Electric Machines: Principles, Components, and Operation

Electric Machines: Electromagnetic and Mechanical Principles

From an electromagnetic and mechanical standpoint, the operation of an electric machine is based on two primary circuits:

• Inductor System: Produces the necessary ampere-turns.
• Induced System: Reflects the flux to produce electricity or mechanical energy.

From a mechanical perspective, machines are classified as rotating or static. Rotating machines include dynamos, motors, and alternators, which consist of a fixed part (stator) and a mobile part (rotor), separated by an air gap. Static machines are primarily transformers.

Constitution of a Rotating Machine

A rotating machine consists of an inductor system and an induced system:

• Inductor System: Composed of inductor nuclei (poles) where magnetic field lines enter and exit. Poles consist of a core and polar expansion. Coils are arranged on these cores to generate the magnetic field, while the yoke serves to close the magnetic force lines.
• Induced System: Includes the armature (coils) consisting of conductors where electromotive force is developed.
• Collector: A cylindrical set of copper sectors welded to the ends of the armature winding, rotating with the axis.
• Brushes: Fixed contacts that rub against the collector to collect or feed the induced load.

Electric Motors

Due to the reversibility of electromagnetic effects, DC machines can function as motors. The line voltage results in a counter-electromotive force in the armature, where torque interacts with the flux and the number of turns.

Types of DC Motors

• Independent Excitation: The field winding is connected to a separate DC network from the armature.
• Shunt Excitation: Field winding connected in parallel.
• Series and Compound Motors: Various configurations including long or short shunt connections.

Dynamos

Dynamos operate using permanent magnets or electromagnets. They are categorized by their excitation source:

• Self-Excited: Defined by the formula E = K · Φ · N, where K depends on the number of poles and construction, N is speed in RPM, and Φ is flux.
• Independent Excitation: Characterized by a total separation between the inductor circuit and the armature circuit, where the inductor current is supplied by an external source.