Calculation of cable thermal rating considering non‐isothermal earth surface

Evaluating environmental conditions that trigger fire-fighting equipment is one of the primary design tasks that have to be taken into account when engineering electrical systems supplying such devices. All of the solutions are aimed at, among others, preserving environmental parameters in a building being on fire for an assumed time and at a level enabling safe evacuation. These parameters include temperature, thermal radiation, visibility range, oxygen concentration, and environmental toxicity. This article presents a new mathematical model for heat exchange between the environment and an electric cable under thermal conditions exceeding permissible values for commonly used non-flammable installation cables. The method of analogy between thermal and electrical systems was adopted for modelling heat flow. Determining how the thermal conductivity of the cable and the thermal capacity of a conductor-insulation system can be applied to calculate the wire temperature depending on the heating time t and distance x from the heat source is discussed. Thermal conductivity and capacity were determined based on experimental tests for halogen-free flame-retardant (HFFR) cables with wire cross-sections of 2.5, 4.0, and 6.0 mm2. The conducted experimental tests enable verifying the results calculated by the mathematical model.

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“…By applying the derivative transformation theorem to the Laplace transform, it can be started that [26,27]:…”

Section: Modelling the Heating Up Of Electrical Cablesmentioning

confidence: 99%

A Method for Determining the Impact of Ambient Temperature on an Electrical Cable during a Fire

Perka

Piwowarski

2021

Energies

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“…Kennelly's hypothesis leads to the definition of the image method, which is useful to calculate the temperature growth at any point of the soil. The cable system is considered an infinitely long cylindrical heat source buried in a uniform medium, and it is not possible to consider the convective boundary conditions at the soil surface [9,21]. The heat source + .…”

Section: Non-infinite Dimension Of the Soilmentioning

confidence: 99%

“…The effect of a non-isothermal ground surface is considered in [21] by adding a fictitious layer that moves the isothermal surface in the direction opposite to the cable location, as an application of the additional wall method shown in [22]. The adaptation proposed in the paper is based on applying the Fourier transform for converting the heat transfer problem from two dimensions to one dimension.…”

Section: Non-infinite Dimension Of the Soilmentioning

confidence: 99%

“…In the transformed Fourier domain, the heat transfer coefficient is no longer dependent on soil thermal resistivity, installation depth, and cable dimensions; it depends only on the physical properties of the air and the heat that is dissipated by the cable. To model the non-isothermal soil surface, [21] proposed an accurate method in which the heat transfer coefficient may be computed in the Fourier domain. The application of this procedure was possible because, after the transformation in the Fourier domain, the heat transfer coefficient depends only on the air physical properties and the heat dissipated by the cable, and does not depend on cable dimensions, cable depth, and soil thermal resistivity ρ.…”

Section: Non-infinite Dimension Of the Soilmentioning

confidence: 99%

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Thermal Assessment of Power Cables and Impacts on Cable Current Rating: An Overview

2020

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The conceptual assessment of the rating conditions of power cables was addressed over one century ago, with theories based on the physical and heat transfer properties of the power cable installed in a given medium. During the years, the evolution of the computational methods and technologies has made more powerful means for executing the calculations available. More detailed configurations have been analysed, also moving from the steady-state to dynamic rating assessment. The research is in progress, with recent advances obtained on both advanced models, extensive calculations from 2D and 3D finite element methods, simplified approaches aimed at reducing the computational burden, and dedicated solutions for specific types of cables and applications. This paper provides a general overview that links the fundamental concepts of heat transfer for the calculation of cable rating to the advanced solutions that have emerged in the last years.

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“…However, radiative heat transfer at the soil-air interface studied by [35][36][37] shows that presence of radiation heat transfer in the evolution of temperature in underground cable systems. On the contrary, radiative heat transfer is unlikely to occur in water as it has higher absorption of radiation at wavelengths of infrared range [38,39].…”

Section: Underground and Submarine Power Cablesmentioning

confidence: 99%

Ampacity and thermal equivalent modeling of subsea power cables for long distance power transmission and optimization

Duraisamy¹

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One of the defining aspects of life in the modern world is the convenience of access to a dependable and plentiful supply of electricity. This essential utility is delivered to consumers from power generating stations via an extensive and intricate network of cables. Submarine power cables are becoming increasingly important to modern power transmission strategies. There has been a large amount of recent investment in projects such as offshore wind farms and international "megagrid" initiatives, of which submarine power cables are essential components.The installation and maintenance costs of such buried cables are far higher than the overhead lines due to the complexity involved. The cable construction and cooling system for the cables are not interchangeable with their overhead counterparts. The maximum allowable cable conductor temperature is limited to avoid cable failures. The maximum current carrying capacity (ampacity) of power cables depends on the heat transferability of its surrounding medium. Submarine power cable ampacity is calculated conventionally following the international standards defined for underground cables. This conservative approach results in the system over design and under-utilization of the cable capacity. In reality, the thermal behavior of submarine environments differs significantly from its underground counterpart as the porous sediments are constantly water-saturated.The research aims to model the electrical and thermal characteristics of such long distance cables for accurately determining the effect of the factors that influence the ampacity and optimize the power flow. The cable ampacity analyses were

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Calculation of cable thermal rating considering non‐isothermal earth surface

Cited by 18 publications

References 14 publications

A Method for Determining the Impact of Ambient Temperature on an Electrical Cable during a Fire

A Method for Determining the Impact of Ambient Temperature on an Electrical Cable during a Fire

Thermal Assessment of Power Cables and Impacts on Cable Current Rating: An Overview

Ampacity and thermal equivalent modeling of subsea power cables for long distance power transmission and optimization

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