Chapter 2

Introduction to Rotating Electrical Machines

2.1. Introduction

Rotating electrical machines are electromechanical energy converters. Their economic importance is considerable because they provide almost all the electrical energy. In addition, electrical motors, usually associated with power electronics static converters, play an ever-increasing part in all industrial areas as well as in day to day life.

These machines are made of two distinct parts, one fixed (the stator) and the other one, mobile (the rotor). Those two parts are mainly constituted of ferromagnetic materials whose high permeability enables us to lead the field lines; they are separated by an air space (the air-gap) and carry a set of conductors (the windings) usually made of copper, a material chosen for its good electric conductivity. Those two armatures have different and complementary roles, illustrated by the terms of “field system” and of “armature” which are allotted to them.

2.2. Main notations

– Be: air-gap flux density.

– e: air-gap thickness.

– He: field within the air-gap.

– Hf: field within the iron.

– ii: phase i instantaneous current.

– L: active length of the machine.

– Li: self-inductance of phase i.

– Mij: mutual inductance between phases i and j.

– n: total number of the machine phases.

– ns: number of turns per stator phase.

– nr: number of turns per rotor phase.

– p: number of pole pairs.

– P: active power.

– Pi: instantaneous value of the electrical power.

– Pm: mechanical power. ...

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