Skin Effect (AC Current Displacement)
The phenomenon whereby alternating current in a conductor is not uniformly distributed across its cross-section but, due to the induced magnetic fields, is pushed toward the outer layer (the 'skin') of the conductor, so that the core carries relatively less current. The effect increases with frequency and conductor diameter, making it mainly relevant at 50 Hz for large cross-sections (typically from roughly 95-120 mm² upward) and strongly relevant at higher frequencies such as in power electronics. The result is a higher effective AC resistance (Rac) than the DC resistance (Rdc) of the same conductor, which is accounted for via a skin-effect factor in the current-carrying capacity calculation for large cables and busbars per IEC 60287.
Bij het dimensioneren van een 400 mm² koperen hoofdvoedingskabel voor een industriële installatie houdt de ontwerper rekening met de skin-effectfactor uit IEC 60287, waardoor de effectieve stroombelastbaarheid lager uitvalt dan een eenvoudige Rdc-berekening zou suggereren.
Bij grote geleiderdoorsneden (bijvoorbeeld 300 mm² en groter) de stroombelastbaarheid uitsluitend baseren op de gelijkstroomweerstand van de geleider, zonder de skin- en nabijheidseffectfactoren mee te nemen — dit leidt tot een te optimistische inschatting van de werkelijke wisselstroombelastbaarheid.
See also
- → IEC 60287-1-1 Skin effect and proximity effect at large cable cross-sections — why AC resistance exceeds DC resistance
- → IEC 61439-6 Busbar trunking systems (IEC 61439-6) — when to use them instead of cable
- → IEC 60865-1 Electrodynamic forces from short-circuit current on busbars and cables (IEC 60865-1) — why support spacing matters as much as cross-section
- → NEMA MG1 Part 30/31 Motor cable length with variable frequency drives — voltage reflection and choosing between a dv/dt and a sine-wave filter
- → IEC 60502-4 (kabeleindsluitingen MS) Stress cone at a medium-voltage cable termination — why the cut-back screen itself creates an electric field problem
- → IEC 60364-5-52 Bijlage B (D1/D2) Current-carrying capacity of buried cables — soil thermal resistivity and grouping, separate from burial depth