Electric Machines & Drives
Topics covered –
1. DC Motors
2. DC Generators
3. AC 3 phase Induction Motors
4. AC 3 phase Synchronous Machines
5. Fundamentals of Power Controls
6. USF Course Material available at;
thomasblairpe.com/EMD
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 4 - DC Generators
AC generator
E = B*L*V
Slip Ring
Component of V
perpendicular to B
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Tom Blair, P.E.
Chapter 4 - DC Generators
Commutator
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Chapter 4 - DC Generators
Which unit below is AC machine
and which is DC machine?
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Tom Blair, P.E.
Chapter 4 - DC Generators
Slot construction
Lap Winding
4 coils = 4 slots =
4 commutator bars
2 poles = 2 brushes
eA+eB+eC+eD = 0
(no circ current)
Brush Volt =
eB+eC or eA+eD
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Chapter 4 - DC Generators
Magnitude ->
angle between V
and B
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Chapter 4 - DC Generators
Voltage in slot 4/10
max
Voltage in slot 1/7 min
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Chapter 4 - DC Generators
Proportional to flux and speed
Off neutral brush effectively reduces Z
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Chapter 4 - DC Generators
Armature reaction
Current produces
Magnetic Field
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Tom Blair, P.E.
Chapter 4 - DC Generators
Armature induced field
adds to pole induced
field.
Resultant field shifts
neutral point.
Also, saturation of points
2 ,3 (Pole Tip
Saturation) causes
reduced EO
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 4 - DC Generators
Commutating Pole
Field proportional to load
Compensate neutral shift
Due to armature reaction
(Slightly greater than
Armature reaction flux)
Note, does not change
Saturation at main poles
-> EO still effected.
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Chapter 4 - DC Generators
No Load operation
Saturation Curve
Field Flux vs
Exciting amps
(similar to B-H
Curve)
Designed to
operate at
“knee” of point a &
b.
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Chapter 4 - DC Generators
Shunt Generator – no external field source needed
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Chapter 4 - DC Generators
Voltage Control
Nonlinear
Moving P to N,
reduced EO
Moving P to M,
increases EO
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Tom Blair, P.E.
Chapter 4 - DC Generators
EO noload – intersection of
Saturation curve & RF
For this example:
RF > 200 W E0=0
Critical Value
(When starting, where
should rheostat
position be??)
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Tom Blair, P.E.
Chapter 4 - DC Generators
Exciting current constant, speed constant, EO
constant
E12 depend on drop across RO
Load Curve Shown – typical drop less than 10%
(Pole Tip Saturation also leads to E12 drop)
Shunt Generator – typical drop about 15% due to EO
drop
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Chapter 4 - DC Generators
Compound Generator – Series & Shunt Coils
Series coil same direction as Shunt – mmf adds
E0 raises as load increases maintaining E12
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Chapter 4 - DC Generators
Over-compound
generator E12
increases.
Differentialcompounded – Series
coil opposite direction
– mmf subtracts, EO
drops as load
increases.
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Chapter 4 - DC Generators
# Poles = # Brush sets
Larger Machine -> More poles -> More brush sets
Control amps per brush (current density)
Also more Brush per Brush set -> reduce current
density.
Generator construction
Field Stationary
Electromagnet –
Salient Poles
Air Gap 1mm - 5mm
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Chapter 4 - DC Generators
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Chapter 4 - DC Generators
Armature
Construction
Rotating
Commutator, Iron
Core, & Coils
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Chapter 4 - DC Generators
# slots = # coils = # commutator sections
Mica insulator between
commutator sections
Coils connected to
commutating element
Eccentricity causes
brush bounce -> arcing
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Chapter 4 - DC Generators
Brush set connection – alternating + and -
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Chapter 5 – DC Motors
Constructed same as DC generator
Torque & Speed control with high efficiency
Starting methods
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Chapter 5 – DC Motors
EO proportional to speed
At rest EO = 0
At steady state
EO = ES – I*R
EO = counterelectromotive force
(CEMF)
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Chapter 5 – DC Motors
Mechanical Power & Torque -
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Chapter 5 – DC Motors
Mechanical Torque – proportional to flux and
armature current
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Chapter 5 – DC Motors
Speed of Rotation – Proportional to Es and
inversely proportional to flux (field current)
Bonus Question, what happens to DC motor on
Loss of Field Current?
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Chapter 5 – DC Motors
Rheostat allows
control of EO ->
speed control
Efficiency very poor
Small motors only.
