Overhead conductor dynamic capacity-increasing method based on three-layer structure cooling capacity-increasing algorithm

Abstract

The invention discloses an overhead conductor dynamic capacity-increasing method based on a three-layer structure cooling capacity-increasing algorithm, which is characterized in that the temperature distribution of an overhead conductor is monitored in real time, and the ambient temperature along the conductor is accurately measured by using a distributed optical fiber temperature measurement technology (BOTDR). The actual temperature of each point of the wire is derived by combining a heat conduction model and a Newton cooling law, and the temperature bottleneck position is identified. Based on this, the algorithm dynamically adjusts the current-carrying capacity of the wire to ensure that the wire operates within a safe temperature range, thereby realizing capacity increase. Simulation results show that the method can significantly improve the transmission capacity of the wire and optimize the design current-carrying capacity on the premise of not influencing the line safety. In addition, the method does not need to additionally install a temperature sensor, reduces the cost of a traditional DTS system, simplifies the maintenance work, improves the reliability and practicability of the system, is suitable for various power grid environments, and gives full play to the potential capacity of a power transmission line.

Description

Technical Field

[0001] The invention relates to the technical field of dynamic capacity increase of overhead conductors, in particular to a dynamic capacity increase method of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm. Background Art

[0002] When overhead transmission lines transmit current, they generate heat due to the existence of resistance. As the load current increases, the temperature of the wire gradually rises. When the temperature of the wire exceeds its maximum allowable operating temperature, it may cause overheating, insulation damage, and even cause the circuit breaker to trip. Therefore, how to scientifically and rationally tap the potential transmission capacity of existing transmission lines and increase the transmission capacity of the lines without affecting the safe operation of the power grid has become a key issue in solving the imbalance between supply and demand during peak power transmission periods in some regions.

[0003] At present, the methods commonly used at home and abroad to increase the current carrying capacity of overhead transmission lines are mainly divided into two categories: static capacity increase and dynamic capacity increase.

[0004] Static capacity expansion technology improves the existing conductor materials, specifications and supporting equipment, and updates the technical standards of the power industry, thereby increasing the maximum allowable operating temperature of overhead transmission lines from 70°C to 80°C, thereby increasing the transmission capacity by about 20%. However, this method has the following limitations: (1) whether it complies with the current design specifications; (2) whether it will affect the service life and mechanical strength of the conductor and its supporting equipment; (3) the increase in conductor temperature will cause the arc sag to increase, which may cause the risk of insufficient safety distance to the ground and reduce the safety factor of the transmission line. Therefore, when using the static calculation method, the unified standards in various regions and the single temperature setting throughout the year cannot fully reflect the actual transmission capacity of the overhead line, resulting in a large amount of grid resources being wasted.

[0005] Dynamic capacity expansion technology improves calculation and measurement methods, monitors the conductor status and surrounding environmental factors such as wind speed, sunshine, temperature, etc. online, and accurately calculates the maximum current carrying capacity of the line. This technology does not change the original line layout and does not affect the safe operation of the power grid. In theory, it can increase the line current carrying capacity by 10% to 30%. At present, scholars at home and abroad generally use the dynamic thermal setting system (DTR system) for dynamic capacity expansion. The system relies on real-time environmental data provided by SCADA to calculate the real-time maximum allowable current carrying value of the conductor. However, the equipment cost of the DTR system is high, the maintenance is complex, and the reliability is difficult to guarantee, which limits its wide application in the power grid and fails to fully realize its potential. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method for dynamic capacity increase of overhead conductors based on a three-layer structure cooling and capacity increase algorithm. The method utilizes distributed temperature sensing technology on an overhead transmission line monitoring device to perform distributed measurement of the ambient temperature around the overhead line, derives the conductor temperature through a heat conduction model, and brings the real-time temperature bottleneck point of the conductor into a new heat balance formula, thereby calculating the real-time current carrying capacity and realizing online dynamic capacity increase of the overhead line.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm provided by the present invention comprises the following steps:

[0009] Step 1: Continuously measure the ambient temperature at each point along the entire transmission line to obtain the ambient temperature-time series at each point along the transmission line;

[0010] Step 2: Convert the measured ambient temperature into the conductor temperature, and record and save the temperature-time series at the maximum conductor temperature;

[0011] Step 3: From the temperature-time series at the maximum temperature of the conductor, select a number of consecutive temperature sampling values ​​and bring them into the heat conduction model to calculate a set of environmental implicit capacity coefficient vectors;

[0012] Step 4: Calculate the real-time maximum current carrying capacity of the overhead line and continuously update it in real time.

[0013] Further, the ambient temperature-time series of each point along the transmission line is obtained in the following manner in step 1, specifically including:

[0014] Step 1.1: Generate pulsed light through the BOTDR device and direct it into the optical fiber channel through one end of the OPGW optical cable optical fiber; when the light pulse propagates in the optical fiber, it will produce Brillouin scattering when it is affected by the sudden acoustic wave field, and a part of the back-scattered Brillouin light carries the temperature and strain information of the optical fiber back to the BOTDR device;

[0015] Step 1.2: By analyzing the frequency drift of the backscattered Brillouin light, the ambient temperature distribution along the entire temperature measuring optical cable is obtained, that is, the ambient temperature of the overhead line is measured.

