature along the power transmission line is set as the preset operating temperature of the power transmission line for the first time. And calculating the impedance of a conductor in the power transmission line at a preset operation temperature, and further calculating a power flow calculation result comprising the current-carrying capacity of the power transmission line and the like through power grid power flow analysis. And calculating the operating temperature of the power transmission line according to the calculated current-carrying capacity, the environmental meteorological parameters of the power transmission line and the IEEE standard heat balance equation. And judging whether the absolute value of the difference value between the preset operation temperature and the operation temperature of the power transmission line is smaller than the preset temperature precision. And when the absolute value is greater than the preset temperature precision, resetting the operation temperature obtained by the calculation as the preset operation temperature, and circularly calculating the impedance, the current-carrying capacity and the operation temperature of the conductor in the power transmission line until whether the absolute value of the difference value between the calculated operation temperature and the preset operation temperature set during the calculation is less than the preset temperature precision or not. And when the absolute value of the difference value between the operating temperature obtained by calculation in a certain cycle process and the preset operating temperature set in the process is smaller than the preset temperature precision, stopping the cycle calculation. And when the cyclic calculation is stopped, the operation temperature of the power transmission line obtained by the last calculation is the actual operation temperature of the conductor in the power transmission line. And judging the heat load margin of the power transmission line according to the calculated actual operation temperature and the critical operation temperature of the conductor of the power transmission line. The method for analyzing the heat load capacity of the power transmission line provided by the invention combines the actual operating temperature of the conductor in the power transmission line, the meteorological parameters of the environment along the line and the IEEE standard heat balance equation, so that the power grid operating state of the power grid tide analysis is closer to the actual operating state of the power grid, and the heat load capacity of the power transmission line can be comprehensively and accurately evaluated. Meanwhile, the active and reactive losses of the power grid can be accurately determined through the calculated heat load capacity.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.
Fig. 1 is a schematic flow chart of a method for analyzing the heat load capacity of a power transmission line according to an embodiment of the present invention;
fig. 2 is a schematic diagram of an ambient temperature curve along a power transmission line according to an embodiment of the present invention;
fig. 3 is a sectional parameter model of a power transmission line according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a power grid structure of a 5-node system according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a transmission line of a 5-node power grid structure after segmentation, provided by the embodiment of the invention.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.
Referring to fig. 1, fig. 1 shows a schematic flow chart of a method for analyzing the heat load capacity of a power transmission line according to an embodiment of the present invention.
The embodiment of the invention provides a method for analyzing the heat load capacity of a power transmission line, which specifically comprises the following steps:
s01: and preliminarily setting the ambient temperature along the power transmission line as the preset operating temperature of the power transmission line.
And under the condition that the load of the power grid is known, preliminarily setting the ambient temperature along the power transmission line as the preset operating temperature of the power transmission line according to the temperature environment along the power transmission line.
Furthermore, in the power transmission line, the overhead power transmission line is exposed outdoors, so that the overhead power transmission line is easily influenced by external environment parameters such as wind speed, wind direction, sunlight intensity and environment temperature, and further influences the operation temperature of the power transmission line. Because the operating temperature of the power transmission line has a large influence on the heat load capacity of the power transmission line, and the operating temperature of the power transmission line continuously changes along with the change of the current-carrying capacity of the power transmission line and the change of the environmental conditions along the power transmission line, the difference between the environmental temperature and the operating temperature of the power transmission line is large. Because the transmission line is long in occupied line and is easily influenced by environmental parameters, and the environmental change along the transmission line is complex, the transmission line is subjected to sectional treatment in order to accurately evaluate the running state of the power grid and obtain the maximum heat load capacity of the transmission line.
In environmental meteorological parameters influencing the operating temperature of the power transmission line, joule heat caused by electrifying the wire and heat absorbed by solar radiation are main factors for promoting the temperature rise of the wire of the power transmission line, and convection heat generated by wind power is a main factor for cooling the power transmission line, wherein the influence of the environmental temperature and the wind speed along the line on the operating temperature of the power transmission line is the largest. Because the influence of the ambient temperature and the wind speed along the line on the operation temperature of the power transmission line is the largest, the ambient temperature and the wind speed can be used as key parameters influencing the operation temperature of the power transmission line. The wind speed change has large randomness, so that the wind speed change is not suitable for being used as an object for segmenting the power transmission line. Therefore, in the embodiment of the invention, the power transmission line is subjected to sectional treatment by taking the sections of the ambient temperature along the line as parameters.
