A DC generator can be described as an electrical device that transforms mechanical energy into electrical energy that is direct current. The energy conversion process can be explained by the idea of producing dynamically induced electromagnetic fields. This article describes the basic structure and operation of an DC generator.
Design and Construction of A DC Machine:
Theoretically, the DC generator could be utilized to operate a DC motor with out any modifications to the structure and vice versa is feasible. Therefore the term “DC generator” is used to describe it is possible to construct a DC generator or DC motor could be described as an DC machine. These fundamental constructional elements can also be used for the creation of the DC motor. Therefore, we can refer to this the the construction of an DC device instead of simply “construction of a DC generator’.
The figure above illustrates the specifics of the construction of a four-pole DC device. A DC machine is comprised of two main components: the stator and the rotor. The basic components of the DC machine are listed in the following.
- Yoke A yoke is the frame that surrounds the DC machine is known as a the yoke. It is constructed of steel or cast iron. It provides not only the strength needed for the entire assembly, but also contains the magnetic flux created from the fields winding.
- Poles as well as pole footwear: Poles are joined to the yoke by bolts, or welds. They support field winding, and pole shoes that are fixed to them. The pole shoes serve two roles; (i) they support field coils, and (ii) disperse the air gap’s flux evenly.
- Field winding These are typically composed from copper. Field coils are wound and then placed on the respective pole, and linked in series. The coils are wound in that, once powered, they form the opposite North as well as South poles.
- Armature core The armature center is the main rotor that is part of an dc machine. It’s cylindrical in form with slots for the winding of the armature. The armature is constructed of thin, laminated circular steel disks to reduce the losses of eddy current. It could be equipped with air ducts that allow for circulation of air in the axial direction to cool functions. The armature is connected onto the shaft.
- Winding of the armature: It is generally a former wrapped copper coil that is positioned within armature slots. The conductors of the armature are separated from each other , and from the core of the armature. The armature winding is wound using one of two methods, lapping winding, or waves winding. Two layer windings, lap windings or waves are typically employed. Double layer winding implies that each armature slot can contain two coils.
- Commutator and brushes The physical connection with the winding of the armature is accomplished through a commutator and brush arrangement. The role of a commutator the case of a DC generator, is to capture the current that is generated by armature conductors. In the case of an dc motor, the it is used to supply current to the conductors of the armature. Commutators are an array of copper segments that are separated from one another. Each segment is equivalent to the number of coils for armature. Each segment is linked with an armature coil. the commutator is connected onto the shaft. Brushes are generally made of graphite or carbon. They are placed on the commutator segments, and then slide onto the segments as the commutator turns, making sure that the contact is maintained to draw or supply current.
Working Principle Of A DC Generator:
In accordance with Faraday’s law of electromagnetic induction when a conductor is put in a magnetic field that is changing (OR the conductor moves within an electromagnetic field) then an electromagnetic force (electromotive force) is induced within the conductor. The strength of the an emf induced can be determined by using the equation of emf in a DC generator. In the event that the wire is fitted with a closed route and the current that is induced will flow through the conduit. In the case of a DC generator field coils, they create an electromagnetic field. The conductors of the armature are rotated in the field. Therefore, an electromagnetically-induced energy field is created within the conductors of the armature. The direction of the current is defined in Fleming’s right left hand rule.
The need for a split ring the commutator
In accordance with Fleming’s right-hand rule The direction of the inducing current is altered when the motion direction of the conductor is changed. Let’s look at an armature that is rotating clockwise, while a conductor to the right side is moving upwards. After the armature has completed one half turn then the motion direction of the particular conductor will reverse to downwards. Therefore, the current direction in each armature conductor will be in alternating. If you take a look at the image above and you’ll see how you can see that direction current changes within an armature conducting. However, with a split-ring connector, the connection to the armature conductors are reversed when current reverses. Therefore, we have unidirectional currents at the terminals.
Types Of DC Generators:
DC generators can be classified into two major categories, namely; (i) Separately excited and (ii) self-excited.
(i) Separately exuberant In this case field coils, they are powered by an outside DC source.
(ii) Self-excited In this case field coils, they are energized by the current generated from the generator. Initial emf production is caused by residual magnetic field in the field poles. The generated emf causes part of the current to flow through fields coils intensifying the field flux and thus increasing the generation of emf. Self-excited DC generators can further be classified into three categories namely
(a) series wound, field winding series along with winding of the armature
(b) (b) Shunt wound field winding the direction of the armature winding
(c) Compound winding – a combination of shunt winding and series