ASHRAE - Variable Speed Drives. By Dan Watkins, LEED BD+C Bornquist, Inc.

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1 ASHRAE - Variable Speed Drives By Dan Watkins, LEED BD+C Bornquist, Inc.

2 Adjustable Frequency Drive Fundamentals How does a VFD actually work VS Pumping Analysis VS Pumping Features Harmonics VFDs and Motors

3 How does a VFD actually work?

4 How does a VFD actually work?

5 How does a VFD actually work? Frequency Controls Motor Speed

6 How does a VFD actually work?

7 Converts AC to DC, then DC to AC 460 V, 60 Hz 640 V, DC 307 V, 40 Hz

8 Basic Drive Diodes Change AC to DC Capacitors Filter the DC Transistors Switch DC to AC

9 V/Hz Curve Depends on ApplicaCon

10 Extended Frequency OperaCon

11 Extended Frequency OperaCon

12 Extended Frequency OperaCon

13 So, why do we want to do variable speed pumping?

14 Variable Speed Pumping Applications = GPM 2 GPM 1 RPM 2 RPM 1 = HEAD 2 HEAD 1 GPM 2 GPM 1 2 HEAD 2 = HEAD 1 RPM 2 RPM 1 2 HP 2 HP 1 = = HP 2 HP 1 GPM 2 GPM 1 3 RPM 2 RPM 1 3

15 Variable Speed Pumping Applications Determine applicability of Variable Volume/Variable Speed Where applicable utilize a system s variable volume characteristics and apply variable speed pumping to maximize the total energy savings and control in the system Primary Only or Primary/Secondary Pumping Arrangements Enhanced System Control Variable Speed Reduction Capability Pressure Sensor Location

16 Variable Speed Pumping Applications

17 Variable Speed Pumping Applications 12.5HP - Constant

18 Variable Speed Pumping Applications

19 Variable Speed Pumping Applications 12.5HP - 7.5HP Depending on Flow 10HP 15HP

20 Variable Speed Pumping Applications

21 Variable Speed Pumping Applications 12.5HP HP 2 = HP 1 = 1.6 HP 1.6HP

22 Variable Speed Pumping Applications

23 Variable Speed Pumping ApplicaCons - Applicability The question of applicability of Variable Volume/ Variable Speed on your system is based on the system s inherent operating characteristics. In system s with generally steady load characteristics and/or limited volume variation - Variable Speed is not generally applied due to poor payback calculations. In system s with varying load characteristics and greater volume variation - Variable Speed is generally applied, based on a payback analysis.

24 Variable Speed Pumping ApplicaCons - Sensor LocaCon ΔP Sensor/Transmitter SOURCE SOURCE ΔP Sensor/ Transmitter

25 Variable Speed Pumping ApplicaCons - Sensor LocaCon Coil P.D. Control Valve P.D. Typical Total P.D Typical Setting Equals Design Pressure Drop Across the Coil, Control Valve, and Circuit Setter.

26 Variable Speed Pumping ApplicaCons - Sensor LocaCon SOURCE SOURCE Pump Trim 5 P.D. ΔP Sensor/ Transmitter PumpOverhea d 0-15% P.D. Typical Setting Equals Total Pump Head Minus Noted Pressure Drops Piping Loss 3-5 P.D. Air Separator 3-5 P.D.

27 Variable Speed Cost Savings Easy Pump Balancing Variable Flow Systems Pressure Booster Packages

28 Variable Speed Pumping Easy Pump Balancing X Pump Selected at: HP required. Duty Point: 30 HP Oversized by 15% 15 head on TDV

29 Variable Speed Pumping

30 Variable Speed Pumping

31 Variable Speed Pumping Variable Volume System

32 Variable Speed Pumping Example Pump Selected at: Variable Speed and System curves shown 20 Control Head 725 RPM Minimum

33 Variable Speed Pumping Example PE Motor

34 Variable Speed Pumping Example PE Motor

35 Variable Speed Pressure BoosCng Height of building 12 stories 150 _. stacc li_ 30 PSI City pressure 30 PSI required at the top 50 piping pressure drop at design flow

36 Variable Speed Pressure BoosCng Pump Selected at: HP required. Duty Point: 25 HP 2950 RPM Minimum Speed

37 Variable Speed Pressure BoosCng

38 Pumps Application-Specific Capabilities Compressors

39 Flying Start Synchronizes the drive to the speed of a coasting fan Searches for the fan s speed in both directions Applies DC braking if needed Provides a smooth start

