Method for protecting temperature of catenary wire of electrified railway

Abstract

The application discloses an electrified railway catenary wire temperature protection method, collects environmental data such as catenary wire current, sunshine intensity, wind speed, wind direction and environmental temperature, calculates the temperature of the wire through a catenary wire thermal circuit model, and starts protection if the temperature of the wire exceeds a protection setting value. The application is safer for the catenary system without increasing measuring devices for measuring the temperature of the catenary wire and other foreign matters, and is simple to realize wire temperature calculation through wire current and environmental data.

Description

Technical Field

[0001] This invention relates to the field of electrified railway power supply technology, and in particular to a method for protecting the temperature of overhead contact wires in electrified railways. Background Technology

[0002] In current line operation, as the load on the traction power supply system gradually increases, overload operation becomes more frequent, leading to occasional overheating of the overhead contact line conductors. The large current generated by prolonged overload operation causes continuous heat accumulation on the conductors, resulting in reduced current-carrying capacity, decreased mechanical strength, and reduced reliability of the overhead contact line system, posing a significant challenge to safe train operation.

[0003] Currently, the protection functions of the overhead contact system, such as distance protection, current protection, and incremental current protection, are all designed for short-circuit faults and cannot provide protection against overload conditions. Patent publication number CN111490521A, "A Method and System for Overheat Protection of Overhead Contact Line Conductors Based on Measured Temperature," describes installing temperature measuring devices on the contact line supports or catenary cables at the substation outlet side to monitor the temperature data of the contact wire and catenary cables, thereby establishing a temperature protection system. However, due to the requirement that the overhead contact system cannot tolerate foreign object intrusion, the method of obtaining conductor temperature by installing temperature measuring devices poses significant safety hazards and is difficult to promote and apply in electrified railways. Summary of the Invention

[0004] The purpose of this invention is to provide a method for temperature protection of overhead contact line conductors in electrified railways. By detecting the current and environmental data of the overhead contact line conductors, the real-time temperature of the conductors is calculated, and temperature protection is provided for the conductors.

[0005] The technical solution to achieve the objective of this invention is as follows:

[0006] A method for temperature protection of overhead contact line conductors in electrified railways, wherein protection is activated if the current temperature of the overhead contact line conductor exceeds a protection setpoint; the current temperature of the overhead contact line conductor... Where, θ n The temperature of the conductor at time n is relative to The temperature rise, It is the ambient temperature of the conductor at time n-1;

[0007] θ n Using recurrence relation It is derived recursively;

[0008] In the formula, θ n-1 This indicates that at time n-1, the conductor is relative to... The temperature rise is given by Δt, where Δt is the time interval between time n and time n-1; τ is the thermal time constant, τ = R. T n-1 ×C T CT For the heat capacity of the conductor, C T = cm, where c is the specific heat capacity of the wire and m is the mass of the wire;

[0009] W I n-1 W represents the Joule heat generated by the conductor at time n-1. I n-1 =(I n-1 ) 2 r,I n-1 Let be the current in the conductor at time n-1, and r be the AC resistance of the conductor;

[0010] W S n-1 W represents the heat absorbed by the conductor due to solar radiation at time n-1. S =α·H n-1 ·D, α represents the absorption of the conductor.

[0011] Rate, H n-1 Let be the solar radiation intensity at time n-1, and D be the diameter of the conductor;

[0012] R T n-1 Let n be the thermal resistance of the wire at time n-1. R c n-1 The convection current of the conductor at time n-1

[0013] Thermal resistance, R r n-1 Let n be the thermal resistance of the conductor at time n-1;

[0014] A represents the perimeter of the conductor's cross-section, and h represents the convective heat transfer coefficient;

[0015] ε represents the emissivity of the conductor, σ sb is the Stefan-Boltzmann constant.

[0016] The advantages of this invention are that it eliminates the need for additional foreign objects such as measuring equipment for measuring the temperature of the contact wires, making the contact wire system safer; and it simplifies the calculation of wire temperature using wire current and environmental data. Attached Figure Description

[0017] Figure 1 This is a thermal circuit model diagram of the overhead contact wire. Detailed Implementation

[0018] This invention discloses a method for protecting the temperature of overhead contact line conductors in electrified railways. The method involves collecting environmental data such as conductor current, solar radiation intensity, wind speed, wind direction, and ambient temperature, and calculating the conductor temperature T using a thermal circuit model of the overhead contact line conductor. If the conductor temperature T exceeds the protection setting value, the protection is activated.