The ambient temperature along the transmission line can be obtained from numerical weather forecast or real-time weather forecast. And drawing an environment temperature curve with the length of the power transmission line as a horizontal axis and the environment temperature as a vertical axis according to the obtained environment temperature, as shown in the attached figure 2. In fig. 2, the starting point of the transmission line is set to xbegThe end point is set to xend. And setting the sectional temperature gradient change value of the temperature of the wire of the power transmission line as delta T according to the requirements of calculation precision and solving speed. Starting point x from transmission line along ambient temperature curvebegStarting to the end point x of the transmission lineendMoving, when the longitudinal temperature difference of the environmental temperature curve reaches the gradient change value delta T of the temperature, a section point x is inserted on the horizontal axis1. Continuing to form the end point x of the power transmission line along the environmental temperature curveendMoving, inserting a segmentation point according to the gradient change delta T of every other temperature until reaching the end point x of the power transmission lineend. If the initial temperature of one section of power transmission line is-10-20 ℃, the power transmission line is divided into six sections according to the temperature gradient change of delta T-5 ℃.
And after the power transmission line is segmented, respectively calculating the environment temperature and the current wind speed of each power transmission line. The calculation formulas of the ambient temperature and the wind speed are respectively as follows:
Tiavg＝(Tibeg+Tiend)/2 Viavg＝(Vibeg+Viend)/2
wherein, TiavgIs the average ambient temperature, T, of each section of transmission lineibegAnd TiendRespectively representing the environmental temperature of the head end and the tail end of each section of power transmission line; viavgIs the average wind speed, V, of each section of transmission lineibegAnd ViendRespectively representing the wind speeds of the head end and the tail end of each section of power transmission line; i is 1,2,3 … … n.
Setting the average ambient temperature T after the segmentation of the transmission line is finished and the calculation of the average ambient temperature and the average wind speed of each segment of the transmission line is finishediavgFor a predetermined operating temperature T of each section of the transmission linec。
S02: and calculating the impedance of the conductor in the power transmission line.
Because the resistance of the conductor of the power transmission line is related to the temperature of the conductor, the resistance calculation formula of the conductor in the power transmission line is as follows: r (T) ═ r (T)0)×[1+α(T-T0)]Wherein r (t) is a resistance value (Ω) at a given temperature; r (T)0) The resistance value is omega at a reference temperature, α is the temperature coefficient of resistance (1/DEG C), T is a given temperature (DEG C)0For reference temperature (. degree. C.), T is usually taken020 ℃. In the method for analyzing the heat load capacity of the power transmission line provided by the embodiment of the invention, the given temperature T is the operating temperature of the power transmission line, and the reference temperature T0The ambient temperature along the transmission line. Namely, the given temperature T is the preset operation temperature T of the power transmission linecReference temperature T0Is the average ambient temperature T along the transmission lineiavg。
The arc sag of the power transmission line easily causes the length change of the power transmission line, and further causes the reactance change of a conductor of the power transmission line. In addition, the reactance of the conductor of the power transmission line is also related to the temperature, and the calculation formula of the reactance of the conductor in the power transmission line is as follows: x is the number ofL(ω,T)＝xL(ω,T0)×[1+β(T-T0)]Wherein x isL(ω, T) is the reactance of the conductor at T (ω); x is the number ofL(ω,T0) For conductors at T0Reactance under (omega), β is reactance temperature coefficient, T is given temperature (deg.C), T is given temperature0The values of α and β depend on the physical material of the conductor for reference temperature (c), ω is the angular frequency of operation, and in the present embodiment α is set to β is set to 0.0039.
The impedance of the conductor in the power transmission line is calculated according to the formula z (T) ═ r (T) + i × xL(ω, T), where z (T) is the impedance.
When the transmission line is segmented according to the ambient temperature, the transmission line is divided into segments. And establishing a power transmission line segmentation model according to the segmented lines, and further respectively calculating the impedance of each segmented power transmission line. Referring to fig. 3, fig. 3 shows a power transmission line section parameter model provided by the embodiment of the invention. In FIG. 3, each box represents a section of the transmission line, dKThe length of the Kth segmented power transmission line; zK(dK,TK) For the conductor of the Kth subsection transmission line at the temperature TKA lower series impedance; y isK(dK) For the conductor of the Kth subsection transmission line at the temperature TKLower parallel admittance; vbegAnd VendThe voltages of the first end and the last end of the power transmission line are respectively; i isbegAnd IendRespectively, the current at the first end and the current at the last end of the power transmission line.
