CN110837672A - Design method of power transmission line iron tower without ground wire - Google Patents
Design method of power transmission line iron tower without ground wire Download PDFInfo
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Abstract
The invention discloses a design method of a power transmission line iron tower without a ground wire, which comprises the following steps: s1, eliminating the ground wire and the ground wire bracket and obtaining related parameters; s2, calculating and canceling the load and resistance of the front and rear iron towers of the ground wire, and establishing a simulation model; s3, eliminating tower material stress of the front and rear iron towers of the ground wire, the maximum deformation of the tower head and the pressure of the bottom surface of the foundation through simulation calculation; s4, calculating the reliability index of the iron tower after the ground wire is cancelled; s5, comparing and canceling the internal stress distribution of the front and rear iron towers of the ground wire, the maximum deformation of the iron towers, the pressure of the foundation bottom surface and the reliability index; and S6, according to the comparison result, reducing a certain proportion to obtain the maximum reduction value and the corresponding iron tower structure parameters of the iron tower internal stress distribution after the ground wire is cancelled, the maximum deformation of the iron tower, the foundation bottom surface pressure less than or equal to the value before the ground wire is cancelled, and the iron tower reliability index not less than 4.2.
Description
Technical Field
The invention relates to the technical field of power transmission lines, in particular to a design method of a power transmission line iron tower without a ground wire.
Background
With the rapid development of power grid construction in China, due to the fact that the transmission distance is long and the coverage range is wide, the power transmission line needs to frequently pass through certain repeatedly iced high and cold mountainous areas with complex terrains, and icing is serious in winter. Compared with a transmission conductor, the ground wire has no current joule heat effect and is positioned above the conductor, the icing of the ground wire is more serious compared with the conductor, and accidents such as ground wire fracture, conductor to ground wire discharge and the like caused by the icing are easy to occur, so that the power supply interruption is caused. Unlike the ice melting of the transmission conductor, the ice melting of the ground wire needs insulation treatment, the modification engineering amount is large, the cost investment is high, and the field implementation is extremely difficult. Therefore, the ground wire of the power transmission line in the repeated ice area is eliminated, so that the accidents of ground wire breakage and wire to ground wire discharge caused by ice coating can be fundamentally eliminated, and the ice resistance of the power transmission line in the repeated ice area is improved.
After the ground wire of the transmission line is canceled, the ground wire support of the transmission tower can be canceled, but the structure of the whole transmission tower wire system changes at this moment, particularly the tower material stress, deformation and foundation pressure of the transmission tower under the ice coating condition also change, the original transmission tower design method can not be applied to the tower and foundation design after the ground wire is canceled, if the tower is designed, the ground wire support is simply canceled, and the design standard of the transmission tower and the foundation size when the ground wire exists is still referred to (DL/T5154 plus 2012) for the structure design of the overhead power transmission line tower, so that the construction cost of the ground-free transmission line is increased, and the economy is reduced. Therefore, it is necessary to provide a design method for the transmission line iron tower without the ground wire.
Disclosure of Invention
Technical problem to be solved
Based on the problems, the invention provides a design method of a power transmission line iron tower without a ground wire, which is suitable for a power transmission line tower wire system without the ground wire, improves the safety and reliability of the power transmission line in the repeated icing area, reduces the consumption of tower materials of the iron tower, and saves the line construction cost.
