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VFD Engineering

VFD Engineering. Daniel C. Merkel VFD Specialist, Texas AirSystems. CV. CV. Agenda. Introduction Part I Why Drives? Motor Review Applications Part II VFD Basics Application Engineering Redundancies Part III Enclosure types Harmonics [intro] Part IV Design Criteria

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VFD Engineering

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  1. VFD Engineering Daniel C. Merkel VFD Specialist, Texas AirSystems

  2. CV CV Agenda Introduction Part I Why Drives? Motor Review Applications Part II VFD Basics Application Engineering Redundancies Part III Enclosure types Harmonics [intro] Part IV Design Criteria VFD Schedules Part V Maintenance Questions Target 1 hr

  3. Why Use Adjustable Speed Drives? Reduced Energy Consumption Improved Process Control / Efficiency Increased Product Quality Expanded Automation / Integration Broader Equipment Flexibility / Versatility Increased Reliability / Availability Reduced Maintenance $

  4. Applications - Types Variable Torque Flow varies linearly with speed Torque requirement varies as the square of speed Power requirement varies as the cube of speed

  5. Energy Requirements - Example 100Hp, 1800RPM, 480VAC, 120FLA motor Running below 30% usually results in turbulence and energy savings is negligible. Motor cooling is an issue below 10% speed for variable torque loads (without any Flux Optimization).

  6. Motor & VFD Review How Do Induction Motors Work With Drives? always controlling three phase induction motor. NoSingle phase motor. VFDs Control of Frequency and Voltage applied to the motor. And the result is control of the motor speed

  7. Typical Installation

  8. Review Fan Stator Bearings Fan End Bell Rotor End Bell

  9. Motor Speed (RPM) Where: F = Frequency Applied P = Number of Stator Poles 120 X F RPM = P = 1800 120 X 60 Example: RPM = 4 What to remember: 900RPM , 1800RPM, 3600RPM are typical ideal speed numbers. Torque output and current draw is different for different speed motors of the same nameplate Hp. Hp is imaginary calculated number. Amp draw is your main concern. Horsepower = Torque (ft lbs) X RPM 5252

  10. Multiple Motor Application MMP / MOP

  11. Multiple Motors

  12. Common VFD HVAC Applications

  13. VAV - AHU

  14. Sample Air Handler

  15. Sample Chilled Water

  16. Sample Cooling Tower

  17. Motor & VFD Review Motor Slip: Reality is that motors run slower than “Ideal “ speed they have to in order to generate any torque This difference in speed is called slip 120 X F Shaft Speed = - Slip P Slip for NEMA B Motor = 3% of Base Speed (1800 RPM) at Full Load 120 X 60 Hz Example: Shaft Speed = - 54 = 1746 RPM 4 What to remember: Always Enter the Nameplate “Slip” speed into the drive so the drive knows the characteristics of the motor

  18. Slip Speed = Synchronous Speed

  19. Motor & VFD Review If 230 VAC Power Line: 230 V 460 V V Hz V Hz 460 = 7.67 = 3.83 60 Hz 60 Hz Volts 460 V Motor 230 230 V Motor 0 30 60 Hertz A VFD varies both Voltage and Frequency to the motor, When linear, this is called Volts per Hertz operation

  20. Flux Optimization ™ VFD Operation Traditional VFD Operation: Linear V/Hz F l u x

  21. Acronyms These ALL are the same thing! VFD (Variable Frequency Drive) VSD (Variable Speed Drive) ASD (Adjustable Speed Drive) AFD (Adjustable Frequency Drive) Others? (POS does not count!)

  22. Motor & VFD Review Variable Frequency Drive Definition (VFD): Variable Frequency Drives control an AC motor. It converts the incoming line constant voltage and frequency to an adjustable voltage and frequency. The adjustable voltage and frequency is applied to a squirrel cage induction motor.

  23. How Do Induction Motors Work With Drives? Control of Speed and Energy vs Control of Speed and Torque

  24. VFD ReviewBlock Diagram of PWM Drive L1 L2 Motor L3 Diode Bridge IGBT’s

  25. VFD Review + + _ _ L + + + + L1 C Motor L2 L3 _ _ _ _ Input Converter (Diode Bridge) DC Bus (Filter) Output Inverter (IGBT’s)

  26. Measurements: Bearing Voltage 20 Volt Peak: Shaft to GND 1.32 Volt Peak: Shaft to GND

  27. Discharge heat is extreme! Illustration of Bearing/Race Heating and Pitting

  28. Multiple pits create ‘Frosting’ Both races and rolling elements are affected Race with excessive pitting

  29. Bouncing Ball Ball bouncing on the race

  30. With resonance, bearings of line-operated motors will also flute! Steady-state operation creates this pattern Fluted bearing

  31. Power Factor

  32. Utilities may impose penalties due to low power factor Improved power factor reduces load on cables and transformers Power Factor Possible Solutions • Drives where no drives are present • Drives with an Active Front End • Can control power factor to near unity • Added benefit of ability to regenerate energy back to the line

  33. VFD Vs Bypass Vs Redundant Drive VFD – Varies voltage, frequency, and FLOW Bypass – across the line starter work around for a VFD or other device. 60Hz ONLY! Redundant Drive – Backup for the primary VFD should it fail, a will continue to offer varied voltage, frequency, and FLOW

  34. What is a Bypass?Alternate Path for power to get to the motor around the VFD VFD

  35. Redundant VFDs

  36. Enclosures

  37. Too High Ambient Temperature

  38. Enclosures

  39. Load-side Disconnects

  40. Hardware Protection 5% line reactor DC Link Choke Software Protection

  41. Harmonics

  42. Harmonics

  43. Passive Filters All are 50HP Drives: 12 and 18 pulse VFD’s 6 Pulse Active Rectifier 6 Pulse

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