Fig. 291.—Formation of eddy currents in a solid bar inductor. On account of its appreciable size, the field is sometimes weaker at one point than another, hence the unequal electromotive forces thus produced will induce eddy currents.
Ques. What should be noted in seeking a remedy for eddy currents?
Ans. It should be noted that eddy currents are due to very small differences of pressure and that the currents are large only because of the very low resistance of their circuits.
Ques. What is the best means of reducing eddy currents?
Ans. Lamination.
Ques. Explain this mode of construction with respect to the bar inductor [fig. 291].
Ans. In the case of a large bar inductor such as shown in [fig. 291], it could be replaced by a number of small wires soldered together only at the ends. The layer of dirt or oxide on the outside of the wires will furnish sufficient resistance to practically prevent the eddy currents passing from wire to wire.
Fig. 292.—Eddy currents induced in a solid armature core. Eddy currents always occur when a solid metallic mass is rotated in a magnetic field, because the outer portion of the metal cuts more lines of force than the inner portion, hence the induced electromotive force not being uniform, tends to set up currents between the points of greatest and least potential. Eddy currents consume a considerable amount of energy and often occasion harmful rise in temperature.