(II) technical scheme
Based on the technical problem, the invention provides a design method of a power transmission line iron tower without a ground wire, which comprises the following steps:
s1, eliminating a ground wire of the iron tower of the power transmission line and a ground wire bracket on the iron tower, and acquiring structural parameters, environmental meteorological parameters, icing parameters, and parameters of a wire and the ground wire of the iron tower of the power transmission line before and after the ground wire is eliminated;
s2, calculating and canceling self-gravity loads, icing force loads and wind pressure loads of the lead wires and the ground wires of the iron towers of the power transmission lines before and after the ground wires are canceled, and the structural member resistance of the iron towers, and establishing simulation calculation models of the mechanical properties of the iron towers before and after the ground wires are canceled;
s3, eliminating tower material stress sigma of front and rear power transmission line iron towers with ground wires through simulation calculationFront side、σRear endMaximum deformation amount epsilon of tower headFront side、εRear endPressure of foundation bottom surface PFront side、PRear end；
S4, calculating reliability indexes β of the iron tower before and after the ground wire is cancelled according to the probability distribution function of the load and the resistance of the structural member of the iron towerFront side、βRear end；
S5, comparing whether sigma isRear end≤σFront side、εRear end≤εFront side、PRear end≤PFront sideAnd βRear endIf yes, continuing to step S6; if not, go to step S7;
s6, reducing the size of the power transmission line iron tower without the ground wire by a certain proportion, wherein the power transmission line iron tower without the ground wire after the reduction is a new power transmission line iron tower without the ground wire, and repeating the steps S2-S5;
s7, obtaining the condition of satisfying sigmaRear end≤σFront side、εRear end≤εFront side、PRear end≤PFront sideAnd βRear endThe maximum reduction value is more than or equal to 4.2, and the corresponding structural parameter is the structural parameter of the iron tower with the least steel consumption and the least iron tower base size after the ground wire is cancelled.
Further, the calculation formula of the self-gravity load in step S2 is as follows:
in the formula, gamma is the specific load of the ground wire and the conducting wire under the working condition of icing wind, and l is the line span;
the calculation formula of the icing force load described in step S2 is:
D＝ρqg
in the formula, rho is the icing density, q is the icing thickness, and g is the gravity acceleration;
the wind pressure load calculation formula in step S2 is:
V＝0.625Cv2
wherein v is the wind speed and C is the wind speed drag coefficient;
the resistance of the structural member of the iron tower in the step S2 includes the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower, and the calculation formula of the stress resistance of the axis of the iron tower is as follows:
R1＝ΩPmAf
in the formula, omegapCalculating a mode uncertainty coefficient for the resistance; m is the strength reduction coefficient; a is the cross-sectional area of the steel of the iron tower, and f is the strength of the steel of the iron tower;
the calculation formula of the iron tower axis compression stability resistance is as follows:
R2＝ΩPΦmNAf
in which phi is pressed as axisA member stability factor; m isNThe reduction coefficient of the stable strength of the iron tower steel is obtained.
Further, the tower material stress in the step S3 refers to the maximum value of the main material stress of the iron tower of the power transmission line under the working condition of icing wind and the corresponding position;
the maximum deformation quantity of the tower head in the step S3 is the maximum deformation quantity of the cross arm position of the tower head under the working condition of icing wind;
the calculation formula of the base floor pressure described in step S3 is:
in the formula, FvDesigned down-axis force, G, for acting on the top surface of the tower foundationfIs the self-gravity of the iron tower foundation, G0Is the gravity of the soil right above the top plate of the iron tower foundation, SFoundationThe calculated area of the iron tower foundation bottom plate is shown.
Further, the calculation formula of the reliability index described in step S4 is:
wherein β is the reliability index of iron tower, muS、σSThe average value and the standard deviation of the load of the structural member of the iron tower are obtained, and the acting load of the structural member of the iron tower comprises the self-gravity load, the icing load and the wind load of the iron tower; mu.sR、σRThe resistance values of the structural members of the iron tower comprise the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower, and the numerical values of the resistance values obey the statistical characteristics when the reliability index β is calculated.
Further, probability distribution functions of the conductor, ground wire self-gravity load, icing load, wind load and resistance of the structural member of the iron tower respectively meet the following requirements:
the self-gravity load G of the conducting wire and the ground wire borne by the power transmission iron tower is a permanent load and follows normal distribution;
the probability of the icing load D borne by the power transmission iron tower follows extreme value I type distribution;
the probability of the wind pressure load V borne by the power transmission iron tower follows the extreme value I-type distribution;
the probability of the resistance R of the structural member of the iron tower borne by the power transmission iron tower follows the log-normal distribution.
Preferably, the size of the power transmission line iron tower in step S6 is the size of the main material of the iron tower and the size of the foundation slab of the iron tower, and the reduction is performed by a certain ratio, specifically, the thickness and the width of the main material of the power transmission line iron tower after the ground wire is removed are reduced by 3% to 5% and the diameter and the buried depth of the foundation slab of the iron tower are reduced by 3% to 5% in each reduction.
