Prefabricated overhead conductor length calculation method for compensating plastic creep elongation

Abstract

The invention provides a method for calculating the length of a prefabricated overhead conductor for compensating plastic creep elongation, and the method comprises the steps: 1, carrying out a creep test of the conductor, and collecting displacement data under the action of constant tension; 2, acquiring a coefficient in a creep equation by using creep test data, and predicting the creep rate of the prefabricated wire during stringing and running for 10 years; 3, carrying out a creep test on the wire to obtain a large number of creep rate data samples; step 4, statistical analysis is carried out on the creep rate data sample, and a normal distribution probability density function is used to describe the creep rate data sample of the conductor; 5, deducing an equivalent design relation between the creep rate and the stringing air temperature by using the stringing stress state equation of the overhead line; and 6, calculating the length of the prefabricated lead frame wire for compensating the plastic creep elongation by reducing the temperature of the frame wire. The method is high in operability, and can effectively prevent safety accidents caused by plastic creep elongation of the overhead line.

Description

Technical Field

[0001] The invention relates to the technical field of overhead power transmission line engineering design and application, and in particular provides a method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation. Background Art

[0002] Overhead lines are not actually completely elastic. After being installed on poles and towers, they will produce permanent plastic creep elongation due to the tension. A slight change or error in the length of the overhead line will cause a considerable change in stress and sag. Plastic creep elongation will increase the length of the conductor between the sections, thereby increasing the sag, which may reduce the electrical clearance between the overhead line and the ground or the crossing object, causing an accident.

[0003] By adding a pre-tensioning link in the production process of overhead conductors, the plastic creepage elongation after wiring can be pulled out in advance, so that the conductors can enter a long-term operation state at the initial stage of wiring, thereby eliminating most of the impact of plastic creepage elongation on the electrical safety of the line.

[0004] For this type of prefabricated overhead line, the length of the conductor in long-term operation should be calculated in accordance with relevant specifications in the field of power transmission line design. However, due to the lack of theoretical research on the plastic creep elongation of prefabricated conductors, the length of the prefabricated conductors required for stringing can only be evaluated through experience in actual engineering, and it is difficult to accurately calculate it.

[0005] Therefore, it is necessary to combine the results of creep test research, through theoretical analysis and calculation, to propose an accurate calculation method for the required line length for the construction of prefabricated overhead conductors that takes into account the compensation of plastic creep elongation, in order to improve the safety of transmission lines.

[0006] People are eager to obtain a method for calculating the length of prefabricated overhead conductors with excellent technical effects and compensating for plastic creep elongation. Summary of the invention

[0007] The invention provides a method for calculating the length of a prefabricated overhead conductor for compensating for plastic creep elongation.

[0008] The technical solution of the present invention is:

[0009] The invention discloses a method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation, the technical key of which is:

[0010] The steps and contents are:

[0011] Step 1: Under constant temperature and constant tension conditions, a creep test of the conductor is performed to collect displacement data under constant tension; the above calculation steps are prior art;

[0012] Step 2: Using creep test data, perform linear regression of creep elongation of stranded wire and time on double logarithmic coordinates to obtain the coefficients in the creep equation, and then use the creep equation to predict the creep rate of prefabricated conductors during stringing and after 10 years of operation;

[0013] Step 3: Conduct creep tests on the same type of conductors from different manufacturers and different production batches to obtain a large number of creep rate data samples;

[0014] Step 4: Perform statistical analysis on the creep rate data samples and use the normal distribution probability density function to describe the wire creep rate data samples;

[0015] Step 5: Using the overhead line stress state equation, derive the equivalent design relationship between creep rate and overhead line temperature;

[0016] Step 6: Calculate the length of the prefabricated conductor stringing line to compensate for plastic creep elongation by lowering the stringing temperature.

[0017] The method for calculating the length of a prefabricated overhead conductor compensating for plastic creep elongation of the present invention preferably claims the following:

[0018] In step 1, the ambient temperature of the test device should be controlled at about 20°C, and the test tension should be divided into two groups of 40% and 25% of the rated breaking force (RTS).

[0019] In step 2, the process of processing creep test data is:

[0020] The relationship between the creep elongation of stranded wire and time changes according to the exponential law. c =a×t b Converted into the double logarithmic expression logε for creep elongation and time c =log a×b log t; where: ε is the elongation due to creep (creep rate), t is the time unit h, a and b are constants;

[0021] The measured creep values ​​are plotted on a logarithmic coordinate graph and form a curve, which approaches a straight line when the time range of the data is long;

[0022] Linear regression is performed on creep test data, requiring the values ​​to be evenly distributed along the regression line;

[0023] For the creep test data of the conductor with 40% RTS, the regression curve is used to obtain the creep rate of 3h; and for the creep test data of the conductor with 25% RTS, the regression curve is used to obtain the creep rate of 10 years.