S03: and carrying out load flow analysis on the power grid according to the impedance to obtain a load flow calculation result, wherein the load flow calculation result comprises the current-carrying capacity of the power transmission line.
And carrying out load flow analysis on the power grid according to the impedance parameters of the conductors in the power transmission line, which are obtained through calculation in the step, so as to obtain a load flow analysis result. And the calculated power flow analysis result comprises the voltage, the current-carrying capacity, the power and the active loss of the power transmission line.
S04: and calculating the operating temperature of the power transmission line according to the current-carrying capacity, the environmental meteorological parameters of the power transmission line and an IEEE standard thermal balance equation.
Since the environmental parameters affecting the operating temperature of the power transmission line include joule heat caused by the energization of the wire, the heat absorbed by solar radiation, and the convection heat radiation generated by wind power, the environmental meteorological parameters in the embodiment of the present invention include heat values generated by the ambient temperature, the wind speed, the wind direction, the solar intensity, and the like, such as the convection heat radiation caused by the wind speed, the wind direction, the radiation heat radiation caused by the temperature difference between the ambient temperature and the power transmission line, and the solar radiation heat absorption.
The operation temperature of the conductor of the power transmission line continuously changes along with the change of the current-carrying capacity of the power transmission line and the change of the environmental meteorological conditions along the line, so that the dynamic change of the conductor temperature in the power transmission line conforms to the IEEE standard transient thermal balance equation. The calculation formula of the IEEE standard transient heat balance equation is as follows:
wherein q iscThe convection heat dissipation caused by wind speed and wind direction is realized; q. q.srRadiating heat for radiation caused by a temperature difference between an ambient temperature and a power transmission line; q. q.ssAbsorbing heat for solar radiation; i is carrying capacity; t is conductor operating temperature; r (T) is the conductor resistance at temperature T; m is the conductor mass; cpIs the conductor specific heat capacity; t is time.
When the current carrying value in the power transmission line is determined and the ambient weather condition is in a stable state, the heat productivity and the heat dissipation capacity of the power transmission line are finally in a balanced state, and at the moment, the IEEE standard transient state thermal balance equation is the IEEE standard steady state thermal balance equation. The calculation formula of the IEEE standard steady-state heat balance equation is as follows: q. q.sc+qr＝qs+I2R(T)。
And calculating the operating temperature T of each section of power transmission line according to the current-carrying capacity obtained by the power grid load flow analysis and calculation, the environmental meteorological parameters of each section of power transmission line and an IEEE standard steady-state thermal balance equation.
S05: and judging whether the absolute value of the difference between the operating temperature and the preset operating temperature is smaller than the preset temperature precision or not.
When the power transmission line normally operates, a difference value exists between the operating temperature of the power transmission line and the ambient temperature along the power transmission line. The actual operating temperature of the conductor in the power transmission line can be obtained by judging the relationship between the operating temperature of the power transmission line, the meteorological environment along the line and the current carrying of the power transmission line.
In order to obtain the actual operation temperature of a conductor in the power transmission line according to the relation between the operation temperature of the power transmission line, the meteorological environment along the power transmission line and the current carrying of the power transmission line, the precision of the difference value between the operation temperature of the power transmission line and the preset temperature is preset to be delta, wherein the preset temperature is the preset operation temperature of the power transmission line, namely the environment temperature along the power transmission line; the precision delta is a preset temperature precision. According to the actual operation temperature T of the power transmission line obtained by calculation and the preset operation temperature T of the power transmission line preliminarily setcJudging the actual operating temperature T and the preset operating temperature TcWhether the absolute value of the difference is less than the preset temperature accuracy delta. The specific judgment formula is as follows: i T-TcIn the embodiment of the present invention, | < Δ, Δ is selected to be 0.0001.
S06: and if the absolute value is greater than or equal to the preset temperature precision, resetting the calculated operation temperature as the preset operation temperature of the power transmission line, and repeating the steps S02-S05 until the absolute value is less than the preset temperature precision.