Preferably, the structural parameters in step S7 include the main material size of the iron tower, the size of the foundation slab of the iron tower, and the weight of the iron tower.
Further, the parameters of the iron tower structure of the power transmission line, the environmental meteorological parameters, the icing parameters, the lead and the ground wire of the power transmission line in the step S1 respectively include a structural size diagram of the tower structure of the power transmission line, a rated voltage of the line, a span and a breath height of the line, an environmental temperature, a wind speed, an icing thickness, an icing density, diameters, sectional areas and line collision coefficients of the lead and the ground wire, a calculated breaking force, an allowable stress, an elastic modulus, a unit length weight and a safety coefficient.
The power transmission line iron tower without the ground wire is designed according to the design method of the power transmission line iron tower without the ground wire, and compared with a common iron tower, the iron tower is not provided with the ground wire and a ground wire bracket and has the iron tower structure parameters in the step S7.
(III) advantageous effects
The technical scheme of the invention has the following advantages:
(1) by carrying out the optimized design after the ground wire is cancelled on the power transmission line iron tower in the repeated ice-covered area, the ground wire fracture caused by ice covering and the accidents of discharging of the lead to the ground wire are thoroughly eliminated, the anti-ice capacity of the power transmission line is effectively improved, and the safety and reliability of the power transmission line are improved;
(2) the obtained power transmission line iron tower without the ground wire has the same or similar internal stress distribution, the maximum deformation of the iron tower, the pressure of the bottom surface of the foundation and enough reliability as those before the ground wire is removed, meanwhile, the sizes of main materials of the iron tower and the foundation of the iron tower are reduced, the consumption cost of tower materials of the iron tower is reduced, the line construction cost is saved, and the economy is improved;
(3) the method is easy to realize, has strong operability, and improves a complete and reliable solution scheme for canceling the optimized design of the ground wire transmission line iron tower for repeated ice coating;
(4) the method is wide in application and suitable for iron tower design of 10-500 kV voltage class in the repeated ice region and capable of eliminating ground wire transmission lines.
Drawings
The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:
fig. 1 is a schematic step diagram of a method for designing a transmission line iron tower without a ground wire according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an iron tower before and after a ground wire is canceled according to an embodiment of the present invention;
FIG. 3 shows finite element simulation models of mechanical properties of the transmission line iron tower before and after the ground wire is cancelled in the embodiment of the invention;
FIG. 4 is a schematic diagram of the stress of the iron tower foundation of the power transmission line after the ground wire is removed in the embodiment of the invention;
in the figure: 1: an iron tower foundation; 1: tower legs; 3: a tower body; 4: a tower head; 5: a cross arm; 6; a ground wire bracket; 61: a ground wire; 7: an I-type insulator string; 71: a side phase conductor; 8: a V-shaped insulator string; 81: a middle phase conductor; 9: a main material; 10: oblique material; 11: the diaphragm material.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
A method for designing a power transmission line iron tower without a ground wire, as shown in fig. 1, specifically described by an embodiment, in this embodiment, a 110kV power transmission line iron tower is designed with a model of 1ZT431-24, a model of a lead is LGJ-240/40, and a model of a ground wire is GJ-100, and the ground wire is eliminated for the 110kV power transmission line in an ice-repeatedly covered area, and the method for designing includes the following steps:
s1, eliminating the ground wire of the transmission line iron tower and the ground wire bracket on the iron tower, and obtaining the structural parameters of the transmission line iron tower before and after the ground wire is eliminated, environmental meteorological parameters, icing parameters, and transmission line lead and ground wire parameters.