[0024] In step 3, the process of obtaining a large number of creep rate data samples is as follows:

[0025] Repeat steps 1 and 2 for the same type of wires from different manufacturers and different production batches, and make sure that the temperature and tension in the creep test environment are consistent.

[0026] The creep rate samples of the wires obtained are numbered, and at least 20 groups of creep rate samples of the wires are obtained;

[0027] If the manufacturer's test data under the same test conditions can be obtained, it can be introduced into the data sample, thereby expanding the sample size.

[0028] In step 4), the process of statistically analyzing the creep rate data samples is as follows:

[0029] Assume that the creep rate data sample under the same tension obtained in step 3) conforms to the normal distribution. The probability density function of the normal distribution is: Among them, μ is the mean, σ is the mean square error;

[0030] Using the sample value when the probability reaches 95%, μ and σ are calculated by using the creep rate data sample, and then substituted into the probability density function expression of the normal distribution. Then the probability density curve can be drawn, and the sample value corresponding to the specific probability value can be obtained;

[0031] The sample value when the conductor is under 40% RTS condition for 3 hours and the probability reaches 95% is taken as the reference and recorded as ε J1 ; ε J1 It can express the plastic creep deformation rate of prefabricated overhead conductor after pre-tensioning;

[0032] The sample value when the conductor is under 25% RTS condition for 10 years and the probability reaches 95% is taken as the reference, denoted as ε J0 ; ε J0 It can indicate the creep rate of overhead lines under average operating tension over 10 years.

[0033] In step 5), the process of deriving the equivalent design relationship between creep rate and air temperature is:

[0034] Based on the actual stress-strain characteristics of overhead lines, the most commonly used oblique parabola state equation in engineering is used to consider reducing the plastic creep elongation ε of overhead lines. J , the stress state equation of the overhead line can be derived as:

[0035]

[0036] Among them, σ J and σ0 are the overhead line stress considering plastic creep elongation and the overhead line stress under known final operating conditions, respectively. Jand t are the temperatures during the stringing and final operation, respectively; l is the span of the gear; β is the height difference angle; α is the temperature linear expansion coefficient of the overhead wire; E is the elastic coefficient under the final operating conditions; ε J is the plastic creep deformation rate of the overhead conductor;

[0037] Combining the last two terms on the right side of the above equation, we get:

[0038] αEcosβ(t J -t)-Eε J cosβ=αEcosβ(t J -t-ε J / α)=αEcosβ(t J -t-Δt)

[0039] This shows that increasing the stringing stress is equivalent to reducing the temperature during stringing by Δt. The value of Δt can be determined based on ε J Calculation; This method of reducing the temperature of the overhead wire can easily consider the influence of the plastic creep effect on the stress-sag; the specific calculation formula is:

[0040]

[0041] In step 6), the method for calculating the length of the prefabricated conductor rack line that compensates for plastic creep elongation is:

[0042] When the temperature reduction method mentioned in step 5) is used to compensate for the plastic creep elongation of the prefabricated conductor, the length released during the factory pre-tensioning process should be deducted, and the temperature reduction value should be calculated based on the plastic creep elongation that has not been released during the life of the conductor after pre-tensioning;

[0043] The pre-stretching length of the prefabricated conductor during the tension stringing is measured by the plastic creepage elongation of the conductor under 40% RTS for 3 hours. Since the prefabricated conductor will gradually release the plastic creepage elongation during its service life, and the release speed is from fast to slow, the plastic creepage elongation of the conductor after 10 years of operation can be ignored. Therefore, ε is not used when calculating the temperature drop value. J0 The 10-year plastic creep elongation of the conductor under the average operating tension can be taken, that is, the 10-year plastic creep elongation of the conductor under the condition of 25% RTS;

[0044] After considering the factory pre-tensioning process of prefabricated conductors, the calculation formula for the temperature drop value is:

[0045]

[0046] Then the stress state equation of the prefabricated conductor string after considering the plastic creep elongation using the cooling method can be expressed as:

[0047]

[0048] By solving the above stringing stress state equation, the prefabricated conductor stringing stress σ considering the influence of plastic creep elongation can be obtained. J ;

[0049] The obtained stress σ during cable stringing J Bring in The sag of the conductor during the prefabricated conductor stringing can be obtained and brought into That is, the line length within the time range of prefabricated conductor stringing can be obtained.