[0019] The thermal characteristics of contact wires are determined by the interaction between the current flowing through them and the environmental conditions, and constantly change by balancing heat generation, heat absorption, and heat dissipation. Heat generation refers to the Joule heat generated by the current flowing through the wires themselves, heat absorption mainly refers to solar radiation, and heat dissipation includes radiative and convective heat dissipation.

[0020] In the temperature calculation of contact wires, this invention establishes a method based on thermoelectric analogy theory, as follows: Figure 1 The thermal circuit model of the conductor is shown.

[0021] Figure 1 In the middle, W I Joule heating is generated by the current flowing through the conductor itself; W S The conductor absorbs heat from sunlight; θ represents the temperature rise of the conductor, i.e., the portion of the conductor's temperature that exceeds the ambient temperature; C T R represents the heat capacity of a conductor, indicating the internal energy absorbed or released by the conductor when its temperature changes by a unit amount. T Thermal resistance is the thermal resistance between the conductor and the surrounding environment, reflecting the ease or difficulty of heat exchange between the conductor temperature and the ambient temperature.

[0022] For the thermal circuit model of the conductor, the following relationship can be obtained based on the basic theory of heat transfer:

[0023]

[0024] Using the thermal time constant τ=R T ×C T Then formula (1) can be further expressed as:

[0025]

[0026] In the formula, R T C represents the thermal resistance in the thermal circuit model; T This represents the heat capacity in the thermal circuit model.

[0027] Further expanding formula (2) into a recursive discrete form:

[0028]

[0029] In the formula, θ n and θ n-1This represents the temperature rise of the contact wire at two consecutive sampling times, where Δt is the time interval between the two sampling times, i.e., the sampling period. By rearranging formula (3), the current value of the wire temperature rise within each sampling period can be obtained:

[0030]

[0031] Formula (4) is the recursive formula for the conductor temperature, which can solve for the conductor temperature from the initial time to any other time, enabling real-time calculation of the conductor temperature. The conductor temperature is the ambient temperature plus the conductor's temperature rise, i.e.:

[0032] T = θ + T amb (5)

[0033] In the formula, T is the calculated temperature of the conductor; θ is the temperature rise of the conductor relative to the ambient temperature; T amb It refers to the ambient temperature.

[0034] In the thermal circuit model, the heat generated is W I The Joule heat generated in a conductor by an electric current is calculated using the following formula:

[0035] W I =I 2 r (6)

[0036] In the formula, I is the current flowing through the conductor; r is the AC resistance of the conductor.

[0037] Heat absorption W S This indicates that the heat absorption of the conductor due to solar radiation can be described according to the CIGRE standard model:

[0038] W S =α·H·D (7)

[0039] In the formula, α is the absorptivity of the contact wire; H represents the solar radiation intensity; and D represents the diameter of the contact wire.

[0040] In traditional thermal circuit models, heat capacity, by definition, represents the internal energy absorbed or released per unit mass of an object when its temperature changes by one unit. The heat capacity C of a conductor... T The calculation formula is as follows:

[0041] C T =cm (8)

[0042] In the formula, c is the specific heat capacity of the conductor; m is the mass of the conductor.

[0043] Thermal resistance of a conductor indicates the ease with which a conductor exchanges heat with its surroundings. Based on the definition of thermal resistance, the formula for calculating it can be derived as follows:

[0044]

[0045] In the formula, ΔT represents the temperature change of the conductor; q represents the heat absorbed or released by the conductor.

