Construction of a DC Generator

Dc generator definition

A DC generator is defined as an electrical device that converts mechanical energy into direct current (DC) electricity. It works according to the principle of electromagnetic induction, when a conductor passes through a magnetic field, it creates a potential difference in the conductor, which, if connected to a closed circuit, causes a current to flow.

Structure of DC generator

Yoke

The yoke is usually made of cast iron or cast steel, depending on the size and weight of the generator.

Yoke use

It holds the magnetic poles of the generator in place and acts as a protective cover for the machine.

It carries the magnetic flux produced by the field winding.

Magnetic poles and field windings

The magnetic poles and field windings are the stationary components of a DC generator that generate the main magnetic field in the machine. They are bolted to the inside and outside of the yoke.

The vertical rod is made of laminated steel or solid cast iron or steel. Lamination reduces eddy current losses in the magnetic poles. The poles are protruding, which means they protrude inward from the yoke.

Armature

The armature is defined as the rotating part of a DC generator that carries the armature winding in which the electromotive force is induced by the magnetic field. It is mounted on a shaft that rotates between the poles.

The armature core is made of laminated steel with grooves on its outer surface. These slots are used to hold the armature conductors insulated from each other and from the core. Lamination reduces eddy current losses in the core.

Armature winding is formed by connecting several coils of insulated copper wire or tape in a specific pattern. There are two types of armature winding: lap winding and waveform winding.

Lap winding: In this type of winding, each coil end is connected to an adjacent commutator segment and another coil end on the same side of the armature.

Waveform winding: In this type of winding, each coil end is connected to a commutator segment that is one pole distance away from the commutator segment and connected to another coil end on the other side of the armature.

Commutator

A commutator is a mechanical device that converts the AC electromotive force induced in the armature winding into the DC voltage at both ends of the load terminal. It acts as a rectifier for DC power generation.

The commutator consists of wedge-shaped segments of hard-drawn or fall-wrought copper that are insulated from each other and from the shaft by mica sheets. Each segment is connected to the armature conductor via a riser or connector.

The commutator segments are arranged in a cylindrical shape on the axis and rotate with the axis. The number of segments depends on the number of coils in the armature winding.

Electric brush

Brushes are made of carbon or graphite blocks that collect current from the commutator segment and transmit it to an external circuit. They also provide electrical contact between the stationary and rotating parts of the generator.

Brushes are housed in rectangular boxes called brush brackets, which are attached to a yoke or bearing bracket. The brush holder has a spring that allows the brush to be pressed against the commutator with appropriate pressure. The brush should be placed on the commutator where the induced electromotive force in the armature conductor changes its direction. These locations are called neutral zones or geometric neutral axes (GNA).

Bearing

Bearings are used to support the rotating shaft of the generator and reduce friction between the shaft and the stationary components. They also allow the shaft to rotate smoothly and evenly.

For small generators, ball bearings are used because they have low friction and high efficiency. For large generators, roller bearings are used because they can withstand heavy loads and shocks.

Bearings must be properly lubricated to ensure smooth operation and long service life of the generator. Lubrication can be done through oil rings, oil baths, grease cups or forced lubrication systems.

Working principle

When the armature rotates in a magnetic field, it induces an electromotive force in the conductor according to Faraday's law of electromagnetic induction.

Type of DC generator

Individually excited DC generator: In this type, the excitation coil is excited by an independent external DC power source, such as a battery or other DC generator.

Self-excited DC generator: In this type, the excitation coil is excited by its own generated voltage after initial magnetization through residual magnetism. There are three subtypes: series winding, split winding and compound winding.

Permanent magnet DC generator: In this type, there is no magnetic field coil, but a permanent magnet that provides a constant magnetic flux.

Apply

• Charge batteries for cars, inverters and solar panels.

• Power traction motors for electric cars, trains and cranes.

• Power supply for arc welding machine, electroplating equipment and electrolytic process.

• Provide power to remote areas where AC transmission is not feasible or economical.

• Supply power to test AC machines and circuits.

Conclusion

Dc generator is an important device for converting mechanical energy into electric energy by electromagnetic induction. It has several components, such as a yoke, pole, field winding, armature, commutator, brush and bearing, which work together to produce direct current. Dc generators can be divided into different types according to their excitation method. Dc generators have a variety of applications in different fields such as battery charging, traction, welding, electroplating, electrolysis and remote power supply.