Transformer
A transformer is a static electrical machine that transfers AC energy between two or more windings by electromagnetic induction, changing voltage and current levels while keeping frequency constant. A laminated silicon-steel core carries the magnetic flux that links the primary and secondary windings, and the voltage ratio follows the turns ratio. Distribution and power transformers step voltage down to supply consumers or up for transmission, while instrument transformers (CT, VT) scale signals for metering and protection. Construction is either oil-immersed or dry-type (cast resin or VPI). Selection parameters include rated power in kVA or MVA, primary and secondary voltages, vector group, impedance voltage, cooling class (ONAN, ONAF, AN, AF), insulation class, tap-changer range, no-load and load losses, and permissible temperature rise. Key standards are the IEC 60076 series and IEEE C57.
Examples
- Oil-immersed 11/0.433 kV distribution transformer for a substation
- Cast-resin dry-type transformer for indoor commercial buildings
- Current transformer (CT) feeding a protection relay