The iron tower before the ground wire is cancelled and the iron tower after the ground wire is cancelled are respectively shown as a and b in fig. 2, and comprise an iron tower foundation 1, a tower leg 2, a tower body 3, a tower head 4 and a cross arm 5 at the top end of the tower head 4 from bottom to top, an I-shaped insulator string 7 and a V-shaped insulator string 8 which are respectively connected with the two ends and the middle part of the cross arm 5, an edge phase lead 71 is hung at the lower end of the I-shaped insulator string 7, a middle phase lead 81 is hung at the lower end of the V-shaped insulator string 8, the iron tower foundation 1 is of a cylindrical concrete structure, the tower leg 2, the tower body 3 and the tower head 4 are of a steel space truss structure, the space truss comprises a main material 9 for bearing acting load, an oblique material 10 for stabilizing the whole iron tower and a transverse diaphragm material 11 for; compared with the iron tower without the ground wire in fig. 2a, the iron tower without the ground wire in fig. 2b has the advantages that the ground wire support 6 above the cross arm 5 and the ground wire 61 connected with the ground wire support 6 are reduced, the mechanical stress of the iron tower is reduced, the sizes of the main material 9 and the iron tower foundation 1 can be reduced, the steel consumption and the construction cost of the iron tower are reduced, and the construction economy of the power transmission line is improved.
The structural parameters of the transmission line iron tower before and after the ground wire is cancelled are shown in table 1, the environmental meteorological parameters and the icing parameters are shown in table 2, and the wire and ground wire parameters of the transmission line are shown in table 3.
TABLE 1 model 1ZT431-24 iron tower construction parameters before and after ground wire cancellation
| Ambient temperature | Wind speed v | Thunderstorm day | Thickness q of ice coating | Relative humidity | Air pressure | Days of icing |
| -10℃ | 10m/s | 51.0d | 25mm | 86.8％ | 822hPa | 60d |
TABLE 2 cancellation of environmental meteorological parameters and icing parameters for ground line transmission towers
| Cable model | LGJ-240/40 | GJ-100 |
| Calculating the diameter d/mm | 21.66 | 13.0 |
| Comprehensive cross-sectional area SCutting block/mm2 | 277.75 | 100.83 |
| Line impact coefficient α/° C-1 | 18.9×10-6 | 1.15×10-5 |
| Calculating the breaking force Tj/kN | 83.37 | 109.897 |
| Allowable stress sigma/MPa | 286.45 | 1035.4 |
| Modulus of elasticity E/MPa | 76000 | 181000 |
| Weight per unit length M0/kg.m-1 | 0.964 | 0.8594 |
| Factor of safety k | 2.5 | 2.5 |
Table 3 LGJ-240/40 wire and GJ-100 ground wire parameters S2, calculating the self-gravity load, icing load, wind pressure load of the wire and the tower structure member resistance of the transmission line tower before and after the ground wire is cancelled, and establishing a tower mechanical property simulation calculation model in ANSYS finite element analysis software; the simulation calculation models of the mechanical properties of the iron tower before and after the ground wire is cancelled are shown as a and b in fig. 3.
S2.1, the calculation formula of the self-gravity load of the lead wire and the ground wire is as follows:
wherein gamma is the specific load of the ground wire and the lead wire under the ice-covered wind condition, l is the line span, the numerical values of the parameters are substituted, and for the LGJ-240/40 lead, l is 250m, and gamma is 151.73 multiplied by 10-3MPa/m, G ═ 18.97 MPa; for GJ-100 ground wire, l is 250m, and gamma is 348.00X 10-3MPa/m，G＝43.50Mpa。
S2.2, the icing force load calculation formula is as follows:
D＝ρqg
where ρ is an icing density, q is an icing thickness, and g is a gravitational acceleration. In a certain icing period, the icing thickness q is 25mm, and the icing density rho is 0.9kg/m3(ii) a For the power transmission iron tower before and after the ground wire is cancelled, D is 0.2205 multiplied by 10- 3MPa。
S2.3, the wind pressure load calculation formula is as follows:
V＝0.625Cv2
wherein v is the wind speed and C is the wind speed drag coefficient. According to the environmental meteorological parameters in table 2, V is 10m/s, C is 1.0, and V is 0.0625 × 10 for the power transmission towers before and after the ground wire is cancelled-3MPa。
S2.4, the resistance of the structural member of the iron tower comprises the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower, and the calculation formulas are respectively as follows:
R1＝ΩPmAf
in the formula, omegapCalculating a mode uncertainty coefficient for the resistance; m is the strength reduction coefficient; a is an iron towerThe cross section area of steel, and f is the strength of the steel of the iron tower.
