introduction tio Motors

1. Motors
By: The University of Faisalabad

2. Motors
AC-Motors
Parts of an Electric Motor
A. Stator : Stationary Frame
B. Rotor : Revolving Part
The rotary motion in an ac-motor is caused by the fundamental
law of magnetism.
This law states that like poles repel and unlike poles attract.

3. Diagram of an ac-motor
• This shows a three
phase, two pole
stator.
• Where A, B, and C are
the three phases

4. Diagram of the Three Phases
• Poles 1 and 4 are at their greatest magnetic field
at time equal to one, because phase A (red line) is
connected to those poles, and the same for the
other poles when their corresponding phases are
at maximum current magnitude.

5. Synchronous Speed
Speed at which it takes the motor to go one cycle and
one revolution.
S=[120*frequency}]
(# poles)
Example:
For a three-phase, 60 Hertz, 2 pole motor:
S=[120*60]/2=3600 revolutions per minute

6. Single-Phase Motors
• Supplied by single source of ac voltage
• Rotor must be spun by hand in either direction, does
not have a starting mechanism
• Has no starting torque
• Three different types of single-phase motors: split-
phase, capacitor start, permanent split-capacitor,
and shaded-pole motors

7. Resistance Split-Phase Motors
• Has a start winding and a main
winding
• Winding currents are out of
phase by 30 degrees, this
produces a flux field that starts
the motor
• Main winding current (IM) and
start winding current (IS) lags
supply voltage (VL)
• Start (inrush) current is high
• Needs centrifugal starting
switch or relay to disconnect
the start winding (protects it
from over heating)
• Efficiency is between 50-60%

8. Capacitor-Start Motors
• Has the same winding and
switch mechanism
arrangement as split-phase but
adds a short time-rated
capacitor in series with the
start winding
• The time shift phase between
the main and start winding is
close to 90 degrees
• IS leads VL
• Efficiency is between 50-65%
• Capacitor controls the inrush
current

9. Permanent Split-Capacitor Motors
• Winding arrangement is the
same as the capacitor and split-
phase motors
• Capacitor can run continuously,
rated in microfarads for high-
voltage ratings
• No centrifugal switch is needed
• IM lags VL, while IS leads VL
• Efficiency is between 50-70%

10. Shaded Pole Motors
• Simple construction, least
expensive
• Has a run winding only, shading
coils are used instead of the
start winding
• Stator is made up of a salient
pole, one large coil per pole,
wound directly in a single large
slot
• A small shift in the rotor causes
torque and starts the motor
• Efficiency is between 20-40%

11. DC Motors
• Consists of an armature winding and a stator winding
• Armature windings act as the rotor
• Has three different classifications: constant torque,
constant horsepower, or a combination of the two
• Standard industrial dc motors are shunt wounded
• Modifications of the dc motor are: shunt wound,
stabilized shunt exciting fields, compound wound
motors, and series wound motors

12. Armature Voltage Control
• Is used for motor speeds below base speed
• Output torque= T=k*ø*IA
k is machine constant
ø is the main pole flux
IA is the armature current

13. Shunt Field Control
• Is used for motor speeds above base speed
• Horsepower, (HP)= Torque*rpm
5252
Where torque is in lb-ft

14. Brushless DC Motors
• Three phase ac power is converted into dc by
the input side of the motor to charge up a
bank of storage capacitors.
• These capacitors are called the Buss.
• The purpose of the buss is to store energy and
supply dc power to transistors in the output
side as the motor requires the power to start
up.

15. Brushless DC Motors
• It consists of three fuses, six diodes, a choke, and
two capacitors
• The fuses protect the diodes
• The choke protects against line transients
• The motor control may run at very low speeds at
very high torques while drawing little current from
the ac line

16. Brushless DC Motors
• This picture is a
representation of the
encoders (rotor part
of the motor) telling
the corresponding
transistors (stator) to
turn on in order to get
maximum torque from
the motor

17. Picture of a Brushless Motor

18. Standard Modes of Operation
• Motor voltage gradually increases during
acceleration
• Creates a kick start pulse of 500% of full load
amperage for high friction
• Used when necessary to limit current
• Used when motor requires a full voltage start