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Variable Speed Drives
Presented by: Nguyen Huu Loi
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PART 1
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ENERGY:
The motor changes electric energy into mechanical work which, once adapted to theproduction needs, becomes the effective work.
The sizing of the mechanical system and of the motor will be performed from those dataabout the effective work, in order to:
Ensure the energy transfer,
Limit mechanical and electrical losses.
WORK:
Work is the product of a force by a distance covered under the effect of that force. It isexpressed in joules and is independent from time.
As far as an angular motion is concerned, it is the work of a force torque whose action isequal to 2F1 x r. This action which is commonly called torque, is expressed inNewton-meters.
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WORK
Linear motion
A B
F
Work = force x distance
W(J) = F(N) x I(m)
Angular Motion
r
F
A
B rB
A
F1
F1
Work = force x distance
W = 2F1x r
W(J) = C(Nm) x (rd)
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POWER - TORQUE - SPEED
Transportation of 50 kg in one go Transportation of 5 kg in 10 times
WORK WORK
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FOR AN ANGULAR MOTION:
Hence:P(w) = T(Nm) x (rd/s)
POWERt
W
t
T
t
WP
t
and: angular speed in
radians/second
Power is defined by WORK divided by the total time spent to perform the task.
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The mechanical power required by the application represents the
ability of the motor to provide a work in a given time.
The rated power corresponds to the work provided in one
second by the motor in permanent normal state. It is expressed
in WATT.
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THE RESISTANT TORQUE
It is opposed to the motion whatever the direction of the rotation.
The machine is driven by the motor.There are several types of resistant torques:
- Constant resistant torque: Tr = constant
- Resistant torque proportional to speed: Tr = k
- Resistant torque proportional to square speed: Tr = k2
- Resistant torque inversely proportional to speed:
- Pull-up torque or starting overtorque
- Some machines have a high variation of torque
THE TRAILING (OVERHAULING) TORQUE
This makes the motion easier whatever the direction of the rotation.
The machine drives the motor.
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POWER:
Power is proportional to speed.
P = Tr , Tr = constant P = k
MACHINES:
Conveyor belts
Conveyors, Hoisting & Lift(80% of the cases)
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AMACHINES WITH CONSTANT RESISTANT TORQUE
Tr = constant
Speed
Tr
0 Torque
Graph
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POWER:
The power changes according to the square speed.
P = Tr , Tr = k P = k2
MACHINES: Rare cases (some worm conveyors based on theprinciple of Archimedean screw and spiral pumps).
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B MACHINES WITH RESISTANT TORQUE PROPORTIONAL TOSPEED
Tr = kSpeed
Torque0
Tr
Graph
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POWER:
The power changes according to the cube of the speed.
P = Tr , Tr = k2 P = k3
MACHINES:
Centrifugal pumpsVentilators
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CMACHINES WITH RESISTANT TORQUE PROPORTIONAL TOSQUARE SPEED TR = K2
Speed
Torque
0
Tr
Graph
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POWER:
The power is constant:
P = Tr , P = k
MACHINES:
Machines tools broaches (cutter bar or bit)
Windings and unwinding machines
k
Tr
Textile machines
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D MACHINES WITH RESISTANT TORQUE INVERSELY
PROPORTIONAL TO SPEED
k
Tr
Torque
Speed
Maximum
speed
Minimum
speedMinimum
torque0 Maximum
torque
Tr
Graph
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E PULL-UP TORQUE OR STARTING OVERTORQUE
Torque
Speed Tr = constant
Tr = k
Tr = k2
0Tp
PULL-UP TORQUE
kTr
Graph
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PART 2
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- Reduction of Mechanical Stress
Importance of Speed Control
Speed
TimeDECACCLift & Elevator
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-Reduction of Current peaks, voltage dropsand protection motor
Importance of Speed Control
I/In
N/Ns0
1
2
3
This curve willchange
according tothe load
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- Process Regulation
Importance of Speed Control
Conveyor
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- Power Saving
Importance of Speed Control
HVAC System
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Methods of Varying Motor Speed
Mechanical method Clutch Variable Gear Reducers
Electrical method Variable transformers Steps resistors Motor Winding Electronic motor drives
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Where it is commonly used ?