40 Vibration Avoidance Avoids speed that can cause mechanical resonant vibration Up to four frequency bands of individual sizes Simple, prompted automated setup

41 Other Pump-Protection Functions Dry pump detection Over-flow ( end of curve ) protection

42 Power Line Harmonics Their Cause and Solutions

43 What are Harmonics? A sinusoidal waveform is a pure frequency All waveforms have a fundamental frequency Harmonics are integer multiples of the fundamental frequency The first harmonic is the fundamental frequency

44 What is Harmonic Distortion? Harmonic distortion results when harmonics currents are combined with a fundamental frequency The resulting waveform is no longer a pure sine wave Harmonic currents operate at the same time as the fundamental, but at faster rate Harmonic currents are additive, producing a distorted sine wave Fundamental = 60Hz 5th Harmonic = 300Hz

45 Why are Harmonics a concern? Overheating of power distribution transformers Overheating of conductors, especially neutral wiring Overheating of induction motors Torque reduction of induction motors Overheating of power factor correction capacitors Nuisance tripping of circuit breakers Blown fuses

46 Why are Harmonics a concern? Carrier current signals Lighting systems (Leviton) Some security systems Sensitive electronic equipment Communication Research Computers Airport Electronics Medical Security Stand-by generators

47 What Causes Harmonics? NON-LINEAR LOADS - Loads which do not draw sinusoidal current from the line Non-incandescent lighting Computers Uninterruptible power supplies Telecommunications equipment Copy machines Battery chargers Electronic variable speed drives Any load with an AC to DC power converter

48 Harmonics For a typical 6 pulse inverter, these multiples are: Fundamental = 60 Hz 5th Harmonic = 60 x 5 = 300 Hz 7th Harmonic = 60 x 7 = 420 Hz 11th Harmonic = 60 x 11 = 660 Hz 13th Harmonic = 60 x 13 = 780 Hz 17th Harmonic = 60 x 17 = 1,020 Hz

49 One Drive in Different Buildings Strong Power Line Total harmonic voltage distortion 1.1% Weak Power Line Total harmonic voltage distortion 5.1%

50 IEEE Designed to protect the utility power grid Measured at the Point of Common Coupling (PCC) This recommendation focuses on the point of common coupling (PCC) with the consumer-utility interface. some harmonic effects are unavoidable at some points in the system. (IEEE Std , sec. 10.1) The PCC is not at the wiring to an individual device

51 Drive Manufactures Addressing Harmonics Some just ignore the problem Build in DC link chokes Built in line reactors Build special 12 and 18 pulse drives Optional separate filters Product Selection Goal: Select products that give you performance without excess cost

52 Harmonic Reduction: DC Link Reactors Generally a standard part of the drive; not an option.

53 Harmonic Reduction: AC Line Reactors Often used when the drive has no built-in filtering

54 DC Link + AC Line Reactors? Typical example (from drivesmag.com) no reactors 62% current distortion 3% DC reactor 31% current distortion 3% AC reactor 37% current distortion 3% DC reactor + 3% AC reactor 28% current distortion Remember, the goals are: Keep harmonic distortion from causing a problem Avoid wasting money

55 12-Pulse (and Higher) Rectifier to the rest of the drive Theoretically eliminates the 5th and 7th harmonics Uses two sets of input diodes to the power line

56 12-Pulse (and Higher) Rectifier But 12 pulse is no different than 6 pulse unless a phase-shifting transformer is used Shifts the phase of voltage applied to each rectifier Might not be supplied with the drive Δ Y transformer to the power line to the rest of the drive

57 Connects in parallel with the power line to correct harmonic distortion Active Filter

58 Comparing All Harmonic Solutions

59 Adjustable Frequency Drives and Motor InteracCon

60 Drive and Motor Interaction Audible Motor Noise Motor Overheating Motor Insulation Stress Motor Bearing Damage

61 Audible Motor Noise Caused by the pulses of electrical energy that the drive uses to power the motor The loudness depends on Motor design Pulse frequency Motor current