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Chapter 5 – DC Motors
Speed control via
field control
Flux increase ->
speed decrease
Operate above base
speed
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Chapter 5 – DC Motors
As load increases,
Tload increases,
causing armature
current to increase
causing speed to
drop
Speed regulation
good (10%-20%)
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Chapter 5 – DC Motors
Series Motor – Different
torque speed
characteristic
Starting torque higher
Reduction in load =
reduced flux = higher
speed
Bonus Question – what
happens if load
removed?
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Chapter 5 – DC Motors
As load decreases,
Tload decreases,
causing armature current
to decrease causing flux
to drop causing speed to
increase rapidly
Speed regulation poor
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Tom Blair, P.E.
Chapter 5 – DC Motors
Compound DC Motor –
Both series & shunt field
No load, shunt field
controls max speed
Full load, series field
adds to mmf ->
increased flux -> speed
decreases
Regulation 10% - 30%
Differential Compound –
series field mmf
subtracts from shunt
field mmf
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Chapter 5 – DC Motors
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Chapter 5 – DC Motors
Direction of Rotation – Reverse Armature or Field
Commutation polarity associated with Armature polarity
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Tom Blair, P.E.
Chapter 13 – Three Phase Induction
Machines
Stator – laminated core, slots, 3phase winding
Rotor – laminated core, slots, 3phase winding or
squirrel cage winding
Squirrel cage induction motor
Bare copper (aluminum) bars welded to copper
(aluminum) end rings
Wound rotor induction motor
Three phase insulated winding
– three slip rings – external resistor
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Chapter 13 – Three Phase Induction
Machines
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Chapter 13 – Three Phase Induction
Machines
Faraday’s Law
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Lorentz Force
Tom Blair, P.E.
Chapter 13 – Three Phase Induction
Machines
Field speed = 120
*f/p
Salient Pole
Stator -> Smooth
Stator
Phase group ->
group = #phase *
#poles(*#winding)
Group = 3*2=6
#slot = #coils
Lap wound coil
construction
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Chapter 13 – Three Phase Induction Machines
stator
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41
Chapter 13 – Three Phase Induction Machines
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42
Tom Blair, P.E.
Chapter 13 – Three Phase Induction Machines
Motor enclosures
TENV – totally enclosed, non ventilated
TEFC – totally enclosed, fan cooled
TEBC – totally enclosed, blower cooled
TEWAC – totally enclosed, water to air cooled
TEAAC – totally enclosed, air to air cooled
WPII – Weather protected (two 90 degree turns in
air path)
ODP – Open drip proof
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43
Tom Blair, P.E.
Chapter 13 – Three Phase Induction
Machines
Synchronous speed vs. asynchronous speed
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Chapter 13 – Three Phase Induction
Machines
Starting Characteristics –
1. Revolving field set up by applied stator voltage
2. Field induced voltage (E2) in rotor bars.
3. Induced voltage induces current in rotor bars.
4. Induced current in magnetic field induces force
on conductors in direction of rotating magnetic
field.
5. As rotor speed increases – rate at which rotor
bars cut field reduces (reducing E2)
6. Reduced E2 -> reduced rotor current ->reduced
force
7. When load torque = motor torque, steady state
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Chapter 13 – Three Phase Induction
Machines
Power & PF vs
loading while
motor at speed.
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Chapter 13 – Three Phase Induction
Machines
Percent difference between synch speed and
actual speed = slip
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Chapter 13 – Three Phase Induction
Machines
Rotor Voltage (E2) and frequency (f2)
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Chapter 13 – Three Phase Induction
Machines
Induction motors are designed to operate successfully
with voltage variations of ±10%.
Effects of a 10% variation on a typical design B induction
motor at full load shown below.