Constant Torque loads, Hoisting & Lift Conveyors Crushers
Variable Torque loads Pumps Fans Beam Winders
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M
Line
Frequencydrive
3 PhaseMotor
AC
DC
PWM
PWM -Pulse Width Modulated wave
Basic Theory
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Fv -Frequency VariableFc -Frequency Carrier
Fv
Fc
PWM wave
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TECHNOLOGY
TYPICAL POWER DIAGRAM
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We have the definition to calculate the speed of the motor bases on the frequency and
number poles of the rotor:
The function of the inverter is changing the speed of the motor and keeping the moment of
the motor is a constant at any speed. In order to do so, the flux must be a constant
according to the formula below:
T = K I cos = constant
We can see that the moment is propositional to the current of the motor and it will be a
constant like:
T = constant if = constant
60f
Nsp
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In an asynchronous motor, the stator create a flux:
= L I At the voltage U, and frequency is f.
The Ohm law is: U = Z I
The impedance of the solenoid (without resistance) is :Z = L So :U = L I
is represented by: = 2 f
We have the current of the motor :
The flux is finally calculated :
In order to keep the flux in constant, i.e moment is contant, the ratio must be a constant at any speed of the
motor.
Conclusion: with the inverter, the voltage and frequency are changed propositionally.
f LI u
2
12
Uf
cst UF
cst
UF
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PART 3
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CENTRIFUGAL LOADS
70% OF ALL CONSUMED ELECTRICAL ENERGY
IS:
PUMPS
FANS
BLOWERS
COMPRESSORS
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Pumpingis an art of moving liquid and gasses
Pumps and Fans are designed to make water or air flow
and most of them are categorized asVariable Torque Load
InVariable Torque Loadthe torque required to drive the loadchanges according to the speed.As the speed of the load isreduced the torque required to drive it is decreased as a squaredof the speed
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Variable Torque Profile
0
0.2
0.4
0.6
0.8
1
%T
orque
0 0.2 0.4 0.6 0.8 1
% Speed
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Pump & Fans Princilple
CONSTRUCTION :ROTATING IMPELLER INSIDE OF A SPECIALLY SHAPEDSHELL
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PRINCIPLE :THE FLUID IS DRAWN IN AT THE AXIS ANDACCELERATED ALONG THE VANES OF THE IMPELLER
Pump & Fans Princilple
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PRINCIPLE :
THE FLUID IS MOVING FASTER AT THE TIPS OF THEIMPELLER, INCREASING BOTH ITS FLOW AND
PRESSURE
Pump & Fans Princilple
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PRINCIPLE :THE DIFFERENCE IN PRESSURE IS ALSO THE FORCETHAT DRAWS MORE FLUID INTO THE AXIS
Pump & Fans Princilple
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Typical Pump Curve
0
20
40
60
80
100
120
140
160
0 200 400 600 800 1000 1200 1400 1600
Flow
Pressure
Reminder
60
50
4030
Point A
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TYPICAL OUTPUT CONTROLS
THROTTLE VALVES
OUTLET DAMPERS
INLET VANES
MECHANICAL SPEEDCHANGES
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A SCARY ANALOGY
CONTROLLING A SYSTEM
LIKE THIS IS LIKE DRIVING ACAR WITH YOUR FOOT TO THE
FLOOR ON THEACCELERATOR WHILECONTROLLING THE SPEEDWITH A BRAKE.
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Variable Torque Loads
Fans and Pumps are designed to make air or water flow.As
the rate of flow increases, the air or water is has greaterchange in speed put into it by the fan or pump,increasingit inertia.
The effect that reduced speed has on variable torquefan or pump are summarized by set of rules known as the
AFFINITY LAW .
VSD Relation to Energy Savings
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0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
% Speed
Flow
Affinity Law
- Flow produced by the device is proportional to the motor speed
1st Law
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0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
% Speed
Pressure
- Pressured produced by the device is proportional to the motor speed squared.