62 Drive and Motor Interaction Audible Motor Noise Motor Overheating Motor Insulation Stress Motor Bearing Damage

63 Motor Overheating Variable Torque Not a concern for variable torque applications Variable torque applications require little motor current at low speed A properly adjusted variable torque drive will not cause a motor driving a variable torque load to overheat

64 Drive and Motor Interaction Audible Motor Noise Motor Overheating Motor Insulation Stress Motor Bearing Damage

65 Motor Insulation Stress Shows up first as an over current trip, ground fault trip or fuse blowing in bypass Motor insulation looks and smells good Megger or Hi Pot test shows shorting between windings or from a winding to ground

66 Cause of Motor Insulation Stress When current is switched, a coil generates a back voltage The faster the change (dv/dt), the greater the back voltage This can arc through motor insulation

67 Minimizing Motor Insulation Stress Better motor insulation Standard Motor NEMA MG 1, Part 30: 1000 V peak voltage, 2 µs rise time Special-Purpose Motor NEMA MG 1, Part 31: 1600 V peak voltage, 0.1 µs rise time

68 Minimizing Motor Insulation Stress Better motor insulation Short wire length to the motor The longer the motor leads, the less the effect of the diodes.

69 Short Wire Length to the Motor 1000 V 10 Foot Motor Lead 90 Foot Motor Lead 210 Foot Motor Lead Waveforms are for a soft switching drive 200 V/div vertical; 0.2 µs/div horizontal

70 Slow Switching Power Components So_ Switching IGBT Standard IGBT 90 ft motor leads 200 V/div vertical; 0.5 µs/div horizontal

71 Output Reactor

72 Output Reactor Waveforms Drive did not have soft switching No Reactors No Reactors No Reactors With Reactors With Reactors With Reactors 10 Ft Motor Lead 90 Ft Motor Lead 210 Ft Motor Lead 200 V/div vertical; 2 µs/div horizontal

73 Output dv/dt Filter

74 Output dv/dt Filter Waveforms Drive did not have soft switching No Filter No Filter No Filter dv/dt Filter dv/dt Filter dv/dt Filter 10 Ft Motor Lead 90 Ft Motor Lead 210 Ft Motor Lead 200 V/div vertical; 2 µs/div horizontal

75 Reduce the DC Bus Voltage 208 and 230 V: no problem 460 V: some problems, particularly with 10 HP and smaller motors 575 V: more potential problems

76 Drive and Motor Interaction Audible Motor Noise Motor Overheating Motor Insulation Stress Motor Bearing Damage

77 Motor Bearing Damage This can cause a washboard pattern to be etched into the bearings Capacitive coupling can couple voltage from the stator to the rotor If this gets too high, voltage can discharge through the motor bearings

78 Motor Bearing Damage Solutions Reduced motor peak voltage Drives which reduce motor insulation stress also reduce the possibilities of bearing damage

79 Motor Bearing Damage Solutions Reduced motor peak voltage Fewer pulses from the drive Insulate the bearings Conductive bearing grease Tighter motor manufacturing tolerances Ground the motor shaft

80 Motor Bearing Damage Solutions Reduced motor peak voltage Fewer pulses from the drive Insulate the bearings Conductive bearing grease Tighter motor manufacturing tolerances Ground the motor shaft

81 Motor Bearing Damage Solutions Reduced motor peak voltage Fewer pulses from the drive Insulate the bearings Sleeve Ceramic bearings SKF Insocoat TM bearings Conductive bearing grease Tighter motor manufacturing tolerances Ground the motor shaft

82 Motor Bearing Damage Solutions Reduced motor peak voltage Fewer pulses from the drive Insulate the bearings Conductive bearing grease Tighter motor manufacturing tolerances Ground the motor shaft

83 Motor Bearing Damage Solutions Reduced motor peak voltage Fewer pulses from the drive Insulate the bearings Conductive bearing grease Tighter motor manufacturing tolerances Ground the motor shaft

84 Motor Bearing Damage Solutions Reduced motor peak voltage Fewer pulses from the drive Insulate the bearings Conductive bearing grease Tighter motor manufacturing tolerances Ground the motor shaft Next presentation topic!

85 Thank You! Questions?

Common Bus and Line Regeneration

Common Bus and Line Regeneration Addressing VFD applications when Regenerative Energy is Present Steve Petersen, Drives Technical Training Yaskawa America, Inc. Variable frequency drives (VFDs) are implemented