R2＝ΩPΦmNAf
In the formula, phi is a stability coefficient of the compression component with the axis; m isNThe reduction coefficient of the stable strength of the iron tower steel is obtained. For the power transmission iron tower before and after the ground wire is cancelled, the model of the tower material is Q235 angle steel and omegap＝1.05，m＝0.7，A＝1，f＝210Mpa，Ф＝1.097，mNR was calculated as 0.9111＝154.35MPa，R2＝220.36MPa。
S3, eliminating tower material stress sigma of front and rear power transmission line iron towers with ground wires through simulation calculationFront side、σRear endMaximum deformation amount epsilon of tower headFront side、εRear endPressure P of the base bottomFront side、PRear end；
Applying the guide, ground wire self-gravity load G, icing force load D and wind load V of the iron tower before and after the ground wire is cancelled, which are obtained by the calculation in the step S2, to the established iron tower mechanical property simulation calculation model shown in the figure 3, and obtaining the tower material stress sigma of the iron tower of the power transmission line before and after the ground wire is cancelled by simulation calculationFront side、σRear endMaximum deformation amount epsilon of tower headFront side、εRear endPressure P of the base bottomFront side、PRear endThe results are shown in Table 4 below.
Table 41 ZT431-24 model iron tower mechanical property simulation calculation result before and after ground wire cancellation
The tower material stress refers to the maximum value and the corresponding position of the main material stress of the iron tower of the power transmission line under the working condition of icing wind; the maximum deformation quantity of the tower head is the maximum deformation quantity of the cross arm position of the tower head under the working condition of icing wind; the pressure of the bottom surface of the foundation refers to the stress of the iron tower foundation of the power transmission line under the action force, the stress analysis of the iron tower foundation is shown in figure 4, and the calculation formula is as follows:
in the formula, FvDesigned down-axis force, G, for acting on the top surface of the tower foundationfIs the self-gravity of the iron tower foundation, G0Is the gravity of the soil right above the top plate of the iron tower foundation, SFoundationThe calculated area of the iron tower foundation bottom plate is shown.
S4, calculating reliability indexes β of the iron tower before and after the ground wire is cancelled according to the probability distribution function of the load and the resistance of the structural member of the iron towerFront side、βRear endβ is calculated as:
wherein β is the reliability index of iron tower, muS、σSThe average value and the standard deviation of the load of the structural member of the iron tower are obtained, and the acting load of the structural member of the iron tower comprises the self-gravity load, the icing load and the wind load of the iron tower; mu.sR、σRThe method comprises the following steps of calculating a reliability index β, wherein the numerical value of the reliability index obeys statistical characteristics, and the probability distribution functions of the resistance of the iron tower structural member, the resistance of the iron tower structural member comprise the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower are respectively as follows:
s4.1, the self-gravity load G of the lead wire and the ground wire of the power transmission iron tower is a permanent load which generally follows normal distribution, and the probability distribution function is as follows:
in the above formula,. mu.G、σGThe mean value and standard deviation of the lead and ground wire self-gravity load random variable G are respectively.
S4.2, the probability of the icing load D borne by the power transmission iron tower follows extreme value I-type distribution, and the annual maximum value distribution function is as follows:
F(D)＝exp{-exp[-α(D-β)]}
wherein α is the scale parameter of the annual maximum distribution of icing load, β is the position parameter of the annual maximum distribution of icing load, the scale parameter, the position parameter and the average value mu of the random variable D of icing loadDAnd standard deviation sigmaDThe relationship of (1) is:
s4.3, the probability of the wind pressure load V borne by the power transmission iron tower is distributed according to an extreme value I type, and the distribution function is as follows:
F(V)＝exp{-exp[-a(V-b)]}
wherein, a is the scale parameter of the extreme value I type distribution, and b is the position parameter of the extreme value I type distribution. Mean value mu of the wind load and the wind load random variable VVAnd standard deviation σVThe relationship of (1) is:
s4.4, the probability of the resistance R of the structural member of the iron tower borne by the power transmission iron tower follows the log-normal distribution, and the distribution function is as follows:
in the formula, muR、σRThe calculation results of the reliability indexes of the iron tower before and after the ground wire is cancelled are shown in table 5.