[0050] The beneficial effects of the present invention are:

[0051] The method for calculating the length of a prefabricated overhead conductor that compensates for plastic-creep elongation described in the present invention integrates the creep test of the overhead conductor into the calculation of the line length required when the prefabricated conductor is strung, thereby achieving accurate sag and line length design of the prefabricated overhead conductor after considering creep. This can guide the application of prefabricated overhead conductors in the field of power transmission line engineering and effectively prevent safety accidents caused by plastic-creep elongation of the overhead conductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The principle flow chart of the method for calculating the length of a prefabricated overhead conductor for compensating for plastic creep elongation described in Example 1;

[0053] Figure 2 This is the linear regression curve of creep test data that needs to be drawn in step 2) of Example 1. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the embodiments and the accompanying drawings, but is not limited thereto.

[0055] Example 1

[0056] A method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation, the key technology of which is:

[0057] The steps and contents are:

[0058] Step 1: Under constant temperature and constant tension conditions, a creep test of the conductor is performed to collect displacement data under constant tension; the above calculation steps are prior art;

[0059] Step 2: Using creep test data, perform linear regression of creep elongation of stranded wire and time on double logarithmic coordinates to obtain the coefficients in the creep equation, and then use the creep equation to predict the creep rate of prefabricated conductors during stringing and after 10 years of operation;

[0060] Step 3: Conduct creep tests on the same type of conductors from different manufacturers and different production batches to obtain a large number of creep rate data samples;

[0061] Step 4: Perform statistical analysis on the creep rate data samples and use the normal distribution probability density function to describe the wire creep rate data samples;

[0062] Step 5: Using the overhead line stress state equation, derive the equivalent design relationship between creep rate and overhead line temperature;

[0063] Step 6: Calculate the length of the prefabricated conductor stringing line to compensate for plastic creep elongation by lowering the stringing temperature.

[0064] In step 1, the ambient temperature of the test device should be controlled at about 20°C, and the test tension should be divided into two groups of 40% and 25% of the rated breaking force (RTS).

[0065] In step 2, the process of processing creep test data is:

[0066] The relationship between the creep elongation of stranded wire and time changes according to the exponential law. c =a×t b Converted into the double logarithmic expression logε for creep elongation and time c =log a×b log t; where: ε is the elongation due to creep (creep rate), t is the time unit h, a and b are constants;

[0067] The measured creep values ​​are plotted on a logarithmic coordinate graph and form a curve, which approaches a straight line when the time range of the data is long;

[0068] Linear regression is performed on creep test data, requiring the values ​​to be evenly distributed along the regression line;

[0069] For the creep test data of the conductor with 40% RTS, the regression curve is used to obtain the creep rate of 3h; and for the creep test data of the conductor with 25% RTS, the regression curve is used to obtain the creep rate of 10 years.

[0070] In step 3, the process of obtaining a large number of creep rate data samples is as follows:

[0071] Repeat steps 1 and 2 for the same type of wires from different manufacturers and different production batches, and make sure that the temperature and tension in the creep test environment are consistent.

[0072] The creep rate samples of the wires obtained are numbered, and at least 20 groups of creep rate samples of the wires are obtained;

[0073] If the manufacturer's test data under the same test conditions can be obtained, it can be introduced into the data sample, thereby expanding the sample size.

[0074] In step 4), the process of statistically analyzing the creep rate data samples is as follows:

[0075] Assume that the creep rate data sample under the same tension obtained in step 3) conforms to the normal distribution. The probability density function of the normal distribution is: Among them, μ is the mean, σ is the mean square error;

[0076] Using the sample value when the probability reaches 95%, μ and σ are calculated by using the creep rate data sample, and then substituted into the probability density function expression of the normal distribution. Then the probability density curve can be drawn, and the sample value corresponding to the specific probability value can be obtained;

[0077] The sample value when the conductor is under 40% RTS condition for 3 hours and the probability reaches 95% is taken as the reference and recorded as ε J1 ; ε J1 It can express the plastic creep deformation rate of prefabricated overhead conductor after pre-tensioning;

[0078] The sample value when the conductor is under 25% RTS condition for 10 years and the probability reaches 95% is taken as the reference, denoted as ε J0 ; ε J0 It can indicate the creep rate of overhead lines under average operating tension over 10 years.