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Chapter 13 – Three Phase Induction
Machines
Unbalanced voltage -> derate of motor capability
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Chapter 13 – Three Phase Induction
Machines
Estimate of motor current
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Pe – Active stator power input
Pjs – I2R loss in stator
Pf – Iron loss in stator
Pr – active power supplied to rotor
Pjr – I2R loss in rotor
Pm – Mechanical power of rotor
Pv – windage / friction losses
PL – power to load
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Chapter 13 – Three Phase Induction
Machines
Efficiency = Pout to Pin
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Chapter 13 – Three Phase Induction
Machines
Rotor loss and mechanical power relation to slip
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Chapter 13 – Three Phase Induction
Machines
Mechanical torque developed by shaft
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Chapter 13 – Three Phase Induction
Machines
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Chapter 13 – Three Phase Induction
Machines
Effect of rotor resistance
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Chapter 13 – Three Phase Induction
Machines
Starting Torque increased, slip increased, starting
current reduced, breakdown torque not effected (to
a point)
Start -> high resistance, Run -> low resistance
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Chapter 13 – Three Phase Induction
Machines
Wound Rotor Characteristics
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Chapter 13 – Three Phase Induction
Machines
Three phase winding design –
Salient pole design vs lap winding design
Phase groups = #poles X #phases (X #windings)
Increase # of coils per group -> better starting torque &
less noise
#slots = # coils
Pole pitch = # coils / # poles
Coil Pitch = width of coil (typical 80%-100% pole pitch)
120O electrical separation between phases
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Chapter 13 – Three Phase Induction
Machines
May be wye or delta connection
Convert from measured resistance to per winding
resistance RA1-B1 = 2*Rwinding
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RA1-B1 = (2/3)*Rwinding
Tom Blair, P.E.
Chapter 13 – Three Phase Induction
Machines
Pole Pitch vs Coil Pitch
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Chapter 13 – Three Phase Induction
Machines
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Chapter 13 – Three Phase Induction
Machines
Linear Induction Motor –
Linear speed – depends on frequency & pole pitch
Typically 2 stator sides to one rotor or alternately
stator moving and rotor stationary
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Chapter 13 – Three Phase Induction
Machines
Linear Induction
Motor
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Chapter 13 – Three Phase Induction
Machines
Linear Induction Motor Properties
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Chapter 13 – Three Phase Induction
Machines
Horizontal Force (Thrust) developed based on
Work = F * d,
P = v*F
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Chapter 13 – Three Phase Induction
Machines
Doubly-fed wound rotor motor
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Chapter 13 – Three Phase Induction
Machines
Supersynchronous
Rotor abc – stator acb
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Subsynchronous
Rotor abc – stator abc
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Subsynchronous Motor
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Supersynchronous Motor
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Subsynchronous Generator
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Supersynchronous Generator
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
NEMA design starting characteristics
Shallow bars = higher resistance
Deep bars reduced resistance
Starting – current mostly in shallow bar
Running – current shared and deep bar resistance low
IEEE EMD Seminar
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
Two Speed Motor designs –
1. Multiple windings with multiple poles
2. Simulated or “consequent” pole generation
Coil pitch only 50% of pole pitch.
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
Series connection for 4 pole, 900 RPM (60hz)
Parallel connection for 8 pole, 450 RPM (60hz)
HS – pwr -> 1, 2, 3, LS – pwr -> 4, 5, 6 (1, 2, 3, neutral)
Constant power / constant torque / variable torque config
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
Between NL and FL – torque curve linear
s = slip
T = torque
R = rotor resistance
E = stator voltage
k = constant due to rotor construction
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
Starting an induction motor – LRA vs. FLA, LRT, PUT,
BDT, FLT
Rule 1 true if no load on motor during start – If load
on motor during accel, Heat dissipated in rotor
greater than rule 1.
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
Induction Generating region –
n > ns – Torque changes direction -> power is toque
X speed -> motor is now generator (asynchronous
generator)
Power proportional Torque X Speed
VAR required from system to provide energy for
magnetic field generation
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
Induction motor in generating mode –
Motor is active power source but still reactive power sink
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Chapter 14 – Selection & Application of 3
Phase Induction Machines
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Induction Braking, Motoring, Generating
Motoring Region
+Ve Torque
Braking Region
Regenerating Region
Voltage
-Ve Torque
Motoring
Regenerating
Synchronous Speed
(Rotating Field Speed)
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Current
Chapter 15 – Equivalent Circuit of the
Induction Motor
Similar to Transformer – circuit similar
Wye connection – 1:1 transformer
Motor magnetizing component NOT negligible
2HP, shift magnetizing circuit to source side
Frequency in rotor circuit = s*f
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Active Power – (Independent of magnetizing ckt)
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Reactive Power -
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Apparent Power -
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Line Current -
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Power to Rotor (includes shaft power + rotor loss) –
– (Independent of magnetizing ckt)
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Rotor I2R losses – (Independent of magnetizing ckt)
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Mechanical Power (Shaft Power) – (Independent of
magnetizing ckt)
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Torque – (Independent of magnetizing ckt)
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Efficiency -
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Chapter 15 – Equivalent Circuit of the
Induction Motor
No Load Test Arrangement
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Chapter 15 – Equivalent Circuit of the
Induction Motor
No Load Test to determine magnetizing circuit –
I1 small compared to Io – only magnetizing branch
applies
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Chapter 15 – Equivalent Circuit of the
Induction Motor
Following calculations apply
Note: three phase power
Windage, Friction, Iron loss =
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Chapter 15 – Equivalent Circuit of the
Induction Motor
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Chapter 15 – Equivalent Circuit
of the Induction Motor
Locked Rotor – Reduced voltage
Calculate:
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Tom Blair, P.E.