TABLE 51 calculation results of reliability indexes before and after canceling ground wire of model ZT431-24 iron tower
S5, comparing whether sigma isRear end≤σFront side、εRear end≤εFront side、PRear end≤PFront sideAnd βRear endIf yes, continuing to step S6; if the result is noThen, go to step S7;
s6, reducing the main material size of the power transmission line iron tower without the ground wire and the base size of the iron tower by a certain proportion, wherein the reduced power transmission line iron tower without the ground wire is a new power transmission line iron tower without the ground wire, and repeating the steps S2-S5; the reduction by a certain proportion specifically refers to a proportion that the thickness and the width of a main material of the power transmission iron tower after the ground wire is cancelled are reduced by 3-5% and the diameter and the burial depth of a foundation slab of the iron tower are reduced by 3-5% during each reduction;
s7, obtaining the condition of satisfying sigmaRear end≤σFront side、εRear end≤εFront side、PRear end≤PFront sideAnd βRear endThe maximum reduction value is more than or equal to 4.2, and the corresponding structural parameter is the structural parameter of the iron tower with the least steel consumption and the least iron tower base size after the ground wire is cancelled. The reliability index is more than or equal to 4.2 and is determined according to a table look-up table about the safety level and the damage pattern of the structural member in the GB50068-2001 'unified design Standard for reliability of building Structure': the safety level of the power transmission iron tower is first grade, the damage type is brittle damage, and the reliability index obtained by looking up a table is required to be more than or equal to 4.2. The structural parameters of the iron tower comprise the size of a main material of the iron tower, the size of a foundation bottom plate of the iron tower, the weight of the iron tower and the like, and the design of the power transmission line iron tower without the ground wire is completed.
TABLE 6 parameter calculation results after reduction of main material and base size of power transmission tower
As can be seen from Table 6, when the dimensions of the main material of the power transmission tower and the foundation of the tower are reduced by 10% after the ground wire is canceled, the pressure of the bottom surface of the foundation of the tower is close to the value (P) before the ground wire is canceledRear end＝3.51MPa，PFront side3.55MPa), the internal stress of the iron tower and the maximum deformation of the iron tower are both smaller than the value (sigma) before the ground wire is cancelledRear end＝167.43MPa<σFront side＝182.5MPa，εRear end＝89.73mm<εFront side97.05 mm); when the size ratio of the main material of the transmission tower to the foundation of the tower is 13% after the ground wire is eliminated, the internal stress of the tower and the maximum shape of the towerThe variable being close to the value (σ) before canceling the groundRear end＝181.74MPa，σFront side＝182.5MPa；εRear end＝94.66mm，εFront side97.05mm) but the pressure P of the bottom surface of the iron tower foundationRear end3.79MPa, the value (P) before the ground line is cancelled has been exceededFront side3.55MPa), the tower structure with the reduced proportion of the main material of the transmission tower and the size of the tower foundation of 10 percent is used as the tower structure of the transmission tower with 110kV transmission lines after the ground wire is cancelled, the steel consumption is the minimum, and the size of the tower foundation is the minimum, at the moment, the reliability index of the transmission tower is βRear end＝5.1135>4.2。
Finally, the structural parameters of the 110kV power transmission line iron tower without the ground wire are shown in table 7, and the design of the power transmission line iron tower without the ground wire is completed.
| After the ground wire and the ground wire bracket are cancelled | Before the earth wire is cancelled | |
| Size of main material | L3000×80×10mm | L3000×90×12mm |
| Size of foundation slab | Φ1200×6800mm | Φ1350×7600mm |
| Weight of iron tower | 7.87 ton | 8.7 ton |
TABLE 7 structural parameters of 110kV transmission tower after ground wire cancellation and comparison thereof with those before ground wire cancellation
The design method of the power transmission line iron tower without the ground wire is not only suitable for the optimal design of the power transmission line iron tower without the ground wire in the embodiment of 110kV model 1ZT431-24, but also suitable for the optimal design of the power transmission line iron tower with the voltage class of 10-500 kV in the repeated ice region and the ground wire capable of being cancelled.
