Transformer Core — Transformer Glossary

The laminated magnetic circuit that provides the path for magnetic flux between the primary and secondary windings.

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Transformer Core

The laminated magnetic circuit that provides the path for magnetic flux between the primary and secondary windings.

Transformer cores are constructed from thin laminations (0.23–0.35 mm) of grain-oriented silicon steel, stacked and clamped together. The laminations are insulated from each other (usually by a thin oxide coating or varnish) to reduce eddy currents. Core configurations include: three-limb (standard for three-phase), five-limb (for transport-limited designs), and shell-type (for special applications). The core represents 25–35% of the transformer's total weight and is the primary determinant of no-load losses.

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Core Loss (No-Load Loss)Power dissipated in the transformer core due to hysteresis and eddy currents. Present whenever the transformer is energized, regardless of load.

Core SaturationThe condition where the core's magnetic flux density reaches a level where further increases in magnetizing current produce diminishing increases in flux.

Step-Lap Core JointCore lamination stacking technique where adjacent layers are offset in steps rather than aligned, reducing air gaps at joints.