Transformers
Construction, EMF equation, equivalent circuit, losses, efficiency and regulation.
A transformer has primary and secondary windings on a laminated iron core.
EMF equation:
Ideal ratios: . Ratings are given in kVA because losses depend on voltage and current, not on the load's power factor.
Types: core and shell construction; power transformers (efficient at full load) and distribution transformers (designed for best all-day efficiency); auto-transformers; instrument transformers (CTs, PTs).
Sub-topics (3)
Transformer Equivalent Circuit
Model a real transformer with winding resistance, leakage reactance and a magnetising branch.
Transformer Losses and Efficiency
Core losses are constant; copper losses rise with the square of load. Efficiency peaks where they are equal.
Voltage Regulation
The change in secondary voltage from no load to full load, as a percentage of full-load voltage.
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