In summary, the design method of the power transmission line iron tower without the ground wire has the following advantages:
(1) by carrying out the optimized design after the ground wire is cancelled on the power transmission line iron tower in the repeated ice-covered area, the ground wire fracture caused by ice covering and the accidents of discharging of the lead to the ground wire are thoroughly eliminated, the anti-ice capacity of the power transmission line is effectively improved, and the safety and reliability of the power transmission line are improved;
(2) the obtained power transmission line iron tower without the ground wire has the same or similar internal stress distribution, the maximum deformation of the iron tower, the pressure of the bottom surface of the foundation and enough reliability as those before the ground wire is removed, meanwhile, the sizes of main materials of the iron tower and the foundation of the iron tower are reduced, the consumption cost of tower materials of the iron tower is reduced, the line construction cost is saved, and the economy is improved;
(3) the method is easy to realize, has strong operability, and improves a complete and reliable solution scheme for canceling the optimized design of the ground wire transmission line iron tower for repeated ice coating;
(4) the method is wide in application, and is suitable for iron tower design of a 10-500 kV voltage class capable of canceling ground wire transmission lines in a repeated ice region;
(5) the design method is comprehensive in consideration, simultaneously considers the action effects of self-gravity load, icing force load and wind pressure load, the resistance effects of the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower, and considers the influence of environmental weather on the iron tower of the power transmission line, so that the optimal design of the iron tower of the power transmission line without the ground wire obtained by the method can be fully suitable for the repeated icing area.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.
Claims (9)
1. A design method for a power transmission line iron tower without a ground wire is characterized by comprising the following steps:
s1, eliminating a ground wire of the iron tower of the power transmission line and a ground wire bracket on the iron tower, and acquiring structural parameters, environmental meteorological parameters, icing parameters, and parameters of a wire and the ground wire of the iron tower of the power transmission line before and after the ground wire is eliminated;
s2, calculating and canceling self-gravity loads, icing force loads and wind pressure loads of the lead wires and the ground wires of the iron towers of the power transmission lines before and after the ground wires are canceled, and the structural member resistance of the iron towers, and establishing simulation calculation models of the mechanical properties of the iron towers before and after the ground wires are canceled;
s3, eliminating tower material stress sigma of front and rear power transmission line iron towers with ground wires through simulation calculationFront side、σRear endMaximum deformation amount epsilon of tower headFront side、εRear endPressure of foundation bottom surface PFront side、PRear end；
S4, calculating reliability indexes β of the iron tower before and after the ground wire is cancelled according to the probability distribution function of the load and the resistance of the structural member of the iron towerFront side、βRear end；
S5, comparing whether sigma isRear end≤σFront side、εRear end≤εFront side、PRear end≤PFront sideAnd βRear endIf yes, continuing to step S6; if not, go to step S7;
s6, reducing the size of the power transmission line iron tower without the ground wire by a certain proportion, wherein the power transmission line iron tower without the ground wire after the reduction is a new power transmission line iron tower without the ground wire, and repeating the steps S2-S5;
s7, obtaining the condition of satisfying sigmaRear end≤σFront side、εRear end≤εFront side、PRear end≤PFront sideAnd βRear endThe maximum reduction value is more than or equal to 4.2, and the corresponding structural parameter is the structural parameter of the iron tower with the least steel consumption and the least iron tower base size after the ground wire is cancelled.