If the operating temperature T of the transmission line is equal to the preset operating temperature TcThe absolute value of the difference is greater than a predetermined temperature accuracy Delta, i.e. | T-TcAnd if the | is more than or equal to the delta, the operation temperature T of the power transmission line needs to be calculated again in an iterative manner. When the operation temperature T of the power transmission line is calculated again in an iterative manner, the operation temperature of the power transmission line obtained in the current calculation is used as the preset operation temperature of the power transmission line, that is, the preset operation temperature of the power transmission line set in step S01The row temperature is the operating temperature calculated this time. And repeating the steps S02-S05 according to the preset operation temperature of the reset power transmission line. If the operating temperature of the power transmission line repeatedly calculated in the second iteration and the preset operating temperature which is reset do not accord with the absolute value T-TcWhen | < delta, the operation temperature of the power transmission line obtained in the calculation process is set again as the preset operation temperature of the power transmission line until the operation temperature T of the power transmission line obtained through calculation and the preset operation temperature TcConform to | T-Tc< Δ. Generally, iteratively repeating the steps S02-S05 three to five times can satisfy the | T-Tc|＜Δ。
S07: if the absolute value is smaller than the preset temperature precision, the operation temperature of the power transmission line is the actual operation temperature; and judging the heat load capacity margin of the power transmission line according to the actual operation temperature and the critical operation temperature of the conductor of the power transmission line.
Each transmission line has its highest operating temperature, i.e. critical operating temperature. And when the operating temperature of the power transmission line reaches the critical operating temperature of the conductor, the current-carrying capacity of the power transmission line is the maximum heat load capacity of the power transmission line. The critical operating temperature of each transmission line is related to the nature of the line itself. In general, the critical operating temperature of each transmission line is a fixed value.
If the operating temperature T of the transmission line is equal to the preset operating temperature TcThe absolute value of the difference is less than a predetermined temperature accuracy, i.e. | T-TcIf the absolute value is less than delta, the operation temperature obtained by calculation in the last iterative calculation process is the temperature of the conductor of the power transmission line in the actual operation process, namely the actual operation temperature. Because the actual operating temperature of the transmission line conductor and the critical operating temperature of the transmission line conductor are determined, the heat load margin of the transmission line can be determined by comparing the actual operating temperature and the critical operating temperature of the transmission line conductor.
Specifically, when the difference between the critical operating temperature of the conductor of the power transmission line and the actual operating temperature of the conductor of the power transmission line is smaller than or equal to the temperature threshold, the actual operating temperature of the conductor of the power transmission line is about to reach the critical operating temperature due to the smaller difference between the actual operating temperature of the conductor of the power transmission line and the critical operating temperature, so that the actual operating temperature of the conductor of the power transmission line has a small lifting space, and the power transmission line has a small heat load margin. When the difference between the critical operating temperature of the conductor of the power transmission line and the actual operating temperature of the conductor of the power transmission line is greater than the temperature threshold value, the critical operating temperature of the conductor of the power transmission line is far higher than the actual operating temperature of the conductor of the power transmission line, so that the actual operating temperature of the conductor of the power transmission line has a large lifting space, and the power transmission line has a large heat load margin. In the embodiment of the invention, the temperature threshold is set to be 5-10 ℃.
The method for analyzing the heat load capacity of the power transmission line, provided by the embodiment of the invention, can be used for obtaining the conductor parameters of the power transmission line of the power grid through calculation to carry out power flow analysis on the power grid under the condition of considering the actual meteorological condition in the power grid and the actual operating temperature of the conductor of the power transmission line under load, so as to obtain the result which is closer to the actual operating state of the power grid, and further obtain the maximum heat load capacity of the power transmission line. The calculated result close to the actual running state of the power grid is beneficial to analysis of the power grid, and further active and reactive power losses of the power grid and active and current flow distribution of the power transmission line are accurately determined, so that the method has a high application value.
In order to verify the application value of the method for analyzing the heat load capacity of the power transmission line provided by the embodiment of the invention, the embodiment of the invention performs a load flow analysis example on a simple 5-node system under different environmental situations, and fig. 4 shows a schematic diagram of a power grid structure of the 5-node system, wherein the parameters are per unit value parameters, and the power transmission line is 2-1, 3-1 and 2-3.
