Post on 12-Apr-2017
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NUE046 Alternating Current Machines
3 phase motors1 phase motors
StartersAlternators
Synchronous motors
Learning outcome 1
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This is an 80 hour module.
Divided into 3 sections
1. three phase motors and their basic theory
2. Single phase motors
3. Synchronous machines (including alternators)
ALL prac. work MUST be satisfactorily completed with a short report on each prac.
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This is an 80 hour module.
Divided into 3 sections
1. three phase motors and their basic theory
2. Single phase motors
3. Synchronous machines (including alternators)
ALL prac. work MUST be satisfactorily completed with a short report on each prac.
It is your responsibility to be an active participant in the group…… Check the forums etc.
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12 Learning outcomes
1 Principles and characteristics2 Motor Protection
3 starters4 connections to starters
5Wiring rules6 Operating principles of single phase motors
7 Parts and connections of 1 phase motors8 Comparison of 1 phase motors
9 Motor faults10 Synchronous motors
11 Loading and excitation of synchronous motors and alternators(including pracs)
12 Construction of 1 phase synchronous motors
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3 phase induction motors are common in industry.
They are rugged and reliable
Less vibration than 1 phase motors
More efficient than the same size 1 phase motor
Ref. Page 223L/O 1.1 & 1.2
Construction features
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The magnetic field rotates at a set speed.
This depends on.. 1. The number of poles
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The magnetic field rotates at a set speed.
This depends on.. 1. The number of poles
2. Supply frequency
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There are 3 magnetic fields in the stator each is produced by its own
AC current….
A phaseB phaseC phase
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The magnetic field rotates at synchronous speed
n (sync) = 120f
p
L/O 1.3 10.3.2 p 226
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The magnetic field rotates at synchronous speed
n (sync) = 120f
p
120 = 2 x 60
60 converts cycles per second to minutes.
2 because there ate north and south poles
L/O 1.3 10.3.2 p 226
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The magnetic field rotates at synchronous speed
n (sync) = 120f
p
120 = 2 x 60
60 converts cycles per second to minutes.
2 because there ate north and south poles
n is the synchronous speed
F is the frequency (Hz)
P the number of poles eg; 2, 4, 6, 8
L/O 1.3 10.3.2 p 226
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Induction The rotor gets its power from the stator by transformer action (induction).
L/O 1
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Induction The rotor gets its power from the stator by transformer action (induction).
Voltage (EMF) is induced into the rotor and hence current flows.
L/O 1
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Induction The rotor gets its power from the stator by transformer action (induction).
Voltage (EMF) is induced into the rotor and hence current flows.
This flow of current has with it a strong magnetic field.
L/O 1
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Induction The rotor gets its power from the stator by transformer action (induction).
Voltage (EMF) is induced into the rotor and hence current flows.
This flow of current has with it a strong magnetic field.
The magnetic field on the rotor reacts with the magnetic field of the stator.
L/O 1
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Induction The rotor gets its power from the stator by transformer action (induction).
Voltage (EMF) is induced into the rotor and hence current flows.
This flow of current has with it a strong magnetic field.
The magnetic field on the rotor reacts with the magnetic field of the stator.
This causes rotation.
L/O 1
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2 main types of connections
Delta connection (most common)
L/O 1.1 10.2.4 p 224
STATOR CONNECTIONS
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2 main types of connections
Delta connection (most common)Star connection
L/O 1.1 10.2.4 p 224
STATOR CONNECTIONS
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Star and Delta
Some motors have star/delta starters.
Here the motor is first connected in star then automatically reconnected into delta as the load is applied to the motor.
In star the motor gets 230 V across the winding.
In delta it gets 415 V.
The torque is much lower in star. T α V²
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Main types of rotor
• Typical standard cage rotor• Wound rotor
We might see a conical type rotor in some special applications eg; cranes.
There are many different styles and designs but these are usually specialist machines.
L/O 1.1, 1.2, 1.3, 1.5
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Conical rotor for Demag cranes and hoist motors
brakeThe rotor moves forward and releases the brake.
spring
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Rotor frequencyAt stand still the frequency in the rotor is the same as the stator (50Hz).
At synchronous speed the rotor frequency is 0 Hz
The characteristics and performance of the motor depend on the rotor frequency due to the interaction of the 2 magnetic fields.
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Rotor frequencyAt stand still the frequency in the rotor is the same as the stator (50Hz).
At synchronous speed the rotor frequency is 0 Hz
The characteristics and performance of the motor depend on the rotor frequency due to the interaction of the 2 magnetic fields.
L/O 1.4 10.4.3 p 228
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Torque Torque is the turning effect of a motor shaft.
The torque of a motor is usually measured in newton-metres.
L/O 1.3, 1.4
1.4.1 p 5
Torque is proportional to the voltage squared.
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Torque Torque is the turning effect of a motor shaft.
The torque of a motor is usually measured in newton-metres.
L/O 1.3, 1.4
1.4.1 p 5
Torque is proportional to the voltage squared.
If you halve the voltage you get only ¼ of the torque.
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BREAKDOWN TORQUE
Torque = Turning ForceBreakdown Torque is the maximum torque
produced by the motor.This occurs then:Rotor Resistance = Rotor Reactance
RR = XLR
B.C.
p. 229 & 230
L/O 1.4
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POWEROutput power
P = ---------------2 x π x n x T
60
n = RPM
T = Torque
60 converts mins. to seconds
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POWEROutput power
P = ---------------2 x π x n x T
60
n = RPM
T = Torque
60 converts mins. to seconds
See example 1.6 p 5
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Losses and efficiency
All motors have losses.
We compare the input power (electrical Watts) to the output power (mechanical Watts)
Make a list of ALL losses in an electric motor.
L/O 6 1.4.2 and examples 1.7 & 1.8
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Efficiency also depends on the “quality” of the electrical supply.
η = -------P (out)
P (in)X 100
This is a percentage.
Check out the figure 10.21. P 231.
The efficiency follows closely to the power factor of the machine.
L/O 1.6
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Nameplate DataWhat useful information do we find on the nameplate of a motor?
Voltage
Current
Watts out
Power factor
Insulation type
L/O 1.5
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Nameplate DataWhat useful information do we find on the nameplate of a motor?
Voltage
Current
Watts out
Power factor
Insulation type
WHAT ELSE ?????
L/O 1.5
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Name plate for refrig.compressor motor
Note… star/star
2 Windings are in parallel.
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