Affinity Law
2nd Law
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0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
% Speed
Power
- Power produced by the device is proportional to the motor speed cubed
Affinity Law
3rd Law
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0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
% Speed
%Fl
ow,Pressure,H
P
FlowPressure
Horse Power
Affinity Law
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THROTTLE VALVE vs VSD
0
20
40
60
80
100
120
THROTTLE VALVE
VFD
PERC
ENTPOWER
PERCENT FLOW
10040
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INLET VANES vs VSD
0
20
40
60
80
100
120
INLET VANES
VFD
PERC
ENTPOWER
PERCENT FLOW
100
F l
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Cost to run a motor at 100% speed:
(Power) x (Time) x ($/VND/KWhr)
Cost to run a motor with variable speed drive
(%speed) for (%time) is to:(Power) x (%speed)3x (%time) x ($/VND/KWhr)
Savings
Cost w/o Drive - Cost w/ Drive
Formula :
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Example:
-Consider a 50 Hp (37.3 KW) drive at 2000 VND/KWhrrunning at 250 days a year for 10 hrs per day (2500 hrs).
Cost to run the motor at 100% speed
= (37.3 KW) x (2500 hrs) x (2000 VND/KWhr)
= 186.5 MVND
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Annual Duty Cycle using Drives
100
80
60
40
20
0
%Speed625 hrs.
625 hrs.
1250 hrs.
100% speed for 25% time= (37.3KW) x (1.0)
3x (625) x (2000 VND/KWhr)
= 57.625 MVND
80% speed for 50% time= (37.2KW) x (0.8)3x (1250) x (2000 VND/KWh= 47.616 MVND
60% speed for 25% time= (37.2KW) x (0.6)
3x (625) x (2000 VND/KWhr)
= 10.044 MVND
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Estimated yearly cost of saving based on use
= 186.5 115.285
Total cost based on duty cycle
= 57.625 + 47.616 + 10.044= 115.285 MVND
= 71.215 MVND
= 4.522 USD
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PART 4
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Flux Vector Control
Constant Speed
Reference
Set point
Rotary Encoder
Motor
Tacho & Pulse generatorfeedback option card
ATV58
Drive
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Motor 1 Motor 2
Motor Switching option
2 Motor performing differentfunction
Parameter Switchingoption card
ATV 58
PI Regulation
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PressureSensor
Pump
PI Regulation
Constant Pressure
Gauge
ATV58Drive
Reference
Set point
Pipe Line
ATV38Drive
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Automatic catch on the fly with speed retrieval
When the mains supply returns, the productcarries out a speed search andre-accelerates on the ACC ramp
N
ATV58 & ATV18
acceleration ramp
speed retrieval
without speed retrieval
U
Operatingvoltage
t
t
Power Interruption
Operatingspeed
ATV58Drive
ATV38
Drive
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A very completebasic product
Operator terminalon the drive or on the enclosure door
5 languagesdownloading of 4 files
PC software under Windows 95Disk upload / down load
Programming terminaladjust config storage
Program and mornitor byPowerSuiteSoftware
Catalogued option cards tosuit your needs
I/O extension
multiparameter
pump switching
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Built-in Modbus RS485
communication port
Remotable display unit
ATV58 X 4
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Built-in Modbus RS485
communication port
One dialogue multi-drive
Control by PC or PLC
ATV58
PC HMI PLC
X 4
Fast communication cards
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Fast communication cards
FIPIO ; Modbus + Interbus-SProfibus DP
AS-IDevice-NetCan OpenUnitelwayEthernet
ATV58
Communicationoption card
PLC
PC
PLC
ATV31
Pump Switching Option
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Pump Switching Option
Flow Rate
Number of Pumps
PV
PV
PV
PV
P1 P1 P1
P2 P2
P3
PV P1 P2 P3
Pressure Measurement
ATV 58
Sensor
Power Line
MotorStarter
Gauge
Flow
MotorStarter
MotorStarter
Motor Switchingoption card
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Any Questions?
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