Hardware Reference
In-Depth Information
Figure 4.17: Ampere's force and left-hand rule.
If a coil is placed in a magnetic
fi
eld, then the Ampere's force acts on both
the effective sides of the coil. However, the direction of the force acting on one
of the sides is opposite to that acting on the other side. These forces form a
torque acting on the coil as illustrated graphically in Figure 4.18.
Figure 4.18: Electromagnetic torque acting on a coil.
In the
fi
gure, r is the distance between the conductors on the rotating shaft,
S the direction of the surface formed by the coil, θ the angle between S and B.
In the electric machine, this kind of magnetic
fi
eld (B) is also called exciting
fi
eld.IfB is evenly distributed, then the torque T can be calculated as,
T =2W
c
lBIr sin(θ),
(4.43)
where, W
c
is the number of turns in the coil winding. It is obvious that the
torque acting on the coil varies with the rotational angle of the coil, and the
torque is maximum when the surface of the coil is vertical to the magnetic
