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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

Methods of Variable Flow Control Fans Pumps Damper Control Throttling Valve Control Inlet Vane Control Variable Frequency Drive

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

AC MOTOR BASICS

Purpose of an “AC Motor” Electrical Energy Mechanical Energy The purpose of an AC Motor is to Convert Electrical Energy into Mechanical Energy

Stator Winding Assembly AC MOTOR CONSTRUCTION Motor Frame Assembly Rotor Assembly Stator Winding Assembly

AC Motor Basics 2 Pole Motor Motor RPM is equal to: 120 * Frequency # Motor Poles Note that Frequency is the only variable to affect motor speed Rotating Magnetic Field of a 2 Pole AC Induction Motor

Types of Variable Speed Control Before AC Variable Speed Drives Control Valves, Dampers and Vanes Fossil Fuel Engines Eddy Current Clutches Hydraulic Couplings Variable Pitch Sheaves Motor Generator Sets

AC Drive M Inverter - Changes fixed DC to adjustable AC Rectifier DC Bus Inverter AC Power Supply M 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

Adjustable Speed Drive Availability 110V Single Phase Fractional HP Medium Voltage (4160V) Thousands of HP Most are 460Volt 1-500 HP

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

Variable Torque Loads(Fans & Pumps)

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

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

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  

Some Considerations When Applying ASD to AC Motors Thermal considerations of motor operation with a VFD should be one of the first areas of attention for successful application. 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.

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).