[0079] In step 5), the process of deriving the equivalent design relationship between creep rate and air temperature is:

[0080] Based on the actual stress-strain characteristics of overhead lines, the most commonly used oblique parabola state equation in engineering is used to consider reducing the plastic creep elongation ε of overhead lines. J , the stress state equation of the overhead line can be derived as:

[0081]

[0082] Among them, σ J and σ0 are the overhead line stress considering plastic creep elongation and the overhead line stress under known final operating conditions, respectively. J and t are the temperatures during the stringing and final operation, respectively; l is the span of the gear; β is the height difference angle; α is the temperature linear expansion coefficient of the overhead wire; E is the elastic coefficient under the final operating conditions; ε J is the plastic creep deformation rate of the overhead conductor;

[0083] Combining the last two terms on the right side of the above equation, we get:

[0084] αEcosβ(t J -t)-Eε J cosβ=αEcosβ(t J -t-ε J / α)=αEcosβ(t J -t-Δt)

[0085] This shows that increasing the stringing stress is equivalent to reducing the temperature during stringing by Δt. The value of Δt can be determined based on ε J Calculation; This method of reducing the temperature of the overhead wire can easily consider the influence of the plastic creep effect on the stress-sag; the specific calculation formula is:

[0086]

[0087] In step 6), the method for calculating the length of the prefabricated conductor rack line that compensates for plastic creep elongation is:

[0088] When the temperature reduction method mentioned in step 5) is used to compensate for the plastic creep elongation of the prefabricated conductor, the length released during the factory pre-tensioning process should be deducted, and the temperature reduction value should be calculated based on the plastic creep elongation that has not been released during the life of the conductor after pre-tensioning;

[0089] The pre-stretching length of the prefabricated conductor during the tension stringing is measured by the plastic creepage elongation of the conductor under 40% RTS for 3 hours. Since the prefabricated conductor will gradually release the plastic creepage elongation during its service life, and the release speed is from fast to slow, the plastic creepage elongation of the conductor after 10 years of operation can be ignored. Therefore, ε is not used when calculating the temperature drop value. J0 The 10-year plastic creep elongation of the conductor under the average operating tension can be taken, that is, the 10-year plastic creep elongation of the conductor under the condition of 25% RTS;

[0090] After considering the factory pre-tensioning process of prefabricated conductors, the calculation formula for the temperature drop value is:

[0091]

[0092] Then the stress state equation of the prefabricated conductor string after considering the plastic creep elongation using the cooling method can be expressed as:

[0093]

[0094] By solving the above stringing stress state equation, the prefabricated conductor stringing stress σ considering the influence of plastic creep elongation can be obtained. J ;

[0095] The obtained stress σ during cable stringing J Bring in The sag of the conductor during the prefabricated conductor stringing can be obtained and brought into That is, the line length within the time range of prefabricated conductor stringing can be obtained.

Claims

1. A method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation, characterized in that: The steps and contents are: Step 1: Conduct a creep test of the conductor under constant temperature and constant tension conditions, and collect displacement data under constant tension; Step 2: Using creep test data, perform linear regression of creep elongation of stranded wire and time on double logarithmic coordinates to obtain the coefficients in the creep equation, and then use the creep equation to predict the creep rate of prefabricated conductors during stringing and after 10 years of operation; Step 3: Conduct creep tests on the same type of conductors from different manufacturers and different production batches to obtain a large number of creep rate data samples; Step 4: Perform statistical analysis on the creep rate data samples and use the normal distribution probability density function to describe the wire creep rate data samples; Step 5: Using the overhead line stress state equation, derive the equivalent design relationship between creep rate and overhead line temperature; Step 6: Calculate the length of the prefabricated conductor stringing line to compensate for plastic creep elongation by lowering the stringing temperature.

2. The method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation according to claim 1, characterized in that: In step 1, the ambient temperature of the test device should be controlled at around 20°C, and the test tensile force should be divided into two groups of 40% and 25% of the rated breaking force.

3. The method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation according to claim 1 or 2, characterized in that: In step 2, the process of processing creep test data is: The relationship between the creep elongation of stranded wire and time changes according to the exponential law. c =a×t b Converted into the double logarithmic expression logε for creep elongation and time c =loga×blogt; where: ε is the elongation due to creep, t is the time unit h, a and b are constants; The measured creep values ​​are plotted on a logarithmic coordinate graph and form a curve, which approaches a straight line when the time range of the data is long; Linear regression is performed on creep test data, requiring the values ​​to be evenly distributed along the regression line; For the creep test data of the conductor with 40% RTS, the regression curve is used to obtain the creep rate of 3h; and for the creep test data of the conductor with 25% RTS, the regression curve is used to obtain the creep rate of 10 years.

