A dc generator is an electrical machine which converts mechanical energy into direct current electricity. This energy conversion is based on the principle of production of dynamically induced emf. This article outlines basic construction of a DC generator.
A DC generator can be used as a DC motor without any constructional changes and vice versa is also possible. Thus, a DC generator or a DC motor can be broadly termed as a DC machine. These basic constructional details are also valid for the construction of a DC motor. Hence, let’s call this point as construction of a DC machine instead of just ‘construction of a dc generator’.
Table of Contents
Construction of DC Generator
A DC Generator is an electrical device which converts mechanical energy into electrical energy. It mainly consists of three main parts, i.e. Magnetic field system, Armature and Commutator and Brush gear. The other parts of a DC Generator are Magnetic frame and Yoke, Pole Core and Pole Shoes, Field or Exciting coils, Armature Core and Windings, Brushes, End housings, Bearings and Shafts.
The diagram of the main parts of a 4 pole DC Generator or DC Machine is shown below.
The above figure shows the constructional details of a simple 4-pole DC machine.
Magnetic Field System of DC Generator
The Magnetic Field System is the stationary or fixed part of the machine. It produces the main magnetic flux. The magnetic field system consists of Mainframe or Yoke, Pole core and Pole shoes and Field or Exciting coils. These various parts of DC Generator are described below in detail.
Magnetic Frame and Yoke
The outer hollow cylindrical frame to which main poles and inter-poles are fixed and by means of which the machine is fixed to the foundation is known as Yoke. It is made of cast steel or rolled steel for the large machines and for the smaller size machine the yoke is generally made of cast iron.
The two main purposes of the yoke are as follows:-
- It supports the pole cores and provides mechanical protection to the inner parts of the machines.
- It provides a low reluctance path for the magnetic flux.
Pole Core and Pole Shoes
The Pole Core and Pole Shoes are fixed to the magnetic frame or yoke by bolts. Since the poles, project inwards they are called salient poles. Each pole core has a curved surface. Usually, the pole core and shoes are made of thin cast steel or wrought iron laminations which are riveted together under hydraulic pressure. The poles are laminated to reduce the Eddy Current loss.
The figure of pole core and pole shoe are…
The poles core serves the following purposes given below.
- It supports the field or exciting coils.
- They spread out the magnetic flux over the armature periphery more uniformly.
- It increases the cross-sectional area of the magnetic circuit, as a result, the reluctance of the magnetic path is reduced.
Field or Exciting Coils
Each pole core has one or more field coils (windings) placed over it to produce a magnetic field. The enamelled copper wire is used for the construction of field or exciting coils. The coils are wound on the former and then placed around the pole core.
When direct current passes through the field winding, it magnetizes the poles, which in turns produces the flux. The field coils of all the poles are connected in series in such a way that when current flows through them, the adjacent poles attain opposite polarity.
Armature of DC Generator
The rotating part of the DC Generator is called the Armature.The armature consists of a shaft upon which a laminated cylinder, called Amature Core is placed.
The armature core of DC Generator is cylindrical in shape and keyed to the rotating shaft. At the outer periphery of the armature has grooves or slots which accommodate the armature winding as shown in the figure below.
The armature core of a DC generator or machine serves the following purposes.
- It houses the conductors in the slots.
- It provides an easy path for the magnetic flux.
As the armature is a rotating part of the DC Generator or machine, the reversal of flux takes place in the core, hence hysteresis losses are produced. The silicon steel material is used for the construction of the core to reduce the hysteresis losses.
The rotating armature cuts the magnetic field, due to which an emf is induced in it. This emf circulates the eddy current which results in Eddy Current loss. Thus to reduce the loss the armature core is laminated with a stamping of about 0.3 to 0.5 mm thickness. Each lamination is insulated from the other by a coating of varnish.
Construction of DC Generator Conclusion
After going through the above portion of construction of dc generator we can now establish working principle of DC Generator. I hope you enjoy when reading this article, thank you.