Overview
IEC 60287-2-3:2017 is an international standard published by the International Electrotechnical Commission (IEC) that provides a standardized method for calculating the continuous current rating of electric cables installed in ventilated tunnels. This part of the IEC 60287 series focuses specifically on the thermal resistance aspect of such cable installations, addressing both natural and forced ventilation scenarios. It applies across all cable voltage levels and types, offering a practical approach to ensure safe and efficient cable operation under steady-state thermal conditions.
The standard assumes negligible longitudinal heat transfer within individual cables or the tunnel structure itself. Additionally, it requires uniformity in cable type throughout the tunnel and assumes a consistent tunnel cross-section without variation along its length.
Key Topics
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Calculation Method for Current Rating Factor
IEC 60287-2-3:2017 provides essential formulae and calculation procedures for determining the permissible continuous current that cables can safely carry in ventilated tunnel environments.
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Thermal Resistance and Heat Transfer
The method addresses various modes of heat transfer including:
- Radial conduction within cables
- Radiative heat exchange between cable surfaces and tunnel walls
- Convective heat transfer from cables to tunnel air, and from tunnel air to tunnel walls
- Longitudinal convective heat transfer via airflow (natural or forced ventilation)
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Ventilation Types
Both natural and forced ventilation scenarios are covered, allowing flexibility in application depending on tunnel design and environmental conditions.
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Steady-State Conditions
The calculation technique focuses on steady-state thermal behavior, wherein cable load and air temperature remain constant for sufficient duration to achieve thermal equilibrium.
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Assumptions and Simplifications
- Neglects longitudinal heat conduction within cables and tunnel soil
- Assumes all cables within the tunnel are identical
- Assumes unchanging tunnel cross-section along its length
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Reference to Related Parts of IEC 60287
This part complements other sections such as IEC 60287-2-1 (cables in free air) and IEC 60287-2-2 (cables grouped in free air), filling the gap for ventilated tunnel installations.
Applications
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Design of Cable Systems in Tunnels
Ensuring accurate current ratings to prevent overheating and enhance the longevity of cables installed in transportation tunnels, utility tunnels, or mining applications.
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Electrical Power Distribution in Subterranean Environments
Applicable to cable installations in subway systems, road tunnels, and underground power corridors requiring reliable current-carrying capacity assessments under dynamic ventilation conditions.
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Safety and Compliance
Facilitates adherence to international standards and safety norms by providing a globally recognized calculation method for cable thermal management in tunnels.
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Engineering and Planning
Engineers can use the standard to optimize tunnel ventilation designs and cable layouts, balancing effective cooling with operational efficiency.
Related Standards
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IEC 60287-1-1: Current rating equations and calculation of losses
Provides foundational current rating equations applicable across various cable installations.
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IEC 60287-2-1: Thermal resistance of cables installed in free air
Offers methods focused on cables installed overhead or in open air, addressing radial heat transfer without ventilation effects.
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IEC 60287-2-2: Cables in groups running horizontally in free air
Addresses the current rating reduction factors caused by group thermal interactions in horizontal configurations.
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CIGRE Reports on Forced Ventilation of Cable Tunnels
Supplements knowledge on forced ventilation effects explored within the standard.
Keywords: IEC 60287-2-3, cable current rating calculation, ventilated tunnels, electrical cable thermal resistance, forced ventilation, natural ventilation, steady-state cable rating, thermal current rating, tunnel cable installation, IEC electrical standards, cable heat transfer calculation.
Open preview (PDF)Electric cables - Calculation of the current rating - Part 2-3: Thermal resistance - Cables installed in ventilated tunnels