In the example provided by the embodiment of the invention, the environmental condition of the power grid is set to be the situation of extreme meteorological condition or the condition of a meteorological condition parameter space distribution comparison rule, the reference voltage of the power grid is set to be 220kV, the reference capacity is 100MVA, the lengths of the power transmission lines 2-1, 3-1 and 2-3 are respectively 120km, 120km and 200 km., the power transmission line conductors adopt L GJ-400/50 type leads, the diameters of L GJ-400/50 type leads are 27.63mm, and the cross section area of an aluminum wire part is 399.73mm2L GJ-400/50 type power transmission lineThe resistance of the circuit conductor at 20 ℃ is 0.07232 omega/km, and the temperature coefficient of resistance is 0.0039 omega/DEG C, and the critical operating temperature of the L GJ-400/50 type lead is 70 ℃.
In the embodiment of the present invention, 5 scenes are set, which are scene 1, scene 2, scene 3, scene 4, and a reference scene. Wherein, the scene 1, the scene 2 and the reference scene are the distribution of the power grid power flow in the time season for comparison; and comparing the scenes 3 and 4 with the reference scene, namely the distribution of the power grid flow on the space. The setting of 5 scenarios and the result of power flow analysis are described in detail below.
Reference scene
Under the reference scene, the conductor operating temperature of each power transmission line is 20 ℃ under the assumption that the environmental meteorological parameters along the power transmission line are not considered. According to the method for analyzing the heat load capacity of the power transmission line, the actual operation temperature of conductors of the power transmission line 2-1, 3-1 and 2-3 in operation, the conductor parameters of the power transmission line and the current value obtained by load flow analysis are calculated. Please refer to table 1 for specific data of the actual operating temperature, conductor parameters and current value of the power transmission line.
Table 1: operating temperature, conductor parameters and current values in a reference scenario
| Branch circuit | Operating temperature (. degree.C.) | r | x | I(A) |
| 2-1 | 20 | 0.0179 | 0.1004 | 519.66 |
| 3-1 | 20 | 0.0179 | 0.1004 | 359.94 |
| 2-3 | 20 | 0.0298 | 0.1674 | 114.94 |
In table 1, r is a per unit value of the conductor resistance of the power transmission line, x is a per unit value of the conductor reactance of the power transmission line, and I is a current value of each power transmission line branch.
Setting the environmental conditions of the power grid as follows: the environmental temperature is-40 ℃, and the wind speed is 22m/s (such as strong wind and extreme cold areas in winter in northern China). The method for analyzing the heat load capacity of the power transmission line is adopted to calculate the actual operating temperature, the wind speed, the conductor parameters of the power transmission line and the current value obtained by analyzing the power flow of the power transmission line 2-1, 3-1 and 2-3 conductors. Please refer to table 2 for specific data of the actual operating temperature, wind speed, conductor parameters and current value of the transmission line.
Table 2: operating temperature, wind speed, conductor parameters, and current values under scenario 1
As can be seen from Table 2, the actual operating temperature of the transmission line is about-37 ℃ under the conditions that the ambient temperature along the transmission line is-40 ℃ and the wind speed is 22 m/s. The actual operating temperature of the power transmission line is far lower than the critical operating temperature of the wire of the power transmission line, so that the heat load capacity of the power transmission line has great potential under the conditions that the ambient temperature is-40 ℃ and the wind speed is 22m/s (corresponding to a windy area in winter). Namely, in the area with strong wind in winter, the maximum current-carrying capacity of the power transmission line is far larger than 510.23A.
The environmental meteorological conditions of the power grid are set as follows: the environmental temperature is 40 ℃, and the wind speed is 0.5m/s (such as high-temperature and low-wind areas in summer). The method for analyzing the heat load capacity of the power transmission line is adopted to calculate the actual operating temperature, the wind speed, the conductor parameters of the power transmission line and the current value obtained by analyzing the power flow of the power transmission line 2-1, 3-1 and 2-3 conductors. Please refer to table 3 for specific data of the actual operating temperature, wind speed, conductor parameters and current value of the transmission line.
Table 3: operating temperature, wind speed, conductor parameters, and current values under scenario 2
As can be seen from table 3, under the conditions that the ambient temperature of the power transmission line is 40 ℃ and the wind speed is 0.5m/s, the actual operating temperature of the power transmission line is about 60 ℃, and the maximum operating temperature reaches 65.9 ℃, which is close to the critical operating temperature of the wire of the power transmission line. It can be shown that the thermal load capacity of the transmission line is close to the limit under the conditions that the ambient temperature is 40 ℃ and the wind speed is 0.5m/s (corresponding to the high-temperature and low-wind area in summer). In the high-temperature and low-wind areas in summer, the current-carrying capacity of the power transmission line is maximized.
