Three-Phase Circuits

Three-Phase Circuits


This is the ninth lesson in the Electrical Theory for Troubleshooters Course. This lesson defines 3-phase AC, describes the components and operating principle of 3-phase generators, and using the formula for frequency, shows how rotor speed and the number of poles is related to frequency.

Module Objectives

  • Define 3-phase AC and differentiate between 3-phase and 1-phase AC.
  • Describe the components and operating principle of a 3-phase generator.
  • Use a sine wave to show how 3-phase voltage changes over time.
  • Explain the relationship between frequency and rotor speed.
  • State and apply the formula for frequency.
  • Describe how rotor speed and the number of poles relate to frequency.


These lessons are excellent for the training of electricians and electronic technicians as well as for the multi-craft training needs of process and manufacturing facilities. The first four lessons in this course cover basic electrical concepts including Ohm’s Law and Kirchhoff’s Law, as well as the use of these laws to determine voltage, current, and resistance in series and parallel circuits.


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