Hardware Reference
In-Depth Information
Figure 4.8: Demagnetization curve and load line
4.2 Electric Motor Fundamentals
The electric motor is used to convert electric power to mechanical power. Only
electro-magnetic (EM) motors are considered in this topic. For this kind of
motors, the magnetic
fi
eld is a necessary medium for realizing this conversion
of energy. Electrical, magnetic and mechanical in
fl
uences on the operation of
the motor must be considered in the analysis of electric motors.
Based on the background knowledge in magnetic
fi
elds and its calculation
described in section 4.1, some basic concepts used for analysis of electric ma-
chines and the application of the magnetic circuit method are discussed in this
section.
4.2.1 MMF Generated by Distributed Winding
Let us consider a simple motor construction shown in Figure 4.9. This motor
has a solid cylindrical stator inside a hollow cylindrical outer rotor. Several
conductors are distributed on the surface of the stator. The space interval
between adjacent conductors with the symbol A
+
is 15 degrees. It is the
same for the conductors with symbol A
−
. The distance between the centers
of the conductors A
+
and A
−
is 180 degrees. The stator core and rotor core
are made of steel. The length of the motor is l
c
, and the airgap length is
g. Each conductor is formed by W
c
wires and the current in each wire is
I. To make the analysis simple and concise, both cores are assumed to have
in
fi
nite permeability. This system is considerably more complicated than those
introduced in section 4.1.6. It is of interest to know how the magnetic
fi
eld is
distributed in the airgap and whether this
fi
eld can be determined using the
magnetic circuit method.
