Electrical Machines: D.C. Machine as a Generator

Principles of Generators

• Generators operate on the principle of electromagnetic induction, where a change in magnetic field induces an electromotive force (e.m.f) in a conductor.

Induced e.m.f Magnitude

• The magnitude of the induced e.m.f in a conductor is determined by the rate of change of magnetic flux through the conductor, the strength of the magnetic field, and the number of turns in the coil.

Relative Motion for Inducing e.m.f

• Relative motion between a magnetic field and a conductor is required to induce an e.m.f. This can occur through either the movement of the conductor within a magnetic field or the movement of the magnetic field around the conductor.

Winding in Generators

• The winding formed by connecting a number of conductors together is known as a coil.

Armature Winding in D.C. Machines

• In a D.C. machine, the armature winding is typically kept on the rotor, which is the rotating part of the machine.

Function of the Yoke in D.C. Machines

• The yoke provides mechanical support for the internal parts of the D.C. machine and acts as a protective enclosure. It also connects the poles, ensuring magnetic continuity.

Material Choice for Yoke

• Cast iron is chosen for making the yoke in D.C. machines due to its strength, durability, and magnetic properties, which help in reducing magnetic losses.

Function of the Pole Shoe

• The pole shoe in a D.C. machine serves to spread the magnetic flux over a larger area of the armature, ensuring more efficient magnetic coupling and minimizing saturation effects.

Laminated Poles in D.C. Machines

• Laminated construction is used for making the poles in a D.C. machine to reduce eddy current losses. By laminating the material, the path for the currents is broken up, diminishing energy wastage.

Role of Field Winding

• The field winding in a D.C. machine generates the magnetic field necessary for operation. It can be arranged in series or parallel configurations with respect to the armature to affect the machine’s performance characteristics.