The turning force torque experienced the rotor produced induc-
ing emf into the rotor conductors due the relative motion between
the conductors and the rotating field. In
small motors the rotor cast aluminium. The rotating
magnetic flux cuts the conductors the rotor and induces emf the
rotor conductors Faraday’s law, which states that when conductor cuts
or cut magnetic field, emf induced that conductor, the mag-
nitude which proportional the rate which the conductor cuts or
is cut the magnetic flux.
Stator
F
Rotor
(a)
Stator
F
Rotor
(b)
.18. Better starting and quieter
running are achieved the bars are slightly skewed. 10. This type rotor is
extremely robust and since there are external connections there no
need for slip rings brushes. The cage rotor consists laminated cylinder silicon steel
with copper aluminium bars slotted holes around the circumference
and short circuited each end the cylinder shown Fig.16(b). This induced emf causes rotor currents flow
and establish magnetic flux which reacts with the stator flux and causes
a force exerted the rotor conductors, turning the rotor shown in
Fig.16
Segment taken out induction motor show turning force: (a) construction induction motor
and (b) production torque magnetic fields. 10.
Rotor construction
There are two types induction motor rotor the wound rotor and the
cage rotor.17.
A machine with the characteristic shown curve (a) Fig. 10.16(a), rotating magnetic flux produced. The torque produces rotation the
same direction the rotating magnetic field.Alternating current theory and electrical machines
209
shown Fig. 10.18 would
not start since the load torque greater than the machine starting torque.
FIGURE 10. 10. machine fitted with cage rotor does suf-
fer from low starting torque and the machine must chosen which has
a higher starting torque than the load, shown curve (b) Fig
