Overview
A transformer is where coils and wire meet. Two or more insulated windings share a changing magnetic field. Energy can move from one winding to another without a direct electrical connection between them—except in an autotransformer, where part of the winding is shared.
Primary and secondary
The winding connected to the source is the primary. A winding supplying a load is a secondary. Transformers may have several secondaries, center taps, or windings that can be connected in series or parallel.
Turns ratio
Current ratio
Voltage and current trade places through the turns ratio while apparent power remains approximately the same, apart from losses.
What transformers do
- Step AC voltage up or down.
- Provide galvanic isolation.
- Match impedances.
- Couple audio and RF signals.
- Measure large currents and voltages through CTs and PTs.
- Create multiple isolated supplies.
- Connect three-phase systems in wye, delta, and other arrangements.
Why changing current matters
A transformer works because changing current creates changing magnetic flux, and changing flux induces voltage in another winding. Steady DC does not continuously induce secondary voltage.
Families
| Type | Main purpose |
|---|---|
| Power / distribution | Transfer useful power between voltage levels. |
| Isolation | Separate input and output electrically. |
| Autotransformer | Change voltage using a shared winding; compact but not isolated. |
| Audio / RF | Couple signals and match impedance. |
| CT / PT | Scale current or voltage for metering and protection. |
Continue
Basics covers ratios, VA, regulation, and loading. Windings & Cores connects conductor size and insulation to magnetic design. Power & Distribution moves into single- and three-phase systems. Isolation & Auto distinguishes isolated from shared-winding designs. Signal & Instrument covers audio, RF, CTs and PTs. NEC & Installation is aimed especially at electricians. History and advanced theory follow on pages 0007 and 0008.