Generators are devices that convert mechanical energy into electrical energy. The generators are normally used as a backup supply when power from the grid is unavailable. Generators are classified based on the output they provide into two categories: AC generator and DC generator.
In this article, we try to understand about DC generator. How does it work? what is its construction, its types, etc, etc?
DC Generator is the electrical machine that converts mechanical energy into electrical energy ( basically into direct current). When the conductor cuts the magnetic field, an emf is generated based on the principle of Faraday’s electromagnetic induction law.
Parts in DC generator
Poles are used to place field windings over them to produce a magnetic field. These poles are made up of steel sheets and are laminated to reduce eddy current loss.
Yoke or frame
Yoke is the outer structure of the DC generators. It is a hollow cylinder made up of cast iron or steel. An even number of the pole is bolted to the yokes. Yoke acts as a protecting cover to the generator.
Pole shoes are used to support field coil.
The armature is the rotating part of the DC generator. The armature consists of two-part the armature core and the armature winding.
A laminated steel cylinder mounted on the shaft is called an armature core. The laminations are insulated from each other and the purpose of using these laminations is to reduce eddy current loss. The armature core has slots on its outer surface.
Armature winding is the connected arrangement of conductors where insulated conductors are put in the slots of the armature core. Armature windings are of two types:
- Lap winding
In lap winding, the ends of each armature coil are connected to the commutator in such a way that the total number of parallel paths and the total number of poles are equal in number. For lap winding A = P
- Wave winding
In wave winding, only two parallel paths are provided between positive and negative brushes. For wave winding A = 2.
AC is produced in the rotating coil. The commutator is needed to change AC into DC in the external circuit. The commutator is made from hard-drawn copper segments which are insulated from each other. Each segment is connected to the end of the armature coil.
Brushes are mounted on the commutator. Brushes collect the current from the armature coil. Current produced in the armature winding is passed on to the commutator and then to the external circuit by the means of brushes.
DC generator works on the principle of Faraday’s law of electromagnetic induction. When a current-carrying conductor is placed in the varying magnetic field, an emf is induced in the conductor. The magnitude of emf can be measured using the emf equation of the generator.
An induced current flows in the path if the conductor has a closed path. The field coils produce emf and the armature conductors are converted to the field in the generator. Therefore, inside the armature conductors, an electromagnetically induced emf is produced. The direction of induced current can be determined by fleming’s left-hand rule.
The e.m.f equation for DC generator is:
E = nφPZ/A
n = speed of rotation of armature in r.p.s ( revolution per second )
φ = Flux per pole in webers
P = total numbers of poles
Z = total number of the conductor in the armature
A = number of parallel within the armature
Types of dc generator
The DC generator can be classified based on excitation methods namely self-excited and separately excited DC generator.
In this type of generator, the field coils are energized by a separate DC source.
In this type of generator, the field coils are energized by the machine itself. Self-excited generators are further classified as:
- Series wound
- Compound wound
Read More: Various types of dc generator