Page 674 - Mechatronics with Experiments

660 MECHATRONICS
common than single phase AC motors in applications that require high efficiency and large
power. The most common type of multi phase AC induction motors are as follows.

1. The squirrel-cage type AC induction motor is the most common type of AC motor.
The stator has phase windings, and the rotor is a squirrel-cage type conductor (copper
or aluminum conductor bars) placed in the rotor frame. The conductor bars are short
circuited with end rings. The rotor has no external electrical connection.
2. Wound-rotor AC induction motors differ from the squirrel-cage type in the construc-
tion of the rotor. The rotor has wound conductors. External electrical connections to
the rotor winding are provided via slip rings.
3. Synchronous motors are used for constant speed applications. The motor design is
such that the motor torque-speed curve in steady-state provides a constant speed for a
wide range of load torque. If the load torque exceeds a maximum value, motor speed
decreases abruptly. Compared to the squirrel-cage motors, the synchronous motor
speed shows much less variation as load torque varies.

Stator and rotor cores are made from thin steel disk laminations. The purpose of the
laminated core is to reduce the eddy current losses.
Conductors of the stator winding are covered with insulation material to protect them
against high temperatures. Motor temperature rises primarily as a result of resistance losses,
called IR or copper losses. There are four major insulation material classes: class A for
◦
◦
temperatures up to 105 C, class B for temperatures up to 130 C, class F for temperatures
◦
◦
up to 155 C, and class H for temperatures up to 180 C.
8.5.1 AC Induction Motor Operating Principles
The main components of an AC induction motor are the stator winding (single phase or
three phase) and a rotor with conductors (Figure 8.35). The rotor of a squirrel-cage type AC
induction motor is made of steel laminations with holes in its periphery. The holes are filled
with conductors (copper or aluminum) and short-circuited to each other by conducting end
rings (Figure 8.36). The air gap between the stator and rotor ranges from less than one
millimeter (i.e., 0.25 mm) for motors up to 10 KW power to a few millimeters (i.e., 3 mm)

Encpder incount with easy
access for coupling; and bolt CATALOG # ZDM2334T
isolators for electrical isolation 20HP, 1780 RPM
H-25 1024 ppr,
industrial encoder Encoder coupling
Heavy gauge steel Cast iron endplate Low loss Grease filling
blower housing lamination
Mounting Lifting eye Cast iron
Fan guard brackets ribbed frame Cast iron
NEMA C face
Two N.C. thermal
protectors
Bearing
retainer

230/460 V, 60 Hz
3 phase blower
Precision balance
MS3112E12-10P Oversized, diagonally split, Dual hole foot for high speed Lub-Lok° Locked
receptacle cast iron conduit box mounting seal bearing
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ISR inverter Spike Resistant Wire
Class H Insulation with 200 °C moisture resistant
FIGURE 8.35: AC induction motor components and assembly view. Source: Baldor.