Page 231 - Fluid Power Engineering

198 Chapter Te n

Current i
Magnetic
Field, H H

Magnetic i
Field, H
i

FIGURE 10-1 Illustration of magnetic field created by current in a conductor.

an electromagnet. In electrical machines cylindrically wound coils are
used in the stator and sometimes in the rotor.
These three basic principles of electromagnetism are illustrated in
Fig. 10-1 and are applicable to generators. 1

Faraday’s Law of Induction
The voltage induced in a conductor is proportional to the rate of
change of lines of magnetic field that pass through the conductor.
It is important to note that for voltage to be induced there must be
cutting of magnetic field. There are several ways to cut magnetic
field. The obvious one is to move the conductor in such a man-
ner that magnetic field is cut. A second method is to fix the con-
ductor, but to generate a magnetic field that changes over time; the
changing magnetic field provides the relative movement that leads
to cutting of magnetic field. A third method is to fix the conductor
and move the magnet or electromagnet, thereby creating the relative
movement.

Lenz Law
Induced voltage from Faraday’s law will cause a current to flow in
a closed circuit in such a direction that the magnetic field, which is
caused by the current, will oppose the change of magnetic field that
induced the voltage.

Lorenz Law or Biot-Savart Law
When a current carrying conductor is placed in a magnetic field in
such a manner that the current is perpendicular to the magnetic field,
then a force is exerted on the conductor. The magnitude of the force is
product of flux density, current, and length of conductor. The direction
of the force is determined by the left-hand rule.