[0046] For overhead contact line conductors, heat dissipation methods include convection and radiation. The corresponding equivalent thermal resistance is also categorized into equivalent thermal resistance R, which indicates the ease of convection heat dissipation. c And the equivalent thermal resistance R, which represents the ease or difficulty of radiative heat dissipation. r Furthermore, since convective heat dissipation and radiative heat dissipation are independent, R in the thermal circuit model... c With R r It is a parallel relationship, that is

[0047]

[0048] According to the thermodynamic definition, the heat dissipated by convection is q. c It can be represented as:

[0049] q c =AhΔT (11)

[0050] In the formula, A represents the convective area per unit length of the conductor, i.e., the perimeter of the conductor's cross-section; h represents the convective heat transfer coefficient, the calculation of which involves four dimensionless quantities: Nusselt number (Nu), Reynolds number (Re), Grashof number (Gr), and Prandtl number (Pr), whose calculation formulas are as follows:

[0051]

[0052]

[0053]

[0054]

[0055] In the formula, k f ρ is the thermal conductivity of air; D is the diameter of the wire; r Relative density; V w For wind speed; v f The kinetic viscosity of air is ρ; g is the acceleration due to gravity; T is the velocity of air. film The temperature of the boundary layer air film (T) film =0.5(T+T) amb )); c f The specific heat capacity at constant pressure; μ f Let be the dynamic viscosity of air. In the above formula, air parameters can be calculated using the following formula:

[0056] k f =2.42×10 -2 +7.2×10 -5 T film (16)

[0057]

[0058] v f =1.32×10 -5 +9.5×10 -8 T film (18)

[0059] P r =0.715 - 2.5 × 10 -4 T film (19)

[0060] In the formula, He represents the altitude.

[0061] Convection can be divided into two types: forced convection and natural convection. For the heat dissipation of conductors by convection, equation (11) can be used for calculation.

[0062] For forced convection cooling of the conductor (in windy conditions), the Nusselt number Nu can be calculated using an experimental correlation of the following form:

[0063] Nu = B(Re) n (20)

[0064] In the formula, B and n are both constants, which can be obtained by looking up tables according to the CIGRE standard.

[0065] For natural convection heat dissipation of the conductor (in the absence of wind), the Nusselt number Nu can be calculated using an experimental correlation of the following form:

[0066] Nu = N(GrPr) m (twenty one)

[0067] In the formula, N and m are both constants, which can also be obtained by looking up tables according to the CIGRE standard.

[0068] Therefore, according to the definition of thermal resistance in equation (9), the thermal resistance of convection heat dissipation R c for:

[0069]

[0070] Radiative heat dissipation thermal resistance R r This indicates the ease with which a conductor, due to its own temperature being higher than the ambient temperature, transfers heat outwards via radiation. According to the Stefan-Boltzmann law, the radiative heat dissipation q of a conductor... r It can be described as:

[0071] q r =πDεσ sb [(T+273.15) 4 -(Tamb +273.15) 4 ] (twenty three)

[0072] In the formula, D represents the conductor diameter; ε represents the conductor emissivity (the conductor emissivity is related to the conductor material and surface roughness, and can be expressed as an empirical value); σ sb This is the Stefan-Boltzmann constant, with a value of 5.67 × 10⁻⁶. -8 ;T amb The ambient temperature is given. Therefore, according to the definition of thermal resistance in equation (9), the radiative heat dissipation thermal resistance R is... r It can be represented as:

[0073]

[0074] In the formula, θ represents the temperature rise of the conductor relative to the ambient temperature.

[0075] The specific implementation method is as follows:

[0076] 1. Temperature protection for contact network conductors used for measuring the current of a single conductor.

[0077] The F-line (also known as the positive or negative feeder) of the overhead contact system is a single conductor, and its conductor current can be collected and calculated from the F-line current transformer at the substation. The protection method pre-sets conductor parameters based on the line conditions, such as AC resistance, absorption rate, conductor diameter, specific heat capacity, and conductor mass. The Joule heat W generated by the current on the contact line is calculated based on the conductor current data and formula (6). I The solar radiation intensity H is collected, and the solar heat absorption W of the contact wire is calculated according to formula (7). S The heat capacity of the conductor is calculated according to formula (8). To determine the thermal resistance of the conductor, the convective thermal resistance and the radiative thermal resistance are calculated separately. For the calculation of the convective thermal resistance, firstly, wind speed, wind direction and ambient temperature data are collected and the conductor temperature at the last sampling time is recorded. The Reynolds number Re is calculated using formulas (13) to (15) and formulas (17) to (19). Then, based on the presence or absence of wind speed and the value of Re, the Nusselt number Nu is calculated using formulas (20) to (21). Secondly, the convective heat transfer coefficient h is calculated using formulas (12) and (16). Finally, the convective thermal resistance of the conductor is calculated using formula (22). For the calculation of the radiative thermal resistance, firstly, the ambient temperature is collected and the conductor temperature at the last sampling time is recorded. The radiative heat dissipation of the conductor is calculated using formula (23). Then, the radiative thermal resistance of the conductor is calculated using formula (24). Based on the Joule heat, solar radiation heat absorption, heat capacity, and thermal resistance of the conductor calculated above, the temperature T of line F can be calculated using formula (4), which is the recursive relationship of conductor temperature. F When T F Temperature exceeds the protection setting T 1set.FWhen the F-line temperature protection trips; when T F Temperature exceeds the second-stage protection setting T 2set.F At that time, the F-line temperature protection stage 2 activated. The F-line temperature stage 1 activated to issue an alarm signal, and the temperature stage 2 activated to trip the circuit breaker.

