Isolation transformer

A transformer sold for isolation is often built with special insulation between primary and secondary, and is specified to withstand a high voltage between windings.

Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers, medical devices, or laboratory instruments.

A grounded Faraday shield between the primary and the secondary greatly reduces the coupling of common-mode noise.

Differential noise can magnetically couple from the primary to the secondary of an isolation transformer, and must be filtered out if a problem occurs.

An example is the Austin transformer for the power supply of air-traffic obstacle warning lamps on radio antenna masts.

Without the isolation transformer, the lighting circuits on the mast would conduct radio-frequency energy to ground through the power supply.

A 230 V isolation transformer
Cross section diagram through a small transformer showing inner winding, dielectric barrier, shield, and outer winding
A simple 1:1 isolation transformer with an extra dielectric barrier and an electrostatic shield between primary and secondary. The grounded shield prevents capacitive coupling between primary and secondary windings.
Halo TG110-S050N2RL 10/100BASE-TX Ethernet pulse transformer in SO-16 package