[0016] Further, the temperature-time series at the maximum temperature of the conductor is obtained in the following manner in step 2, specifically including:

[0017] Step 2.1: Using the nonlinear relationship between conductor current and AC and DC resistance, determine the heat conduction equation of the OPGW and transmission line at the same spatial position, and establish the relationship between conductor temperature and ambient temperature by introducing the heat conduction model;

[0018] Step 2.2: Solve the temperature of the wire using the Newton iteration method to obtain the temperature change of the wire under different environmental conditions.

[0019] Furthermore, in step 3, the environmental implicit capacity coefficient vector is obtained in the following manner: the conductor temperature is calculated according to the measured ambient temperature, a sequence of conductor temperature changes over time is obtained, and the temperature information is introduced into the simplified heat conduction model.

[0020] Further, in step 4, the real-time maximum current carrying capacity of the overhead line is calculated in the following manner:

[0021]

[0022] In the formula, S k =[θ1,θ2,θ3] T is the known current set of coefficient vectors; T k is the initial temperature;

[0023] T max According to the power design regulations of my country, the maximum temperature limit of the conductor of the transmission line is allowed; Ta is the ambient temperature; θ1, θ2, θ3 are the coefficient vector S k =[θ1,θ2,θ3] T The elements in .

[0024] Furthermore, the specific method of the relationship between the conductor temperature and the ambient temperature in step 2.1 is:

[0025] The heat conduction equation of the OPGW and the transmission line at the same spatial position on the overhead transmission line is determined according to the following formula:

[0026] OPGW:

[0027] q co +q ro ―q so =0

[0028] Overhead transmission lines:

[0029] I 2 R(T c )―q cc ―q rc +q sc =0

[0030] In the above formula, I is the current carrying capacity of the transmission line;

[0031] RT C is the temperature T C The AC resistance of the conductor per kilometer;

[0032] q sun,opgw and qsun,cond are the solar heat absorption of OPGW and conductor, both of which are unknown quantities;

[0033] q rad,opgw and q rad,cond They are the radiation heat dissipation of OPGW and conductors;

[0034] q conv,opgw and q conv,cond are the convection heat dissipation of OPGW and conductor respectively; their expressions are:

[0035] Radiative cooling:

[0036] q ro =16.03D o ×10 ―8 [(T o +273) 4 ―(T a +273) 4 ]

[0037] q rc =16.03D c ×10 ―8 [(T c +273) 4 ―(T a +273) 4 ]

[0038] Convection cooling:

[0039]

[0040]

[0041] In the formula, the OPGW optical cable and the overhead transmission line have the same surface material properties, the OPGW and the transmission line are in the same natural space position, and the solar radiation received by both is the same;

[0042] Calculate the solar heat absorption according to the following formula:

[0043]

[0044] Substituting into the above formula we can get:

[0045]

[0046] Where RT c is the AC and DC resistance;

[0047] The ratio of conductor current I to AC and DC resistance β is calculated according to the following formula:

[0048] β=ζI τ

[0049] When calculating the current carrying capacity of the conductor, the AC and DC resistance RT c Calculated according to the following formula:

[0050] R(T c )=βR d

[0051] When the standard cross section of the conductor is determined, ζ and τ are both constants, so:

[0052] R d =R 20 [1+α(T c -20)]

[0053] Among them, R d is the DC resistance at operating temperature, R 20 is the DC resistance at 20°C, and the calculation formula is:

[0054]

[0055] Where, d is the diameter of the aluminum wire; ρ 20 is the resistivity of the aluminum single wire at 20°C; N is the total number of aluminum wires; λ am is the average twisting rate of aluminum wire, calculated according to the average pitch ratio of each layer of aluminum wire; a is the temperature coefficient.

[0056] Furthermore, the step 2.2 calculates the conductor temperature of the overhead transmission line according to the following formula:

[0057] Solve the wire temperature T by Newton iteration method C , define the function:

[0058] f(T c )=I 2 R d (T c )―q sun +q rad (T c )+q conv (T c )

[0059] The derivative is:

[0060] f'(T c )=4D c (T c +273) 3 +h(t)D c ―I 2 R'(T c )

[0061] The Newton iteration formula is:

[0062]

[0063] Where n = 1, 2, 3, dots represents the number of iterations. This method can gradually approximate and.

[0064] Furthermore, in step 3, the environmental implicit capacity coefficient vector is calculated specifically in the following manner:

[0065] The conductor temperature is calculated based on the measured ambient temperature, and the sequence of conductor temperature changes over time is calculated using the following formula: Substitute the temperature information into the thermal balance formula,

[0066]

[0067] Continuously sample the coefficients of several deterministic equations and solve a set of environmental implicit capacity coefficient vectors, as follows:

[0068]

[0069] Among them, T k is the conductor temperature at the kth moment, I k is the current at the kth moment, Δt is the sampling period, θ 1,k ,θ 2,k and θ 3,k is the environmental implicit capacity coefficient.

[0070] Further, the step 4 calculates the real-time maximum current carrying capacity according to the following formula:

[0071]

[0072] According to the maximum allowable temperature of the transmission line conductor, the mean temperature change of multiple consecutive sampling periods is calculated according to the following formula:

[0073]

[0074] Among them, I max Indicates the real-time maximum current carrying capacity; S k is the known current coefficient vector; T k is the initial temperature.

