Week 08
Rotating Magnetic Fields
I revisit magnetic circuits, transformers, and rotating machines around my transformer report and calculation sheets.
What I connect in this unit
Three-phase currents displaced by 120 electrical degrees in time, applied to windings displaced by 120 degrees in space, create an almost constant-magnitude rotating air-gap field. Frequency and pole count set its speed, and reversing phase sequence reverses field direction.
Concept map
- Three-phase currents
- Synchronous speed
- Pole count
- Air-gap field
Technical anchor
Synchronous speed is n_s = 120 f/P rpm, so increasing pole count from two to four at fixed frequency halves the field speed.
How I review it
Place a-b-c and a-c-b current sets on the same time axis and sum their MMF vectors at selected instants to verify direction reversal and near-constant magnitude.
Connection to the full course
Unit 8 of 12. Unit numbers expand the saved report and calculations into a reading sequence rather than an attendance record.