Transcript E2 Subject1

E2 Motors and Motor Starting
(Modified)
#1 Fan Motors
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Basic Electric Motor
• Stator
– Stationary electromagnet
• Rotor
– Rotating magnet
• Movement of the rotor
– Rotates by repulsion and attraction of stator
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Exploded View
of Motor
STATOR
(with windings)
ROTOR
(with shaft)
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Two-pole stator motor
Stator
Rotor
(Stationary)
(Rotates)
N
S
N
S
Polarity reverses
(N to S) on stator
+_
N
S
Stator repels &
attracts rotor into
motion
When stator is energized the
rotor will make a half turn
with each half of current cycle
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Second half of cycle
+ _
S
N
S
N
Stator continues
motion by repelling
and attracting
S
N
Polarity reverses
(N to S) on stator
The alternating current now
changes direction
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Motor Starting
All motors need a phase shift to start rotation
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Motor Tries to Start
Stator
N
Equal and
opposite
attraction
S
Rotor
Equal and
opposite
attraction
Power applied
to stators
Opposite attraction
Rotor will NOT move
N
S
Stator
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A Phase Shift is Needed
Stator
N
A phase shift
causes rotation
S
Rotor
N
This phase shift can be
caused by:
A shaded pole
A start winding
A capacitor
3 separate phases
A magnetic field is
formed at a slightly
different angle
S
Stator
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Shaded-Pole Motors
• Low starting torque
• Low efficiency
• Low cost
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Examples of Shaded-Pole Motors
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Starting a Shaded-Pole Motor
• Each pole has a copper band attached
– The shaded-pole provides the phase shift
needed to start rotation
• Usually impedance protected
– A stalled blade will not cause burned windings
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Rotation toward the Shaded Pole
N
S
N
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S
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Shaded-Pole Motor Wiring
BLACK
GREEN
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LINE
GROUND
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Changing Motor Rotation
• Shaded-pole motors can be reversed:
– First, turn stator around
– Second, turn blade around
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Interesting Motor Fact
Motor efficiency:
A 100 watt 50% efficient motor will put out
50 watts of work, and 50 watts of heat.
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Shaded-pole
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C-frame Motor
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To Reverse
Rotation
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Turn Stator
Around
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Turn fan blade
around
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Rotation is now
reversed
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Multi-speed Shaded-Pole Motors
• Speed depends on winding resistance
– Low speed: most resistance
– High speed: least resistance
• Motor speed is based on where power is
connected into the winding
Common
High
Speed
Medium
Speed
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Low
Speed
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Shaded-Pole 3-Speed Motor Wiring
Common Wire is White (115v) or Black (230v)
BLACK
BLACK-HIGH
LINE
LINE
BLUE-MED
RED-LOW
GREEN
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Split Phase Motors
• Have two separate windings, a run and a
start
• The start winding provides the phase shift
for starting
• More efficient and have more torque than
shaded pole motors
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A Split Phase Motor is a
Two-pole stator motor …
with Start Windings added
Start
Run
Run
TO RUN
WINDINGS
TO START
WINDINGS
R
Start
C
S
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Start & Run Winding Resistances
C
S

Ω
Ω
R
VAC
DC
COM
V/
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Windings of a split phase motor
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Split Phase Motor
This motor needs power to
the start winding to start
C
S
START
WINDING
This motor needs
a start winding for
a phase shift
R
RUN WINDING
This motor
needs power to
the run winding
to run
LINE
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Fan Motor with Centrifugal Switch
• A mechanical switch is used to de-energize the
start winding
• The switch is attached to the motor shaft
• After the motor starts, centrifugal force opens
the switch
• The start winding circuit remains open as long
as the motor is running
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Split Phase Motor with Centrifugal Switch
Centrifugal switch opens start winding
C
S
START
WINDING
R
RUN WINDING
LINE
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Fan Motor with Centrifugal Switch
• The next slide is a picture of a fan motor with
the motor cover removed
• The centrifugal switch is attached to the motor
shaft
• The switch contacts are attached to the end
bell (motor cover)
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Motor with Centrifugal Switch
Start winding
energized
Motor Speed
Increases
Weights shift,
disk moves back
Before starting,
disk pushes bar,
closing contacts
Contacts Open
From Run
Winding
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To Start
Winding
Centrifugal
Disk
Switch
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Permanent Split Capacitor Motors
• A run capacitor is “permanently” wired into
the start winding circuit
• The capacitor provides partial voltage to
the start winding, during start and run
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PSC Motor with run capacitor
Low Starting Torque
Low to Medium Cost
Medium Efficiency
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Split Phase Motor + Run Cap = PSC Motor
C
S
R
Run Capacitor
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Interesting Motor Fact
A PSC motor with a shorted run capacitor
will act like an overloaded motor.
