Reluctance
The "resistance" of the magnetic circuit to the passage of flux.
Definition
Reluctance is the magnetic equivalent of electrical resistance: it expresses a magnetic circuit’s opposition to the establishment of a flux. The lower the reluctance, the easier it is to drive the flux, and the better the transformer’s coupling.
It depends on the core geometry (length and cross-section of the magnetic circuit) and the permeability of the material: a long, narrow core, or a poorly permeable material, has a high reluctance. The presence of an air gap — even a tiny one — greatly increases the reluctance, because air conducts flux very poorly.
Minimising reluctance means minimising the magnetising current needed to establish the flux, thereby improving no-load efficiency.
The ABL tip
Poorly clamped core assemblies create micro air-gaps that increase reluctance, no-load current and noise. ABL Transfo carefully clamps and interleaves the laminations to ensure an optimal magnetic circuit.