[0075] The beneficial effects of the present invention are:

[0076] The present invention provides a method for dynamic capacity increase of overhead conductors based on a three-layer structure cooling and capacity increase algorithm. The method monitors the temperature distribution of overhead conductors in real time and uses distributed optical fiber temperature measurement technology (BOTDR) to accurately measure the ambient temperature along the conductor. Combining the heat conduction model and Newton's cooling law, the actual temperature of each point on the conductor is derived, and the temperature bottleneck position is identified. Based on this, the algorithm dynamically adjusts the current carrying capacity of the conductor to ensure that the conductor operates within a safe temperature range, thereby achieving capacity increase. Simulation results show that this method can significantly improve the transmission capacity of the conductor and optimize the design current carrying capacity without affecting the safety of the line. In addition, this method does not require the installation of additional temperature sensors, reduces the cost of traditional DTS systems, simplifies maintenance work, improves the reliability and practicality of the system, is suitable for various power grid environments, and gives full play to the potential capacity of transmission lines.

[0077] This method provides a new online dynamic capacity expansion method based on a three-layer structure cooling and capacity expansion algorithm. This method introduces a three-layer structure model (inner iron core, inner aluminum wire, and outer coating with a 2 / 3 ring coating structure). This type of structural cooling model dynamically adjusts the heat dissipation efficiency of the conductor in combination with factors such as ambient temperature, wind speed, and sunshine, thereby optimizing the current carrying capacity of the conductor. Specifically, the algorithm uses distributed temperature sensing technology to monitor the temperature distribution along the conductor in real time, and combines Newton's cooling law to deduce the actual temperature change of the conductor. Through the three-layer structure cooling and capacity expansion algorithm, the real-time temperature bottleneck point of the conductor is brought into the new thermal balance formula to calculate the real-time maximum allowable current carrying capacity of the conductor.

[0078] Research shows that this method can effectively improve the current carrying capacity of the line, optimize the power transmission design of the line, and has the following advantages:

[0079] This technical solution effectively reduces equipment costs and simplifies maintenance procedures by efficiently utilizing existing overhead transmission line monitoring devices for distributed temperature measurement. Its simplified hardware structure reduces maintenance difficulty and costs. At the same time, through precise temperature monitoring and dynamic adjustment of heat dissipation efficiency, it significantly improves the reliability of the power grid and avoids failures caused by overheating. In addition, this solution has a wide range of applicability, can adapt to various environments, give full play to the potential of transmission lines, and provide an economical, efficient and reliable new solution for the power industry.

[0080] In summary, the dynamic capacity expansion method based on the three-layer structure cooling and capacity expansion algorithm can not only significantly improve the transmission capacity of overhead transmission lines, but also has low cost and high reliability, providing a strong guarantee for the safe and stable operation of the power grid.

[0081] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for explanation.

[0083] Figure 1 The flowchart of the overhead conductor dynamic capacity increase method based on the three-layer structure cooling and capacity increase algorithm. DETAILED DESCRIPTION

[0084] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0085] Example 1

[0086] like Figure 1 As shown, the overhead conductor dynamic capacity increasing method based on the three-layer structure temperature reduction and capacity increasing technology provided in this embodiment includes the following steps:

[0087] Step 1: Continuously measure the ambient temperature along the overhead wires through a distributed temperature monitoring system;

[0088] In this step, a distributed temperature monitoring system (DTS) is used to monitor the ambient temperature of each point along the entire overhead line in real time to obtain the temperature-time series data of each point along the line. The specific process is as follows:

[0089] Optical pulse emission and Brillouin scattering: The BOTDR device in the DTS system emits a short pulse optical signal through one end of the OPGW optical cable. When the optical signal propagates along the optical fiber and encounters temperature or stress changes, Brillouin scattering occurs. Part of the backscattered Brillouin light carries the temperature and strain information along the optical fiber and returns to the BOTDR device.

[0090] Temperature distribution analysis: By analyzing the frequency drift of the returned Brillouin backscattered light, the DTS system can accurately calculate the ambient temperature distribution at each point along the overhead conductor, forming temperature-time series data, which provides a basis for subsequent temperature conversion and current carrying capacity calculation.

[0091] Step 2: Convert the ambient temperature to the conductor temperature and record the temperature-time series at the maximum temperature point

[0092] In this step, the measured ambient temperature is converted into the actual temperature of the conductor, and the temperature-time series of the highest point of the conductor temperature is recorded. The specific process is as follows:

[0093] Simplified heat balance equation: Considering that the heat transfer characteristics of OPGW optical cables and overhead wires in the same spatial position are similar, the wire temperature can be estimated by simplifying the heat balance equation. The heat balance equation mainly considers factors such as solar heat absorption, radiation heat dissipation and convection heat dissipation of the wire.

[0094] Newton iteration method to solve the conductor temperature: Based on the simplified heat balance equation, the Newton iteration method is used to solve the conductor temperature. Through multiple iterations, the actual temperature value of the conductor is gradually approached to ensure the accuracy of the calculation results. Finally, the temperature-time series of the highest point of the conductor temperature is recorded for subsequent analysis.

[0095] Step 3: Calculate the ambient implicit capacity factor based on temperature changes

[0096] In this step, four consecutive temperature sampling values ​​are selected from the temperature-time series of the highest point of the conductor temperature, and brought into the heat balance equation to calculate a set of environmental implicit capacity coefficient vectors. The specific process is as follows:

[0097] Temperature change analysis: Select the temperature data of four consecutive sampling periods based on the sequence of wire temperature changes over time obtained in step 2. Since there are only three unknown parameters in the thermal balance equation, the coefficients of the equation can be determined by four samplings.