[0078] 2. Temperature protection for contact network conductors used to measure the total current of multiple conductors.

[0079] The T-line of the overhead contact system consists of a contact wire and a catenary wire connected in parallel. Its total current can be collected from the T-line current transformer at the substation. Based on the conductor type and impedance value of the contact wire and catenary wire, the proportion of the contact wire current in the total current, k, and the proportion of the catenary wire current, can be calculated as (1-k). After collecting the total T-line current I, the contact wire current It can be calculated. J =kI, current in the catenary I C = (1-k)I. Similar to the temperature protection of contact wires used for measuring the current of a single conductor, the temperature T of the catenary wire and the contact wire can be calculated separately using the method of this invention combined with environmental data. C and T J When T C Temperature exceeds the protection setting T 1set.C When T... the contact wire temperature protection trips; when T... C Temperature exceeds the second-stage protection setting T 2set.C When T... the contact wire temperature protection stage 2 activates. Stage 1 activates to issue an alarm signal, while stage 2 can be configured to activate either an alarm signal or trip. J Temperature exceeds the protection setting T 1set.J When T... the temperature protection mechanism of the catenary cable is activated; when T... J Temperature exceeds the second-stage protection setting T 2set.J At that time, the catenary cable temperature protection system activated in two stages. The first stage of the catenary cable temperature protection activated by issuing an alarm signal, while the second stage activated by tripping the circuit breaker.

Claims

1. A method for temperature protection of overhead contact line conductors in electrified railways, characterized in that, If the current temperature of the contact wire exceeds the protection setting, the protection will be activated; the current temperature of the contact wire... Where, θ n The temperature of the conductor at time n is relative to The temperature rise, It is the ambient temperature of the conductor at time n-1; θ n Using recurrence relation It is derived recursively; In the formula, θ n-1 This indicates that at time n-1, the conductor is relative to... The temperature rise is given by Δt, where Δt is the time interval between time n and time n-1; τ is the thermal time constant, τ = R. T n-1 ×C T C T For the heat capacity of the conductor, C T = cm, where c is the specific heat capacity of the wire and m is the mass of the wire; W I n-1 W represents the Joule heat generated by the conductor at time n-1. I n-1 =(I n-1 ) 2 r,I n-1 Let be the current in the conductor at time n-1, and r be the AC resistance of the conductor; W S n-1 W represents the heat absorbed by the conductor due to solar radiation at time n-1. S =α·H n-1 ·D, α is the absorptivity of the conductor, H n-1 Let be the solar radiation intensity at time n-1, and D be the diameter of the conductor; R T n-1 Let n be the thermal resistance of the wire at time n-1. R c n-1 R is the convective thermal resistance of the wire at time n-1. r n-1 Let n be the thermal resistance of the conductor at time n-1; A represents the perimeter of the conductor's cross-section, and h represents the convective heat transfer coefficient; ε represents the emissivity of the conductor, σ sb is the Stefan-Boltzmann constant.

2. The method for temperature protection of overhead contact line conductors in electrified railways as described in claim 1, characterized in that, The contact wire is an F-type wire.

3. The method for temperature protection of overhead contact line conductors in electrified railways as described in claim 1, characterized in that, The overhead contact wire is either a contact wire or a catenary wire.

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