Category: DC MACHINES GENERATORS AND MOTORS

An electromechanical energy conversion device (electrical machine) that converts DC electrical energy or power (EI) into mechanical energy or power (ωT) is called a DC motor. Electric motors are used for driving industrial machines such as hammers, presses, drilling machines, lathes, rollers in paper and steel industry, and blowers for furnaces and domestic appliances such…

The open-circuit characteristic of a DC shunt generator are shown in Figure 11.31. The line OX is drawn in such a way that its slope gives the field winding resistance, i.e., Fig. 11.31  Representation of critical resistance In this case, the generator can build up a maximum voltage OB with a shunt field resistance Rsh. A line OY represents a…

The shunt generator is a self-excited DC generator whose field winding is supplied with the current from the output of the generator itself. However, question arises how it can supply current to the field winding before the voltage being generated? And if the field current is not supplied, how can the voltage be generated? Let…

In compound-wound DC generators, the field is produced by the shunt as well as series winding. Generally, the shunt field is stronger than the series field. When the series field assist the shunt field, the generator is called as cumulative compound-wound generator (see Fig. 11.21(a)). However, when the series field opposes the shunt field, the generator…

A DC generator whose field winding is excited by the current supplied by the generator itself is called a self-excited DC generator. In a self-excited DC generator, the field coils may be connected in parallel with the armature, in series with the armature or partly in series, and partly in parallel with the armature winding.…

A DC generator in which current is supplied to the field winding from an external DC source is called a separately excited DC generator. The flux produced by the poles depends upon the field current with in the unsaturated region of magnetic material of the poles (i.e., ɸ ∝ If), but in the saturated region, the flux remains…

For simplicity, consider only one coil AB placed in the strong magnetic field. The two ends of the coil are joined to slip rings A′ and B′, respectively. Two brushes rest on these slip rings, as shown in Figure 11.10. Fig. 11.10  Direction of induced emf/current in internal and external circuit of rotating coil at different instants…

The resistance between the armature terminals is called armature resistance. It is generally represented by Ra. The value of armature resistance is usually quite small (less than 1 Ω). Armature resistance depends upon the following factors:

The complete assembly of various parts in a scattered form of a DC machine is shown in Figure 11.4. The essential parts of a DC machine are described as follows: Fig. 11.4  Main parts of DC machine

An electromechanical device (electrical machine) that converts electrical energy or power (EI) into mechanical energy or power (ωT) is called a motor. Electric motors are used for driving industrial machines, for example, hammer presses, drilling machines, lathes, shapers, blowers for furnaces, etc., and domestic appliances, for example, refrigerators, fans, water pumps, toys, mixers, etc. The…