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## Motors

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### Title: MOTOR CONTROL STARTER Author: Jim Last modified by: Erik Redd Created Date: 11/6/2002 11:43:07 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: Motors

1
Motors Motor Starters
• Prepared By
• Erik Redd
• Jeremy Roberts

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
• Fig. 13-2 Pg. 244
• 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.
• S120frequency
• ( poles)
• Example
• For a three-phase, 60 Hertz, 2 pole motor
• S12060/23600 revolutions per minute

6
Polyphase Squirrel-Cage Induction Motors
• The most common three-phase motor
• Does not have solid poles
• Instead, it has laminations numerous flat sheets
held together in a package. They are insulated
from each other (this reduces Eddy currents)
making up the stator
• The difference between induction and synchronous
motors is that the rotor for an induction motor
can travel at a different speed than the stator.
This is called Slip.
• slip Syn. rpm Motor rpm 100
Syn. rpm

7
• Example.
• A 2 pole, 60 Hz motor runs at a full-load speed
of 1760 rpm.
• What is the slip?

8
• Ans. slip 3600-1760100
• 3600
• 51.1

9
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

10
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

11
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
• Efficiency is between 50-65
• Capacitor controls the inrush current

12
Permanent Split-Capacitor Motors
• Winding arrangement is the same as the capacitor
and split-phase motors
• Capacitor can run continuously, rated in
• No centrifugal switch is needed
• IM lags VL, while IS leads VL
• Efficiency is between 50-70

13
• Simple construction, least expensive
• Has a run winding only, shading coils are used
• 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

14
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

15
Armature Voltage Control
• Is used for motor speeds below base speed
• Output torque TkøIA
• k is machine constant
• ø is the main pole flux
• IA is the armature current

16
Shunt Field Control
• Is used for motor speeds above base speed
• Horsepower, (HP) Torquerpm
• 5252
• Where torque is in lb-ft

17
Speed Regulation
• Speed Regulation

18
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

19
Brushless DC Motors
• Figure 13-21, page 264 shows the input power
section
• 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

20
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

21
Picture of a Brushless Motor
22
Motor Control Starters
• Motor will draw high inrush current while the
starter will slow current down
• Starter reduces the amount of torque needed to
start the motor

23
Magnetic Motor Starter
• Normally open contacts
• Not always possible to control amount of work
applied to the motor
• Motor may be overloaded resulting in damage to
the motor
• Open due to excessive motor current, high
temperature, or a combination of both

24
Full-Voltage Starter
• Contains one set of contacts
• Motor is directly connected to the line voltage

25
Reversing Motor Starter
• Contains two starters of equal size
• Two starters connect to the motor
• Interlocks are used to prevent both starters from
closing their line contacts at the same time
• Figure 14-4A

26
Reduced-voltage Motor Starter
• Applies a percentage of the total voltage to
start (50 - 80)
• After motor rotates, switching is provided to
apply full voltage
• Torque will be reduced when starting
• Four types
• 1) Autotransformer
• 2) Primary Resistance
• 3) Wye Delta
• 4) Part Winding

27
Autotransformer Starter
• Two contactors are used
• 1) Start contactor
• - Closes first and connects motor to the line
• through an autotransformer
• - Deenergizes
• 2) Run contactor
• - Motor switches to this contacter which has
• full voltage

28
Primary Resistor Starter
• Two contactor
• 1) Line contactor
• - First to energize connecting motor to
the
• line voltage through a resistor
• - After preset time, contactor opens
• 2) Accelerating contactor
• - Energizes
• - Causes smooth acceleration to full voltage

29
Wye Delta Starter
• Three contactors are used
• 1) Line contactor and start contactor
• - Energizes first and connects motor in wye
• putting about 58 of line voltage across
• each motor phase
• - Contacts open after preset time
• 2) Run contactor
• - Energizes connecting motor in delta and
• putting full voltage on the motor

30
Part Winding Starter
• Starter supplies about 48 of normal starting
torque
• Not truly a reduced-voltage means
• Two Types
• 1) Two-Step - one winding connected to
• full voltage line and, after a preset
time,
• the other connects
• 2) Three-Step one winding is connected in
series
• with a resistor to the voltage line after
interval, resistor
• is shorted out and then second line is
connected to
• full voltage line

31
Solid-State Motor Starter
• For lower starting torque and smooth acceleration
• Used on conveyors, pumps, compressors, etc.

32
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