Chapter 16 – Synchronous Generators
Stationary Field generator < 5kva
stationary field – rotating armature
slip ring connection to armature
Rotating Field generator (alternator) > 5kva
stationary armature – rotating field
slip ring connection to field
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Chapter 16 – Synchronous Generators
DC generator for field generation of Synchronous
Generator
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Chapter 16 – Synchronous Generators
One complete cycle every time pole pair passed ->
Frequency generated is:
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Chapter 16 – Synchronous Generators
Stator Features: Identical to 3 phase motor
Stacked laminations
Always connected in wye for following reasons:
Voltage per coil 58% line voltage
Third harmonic voltages cancel (same in each
phase), in delta they add and cause circulating
current.
Max term voltage typically 25kv.
IEEE EMD Seminar
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Chapter 16 – Synchronous Generators
Rotor Features:
High speed slotted cylindrical forging
Smaller diameter – centrifugal forces
Longer to get air gap area needed for power
Retaining ring – insulated
Low speed typically salient pole
Larger diameter – lower speed – more poles
Shorter due to more air gap area per foot length
Coils in series (mica strip insulation)
Squirrel cage in pole faces (damper winding) for
transient dampening
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Chapter 16 – Synchronous Generators
Field Excitation - typically .5% to 2% machine rating
Two functions
1. maintain ac line voltage
2. provide reactive power to system
Slip ring and Brush exciter
1. provided by DC generator on same shaft
2. Provided by MG set separately driven
3. Provided by separate sourced solid state
rectifier
Brushless exciter
1. Provided by PMG same shaft via separate
sourced solid state rectifier to alternator on shaft
2. Provided by external source via solid state
rectifier
to alternator on shaft.
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Chapter 16 – Synchronous Generators
Brushless exciter – Less maintenance
Ic controls field current
Frequency > main frequency
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Chapter 16 – Synchronous Generators
Size of synchronous generators:
Larger size -> higher efficiency
Power per KG greater (more power per $)
Cooling of large machines challenge
Indirectly cooled winding
Gas intercooled winding
Water cooled winding
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Chapter 16 – Synchronous Generators
Strand insulation –
reduce eddy current in
conductor
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Chapter 16 – Synchronous Generators
Robel Transposition – equalize magnetic reactance of
each conductor
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Chapter 16 – Synchronous Generators
Connection to liquid cooling system.
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Chapter 16 – Synchronous Generators
Simplified SLE circuit for Synchronous Generator
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Chapter 16 – Synchronous Generators
Synchronous Reactance
Measurement of Xs
Open circuit test – rated speed and open terminals,
excitation raised to meet rated V (En). This is value
of (Ixn)
Short Circuit test – rated speed and shorted
terminals, excitation raised back to Ixn, and armature
current measured (value of Isc)
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Chapter 16 – Synchronous Generators
Short Circuit Ratio (SCR) –
Ratio of Ix1 to Ix2, where Ix1 is field current to
produce nominal open circuit voltage and Ix2 is field
current to produce nominal armature current on short
circuited terminals (steady state)
Xs (pu) = (Ix2 / Ix1) = 1/SCR
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Chapter 16 – Synchronous Generators
Generator supplying lagging load - Lagging PF,
I leads E,
E(Xs) leads I by 90 degrees,
Eo = E + Ex, therefore Eo > E,
Angle between E and Eo is power angle (d)
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Chapter 16 – Synchronous Generators
Generator supplying leading load - Leading PF,
I lags E,
E(Xs) leads I by 90 degrees,
Eo = E + Ex, therefore Eo < E,
Angle between E and Eo is power angle (d)
Note same power angle as before.
