WISA Meeting Help
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Transcript of WISA Meeting Help
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WISA Meeting Help
•Arrange a Speaker, Write Bio, IntroduceFebruary 24, 2015March 24, 2015May 26, 2015
Upcoming MeetingsOctober 28, 2014 Del Tech TourNovember 25, 2014 Career
Development
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Advantages of Adjustable Speed Drives in Process Control
•Motor Driven Pump Systems account for about 20% of Worldwide Energy Use
•Some Plants have usage approaching 50%
•Adjustable Speed Drives can Improve Process Control and Greatly Reduce Energy Costs
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Methods of Variable Flow ControlFans Pumps
Damper Control Throttling Valve Control
Inlet Vane Control
Variable Frequency Drive
Variable Frequency Drive
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High Percentage of Plant Connected Horsepower is for Fans and Pumps•Opportunity to save energy when you can
reduce CFM or process flow rate using a variable speed drive rather than using dampers or a control valve
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AC MOTOR
BASICS
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Purpose of an “AC Motor”
ElectricalEnergy
MechanicalEnergy
The purpose of an AC Motor is to Convert Electrical Energy into Mechanical Energy
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AC MOTOR CONSTRUCTION
Stator Winding Assembly
Stator Winding Assembly
RotorAssembly
RotorAssembly
Motor Frame Assembly
Motor Frame Assembly
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AC Motor Basics
Rotating Magnetic Field of a 2 Pole AC Induction Motor
Motor RPM is equal to:
120 * Frequency
# Motor Poles
2 Pole Motor2 Pole Motor
Note that Frequency is the only variable to
affect motor speed
Note that Frequency is the only variable to
affect motor speed
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Types of Variable Speed ControlBefore AC Variable Speed Drives• Control Valves, Dampers and Vanes
• Fossil Fuel Engines
• Eddy Current Clutches
• Hydraulic Couplings
• Variable Pitch Sheaves
• Motor Generator Sets
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AC DriveDC Bus
• Rectifier
- Converts AC line voltage to Pulsating DC voltage
• Inverter
- Changes fixed DC to adjustable AC
- Alters the Frequency of PWM waveform
• Intermediate Circuit (DC BUS)
- Filters the pulsating DC to fixed DC voltage
V
TT
V V V
T
AC Power Supply
Rectifier Inverter
M
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Adjustable Speed Drive Availability•110V Single Phase Fractional HP
•Medium Voltage (4160V) Thousands of HP
•Most are 460Volt 1-500 HP
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Does my load profile vary sufficiently to justify a AFD?•If the Speed of the Application is constant
DO NOT USE
•If the load is not running at full speed for a large portion of the time then Evaluate the Use
•Sweet Spot is a Variable Torque Load
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Variable Torque Loads(Fans & Pumps)
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Variable Torque Loads
•In these applications:
• Torque varies directly with speed squared
• Power varies directly with speed cubed•This means that at half speed, the
horsepower required is approximately one eighth of rated maximum
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Variable Speed Horsepower Requirements
Flow proportional to speed Q1/Q2= n1/n2
Then: HP2/HP1= (n2/n1)3
Therefore: HP2=HP1(n2/n1)3
At 80% Speed, HP=(.80)3 = .512
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Advantages of a Adjustable Speed Drive
•1. Energy savings on fan and pump applications
•2. Better process control and regulation•3. Speeding up or slowing down a
machine or process•4. Inherent power-factor correction•5. Elimination of Other Mechanical
Control Devices
•
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Some Considerations WhenApplying ASD to AC Motors
Thermal considerations of motor operation with a VFDshould be one of the first areas of attention for successfulapplication.• The ability of a motor to cool itself effectively is
reduced as the motor is slowed down. Over-sizing the motor or providing external forced air ventilation may be required with extended operation at low speeds and high loads.
• Operation at different speeds can cause mechanical resonances in driven equipment. These speeds should be identified and programmed out of the motor’s operating range.
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ASD Considerations •ASD’s generate harmonic voltages and
currents which can, in some cases, cause undesirable effects on the electrical distribution system and affect equipment operation.
•Longer Cable Lengths can cause a voltage reflection of up to two times the applied voltage due to standing waves or a ‘‘ringing effect’’, and becomes more problematic with longer cable runs (typically greater than 15 m or 50 feet).