[0098] Calculation of environmental implicit capacity coefficient: Substitute the temperature data into the simplified heat balance equation to solve a set of environmental implicit capacity coefficient vectors. The estimated results at each moment are independent of each other, ensuring the accuracy of the coefficient calculation. These coefficients reflect the impact of ambient temperature on conductor temperature and provide an important basis for subsequent current carrying capacity calculations.

[0099] Step 4: Calculate and update the maximum current carrying capacity of overhead wires in real time

[0100] In this step, based on the known environmental implicit capacity factor vector and initial temperature, the maximum current carrying capacity of the overhead wire is calculated in real time and continuously updated. The specific process is as follows:

[0101] Current carrying capacity calculation formula: When the current set of coefficient vectors is known

[0102]

[0103] Where: T max It is the maximum allowable temperature limit of the conductor according to the electric power design regulations of my country. k is the initial temperature. 1,k ,θ 2,k ,θ3,k is the current set of coefficient vectors S k =[θ 1,k ,θ 2,k ,θ 3,k ] T The elements in . ΔT is the mean temperature change over four consecutive sampling periods. This formula is used to calculate the maximum current carrying capacity of the wire in the future under a given initial temperature and coefficient vector.

[0104] Real-time update mechanism: As the ambient temperature changes, the system will continuously collect new temperature data and recalculate the environmental implicit capacity coefficient vector, thereby updating the maximum current carrying capacity of the overhead wires.

[0105] This process ensures that the current-carrying capacity of overhead lines is always within a safe range, while achieving the goal of dynamic capacity expansion.

[0106] The specific form of the heat balance equation

[0107] On overhead transmission lines, the thermal balance equation of OPGW optical cables and conductors can be simplified to the following form:

[0108] OPGW optical cable:

[0109] q co +q ro ―q so =0

[0110] Overhead wires:

[0111] I 2 R(T c )―q cc ―q rc +q sc =0

[0112] Where: I is the current carrying capacity of the conductor;

[0113] R(T c ) is the wire at temperature T c AC resistance under

[0114] q cc and q rc They are the solar heat absorption of OPGW optical cables and conductors;

[0115] q ro and q rc They are the radiation heat dissipation of OPGW optical cables and conductors;

[0116] q co and q cc They are the convection heat dissipation of OPGW optical cables and conductors respectively.

[0117] The specific heat dissipation expression is:

[0118] Radiative cooling:

[0119] q ro =16.03D o ×10 ―8 [(T o +273) 4 ―(T a +273) 4 ]

[0120] q rc =16.03D c ×10 ―8 [(T c +273) 4 ―(T a +273) 4 ]

[0121] Convection cooling:

[0122]

[0123]

[0124] It is assumed that the OPGW optical cable and the overhead wire have the same surface material properties, so the convection heat dissipation coefficient (h(t)) is the same.

[0125] Through the above method, the method can realize real-time temperature monitoring and dynamic capacity increase of overhead wires, ensuring the safe operation and efficient utilization of transmission lines.

[0126] 1. Relationship between sunlight absorption and temperature

[0127] In the environment of overhead wires and OPGW (optical fiber composite overhead ground wire), both are in the same natural space position, so they receive the same sunlight radiation. According to the principles of thermodynamics, sunlight absorption can be expressed by the following formula:

[0128]

[0129] Where, Q is the surface emissivity and ξ is the Stefan-Boltzmann constant;

[0130] D O is the diameter of OPGW;

[0131] T O The temperature measured for OPGW;

[0132] T a is the ambient temperature;

[0133] h is the convective heat transfer coefficient;

[0134] For the conductor, its solar heat absorption can be expressed as:

[0135]

[0136]

[0137]

[0138] Among them, D C is the diameter of the wire; T C is the working temperature of the conductor;

[0139] Since the solar heat absorption conditions of OPGW and conductor are the same, it can be concluded that:

[0140]

[0141] After further simplification, the heat balance equation of the conductor is obtained as follows:

[0142]

[0143] Among them, ρ f is the air density; I is the current; RT C is the resistance of the wire at the operating temperature;

[0144] 2. Relationship between resistance and temperature

[0145] When the standard cross-section of the wire is determined, the relationship between resistance and temperature can be expressed by the following formula:

[0146]

[0147] Among them, T C and T a is a constant related to the wire material and structure, R d is the DC resistance of the wire at the working temperature. The specific expression is:

[0148] R(R c )=βR d

[0149] β=ζIτ

[0150] R d =R 20 [1+α(T c ―20)]

[0151] Among them, R 20 is the DC resistance at 20°C, a is the temperature coefficient (0.00403 for aluminum, 1 / °C), d is the diameter of the aluminum wire (mm), ρ 20is the resistivity of aluminum wire (2.8264×10 8 Ω·m), N is the total number of aluminum wires, λ am is the average twisting rate of aluminum wire.

[0152] 3. Solution of wire temperature

[0153] In order to solve the working temperature (Tc) of the wire, the Newton iteration method can be used. First, define the function:

[0154] f(T c )=D c [(T c +273) 4 ―(T a +273) 4 ]+h(t)D c (T c ―T a )―I 2 R(T c )

[0155] Its derivative is:

[0156] f'(T c )=4D c (T c +273) 3 +h(t)D c ―I 2 R'(T c )

[0157] Through iterative calculation, the working temperature of the wire is finally obtained:

[0158]

[0159] Where n is the number of iterations, and the initial value can be set according to the ambient temperature or historical data.