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Chapter 16 – Synchronous Generators
Generator Synchronization:
1. Generator Frequency = System Frequency
(preferred slightly faster) WHY?
2. Generator Voltage Magnitude = System Voltage
Magnitude (preferred slightly higher) WHY?
3. Generator Voltage Phase Angle = System Voltage
Phase Angle (breaker closing time added to
calculation)
4. Generator Phase sequence = System Phase
Sequence
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Chapter 16 – Synchronous Generators
Infinite Bus Characteristics:
1. Adjusting excitation adjusts Eo – controls VAR flow.
2. Adjusting mechanical torque adjusts power angle d
– control watts flow.
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Chapter 16 – Synchronous Generators
Overexcited
System looks like
Inductive Load –
I lags E
Ex in phase with E
E + Ex = Eo
Var transfer to
system
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Chapter 16 – Synchronous Generators
Under excited
System looks like
Capacitive Load –
I leads E
Ex 180O out of
phase with E
E + Ex = Eo
Var transfer to
generator
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Chapter 16 – Synchronous Generators
Increasing Torque,
Eo advances ahead of E,
increased power angle d,
NOTE: even though E and Eo have same magnitude (implying no VAR
transfer) power is still transferred due to power angle d
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Chapter 16 – Synchronous Generators
Rotor Position – no load to full load –
Torque by prime mover advances rotor position
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Chapter 16 – Synchronous Generators
Mechanical angle of rotor pole to stator pole related
to power angle by: (Note for 2 pole generator, a = d )
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Chapter 16 – Synchronous Generators
For Proof of equation, see web site;
http://www.thomasblairpe.com/EMD/PPE_PWR_XFER.pdf
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Chapter 16 – Synchronous Generators
Rated power typically around 30O – Power angle >
90O cause pole slip and out of synch condition.
Note: curve
typical for smooth
cylindrical
machine – curve
modified for
salient pole
machine.
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Chapter 16 – Synchronous Generators
2 pole machines oscillate at 2X line frequency – core
mounting absorbs vibration
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Chapter 16 – Synchronous Generators
Cylindrical Rotor Construction
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Chapter 16 – Synchronous Generators
Bore Copper and terminal stud connector for DC field
circuit
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Chapter 16 – Synchronous Generators
Generator Capability
Curve
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Chapter 16 – Synchronous Generators
V-Curve –
Apparent power
to Field current
for various power
loading
Question – which
side is generator
VAR source /
VAR sink?
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Chapter 17 – Synchronous Motors
Construction similar to Synchronous Generator
Stator slotted wedges
Rotor Salient Poles – damper winding imbedded in
pole face
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Chapter 17 – Synchronous Motors
Rotor poles & stator poles always same
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Chapter 17 – Synchronous Motors
Starting Synchronous motor – amortisseur winding
Short field winding during start - Limit induced voltage
on field winding & improve starting torque
Also reduced voltage start or pony motor start
VFD also used for starting very large synchronous
motor (and combustion turbine generators)
Pull in torque – Applying DC to field generates field –
pulls rotor into synch with stator field (pull in torque)
Detection of position of rotor pole position important
When in synch, amortisseur winding sees no slip ->
no voltage induced in winding
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Chapter 17 – Synchronous Motors
Power & Torque -
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Chapter 17 – Synchronous Motors
Power & Torque – since P is sin
function, T is sin function
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Chapter 17 – Synchronous Motors
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Chapter 17 – Synchronous Motors
Relationship between power angle d and mechanical
angle a between stator and rotor pole centers
Same as Generator – also note for 2 pole machine, a
=d
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 17 – Synchronous Motors
Reluctance torque for salient pole machine –
As power angle d increases, concentration of flux
between rotor and stator poles changes. This
variation in flux leads to variation in torque (known as
reluctance torque)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 17 – Synchronous Motors
Resultant Torque
1 – Reluctance
Torque
2 – Cylindrical
Torque
3 – Resultant
Torque
PEAK – 70O
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 17 – Synchronous Motors
Stopping Synchronous Motor –
Following methods:
1. Coasting (may take time to come to rest)
2. Break by maintain full DC excitation with Armature
short circuit (dynamic braking)
3. Break by maintain full CD excitation with Armature
connected to resistor bank (dynamic braking)
4. Apply mechanical break
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Resistive Battery Charger
I2R losses in resistor
I = E43/R
EMD - Week 10
Tom Blair, P.E.
