Transformer fundamentals

Describe what a transformer changes — voltage, current, impedance reference — and what it conserves.

A transformer trades voltage for current through a turns ratio while conserving apparent power minus losses. Double the voltage, halve the current. Kilovolt-amperes in roughly equal kilovolt-amperes out; the difference is core loss and winding loss.

Impedance matters as much as ratio. A transformer's nameplate impedance (typically 3–6 % for distribution units) sets both the voltage regulation under load and the available fault current on the secondary: lower impedance means stiffer voltage and higher fault duty. That single number links this module to the fault-current work in later paths.

Connection and grounding are separate decisions from ratio. A delta-wye unit provides a neutral and a place to establish a system ground on the secondary, and it shifts phase by 30°, which is why paralleling transformers requires matching vector groups.

Predicting before you experiment is what makes the result stick. There is no penalty for being wrong here.

Load a transformer and observe how ratio, impedance, and loading interact.

1. Set a typical distribution ratio and note the no-load secondary voltage.
2. Increase secondary load and record how secondary voltage changes.
3. Change the nameplate impedance and repeat the loading step.
4. State which impedance value gives better regulation, and what it costs elsewhere.

Describe why a facility with a low-impedance service transformer may have both better voltage stability and a harder equipment-rating problem.