Understand the numbers behind electricity.
Start with volts and amperes, then build up to three-phase power and transformers. Each lesson includes a labelled diagram, a worked calculation and a two-question quiz with explanations.
Educational reference only. Examples and calculator results are not approved installation designs, equipment selections or operating instructions.
Original lessons from Power Stations Worldwide. For deeper study, follow MIT OpenCourseWare’s 6.061, Introduction to Electric Power Systems (Spring 2011): network theory, AC power and polyphase networks. These are independent introductory lessons, not MIT materials, a full course replacement or an endorsement.
Voltage, current and resistance
Distinguish volts from amperes, apply Ohm’s law and calculate power in a hypothetical resistor.
Diagram · Calculation · Quiz LESSON 2 OF 6Single-phase versus three-phase
See the 120° phase relationship and compare single-phase and balanced three-phase load-current calculations.
Diagram · Calculation · Quiz LESSON 3 OF 6kW, kVA and kvar
Use the power triangle to distinguish real, apparent and reactive power without confusing them with energy.
Diagram · Calculation · Quiz LESSON 4 OF 6Power factor and load current
Calculate PF = P/S and see why a lower power factor increases current at fixed real power and voltage.
Diagram · Calculation · Quiz LESSON 5 OF 6Three-phase line and phase quantities
Distinguish line-to-line voltage, winding voltage and line current in balanced wye and delta connections.
Diagram · Calculation · Quiz LESSON 6 OF 6Ideal transformer ratios
Calculate voltage and inverse current ratios from winding turns, and check apparent-power conservation.
Diagram · Calculation · Quiz