IEC 60287-1-3:2023

Overview

IEC 60287-1-3:2023 is part of the IEC 60287 series for calculating cable current ratings. This part provides a rigorous method to compute current sharing between parallel single‑core cables and to calculate circulating current losses (including the sheath loss factor) for any number of conductors per phase and in any physical layout. The standard covers the mathematical formulation (including a matrix solution) for phase and sheath currents at a 100% load factor, with worked examples and coefficient tables. It is Edition 2.0 (2023) and updates the symbol list and computational approach from the earlier edition.

Key topics and technical requirements

• Scope and assumptions
  • Method applies to parallel single‑core cables of the same conductor cross‑section (equations can be adapted for unequal sizes).
  • Sheath losses are calculated assuming sheaths/screens are bonded at both ends.
  • Earth return paths are not modelled (their effect is typically small except in special low‑resistivity/low‑earthing‑resistance cases).
  • Calculations are set for 100% load factor.
• Impedance-based formulation
  • Uses conductor self and mutual reactance and resistance to build simultaneous complex equations for conductor and sheath loops.
  • The impedance voltages are eliminated using phase current constraints; results yield complex conductor currents and sheath circulating currents.
• Matrix solution & computational approach
  • The method typically produces a large system of complex linear equations (6·n for n cables per phase in a 3‑phase system) - computer solution is recommended.
  • Includes derivation, a support matrix [Z], support vectors, and iterative procedure guidance where thermal resistance depends on cable losses.
• Loss metrics
  • Computes sheath loss factor (λ′) and circulating current losses per sheath; includes examples, tables (e.g., coefficients α for hollow core conductors) and informative annexes.

Practical applications and who should use it

• Target users:
  • Cable designers, power system planners, utilities, consultants, manufacturers and installation engineers specifying or analyzing parallel single‑core cable systems.
• Typical applications:
  • Determining unequal current sharing in parallel runs.
  • Calculating circulating current losses for thermal rating, efficiency and lifecycle loss costing.
  • Supporting thermal performance assessments for buried cable groups (in conjunction with external thermal resistance calculations).
  • Informing protection coordination and sizing where mutual coupling impacts voltage drop and loss distribution.

Related standards

• IEC 60287 series (general current rating methodology)
• IEC 60287-1-2 - sheath eddy current losses for two circuits in flat formation
• IEC 60287-2-1:2023 - external thermal resistance methods for buried parallel cables (used iteratively with 1-3 results)

Keywords: IEC 60287-1-3:2023, current sharing, parallel single-core cables, circulating current losses, current rating calculation, sheath loss factor, mutual reactance, matrix solution.