When the method for analyzing the heat load capacity of the power transmission line provided by the embodiment of the invention is used for carrying out power flow analysis, the active power and the active loss of the reference scene, the scene 1 and the scene 2 can be respectively obtained, and then the method is used for comparing the reference scene with the scene 1, and comparing the reference scene with the scene 2. Please refer to table 4 for the active power data, active loss and comparison results of the reference scenario and scenario 1. The active power data, active loss and comparison results of the reference scenario and scenario 2 are shown in table 5.
Table 4: active power data, active loss and comparison results for reference scenario and scenario 1
In table 4, the equation for the difference between the active power and the active loss is (scenario 1-reference scenario)/reference scenario 100%. 2-1(2) represents the head end 2 node of the transmission line 2-1, and the other labels are the same as 2-1 (2). The formula and label for calculating the phase difference in table 5 are the same as those in table 4.
As can be seen from the contents of tables 2 and 4, the difference between the active power in each branch of the reference scenario and the active power in each branch of scenario 1 is not large, and therefore, the active power flow distribution in scenario 1 does not have a significant difference from the active power flow distribution in the reference scenario. The difference between the active loss of the reference scene and the active loss of the scene 1 is 26.16%, and the difference is large. The reason why the active loss of the reference scenario and the scenario 1 is greatly different is that: the operating temperature of the conductor of the power transmission line in scenario 1 is low, resulting in a low impedance value of the conductor of the power transmission line.
Table 5: active power data, active loss and comparison results for reference scenario and scenario 2
As can be seen from the contents of tables 3 and 5, the difference between the active power in each branch of the reference scenario and the active power in scenario 2 is not large, and therefore, the active power flow distribution in scenario 2 does not have a significant difference from the active power flow distribution in the reference scenario. The difference between the active loss of the reference scene and the active loss of the scene 2 is 22.5%, and the difference is large. The reason why the active loss of the reference scenario and the scenario 2 is greatly different is that: in scenario 2, the operating temperature of the conductor of the power transmission line is high, which results in a high impedance value of the conductor of the power transmission line.
And the scenes 3 and 4 are the distribution of the power grid tide on the space and are compared with the reference scene, so that the environmental meteorological parameters along the power transmission line are different. Setting the environmental conditions of the power grid in the scenes 3 and 4 as follows: the ambient temperature of the line 2-1 is 20 ℃ and the wind speed is 0.5 m/s. The environment temperature of the 3 nodes is 0 ℃, and the wind speed is 20 m/s. The ambient temperature and wind speed along the line between lines 2-3 and lines 1-3 are assumed to be linearly distributed.
In scenario 3, the ambient temperature and wind speed of each transmission line are taken from the average values of the head and the tail ends of the transmission line. According to the method for analyzing the heat load capacity of the power transmission line, the actual operation temperature of conductors of the power transmission line 2-1, 3-1 and 2-3 in operation, the conductor parameters of the power transmission line and the current value obtained by load flow analysis are calculated. Please refer to table 6 for the actual operating temperature of the transmission line, the conductor parameters of the transmission line, and the current values.
Table 6: operating temperature, wind speed, conductor parameters, and current values under scenario 3
In scenario 4, the transmission lines 3-1 and 2-3 are segmented according to the ambient temperature. For convenience of calculation, the gradient of the environmental temperature segment is set to be 4 ℃, so that the power transmission lines 3-1 and 2-3 are divided into 5 segments, and reference is made to the attached drawing 5. The ambient temperature and wind speed of each of the transmission lines 3-1 and 2-3 are obtained from the average values of the head and tail ends of each segmented line. According to the method for analyzing the heat load capacity of the power transmission line, the actual operation temperature of conductors of the power transmission line 2-1, 3-1 and 2-3 in operation, the conductor parameters of the power transmission line and the current value obtained by load flow analysis are calculated. Please refer to table 7 for the actual operating temperature of the transmission line, the conductor parameters of the transmission line, and the current values.