139
Chapter 21 – Power Electronics
Inductive Battery Charger
Stored Energy example
Imax = A(+)/L
EMD - Week 10
Tom Blair, P.E.
140
Chapter 21 – Power Electronics
Single Phase Bridge Rectifier
2 pulse rectifier
Fripple = #pulse*fline
= 2 * fline
Ripple = 2*f(line)
Ripplep-p = Epeak
EMD - Week 10
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141
Chapter 21 – Power Electronics
Filters –
L – constant
current
Series w/ load
Line current
square wave
C – constant
voltage
Parallel w/ load
Line current
spike
EMD - Week 10
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142
Chapter 21 – Power Electronics
3 Phase, 6 pulse rectifier – 1.225 < Ed < 1.414
Peak to Peak 1.414 – 1.225 = 0.189 E
Fripple = Fline * Pulse #
Fripple = Fline * 6
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143
Chapter 21 – Power Electronics
Ripple - PIV = Epeak
Conduction 360O / #pulse = 360O/6 = 60O
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Tom Blair, P.E.
144
Current / Voltage
relationships for
various
configurations:
EMD - Week 10
Tom Blair, P.E.
145
Chapter 21 – Power Electronics
Solid state switch – point of conduction controlled
a. Anode positive
b. Gate current injected
c. Anode to cathode current remain positive
EMD - Week 10
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146
Chapter 21 – Power Electronics
!!!SAFETY!!!
SCR output =
input voltage
EMD - Week 10
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147
Chapter 21 – Power Electronics
Natural commutation vs forced commutation
Stop commutation by:
1. Reduce dc supply voltage to zero
2. Open load circuit via switch
3. Force anode current to zero
EMD - Week 11
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148
Chapter 21 – Power Electronics
Rectifier – active load (load has energy source)
Peak current = amp*seconds / inductance
Apparent and real power flow to load
EMD - Week 11
Tom Blair, P.E.
149
Chapter 21 – Power Electronics
Line commutated inverter – active load (load has
energy source, note polarity)
Peak current = amp*seconds / inductance
Apparent power to load, real power to source
DC to AC conversion
EMD - Week 11
Tom Blair, P.E.
150
Chapter 21 – Power Electronics
Line Commutated Inverter –
DC to AC real power conversion
Forced Commutated – commutation by current
reversal within power bridge
Line Commutated – Commutation current provided
by line.
Due to polarity of Ed, Power flows to source.
Source side voltage must be present to provide
needed VAR
EMD - Week 11
Tom Blair, P.E.
151
Chapter 21 – Power Electronics
AC static switch – back to back SCRs
Reactive power draw
Phase angle, zero fired, on/off
EMD - Week 11
Tom Blair, P.E.
152
Chapter 21 – Power Electronics
3 Phase, 6 pulse rectifier – to active load
Ed = 1.35 * E * cos a
Ed > Eo for current flow, Ed < Eo zero current flow
Excel Spreadsheet showing calculation
EMD - Week 11
Tom Blair, P.E.
153
Chapter 21 – Power Electronics
Delayed trigger – rectifier mode
Increased delay angle, reduced Ed
Conduction angle still 60O
Each thyristor still conducts for 120O
EMD - Week 11
Tom Blair, P.E.
154
Chapter 21 – Power Electronics
Conduction angles of 45O and 75O
EMD - Week 11
Tom Blair, P.E.
155
Chapter 21 – Power Electronics
Delayed Trigger – Inverter Mode
Note Polarity of Eo and Ed
EMD - Week 11
Tom Blair, P.E.
156
Chapter 21 – Power Electronics
Inverter mode, 90O < a < 180O
Eo > Ed current flow, Ed > Eo, zero current flow
Power flow to source
EMD - Week 11
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157
Chapter 21 – Power Electronics
EMD - Week 11
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158
Chapter 21 – Power Electronics
Current flow:
I = S(2/3) Id =
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159
Chapter 21 – Power Electronics
Reactive Power draw of bridge dependant on Real
Power draw and delay angle
EMD - Week 11
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160
Chapter 21 – Power Electronics
Rapid Switching –
Where D = Ta/T
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Tom Blair, P.E.