A PSC motor with an open run capacitor
will not start.
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PSC Motor Wiring Diagram
BLACK
LINE
BROWN
CAPACITOR
GREEN
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Motor Speeds
• The synchronous speed of a motor can be
determined by the number of its poles.
• The more poles, the lower the speed.
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Calculating ‘Synchronous’
Motor Speeds
• One cycle has two current flow reversals
• 60 cycles has 120 flow reversals
• Speed = (60 Hz x 120 reversals) ÷ Poles
Example: 7200 ÷ 2 Motor poles = 3600 RPM
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Two Pole Motor Windings
Courtesy of
Copeland
7200  2 = 3600 RPM
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Four Pole Motor
1
1
2
2
4
7200  4 = 1800 RPM
4
3
3
Courtesy of
Copeland
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Actual ‘Rotor’ Motor Speed
• Slippage is the loss of speed from motor load
• The ‘rotor’ speed is less than the
‘synchronous’ speed.
Common motor speeds:
Synchronous: ROTOR:
2 Pole motor:
3600
3450
4 Pole motor:
1800
1750
6 Pole motor:
1200
1050
8 Pole motor:
900
850
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Multi-Speed PSC Motors
• Actually they are “Multi-horsepower”
• The windings are tapped so the motor is
weaker, running slower under load
• Example of a 3-speed 1/3 HP motor:
– High speed is 1/3 HP
– Medium speed is 1/4 HP
– Low speed is 1/6 HP
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Single-Speed PSC Motor
C
S
R
Run Capacitor
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Single-Speed PSC Motor
C
S
R
Run Capacitor
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Multi-speed PSC Motor
High Speed
RH
C
Medium Speed
RM
S
R
Low Speed
RL
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3-Speed PSC Motor Wiring Diagram
BLACK
BLACK-HIGH
LINE
LINE
BLUE-MED
RED-LOW
BROWN
GREEN
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Interesting Motor Fact
• Multi-speed motors must be under a load
to change speeds
– Example: A multi-speed blower removed from
the blower compartment will run at high
speed, no matter which speed tap is used
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PSC 3-speed Motor
Leads for
changing motor
rotation
Run
Capacitor
Leads
Common Wire
Low
Speed
(red)
Medium
Speed
(blue)
High
Speed
(black)
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Three Phase Motors
• High starting torque
• High efficiency
• Medium to high cost
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Three Phase Motors
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Three Phase Motor Starting
• No start windings or capacitors needed
• High torque because the windings are
120° out of phase
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3Ø Motor – Wye Connections
L1
T1
208 V
208 V
T3
T2
L2
208 V
L3
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3Ø Motor – Delta Connections
T1
L1
240 V
T3
240 V
T2
L2
240 V
L3
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Describing Common Motors
• Motor descriptions include the following
information:
– Type
– Enclosure
– Mounting
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Common Motor Types
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Motor Enclosure Types
•
•
•
•
Open
Dripproof
Totally enclosed
Totally enclosed fan cooled
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Open Enclosure Types
Totally Open
Open Dripproof
Note: Prevents direct entry of moisture
Clean and Mostly Dry
Locations
Clean and Dry Locations
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Enclosed Type Motors
Totally Enclosed
Air Over
Cooling from system air
passing over the motor body
Totally Enclosed
Fan Cooled
Cooling from fan forced air
passing over the motor body
Totally Enclosed are good for wet and dirty conditions
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Motor Mounting
• Some of the more common mounts:
– Rigid
– Cradle
– Belly band
– Stud
– C-frame
– Unit bearing
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Cradle Mount
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Rigid Mount
Motor housing is welded to the base
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Belly Band Mounting
Motor slides into ring.
Then band is tightened
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Stud Mounts
Studs are bolted to
fan guard or
housing.
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Other Motor Mounting Styles
C-frame
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Unit bearing
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Motor Nameplate
• Nameplates contain essential information
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Motor Nameplate explained
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Motor Nameplate wiring diagram
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Interesting Motor Facts
• An overloaded motor (too small for the job):
– Lower speed, amperage above 10% of RLA, and
overheating
• An under-loaded motor (too big for the job):
– Little change in speed, amperage 25% below RLA,
and overheating
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