[0160] 4. Impact of ambient temperature changes on conductor temperature

[0161] By continuously monitoring the ambient temperature, the series of conductor temperature changes over time can be obtained:

[0162] T k+1 =θ1T k +θ2T k―1 +θ3T k―2 +Δt·g(T k )

[0163] (T1, T2, Tk). By substituting these temperature information into the heat balance formula, the following discrete equation can be established:

[0164] Where T is the sampling period, TK+1 is a function related to ambient temperature, current, etc., θ1, θ2, θ3 are the environmental implicit capacity coefficients. By sampling four times in a row, this set of coefficient vectors can be determined:

[0165] S k =[θ1,θ2,θ3] T

[0166] 5. Calculation of maximum current carrying capacity

[0167] Knowing the current coefficient vector s k and initial temperature T K , the maximum current carrying capacity can be calculated according to the following formula in the following period of time:

[0168]

[0169] Among them, T max is the maximum temperature limit allowed for the conductor (usually 70°C), and the mean temperature change of four consecutive sampling periods is used to correct the parameters in the model.

[0170] Through the above algorithm, the dynamic capacity increase of overhead lines can be achieved while ensuring the safety of conductors, thereby improving the operating efficiency and reliability of the transmission system.

[0171] Example 2

[0172] This embodiment provides an overhead conductor dynamic capacity increase algorithm based on a three-layer structure for temperature reduction and capacity increase, including the following steps:

[0173] Step 1: Use the BOTDR device to continuously measure the ambient temperature at each point along the entire transmission line to obtain the ambient temperature-time series at each point along the transmission line, including:

[0174] Step 1.1: In the temperature measurement system, the BOTDR device generates a pulse light of a certain width, which is directed into the optical fiber channel through one end of the OPGW optical cable. When the light pulse propagates in the optical fiber, it will produce Brillouin scattering when it is affected by the sudden sound wave field. A part of the back-scattered Brillouin light carries the temperature and strain information of the optical fiber back to the BOTDR device.

[0175] Step 1.2: By analyzing the frequency drift of the backscattered Brillouin light, the ambient temperature distribution along the entire temperature measuring optical cable can be obtained, that is, the ambient temperature of the overhead line can be measured.

[0176] Step 2: Convert the measured ambient temperature into the conductor temperature, and record and save the temperature-time series at the maximum conductor temperature, including:

[0177] Step 2.1: Use the nonlinear relationship between conductor current and AC and DC resistance to simplify the heat conduction equation of the OPGW and transmission line in the same spatial position. By introducing the heat conduction model, considering factors such as conductor heat dissipation and sunlight heat absorption, the relationship between conductor temperature and ambient temperature is established.

[0178] Step 2.2: Solve the temperature of the wire using the Newton iteration method to obtain the temperature change of the wire under different environmental conditions.

[0179] Step 3: From the temperature-time series at the maximum conductor temperature, select four consecutive temperature sampling values ​​and bring them into the heat conduction model to calculate a set of environmental implicit capacity coefficient vectors. Specifically, the conductor temperature is calculated based on the ambient temperature measured in step 2, and the sequence of conductor temperature changes over time is obtained. The temperature information is brought into the simplified heat conduction model. Since there are only three unknown parameters, the coefficients of the equation can be determined by sampling four times in a row. The estimated results are independent of each other, and a set of environmental implicit capacity coefficient vectors can be solved.

[0180] Step 4: Calculate the real-time maximum current carrying capacity of the overhead line and continuously update it in real time, specifically:

[0181] When the current set of coefficient vectors S is known k =[θ1,θ2,θ3] T and initial temperature T k , in the following period of time, the maximum current carrying capacity can be calculated according to the following formula:

[0182]

[0183] Where, T max According to the power design regulations of my country, the maximum temperature limit of the conductor of the transmission line is allowed; Ta is the ambient temperature; the average temperature change of four consecutive sampling periods is taken. θ1, θ2, θ3 are the coefficient vector S k =[θ1,θ2,θ3] T The elements in .

[0184] The specific method of step 2.1 in this embodiment is:

[0185] Since the heat conduction equation of the OPGW and the transmission line at the same spatial position on the overhead transmission line can be simplified as follows:

[0186] OPGW:

[0187] q co +q ro ―q so =0

[0188] Overhead transmission lines:

[0189] I 2 R(T c )―q cc ―q rc +q sc =0

[0190] In the above formula, I is the current carrying capacity of the transmission line;

[0191] RT C is the temperature T C The AC resistance of the conductor per kilometer;

[0192] q sun,opgw and q sun,cond are the solar heat absorption of OPGW and conductor, both of which are unknown quantities;

[0193] q rad,opgw and q rad,cond They are the radiation heat dissipation of OPGW and conductors;

[0194] q conv,opgw and q conv,cond are the convection heat dissipation of OPGW and conductor respectively; their expressions are:

[0195] Radiative cooling:

[0196] q ro =16.03D o ×10 ―8 [(T o +273) 4 ―(T a +273) 4 ]

[0197] q rc =16.03D c ×10 ―8 [(T c +273) 4 ―(T a +273) 4 ]

[0198] Convection cooling:

[0199]

[0200]

[0201] In the above formula, it is assumed that the OPGW optical cable and the overhead transmission line have the same surface material properties (i.e., the convection heat dissipation coefficient h(t) = 0.0205ρ 0.5 ), since OPGW and transmission lines are in the same natural space, they receive the same solar radiation.