Chapter 21 – Power Electronics
Rapid Switching – DC current I0 ->
Source current Is ->
Where D = Ta/T
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Es * Is = Eo * Io, but
Is = Io * D ->
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Ro = Eo / Io = Es * D2 / Is ->
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
2 quadrant DC to DC converter
S1 = D = Ta/T, S2 = 1-D = Tb/T
If, EL>Eo, P flow to Eo (boost), if EL<Eo, P flow to EL
(buck), controlled by D
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
4 quadrant DC to DC converter – bidirectional
EH, Eo
(2 quad converter, unidirectional EH, Eo)
Q1 & Q4 operate in pair for Ta/T = D, Q2 & Q3
operate in pair for Tb/T = 1-D
When D = 0.5, Ell = 0 (note there is still ac
component)
When D = 1, Ell = Eh
When D = 0, Ell = -Eh
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Switching Losses –
Four distinct operations:
1. Turn-on time T1 – Current increases, voltage
decreases
2. On-state time T2 – Current flowing, Vt 2-3
VDC
3. Turn-off time T3 – Current decreases, Voltage
increases
4. Off-state time T4 – Current zero, Voltage high.
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Snubber – During turnoff – controls dv/dt
across device
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Tom Blair, P.E.
Chapter 21 – Power Electronics
DC to AC rectangular converter
E = 0.9 * Eh
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Tom Blair, P.E.
Chapter 21 – Power Electronics
DC to AC converter with PWM
Adjust D waveform, adjust Ell Magnitude and
waveform – fc must be 10 times > f out
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Triangular generation
of PWM waveform
When V>El – off
When V<El – on
NOTE: Technology
has application past
power – example,
fiberoptic converters
Transmit real time
waveform via FO
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
3 phase, DC to AC converter
3 single phase converter shifted 120O
Ean, Ebn, Ecn = E/S3, Em = E*S2, ->
Em = E*S6
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
Q1 closed when Eay>Efc
Q3 closed when Eby>Efc
Q5 closed when Ecy>Efc
Q2 closed when Eay<Efc
Q4 closed when Eby<Efc
Q6 closed when Ecy<Efc
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 21 – Power Electronics
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Tom Blair, P.E.
Chapter 21 – Power Electronics
Converter as Universal Generator Fast response,
Small impedance
No isolation
without
transformer
RLC to filter out fc
C1 to filter DC bus
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
First Quadrant – speed control
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Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Speed varied by changing armature voltage
a initially 90O, switch closed, a decreased to
increase armature Vdc, increasing Id
1. No armature resistors needed (no losses)
2. Power loss reduced, improved efficiency
3. Current limit prevent over current.
4. PF poor during start period
A typically 15O at full conduction
Ed > Eo by Id*Ra
To lower speed, a increased, Id = o, motor coast
to lower speed till Id /= 0
Ripple voltage large, but L gives smooth Id
Motor coast to stop (no breaking)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Two quadrant control via field reversal –
Dynamic Brake – resistor across armature
Regenerative brake – generate power back to
line
Procedure follows:
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
1. Delay gate pulse by 180O (cause Ed to be neg)
2. Reverse If (Delayed)
3. Reduce a so |Ed| < |Eo|
4. Once speed lowered, Delay gate pulse again
by 180O (cause Ed to be positive
5. Reverse back If (Delay)
6. Increase a so |Ed| > |Eo|
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Two quadrant control via armature reversal (single
converter) –
Quicker response – La << Lf
Delay gate pulse by 180O (cause Ed to be neg)
Reverse Eo to reverse Io
Reduce a so |Ed| < |Eo|
Once speed lowered, Delay gate pulse again by
180O (cause Ed to be positive
Reverse back Eo to reverse back Io
Increase a so |Ed| > |Eo|
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Two Quadrant (1&2) control – reversing with
same torque direction
Raise – Quadrant 1 – motoring – 0O<a<90O
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Two Quadrant (1&2) control – reversing with
same torque direction – Eo reverses
Lower – Quadrant 2 – Braking – 90O<a<180O
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Converter 1 –
Rectifier Mode
Converter 2 –
Inverter Mode
Converter 1 –
Inverter Mode
Converter 2 –
Rectifier Mode
IEEE EMD Seminar
Tom Blair, P.E.
Four Quadrant
Drive – Utilizing
2 converter
system
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Tom Blair, P.E.
Chapter 22 – Control of DC Motors
6 pulse converter with freewheeling diode –
Without diode, small values of Ed contain negative
portions of Ed
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Due to lag, reactive current large. Also, I line
120O regardless of a
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Placing diode prevents Ed from being negative
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Tom Blair, P.E.
