Estudo das características de um gerador de corrente contínua

Study of the characteristics of a direct current generator

June 22, 2024 Luciano Bertene

A DC generator is a fascinating electromechanical device. Its design and operation have unique characteristics that differentiate it from other types of generators. By examining these features, we can better understand how the DC generator works and appreciate its importance in various applications. From the complex interaction of magnetic fields to the production of a DC output, studying the functions of a DC generator opens the door to a field of electrical engineering that has shaped the modern world. In this discussion, we will explore the fundamental aspects that define the nature of a DC generator, reveal the secrets behind how it works, and highlight its essential features.

Characteristics

The most important characteristics of a DC generator are:

Idle Features
Internal features
External features

Idle Features

The curve is drawn between the electromotive force generated at idle (E ₀ ), the field current (I _F ) at continuous speed is called OCC. It may also be called the magnetic characteristic or no-load saturation curve. Its character is almost identical for all generators, whether excited or self-excited. OCC curve measurements are obtained in practice by operating the generator at idle and continuous speed and recording the change in source voltage as the field current varies.

Armature Winding Terminology

The armature winding refers to the arrangement of conductors that form the rotating part of the generator, the so-called armature. Several key terms are often used to describe armature winding. First, the armature core refers to the iron or steel structure that supports the winding and provides a path for the magnetic flux.

Internal characteristic (E/I _A )

The curve represents the relationship between the electromotive force generated under load (E) and the armature current (I). _A ) is called the internal characteristic curve – the electromotive force E is less than E ₀ due to the demagnetizing effect of the armature reaction. Therefore, this curve is below the no-load characteristic curve (OCC). This curve cannot be immediately determined experimentally. This is because a voltmeter cannot read the electromotive force. It was created due to the voltage drop in the armature resistance under load. The internal characteristic can be determined from the external characteristic if the winding resistances are known, since both characteristics have a built-in armature feedback effect.

External characteristic curve (V/I _M )

The curve drawn between the terminal voltage (V) and the load current (IL) is called the external characteristic curve. The source voltage V is less than E due to a voltage drop in the armature circuit. This curve is therefore below the inner particle. This characteristic is very important in determining the suitability of a generator for a specific purpose. It can be determined by simultaneously collecting data on the source voltage and load current of a loaded generator (using a voltmeter and an ammeter).

Switching: Conversion of alternating current into direct current

Commutation is the mechanism by which the generator converts the alternating current in the armature windings into a unidirectional current output. This process uses a commutator, a rotating mechanical device made of insulated copper segments. As the armature rotates, the commutator causes the current flowing through the armature windings to change direction at the right time, producing direct current.

Output voltage regulation

The output voltage of a DC generator is also a notable feature. The amount of voltage generated depends on factors such as the strength of the magnetic field, the speed of rotation and the number of turns in the armature windings. The generator output voltage can be controlled by varying these parameters to meet specific requirements.

Self-excitation: Internal generation of a magnetic field

DC generators exhibit a phenomenon called “self-excitation”. This means they can generate their magnetic field without relying on an external source. When a DC generator is started, a small amount of residual magnetism in the windings induces a weak magnetic field. As the armature rotates, this magnetic field is amplified, resulting in increased voltage generation. This self-excitation process allows the generator to maintain its output voltage after starting.