2. The method for designing the power transmission line iron tower without the ground wire according to claim 1, wherein the calculation formula of the self-gravity load in the step S2 is as follows:
in the formula, gamma is the specific load of the ground wire and the conducting wire under the working condition of icing wind, and l is the line span;
the calculation formula of the icing force load described in step S2 is:
D＝ρqg
in the formula, rho is the icing density, q is the icing thickness, and g is the gravity acceleration;
the wind pressure load calculation formula in step S2 is:
V＝0.625Cv2
wherein v is the wind speed and C is the wind speed drag coefficient;
the resistance of the structural member of the iron tower in the step S2 includes the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower, and the calculation formula of the stress resistance of the axis of the iron tower is as follows:
R1＝ΩPmAf
in the formula, omegapCalculating a mode uncertainty coefficient for the resistance; m is the strength reduction coefficient; a is the cross-sectional area of the steel of the iron tower, and f is the strength of the steel of the iron tower;
the calculation formula of the iron tower axis compression stability resistance is as follows:
R2＝ΩPΦmNAf
in the formula, phi is a stability coefficient of the compression component with the axis; m isNThe reduction coefficient of the stable strength of the iron tower steel is obtained.
3. The method for designing the power transmission line iron tower without the ground wire according to claim 1, wherein the tower material stress in the step S3 refers to the maximum value and the corresponding position of the main material stress of the power transmission line iron tower under the working condition of icing wind;
the maximum deformation quantity of the tower head in the step S3 is the maximum deformation quantity of the cross arm position of the tower head under the working condition of icing wind;
the calculation formula of the base floor pressure described in step S3 is:
in the formula, FvDesigned down-axis force, G, for acting on the top surface of the tower foundationfIs the self-gravity of the iron tower foundation, G0Is the gravity of the soil right above the top plate of the iron tower foundation, SFoundationThe calculated area of the iron tower foundation bottom plate is shown.
4. The method for designing the power transmission line iron tower without the ground wire according to claim 1, wherein the reliability index in the step S4 is calculated according to a formula:
wherein β is the reliability index of iron tower, muS、σSThe average value and the standard deviation of the load of the structural member of the iron tower are obtained, and the acting load of the structural member of the iron tower comprises the self-gravity load, the icing load and the wind load of the iron tower; mu.sR、σRThe resistance values of the structural members of the iron tower comprise the stress resistance of the axis of the iron tower and the compression stability resistance of the axis of the iron tower, and the numerical values of the resistance values obey the statistical characteristics when the reliability index β is calculated.
5. The design method of the power transmission line iron tower with the ground wire removed according to claim 4, wherein probability distribution functions of the conductor, the ground wire self-gravity load, the icing load, the wind load and the resistance of the structural member of the iron tower, which are borne by the iron tower, respectively meet the following requirements:
the self-gravity load G of the conducting wire and the ground wire borne by the power transmission iron tower is a permanent load and follows normal distribution;
the probability of the icing load D borne by the power transmission iron tower follows extreme value I type distribution;
the probability of the wind pressure load V borne by the power transmission iron tower follows the extreme value I-type distribution;
the probability of the resistance R of the structural member of the iron tower borne by the power transmission iron tower follows the log-normal distribution.
6. The method for designing the power transmission line iron tower without the ground wire according to claim 1, wherein the size of the power transmission line iron tower in the step S6 is the size of a main material of the iron tower and the size of a foundation slab of the iron tower, and the reduction is performed by a certain proportion, specifically by a proportion that the thickness and the width of the main material of the power transmission line iron tower after the ground wire is removed are reduced by 3% -5% and the diameter and the burial depth of the foundation slab of the iron tower are reduced by 3% -5% in each reduction.
7. The method as claimed in claim 1, wherein the structural parameters in step S7 include a main material size of the tower, a size of a foundation slab of the tower, and a weight of the tower.
8. The method for designing the power transmission line iron tower without the ground wire according to claim 1, wherein the power transmission line iron tower structural parameters, the environmental meteorological parameters and the icing parameters in the step S1 respectively comprise a power transmission line pole tower structure size diagram, a line rated voltage, a line span and a breath height, an environmental temperature, a wind speed, an icing thickness, an icing density, diameters, sectional areas and line collision coefficients of the wire and the ground wire, and the calculated breaking force, allowable stress, an elastic modulus, unit length weight and a safety coefficient.
9. An electric transmission line iron tower without a ground wire is characterized in that the iron tower is designed according to the design method of the electric transmission line iron tower without the ground wire according to any one of claims 1 to 8, is provided with no ground wire and no ground wire bracket relative to a common iron tower, and has the iron tower structural parameters in the step S7.
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