Chapter 22 – Control of DC Motors
For same a, increased Id – increase a angle for
same Id, note I line no longer 120O
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
With Freewheeling diode, calculation of Ed and
I become – (note- eqn only apply for reduced
voltage ( a > 60O) where there is neg comp of
Ed.)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Half Bridge Converter –
3 diode/3 SCR
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Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Note – 3 pulse rectifier – again I line <
120O
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Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Half Bridge Converter –
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 22 – Control of DC Motors
Converter A – 3phase, 6 pulse
Converter B – 3phase, 6 pulse w/ FW diode
Converter C – 3phase, 3 pulse half bridge
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Where DC motors controlled by controlling
Voltage and Current, AC motors controlled with
Voltage and Frequency
Types of AC drives –
1. Static Frequency Changers
2. Static Voltage Changers
3. Rectifier / Inverter Systems with Line
Commutation
4. Rectifier / Inverter Systems with Self
Commutation
5. PWM Systems
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
VFD standards –
NEMA “Application Guide For AC Adjustable
Speed Drive Systems”
Available Free at: http://www.nema.org/
IEEE Std 958 “Guide for Application of AC
Adjustable-Speed Drives for Electric Power
Generating Stations”
IEEE Std 1566 “Standard for Performance of
Adjustable Speed AC Drives Rated 375 kW
and Larger “
Available at: http://www.ieee.org/standards
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
IEEE Std 1566 – sample datasheet (purchaser)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
IEEE Std 1566 – sample datasheet (Vendor)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Static Frequency Changer - convert fline to fload
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Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Static Voltage Controller – Vary AC voltage to motor
to control torque / speed (also used to softstart)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Rectifier / Inverter w/ line commutation – AC to DC
to AC conversion. Rectifier uses Line to
commutate. Inverter uses Motor to commutate
(LCI). Used on Synchronous and Wound Rotor
Motors. (why not induction machines?)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Rectifier / Inverter w/ self commutation – AC to DC
to AC conversion. Rectifier uses self commutation.
Used on squirrel cage induction motors that can not
provide commutation energy.
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
PWM system – AC to DC to AC conversion. Used
on induction motors.
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Synchronous motor current source drive –
Operate like brushless DC motor (control Ia & If)
Es Q speed & If. Gate controlled by rotor
position. Speed controlled by Ia or If.
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Converter 2 in inverting mode -
Converter 1 in rectifying mode -
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Trigged to provide leading PF – provide var for
reactive power needed by converter 2 –
Regen brake by Converter 1 invert, Converter 2
rect, inverting E1 and E2 (Idc same direction)
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Torque speed
curve for variable
speed
If V/F constant,
flux constant,
peak torque same
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Static voltage controller – adjust voltage (not freq)
T Q V2
Greater slip.
Increased rotor heating
Small motor only
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Solidstate voltage
reduction
Adjusting delay angle –
Reduced Vac to motor
Vrms not linear to angle
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Solidstate softstart – reduce mechanical shock,
reduced peak start current.
5 basic type
Ramp down vs DC injection.
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Terminology Soft start
Reduced Voltage Starter (RVS)
Solid State Reduced Voltage Starter (SSRVS)
Purpose of softstart
1. Reduce the inrush current during start
2. Reduce peak torque during start.
Brief review of motor theory for how soft start
effects these parameters
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Ensure sufficient motor available torque to
start the motor.
Acceleration Time (Tacc) is defined as:
Average Acceleration Torque (Avg Acc Trq) is defined as:
This definition does not account for load:
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
ATL start – constant torque load
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
RVS (Limit) – constant torque load
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Trequired = Tmotor + Tload
Evaluate motor and load torque curves.
Ensure sufficient motor accelerating torque
exists throughout acceleration curve.
API 841 recommends Tmotor >1.1*Tload
throughout the speed range.
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
> 2300V
IEEE EMD Seminar
Tom Blair, P.E.
Chapter 23 – Control of AC Motors
Applications for reduced voltage start
Pump Applications; prevent water hammer
Mech. transmission issues; reduce torque
(electronic shear pin)
Weak distribution lines; limit voltage dip
during start
Electronic braking; actively stop loads
Damp applications; motor heating
IEEE EMD Seminar
Tom Blair, P.E.
Conclusion
Tour of Motor Shop 3PM to 5PM.
Questions?
Tom Blair
Office: 813-228-4407
Email: tom_blair@ieee.org
IEEE EMD Seminar
Tom Blair, P.E.