The object of the field magnet is to produce an intense magnetic field within which the armature revolves. It is constructed in various forms, due in a large measure to considerations of economy, and also to the special conditions under which the machine is required to work.
Electromagnets are generally used in place of permanent magnets on account of: 1, the greater magnetic effect obtained, and 2, the ability to regulate the strength of the magnetic field by suitably adjusting the strength of the magnetizing current flowing through the magnet coils.
The field magnet, in addition to furnishing the magnetic field, has to do duty as a framework which often involves considerations other than those respecting maximum economy.
The Make Up of a Field Magnet.—In construction, the electromagnet, used for creating a field in which the armature of a dynamo revolves, consists of four parts:
1. Yoke; 2. Cores; 3. Pole pieces; 4. Coils.
These are shown assembled in figs. 201 to 204.
Ques. What is the object of the yoke?
Ans. The yoke serves to connect the two “limbs,” that is, the cores and pole pieces, and thus provide a continuous metallic circuit up to the faces of the pole pieces.
Ques. How is the yoke constructed?