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Why LV winding is placed near core

Short answer

LV is placed near the core because the core is earthed, so only thin insulation is needed; this keeps winding diameters small, reducing copper weight, loss, and leakage reactance. It also leaves the HV winding outside for easy tapping and repair.

Why is the low voltage winding of transformer placed near to the core in core type transformer?

In a core type transformer the LV winding is placed next to the core, and the HV winding is wound concentrically over it, mainly to save insulation.

  core | thin ins | LV | duct | HV

Reasons

  1. Insulation: the core is earthed. The insulation needed between a winding and the core depends on the winding voltage. LV next to the core needs only thin insulation. If HV were next to the core, a thick insulation barrier for the full HV would be needed there as well as between the windings.
  2. Smaller size and cost: less insulation near the core keeps the winding diameters small. Mean length of turn, copper weight, I2RI^2R loss and cost are reduced.
  3. Lower leakage reactance: a smaller radial gap between core and windings means less leakage flux.
  4. Tappings and maintenance: tappings for voltage control are put on the HV winding (it carries less current). With HV outside, tappings are easy to bring out and the winding is easy to reach for repair.

So the order core → LV → HV gives the most economical and practical design.

✓ Answer checked by Claude Sonnet 5.5

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