[0202] Therefore, the heat absorption by sunlight has the following relationship:

[0203]

[0204] Substituting into the above formula we can get:

[0205]

[0206] In the above formula, when calculating the current carrying capacity of the conductor, the AC and DC resistance RT c The calculation is relatively complicated. In order to simplify the calculation, the practical conclusion that there is a certain nonlinear relationship between the wire current I and the ratio of AC and DC resistance β is introduced, and the formula is as follows:

[0207] β=ζI τ

[0208] Through the above simplification, the real-time temperature and current carrying capacity of the conductor can be calculated more efficiently, thereby realizing the dynamic capacity increase of the overhead line. When calculating the current carrying capacity of the conductor, the calculation of the AC and DC resistance (R(Tc)) is relatively complicated. However, based on a large amount of practical data, there is a certain nonlinear relationship between the conductor current (I) and the AC and DC resistance ratio (β), which can simplify the calculation process. The specific formula is as follows:

[0209] R(T c )=βR d

[0210] When the standard cross section of the conductor is determined, ζ and τ are both constants, so:

[0211] R d =R 20 [1+α(T c -20)]

[0212] Among them, R d is the DC resistance at operating temperature, R 20 is the DC resistance at 20°C, and the calculation formula is:

[0213]

[0214] Where, (d) is the diameter of the aluminum wire, in mm; ρ 20 is the resistivity of aluminum single wire at 20°C, which is 2.826×10 -8 Ω·m; N) is the total number of aluminum wires; λ am is the average twisting rate of aluminum wire, calculated according to the average pitch ratio of each layer of aluminum wire; a is the temperature coefficient, which is 0.00403 for aluminum wire, and the unit is 1 / ℃.

[0215] The specific method of step 2.2 in this embodiment is: solve the wire temperature T by Newton iteration method C , define the function:

[0216] f(T c )=I 2 R d (T c )―q sun +q rad (T c )+q conv (T c )

[0217] The derivative is:

[0218] f'(T c )=4D c (T c +273) 3 +h(t)D c ―I 2 R'(T c )

[0219] The Newton iteration formula is:

[0220]

[0221] Where n = 1, 2, 3, dots represents the number of iterations. This method can gradually approximate and calculate the conductor temperature of the overhead transmission line.

[0222] The specific method of step 3 in this embodiment is:

[0223] The conductor temperature is calculated based on the measured ambient temperature, and the sequence of conductor temperature changes over time is obtained: T1, T2, dots, T K This temperature information is then fed into the thermal balance formula to further analyze the thermal state and current carrying capacity changes of the conductors. In this way, the current carrying capacity of overhead lines can be monitored and adjusted in real time to ensure that they operate within a safe range, thereby achieving dynamic capacity expansion.

[0224] Since the system contains only three unknown parameters, the coefficients of the equation can be determined by four consecutive samplings. The estimation results at each moment are independent of each other, so a set of ambient temperature influencing factor vectors s can be solved k =[θ1,k,θ2,k,θ3,k]T.

[0225] The specific calculation method of step 4 in this embodiment is as follows:

[0226] Knowing the current coefficient vector s k and initial temperature T K , in the subsequent period of time, the maximum current carrying capacity can be calculated by the following formula:

[0227]

[0228] According to my country's power design specifications, the maximum allowable temperature of the transmission line conductor is T max Set to 70°C. Take the average temperature change of four consecutive sampling periods as:

[0229]

[0230] in, Represents the average temperature during the sampling period; T i represents the i-th sample value; i represents the i-th sample;

[0231] This method has the following advantages: it uses the fiber Brillouin optical time domain reflectometry (BOTDR) technology based on OPGW (optical cable composite ground wire) to continuously monitor the ambient temperature of the transmission line, and combines the three-layer structure cooling and capacity increase algorithm to evaluate the maximum current carrying capacity of the overhead line. Compared with the traditional current carrying capacity evaluation method under the worst environment, it is theoretically more accurate.

[0232] In addition, this method does not require additional temperature sensing equipment, reduces the cost of DTR (distributed temperature sensor) equipment, simplifies maintenance work, improves the reliability and applicability of the system, and can give full play to the real capacity of the transmission line.

[0233] Example 3

[0234] The specific implementation steps of this method are described in detail below. The main process is as follows:

[0235] Step 1: Data collection to obtain the ambient temperature of the overhead transmission line being tested

[0236] 1) Using the Brillouin optical time domain sensor, the incident pulse light is detected by the optical time domain analysis method. Under a specific optical frequency difference setting, the power of the incident pulse light and the excitation light are measured respectively, and then the Brillouin scattered light gain of the optical fiber in the OPGW is calculated. According to the gain distribution, the Brillouin scattered light frequency shift of the optical fiber can be obtained, and then the temperature distribution of the entire optical fiber can be calculated through the linear relationship between the frequency shift and the temperature.

[0237] When the optical fiber is not strained, the frequency shift of the Brillouin scattered light is linearly related to the optical fiber temperature:

[0238] Δf B =C1(T―T0)

[0239] The distance L between any point on the OPGW optical fiber and the incident end of the pulse light can be calculated according to the following formula:

[0240]

[0241] Where c is the speed of light in a vacuum, n is the refractive index of the optical fiber, and Δ t It is the time difference between the excitation light emitted by the OTDR device and the backscattered light received by the OTDR device.

