EC-12.2 Transformers
You can explain how a transformer works from the changing flux linking two windings, use the turns ratio to move an impedance from one side to the other, read an equivalent circuit, and account for the two kinds of loss and the efficiency they set.
Before:EC-2. Electromagnetics and Transmission LinesEC-6. Semiconductor Devices and Device Models
The transformer is the reason alternating current won the argument about power distribution, and it is the simplest machine in this module because nothing moves. That makes it the right place to meet magnetic circuits, referred impedances and the loss-and-efficiency reasoning that the rotating machines then reuse without re-explaining.
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The ideal transformer, from the flux that links both windings
A changing current in one winding produces a changing flux in the core, which induces a voltage in the other. The voltages are in the ratio of the turns, and the currents in the inverse ratio.
NPTEL: Electrical Machines I (IIT Kharagpur) · CourseReferring an impedance across the ratio
A load on the secondary appears on the primary multiplied by the square of the turns ratio. That single result is what makes a transformer a matching device as well as a voltage changer.
NPTEL: Electrical Machines I (IIT Kharagpur) · CourseThe practical equivalent circuit
Winding resistance, leakage that does not link both coils, the current needed to magnetise the core and the loss in the core are added to the ideal model. Each element corresponds to a physical effect.
NPTEL: Electrical Machines I (IIT Kharagpur) · CourseThe two tests that find those elements
An open-circuit test at rated voltage finds the core loss and the magnetising path. A short-circuit test at rated current finds the winding resistance and leakage. Between them the model is complete.
NPTEL: Electrical Machines (IIT Delhi) · CourseLosses, efficiency and the load that maximises it
Core loss is nearly constant with load and copper loss grows as the square of current. Efficiency is highest where the two are equal, which is why a transformer is not sized for its peak load alone.
NPTEL: Electrical Machines (IIT Delhi) · CourseRegulation, and the voltage that sags under load
The output voltage falls as load increases, because of the winding resistance and leakage. Regulation is that fall expressed as a fraction, and it is what a supply agreement is actually about.
NPTEL: Electrical Machines I (IIT Kharagpur) · Course
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