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A transformer moves power between two circuits by a changing magnetic field. It does not create energy, and it does not, in the ideal picture, change frequency. Two or more windings share a core. Alternating current in one winding produces alternating flux. That flux links the other winding and induces a voltage. The course that follows this module is the design sequence: core, windings, insulation, cooling, losses, and the tests that show whether the finished unit matches the rating. This module is only the behaviour those later choices have to serve.
Mutual induction, stated without a design
The primary winding is the one that receives power from the source. The secondary is the one that delivers power to the load. Those names describe the direction of power in a two-winding unit. They are not a statement that one winding is always the high-voltage winding. A generator step-up transformer takes a lower voltage from the machine and delivers a higher voltage to the line. The induced voltage in a winding is set by how fast the flux changes and by how many turns link that flux.
For a sinusoidal flux, the root-mean-square voltage induced in a winding is written E = 4.44 · f · N · B · A. Here f is frequency in hertz, N is the number of turns, B is the peak flux density, and A is the net core area that carries the flux. The factor 4.44 is the root-mean-square value of a sine wave’s derivative, √2 · π, rounded. It is not a tolerance, and it is not a value taken from a purchaser’s specification. If the flux is not sinusoidal, the 4.44 factor does not apply as written. Harmonic voltage and a core pushed into saturation both move the flux away from that clean sine.
An ideal transformer has no resistance, no leakage flux, and no magnetising current. Under that fiction the voltage ratio equals the turns ratio, and the currents are in the inverse ratio, so the power in equals the power out. A real transformer spends some of the voltage on winding resistance and on leakage reactance. It draws a magnetising current even with the secondary open. The core dissipates no-load loss as heat. Those four departures are why a nameplate rating is not the same thing as the ideal equation, and why a later module has to size copper, steel, and cooling instead of stopping at the turns ratio.
The rating inputs this course keeps in view
Four inputs drive everything downstream. Rated power, in kilovolt-amperes, is the continuous throughput the cooling on the nameplate can support at rated voltage and rated frequency. It is not a measure of efficiency, and it is not a short-circuit rating. The voltage ratio states the rated voltages of the windings. Frequency is part of the rating because flux depends on voltage, frequency, and turns together. A unit wound and tested at one frequency is not automatically rated at the other. Phases fix whether the currents and voltages in the equation are line quantities or winding quantities. On a three-phase unit, line current and winding current differ when the winding is connected in delta, and line voltage and winding voltage differ when it is connected in star.
IEC 60076-1 is the general requirement used for power transformers in IEC practice. IEEE C57.12.00 is the general requirement used for many liquid-immersed distribution, power, and regulating transformers in IEEE practice. This module names those documents. It does not assign a clause, a table, or a tolerance. The edition in the contract is the one that later modules and the factory test are judged against. A sentence that says the unit shall meet both families, without naming an edition, has not yet chosen a rule for temperature rise, insulation level, or loss tolerance.
- Rated power belongs to a cooling stage. A second power on the same plate belongs to the fans or pumps printed beside it.
- Rated voltage and frequency together set the flux. Changing one and not the other changes the core duty.
- The ideal turns ratio is the start of a design, not the guarantee. Resistance, leakage, magnetising current, and core loss are still to come.
- Line and winding quantities are not interchangeable. The connection decides which voltage and which current the conductor sees.
Later modules size the core, the windings, the insulation, and the cooling, and they work a numerical example. Those pages stay on the paid plan. Nothing in this module is a design you can issue, and nothing in it replaces the edition named in the contract.
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Module 1 is free. The rest of this course stays on the paid plan. The plan is a one-time payment for 12 months of access, with no auto-renewal. This page does not offer a class or a call.