[0242] Step 2: Convert ambient temperature to conductor temperature

[0243] Since the heat balance equation of the OPGW and the transmission line at the same spatial position on the overhead transmission line can be simplified as follows

[0244] OPGW:q co +q ro ―q so =0

[0245] Overhead transmission lines:

[0246] q ro =16.03D o ×10 ―8 [(T o +273) 4 ―(T a +273) 4 ]

[0247] In the formula, I is the current carrying capacity of the transmission line, is the AC resistance of the conductor per kilometer at temperature, and are the solar heat absorption of the OPGW and the conductor, both of which are unknown quantities; and are the radiation heat dissipation of the OPGW and the conductor, and are the convection heat dissipation of the OPGW and the conductor. The expressions are:

[0248] Where I is the current carrying capacity of the transmission line, RT C is the AC resistance of the conductor per kilometer at temperature T;

[0249] qs o , q are the solar heat absorption of OPGW and conductor, both of which are unknown quantities;

[0250] q ro They are the radiation heat dissipation of OPGW and conductors,

[0251] q co They are the convection heat dissipation of OPGW and conductors respectively.

[0252] The expressions are:

[0253] q ro =16.03D o ×10 ―8 [(T o +273) 4 ―(T a +273) 4 ]

[0254] qrc =16.03D c ×10 ―8 [(T c +273) 4 ―(T a +273) 4 ]

[0255] In the formula, OPGW optical cable and overhead transmission line have the same surface material properties (i.e. convection heat dissipation coefficient same);

[0256] ρ f is the air density, kg / m 3 ; T o is the temperature measured by the OPGW sensing fiber, T c is the conductor temperature, T a is the ambient temperature; D o With D c are the diameters of OPGW and conductor respectively. Since OPGW and transmission line are in the same natural space, they are exposed to the same solar radiation, so the solar heat absorption has the following relationship:

[0257] Substituting into the above formula we can get:

[0258]

[0259] In the formula, when calculating the current carrying capacity of the conductor, the calculation of the AC and DC resistance R (Tc) is relatively complicated. However, since the Morgan formula is based on a large number of practices, the practical conclusion that there is a certain nonlinear relationship between the conductor current I and the ratio of the AC and DC resistance β can be used to simplify the calculation process. The formula is as follows:

[0260] β=ζI τ

[0261] When the standard cross section of the conductor is determined, ζ and τ are constants, that is,

[0262] R(T c )=βR d

[0263] R d =R 20 [1+α(T c ―20)]

[0264] Among them, R d is the DC resistance of the conductor at the operating temperature, R 20 is the DC resistance at 20°C.

[0265] Where, d is the diameter of the aluminum wire, mm;

[0266] ρ20 is the resistivity of the aluminum wire, which is 2.8264×10 ―8 (20℃),Ω·m;

[0267] N is the total number of aluminum wires;

[0268] λ am The average twisting rate of aluminum wire is calculated according to the average pitch ratio of each layer of aluminum wire;

[0269] α is the temperature coefficient, aluminum takes 0.00403, T c The temperature of the conductor when it is working;

[0270] In this formula, only the conductor temperature is an unknown variable, which can be solved by Newton's iteration method.

[0271]

[0272] Where N is the number of iterations; n = 1, 2, 3, n is the number of iterations; the conductor temperature of the overhead transmission line can be calculated;

[0273] Step 3: Solve the environmental implicit capacity coefficient vector:

[0274] The conductor temperature is calculated from the measured ambient temperature, and the series of conductor temperature changes over time is obtained: T1, T2, T K , bringing the temperature information into the heat balance formula,

[0275]

[0276] Among them, T k is the conductor temperature at the kth moment, I k is the current at the kth moment, Δt is the sampling period, θ 1,k ,θ 2,k and θ 3,k is the environmental implicit capacity factor;

[0277] Since there are only three unknown parameters, the coefficients of the equation can be determined by sampling four times in a row. Since the estimates at each moment are unrelated, the estimation results are independent of each other, and a set of environmental implicit capacity coefficient vectors can be solved:

[0278]

[0279] Step 4: Calculate the real-time maximum current carrying capacity of overhead transmission lines:

[0280] When the current set of coefficient vectors and the initial temperature T are known K , in the following period of time, the maximum current carrying capacity can be calculated according to the following formula:

[0281]

[0282] In the formula, according to my country's power design regulations, the maximum allowable temperature limit of the conductor of the transmission line is T max Take 70℃.

[0283] Take the average temperature change of four consecutive sampling periods:

[0284] I dynamic =I base +ΔI cooling (T k ,S k )

[0285] Among them, I dynamic Indicates dynamic current carrying capacity; I base Indicates basic current carrying capacity; ΔI cooling (T k ,S k ) indicates; T k Indicates temperature influence; S k Indicates environmental impact.

[0286] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm, characterized in that: The following steps are involved: Step 1: Continuously measure the ambient temperature at each point along the entire transmission line to obtain the ambient temperature-time series at each point along the transmission line; Step 2: Convert the measured ambient temperature into the conductor temperature, and record and save the temperature-time series at the maximum conductor temperature; Step 3: From the temperature-time series at the maximum temperature of the conductor, select a number of consecutive temperature sampling values ​​and bring them into the heat conduction model to calculate a set of environmental implicit capacity coefficient vectors; Step 4: Calculate the real-time maximum current carrying capacity of the overhead line and continuously update it in real time.

2. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm according to claim 1, characterized in that: The step 1 of obtaining the ambient temperature-time series of each point along the transmission line in the following manner specifically includes: Step 1.1: Generate pulsed light through the BOTDR device and direct it into the optical fiber channel through one end of the OPGW optical cable optical fiber; when the light pulse propagates in the optical fiber, it will produce Brillouin scattering when it is affected by the sudden acoustic wave field, and a part of the back-scattered Brillouin light carries the temperature and strain information of the optical fiber back to the BOTDR device; Step 1.2: By analyzing the frequency drift of the backscattered Brillouin light, the ambient temperature distribution along the entire temperature measuring optical cable is obtained, that is, the ambient temperature of the overhead line is measured.

3. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm according to claim 1, characterized in that: The step 2 of obtaining the temperature-time series at the maximum temperature of the conductor in the following manner specifically includes: Step 2.1: Using the nonlinear relationship between conductor current and AC and DC resistance, determine the heat conduction equation of the OPGW and transmission line at the same spatial position, and establish the relationship between conductor temperature and ambient temperature by introducing the heat conduction model; Step 2.2: Solve the temperature of the wire using the Newton iteration method to obtain the temperature change of the wire under different environmental conditions.

4. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm according to claim 1, characterized in that: In step 3, the environmental implicit capacity coefficient vector is obtained in the following manner: the conductor temperature is calculated according to the measured ambient temperature, a sequence of conductor temperature changes over time is obtained, and the temperature information is introduced into the simplified heat conduction model.

5. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm according to claim 1, characterized in that: In step 4, the real-time maximum current carrying capacity of the overhead line is calculated in the following manner: In the formula, S k =[θ1,θ2,θ3] T is the known current set of coefficient vectors; T k is the initial temperature; T max According to the power design regulations of my country, the maximum temperature limit of the conductor of the transmission line is allowed; Ta is the ambient temperature; θ1, θ2, θ3 are the coefficient vector S k =[θ1,θ2,θ3] T The elements in .

6. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm as claimed in claim 3, characterized in that: The specific method of the relationship between the conductor temperature and the ambient temperature in step 2.1 is: The heat conduction equation of the OPGW and the transmission line at the same spatial position on the overhead transmission line is determined according to the following formula: OPGW: q co +q ro ―q so =0 Overhead transmission lines: I 2 R(T c )―q cc ―q rc +q sc =0 In the above formula, I is the current carrying capacity of the transmission line; RT C is the temperature T C The AC resistance of the conductor per kilometer; q sun,opgw and q sun,cond are the solar heat absorption of OPGW and conductor, both of which are unknown quantities; q rad,opgw and q rad,cond They are the radiation heat dissipation of OPGW and conductors; q conv,opgw and q conv,cond are the convection heat dissipation of OPGW and conductor respectively; their expressions are: Radiative cooling: q ro =16.03D o ×10 ―8 [(T o +273) 4 ―(T a +273) 4 ] q rc =16.03D c ×10 ―8 [(T c +273) 4 ―(T a +273) 4 ] Convection cooling: In the formula, the OPGW optical cable and the overhead transmission line have the same surface material properties, the OPGW and the transmission line are in the same natural space position, and the solar radiation received by both is the same; Calculate the solar heat absorption according to the following formula: Substituting into the above formula we can get: Where RT c is the AC and DC resistance; The ratio of conductor current I to AC and DC resistance β is calculated according to the following formula: β=ζI τ When calculating the current carrying capacity of the conductor, the AC and DC resistance RT c Calculated according to the following formula: R(T c )=βR d When the standard cross section of the conductor is determined, ζ and τ are both constants, so: R d =R 20 [1+α(T c -20)] Among them, R d is the DC resistance at operating temperature, R 20 is the DC resistance at 20°C, and the calculation formula is: Where d is the diameter of the aluminum wire; ρ 20 is the resistivity of the aluminum single wire at 20°C; N is the total number of aluminum wires; λ am is the average twisting rate of aluminum wire, calculated according to the average pitch ratio of each layer of aluminum wire; a is the temperature coefficient.

7. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm as claimed in claim 3, characterized in that: The step 2.2 calculates the conductor temperature of the overhead transmission line according to the following formula: Solve the wire temperature T by Newton iteration method C , define the function: f(T c )=I 2 R d (T c )―q sun +q rad (T c )+q conv (T c ) The derivative is: f’(T c )=4D c (T c +273) 3 +h(t)D c ―I 2 R’(T c ) The Newton iteration formula is: Where n = 1, 2, 3, dots represents the number of iterations. This method can gradually approximate and.

8. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm according to claim 1, characterized in that: In step 3, the environmental implicit capacity coefficient vector is calculated specifically in the following manner: The conductor temperature is calculated based on the measured ambient temperature, and the sequence of conductor temperature changes over time is calculated using the following formula: Substitute the temperature information into the thermal balance formula, Continuously sample the coefficients of several deterministic equations and solve a set of environmental implicit capacity coefficient vectors, as follows: Among them, T k is the conductor temperature at the kth moment, I k is the current at the kth moment, Δt is the sampling period, θ 1,k ,θ 2,k and θ 3,k is the environmental implicit capacity coefficient.

9. The method for dynamically increasing the capacity of overhead conductors based on a three-layer structure temperature reduction and capacity increase algorithm according to claim 1, characterized in that: Step 4 calculates the real-time maximum current carrying capacity according to the following formula: According to the maximum allowable temperature of the transmission line conductor, the mean temperature change of multiple consecutive sampling periods is calculated according to the following formula: in, I max Indicates the real-time maximum current carrying capacity; S k is the known current coefficient vector; T k is the initial temperature.

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