Table 7: operating temperature, wind speed, conductor parameters, and current values under scenario 4
As can be seen by comparing table 6 and table 7, the maximum operating temperature of the power transmission line in table 6 is 45.94 ℃, and the maximum operating temperature of the power transmission line in table 7 is 45.08 ℃, so that the maximum operating temperatures of the power transmission lines in scenarios 3 and 4 are relatively similar. In addition, the operating temperatures of the transmission lines 3-1 and 2-3 in Table 6 were 14.52 ℃ and 13.34 ℃ respectively, while the operating temperatures of the transmission lines in the middle section after the segmentation of the transmission lines 3-1 and 2-3 in Table 7 were 14.48 ℃ and 13.23 ℃ respectively. Thus, the two grid parameter models in scenario 3 and scenario 4 have little influence on the operating temperature of the transmission line conductor. In addition, the two power grid parameter models in the scenario 4 can accurately reflect the actual distribution conditions of the operating temperatures of the power transmission lines 3-1 and 2-3.
The current in scenario 3 differs from the current in the reference scenario by 12.84% at the maximum, whereas the current in scenario 4 differs from the current in the reference scenario by 12.93% at the maximum, so that scenarios 3, 4 differ from the reference scenario in terms of current by little. Similarly, the two power grid parameter models in the scenario 4 can accurately reflect the actual distribution conditions of the currents in the power transmission lines 3-1 and 2-3.
When the method for analyzing the heat load capacity of the power transmission line provided by the embodiment of the invention is used for carrying out power flow analysis, the active power and the active loss of a reference scene, a scene 3 and a scene 4 can be respectively obtained, and then the method is used for comparing the reference scene with the scene 3, and the reference scene with the scene 4. Please refer to table 8 for the active power data, active loss and comparison results of the reference scenario and scenario 3. The active power data, active loss and comparison results of the reference scenario and scenario 4 are shown in table 9.
Table 8: active power data, active loss and comparison results for reference scenario and scenario 3
Table 9: active power data, active loss and comparison results for reference scenario and scenario 4
Analysis and comparison of tables 8 and 9 show that the active powers of the power transmission lines 2-1, 3-1 and 2-3 in the scenarios 3 and 4 are not greatly different, but the active powers in the scenarios 3 and 4 are greatly different from the active powers in the reference scenarios, and the maximum active power can reach 16.2%. The reason why the scene 3 and the scene 4 are greatly different from the reference scene is that: the operating temperature of the power transmission line in the scenarios 3 and 4 is inconsistent with the operating temperature of the power transmission line in the reference scenario, so that the parameters of the power transmission line are inconsistent in space, and finally the active power of the power transmission line is different. The active loss of the grid in scenario 3 and scenario 4 is 11.94MW and 11.9MW, respectively, which is comparable to the active loss of the grid in the reference scenario of 11.2 MW.
The method for analyzing the heat load capacity of the power transmission line provided by the embodiment of the invention segments the power transmission line according to the meteorological conditions of the environment along the power transmission line, and respectively calculates the impedance parameter of each segment of the power transmission line. And carrying out power flow analysis on the power grid through the impedance parameters to obtain a power flow analysis result comprising the current-carrying capacity of the power transmission line. And calculating the actual operating temperature of the power transmission line according to the tidal current analysis result, the meteorological parameters along the power transmission line and the IEEE standard thermal balance equation to obtain the actual operating temperature of the power transmission line and the tidal current analysis result. Further, the heat load margin of the power transmission line is judged by comparing the actual operation temperature of the power transmission line with the critical operation temperature of the power transmission line. The method for analyzing the heat load capacity of the power transmission line provided by the embodiment of the invention combines the actual operating temperature of the power transmission line, the meteorological parameters of the environment along the line and the IEEE standard heat balance equation, so that the power grid operating state of the power grid flow analysis is closer to the actual operating state of the power transmission line, and the heat load margin of the power transmission line is comprehensively and accurately evaluated. The example provided by the embodiment of the invention also shows that the active and reactive power losses of the power grid can be effectively evaluated by analyzing the obtained heat load margin and the power flow analysis result in the time seasonal distribution of the power transmission line; on the geographical spatial distribution of the power transmission line, the calculated heat load capacity and the load flow analysis result can accurately calculate the current load flow and the active load flow distribution, and effectively evaluate the heat load capacity of the power transmission line.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It is to be understood that relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The invention is not limited to the precise arrangements described above and shown in the drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (5)
1. A method for analyzing the heat load capacity of a power transmission line is characterized by comprising the following steps:
s01: preliminarily setting the ambient temperature along the power transmission line as the preset operating temperature of the power transmission line;
s02: calculating the impedance of a conductor in the power transmission line;
s03: carrying out load flow analysis on the power grid according to the impedance to obtain a load flow calculation result, wherein the load flow calculation result comprises the current-carrying capacity of the power transmission line;
s04: calculating the operating temperature of the power transmission line according to the current-carrying capacity, the environmental meteorological parameters of the power transmission line and an IEEE standard heat balance equation, wherein the calculation formula is as follows:
in the formula, qcThe convection heat dissipation caused by wind speed and wind direction is realized; q. q.srIs determined by the ambient temperature andradiation heat dissipation caused by temperature difference between the power transmission lines; q. q.ssAbsorbing heat for solar radiation; i is carrying capacity; t is conductor operating temperature; r (T) is the conductor resistance at temperature T; m is the conductor mass; cpIs the conductor specific heat capacity; t is time;
s05: judging whether the absolute value of the difference between the operating temperature and the preset operating temperature is smaller than the preset temperature precision or not;
s06: if the absolute value is greater than or equal to the preset temperature precision, resetting the calculated operation temperature as the preset operation temperature of the power transmission line, and repeating the steps S02-S05 until the absolute value is less than the preset temperature precision;
s07: if the absolute value is smaller than the preset temperature precision, the operation temperature of the power transmission line is the actual operation temperature; judging the heat load margin of the power transmission line according to the actual operation temperature and the critical operation temperature of the conductor of the power transmission line;
wherein, the preliminary setting of the ambient temperature along the power transmission line before the preset operating temperature of the power transmission line comprises:
segmenting the power transmission line according to the ambient temperature along the power transmission line;
calculating the average ambient temperature of the ambient temperature along the power transmission line of each section;
setting the average environment temperature as a preset operation temperature of each section of the power transmission line;
the calculating the impedance of the conductor in the power transmission line comprises the following steps: respectively calculating the impedance of the conductor in each section of the power transmission line according to the sections of the power transmission line, wherein:
the calculation formula of the resistance of the conductor in the power transmission line is as follows: r (T) ═ r (T)0)×[1+α(T-T0)]Wherein r (T) is a resistance value at a given temperature; r (T)0) Is a resistance value at a reference temperature, α is a temperature coefficient of resistance, T is a given temperature, T is a temperature0Is a reference temperature;
the calculation formula of the reactance of the conductor in the power transmission line is as follows: x is the number ofL(ω,T)＝xL(ω,T0)×[1+β(T-T0)]In the formula, xL(ω, T) is the reactance of the conductor at T (ω); x is the number ofL(ω,T0) For conductors at T0Reactance at (omega) β is reactance temperature coefficient, T is given temperature0Is a reference temperature; omega is the operating angular frequency;
the impedance of the conductor in the power transmission line is calculated according to the formula of z (T) ═ r (T) + i × xL(ω, T), wherein z (T) is impedance.
2. The method for analyzing the heat load capacity of the power transmission line according to claim 1, wherein the preset temperature precision is 0.0001.
3. The method for analyzing the heat load capacity of the power transmission line according to claim 1, wherein the environmental meteorological parameters comprise environmental temperature, wind speed, wind direction and sunshine intensity.
4. The method for analyzing the heat load capacity of the power transmission line according to claim 1, wherein the step of judging the heat load margin of the power transmission line according to the operation temperature and the critical operation temperature of the conductor of the power transmission line comprises the following steps:
if the difference between the critical operating temperature of the conductor of the power transmission line and the actual operating temperature is less than or equal to the temperature threshold, the power transmission line has smaller heat load margin;
and if the difference between the critical operation temperature of the conductor of the power transmission line and the actual operation temperature is greater than the temperature threshold value, the power transmission line has larger heat load margin.
5. The method for analyzing the heat load capacity of the power transmission line according to claim 4, wherein the temperature threshold is 5-10 ℃.
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| CN104897304A (en) * | 2015-06-18 | 2015-09-09 | 中国电力科学研究院 | Line temperature identification method for dynamic capacity expansion of power transmission line |
| CN107016253A (en) * | 2017-05-23 | 2017-08-04 | 威海职业学院 | The analysis method and system of a kind of hot current-carrying definite value of overhead transmission line |
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| CN104897304A (en) * | 2015-06-18 | 2015-09-09 | 中国电力科学研究院 | Line temperature identification method for dynamic capacity expansion of power transmission line |
| CN107016253A (en) * | 2017-05-23 | 2017-08-04 | 威海职业学院 | The analysis method and system of a kind of hot current-carrying definite value of overhead transmission line |
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