4. The method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation according to claim 1 or 2, characterized in that: In step 3, the process of obtaining a large number of creep rate data samples is as follows: Repeat steps 1 and 2 for the same type of wires from different manufacturers and different production batches, and make sure that the temperature and tension in the creep test environment are consistent. The creep rate samples of the wires obtained are numbered, and at least 20 groups of creep rate samples of the wires are obtained; If the manufacturer's test data under the same test conditions can be obtained, it can be introduced into the data sample, thereby expanding the sample size.

5. The method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation according to claim 4, characterized in that: In step 4), the process of statistically analyzing the creep rate data samples is as follows: Assume that the creep rate data sample under the same tension obtained in step 3) conforms to the normal distribution. The probability density function of the normal distribution is: Among them, μ is the mean, σ is the mean square error; Using the sample value when the probability reaches 95%, μ and σ are calculated by using the creep rate data sample, and then substituted into the probability density function expression of the normal distribution. Then the probability density curve can be drawn, and the sample value corresponding to the specific probability value can be obtained; The sample value when the conductor is under 40% RTS condition for 3 hours and the probability reaches 95% is taken as the reference and recorded as ε J1 ; ε J1 It can express the plastic creep deformation rate of prefabricated overhead conductor after pre-tensioning; The sample value when the conductor is under 25% RTS condition for 10 years and the probability reaches 95% is taken as the reference, denoted as ε J0 ; ε J0 It can indicate the creep rate of overhead lines under average operating tension over 10 years.

6. The method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation according to claim 4, characterized in that: In step 5), the process of deriving the equivalent design relationship between creep rate and air temperature is: Based on the actual stress-strain characteristics of overhead lines, the most commonly used oblique parabola state equation in engineering is used to consider reducing the plastic creep elongation ε of overhead lines. J , the stress state equation of the overhead line can be derived as: Among them, σ J and σ0 are the overhead line stress considering plastic creep elongation and the overhead line stress under known final operating conditions, respectively. J and t are the temperatures during the stringing and final operation, respectively; l is the span of the gear; β is the height difference angle; α is the temperature linear expansion coefficient of the overhead wire; E is the elastic coefficient under the final operating conditions; ε J is the plastic creep deformation rate of the overhead conductor; Combining the last two terms on the right side of the above equation, we get: αEcosβ(t J -t)-Ee J cosβ=αEcosβ(t J -t-e J / α)=αEcosβ(t J -t-Δt) This shows that increasing the stringing stress is equivalent to reducing the temperature during stringing by Δt. The value of Δt can be determined based on ε J Calculation; This method of reducing the temperature of the overhead wire can easily consider the influence of the plastic creep effect on the stress-sag; the specific calculation formula is:

7. The method for calculating the length of a prefabricated overhead conductor that compensates for plastic creep elongation according to claim 6, characterized in that: In step 6), the method for calculating the length of the prefabricated conductor rack line that compensates for plastic creep elongation is: When the temperature reduction method mentioned in step 5) is used to compensate for the plastic creep elongation of the prefabricated conductor, the length released during the factory pre-tensioning process should be deducted, and the temperature reduction value should be calculated based on the plastic creep elongation that has not been released during the life of the conductor after pre-tensioning; The pre-stretching length of the prefabricated conductor during the tension stringing is measured by the plastic creepage elongation of the conductor under 40% RTS for 3 hours. Since the prefabricated conductor will gradually release the plastic creepage elongation during its service life, and the release speed is from fast to slow, the plastic creepage elongation of the conductor after 10 years of operation can be ignored. Therefore, ε is not used when calculating the temperature drop value. J0 The 10-year plastic creep elongation of the conductor under the average operating tension can be taken, that is, the 10-year plastic creep elongation of the conductor under the condition of 25% RTS; After considering the factory pre-tensioning process of prefabricated conductors, the calculation formula for the temperature drop value is: Then the stress state equation of the prefabricated conductor string after considering the plastic creep elongation using the cooling method can be expressed as: By solving the above stringing stress state equation, the prefabricated conductor stringing stress σ considering the influence of plastic creep elongation can be obtained. J ; The obtained stress σ during cable stringing J Bring in The sag of the conductor during the prefabricated conductor stringing can be obtained and brought into That is, the line length within the time range of prefabricated conductor stringing can be obtained.

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