13(c) shows the effect the combined magnetic fields which are dis-
torted and, because lines magnetic flux never cross, but behave like
stretched elastic bands, always trying find the shorter distance between
a north and south pole, the force exerted the conductor, pushing it
out the permanent magnetic field. Contact with the external circuit made through carbon brushes
rubbing the commutator segments. The series motor has the characteristics high
starting torque but speed which varies with load. Figure
10.
Figure 10.
To understand the force, let consider each magnetic field acting alone. The
armature winding rotates between the poles and connected the com-
mutator. electric
motor uses this magnetic force turn the shaft the electric motor. All d.13(b) shows the magnetic field due the perma-
nent magnet which placed the conductor carrying current. 10. current carrying conductor placed
into the field permanent magnet shown Fig. motors
Practical motors are constructed shown Fig. Let
us try understand this action.14.
F BlI
(N)
F 1125
T N
Practical d.Alternating current theory and electrical machines
207
Direct current motors
All electric motors work the principle that when current carrying con-
ductor placed magnetic field will experience force.
This the basic motor principle, and the force dependent upon the
strength the magnetic field the magnitude the current flowing in
the conductor and the length conductor within the magnetic field l.c.c. motors
contain field winding wound pole pieces attached steel yoke.
SERIES MOTOR
The field and armature windings are connected series and consequently
share the same current.13(c) force will
be exerted the conductor push out the magnetic field. Figure 10. Calculate the force the conductor when 15A flows the coil.13(a) shows the magnetic field due the current carrying con-
ductor only. Figure 10. 10.
The following equation expresses this relationship:
F BlI
(N)
where tesla, metres, amperes and newtons.15 shows
FIGURE 10. Direct current motors are classified
by the way which the field and armature windings are connected, which
may series parallel.
Example
A coil which made conductor some 15m length, lies right angles magnetic
field strength 5T.13
Force conductor magnetic field.
(a)
S
N
(b)
(c)
Force F
S
N
