VFD Theory Craig Hartman, P.E. Specializing in Motors, Drives, Generators, and Electrical Asset Management

Transcription

1 VFD Theory Craig Hartman, P.E. Specializing in Motors, Drives, Generators, and Electrical Asset Management

2 When was the microprocessor invented? Intel 4004, the first general-purpose, commercial microprocessor a) 1969 b) 1942 c) 1921 d) 1977 Specializing in Motors, Drives, Generators, and Electrical Asset Management

3 Answer: a The microprocessor was invented by Ted Hoff, at Intel, for Busicom, a Japanese calculator manufacturer. It was first advertised in November of 1971 and cost thousands of dollars. It is fascinating to note that the first manned landing on the moon was also in Apollo 11 launched from Kennedy Space Center on July 16, Neil Armstrong became the first man to walk on the moon, stepping on its surface on July 20 th. Twelve people have landed on the moon. Specializing in Motors, Drives, Generators, and Electrical Asset Management

4 ENIAC Electronic Numerical Integrator And Computer The first Turing-complete general-purpose electronic computer built to calculate artillery firing tables for the US Army s Ballistic Research Lab. It was a classified military project known as Project PX. Completed on Feb 14, 1946, it utilized 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors, and 5 million hand soldered joints. It weighed 30 tons, occupied 1800 square feet of floor space, and used 160kW of electricity. It was also used in the development of the hydrogen bomb. VFD Theory: 4

5 The First Super-Computer Hard Drive In September, 1956, IBM launched the 305 RAMAC, the first Super-Computer with a hard disk drive (HDD). The HDD weighed over a ton and stored a whopping 5MB of data. This photo shows the portable version. By comparison, a 16GB flash drive holds about 3200 times as much data. VFD Theory: 5

6 How to identify a meth lab VFD Theory: 6

7 6-pulse Converter AC to DC Converter 480 V A B C VFD Theory: 7

8 Add DC bus AC to DC Converter DC Bus +650Vdc 480 V A B C + - 0Vdc VFD Theory: 8

9 Pre-Charge Circuit A B C + - On power-up, the capacitor charges through the pre-charge resistor. Once the dc bus reaches rated voltage, the contactor (or transistor) bypasses the resistor. VFD Theory: 9

10 Add Inverter AC to DC Converter DC Bus +650Vdc DC to AC Inverter 480 V A B C + - M 0Vdc VFD Theory: 10

11 PWM Output to Motor 650V 480 V 60 Hz VFD Theory: 11

12 PWM Output to Motor 650V 480 V 60 Hz 650V 240 V 30 Hz VFD Theory: 12

13 PWM Output to Motor 650V 480 V 60 Hz 650V 240 V 30 Hz 650V 80 V 10 Hz VFD Theory: 13

14 PWM Waveforms Specializing in Motors, Drives, Generators, and Electrical Asset Management

15 Pulse Width Modulation (Pseudo Sine Wave) Carrier Frequency = 1kHz Light Load VFD Theory: 15

16 Pulse Width Modulation Carrier Frequency = 1kHz Light Load Carrier Frequency = 1kHz Full Load VFD Theory: 16

19 PWM frequency Advantages of high carrier frequency Lower acoustic noise level VFD Theory: 19

20 PWM frequency Advantages of high carrier frequency Lower acoustic noise level Disadvantages of high carrier frequency Lower VFD efficiency Increased VFD heating Shortens VFD life Increased motor heating Higher overshoot peak voltages Harder on motor insulation Exacerbates peak voltage concerns Increased radiated electro-magnetic noise Increased ground leakage currents in motor cable and motor capacitances VFD Theory: 20

21 VFD Construction Specializing in Motors, Drives, Generators, and Electrical Asset Management

22 VFD Internals Cooling Fan AC to DC Inverter (2 transistors per module) Heat Sink DC Bus Capacitors DC Bus AC to DC Converter (2 diodes per module) Variable Frequency Drive circa 1980 s AC Power Input Power Output to Motor VFD Theory: 22

23 VFD Internals Transistor Snubber Control Board Capacitor discharge resistors Variable Frequency Drive circa 1980 s Capacitor pre-charge circuit VFD Theory: 23

24 VFD No Harmonic Mitigation AC to DC Converter Filter DC to AC Inverter DC Filter Capacitor M TH Free-wheeling diodes VFD Theory: 24

25 Internals USB programming port Serial Comms RS485 Modbus RTU Option Slots (3)) Variable Frequency Drive circa 2010 s VFD Theory: 25

26 VFD (with line reactor) 6-Pulse VFD Line Reactor 3-Contactor Bypass VFD Theory: 26

27 VFD (2-reactor harmonic filter) 6-Pulse VFD Harmonic Filter Capacitor Harmonic Filter Reactors 3-Contactor Bypass VFD Theory: 27

28 VFD VFD Device Island VFD Theory: 28

29 Why isn t this VFD working? VFD Theory: 29

30 Why isn t this VFD working? VFD Theory: 30

31 VFD VFD Theory: 31

32 Dual VFD s (harmonic filter with dc-link and ac rectors) 6-Pulse VFD Dc-link reactor Harmonic filter capacitors dv/dt filter Harmonic filter reactors VFD Theory: 32

33 VFD (3-reactor harmonic filter with dc link reactor) 6-Pulse VFD Harmonic filter capacitors Dc-link reactor dv/dt filter Harmonic filter reactors VFD Theory: 33

34 VFD s in custom assembly VFD Theory: 34

35 VFD s in custom assembly VFD Theory: 35

36 VFD s in Motor Control Center VFD Theory: 36

37 VFD s in Motor Control Center VFD Theory: 37

38 NEMA 3R Custom Enclosure (front) VFD Theory: 38

39 NEMA 3R Custom Enclosure (internal) VFD Theory: 39

40 NEMA 3R Custom Enclosure (rear) VFD heat sink extends out the rear of the enclosure VFD Theory: 40

41 NEMA 3R Custom Enclosure (rear) VFD heat sink extends out the rear of the enclosure VFD Theory: 41

42 NEMA 3R Custom Enclosure (installed) VFD Theory: 42

43 Constant Torque vs Variable Torque Variable Torque (VT) refers to centrifugal pump and fan applications. Their load torque varies in proportion to the square of motor speed. Constant Torque (CT) refers to most other applications. Their load torque is based on friction losses which are relatively constant at all speeds These terms can be confusing and misleading. With a fixed speed setting, over time, fan and pump loads fluctuate less than many other applications The fundamental difference between VT and CT is the VFD overload rating VT ratings typically range from 0% to 20% overload for one minute CT ratings are typically 50% overload for one minute VFD Theory: 43

44 Speed Range VFD Theory: 44

45 Control Methods F700 A500 A700 A700/ V500 Speed Control Torque Control Position Control VFD Theory: 45

46 Regenerative Braking Resistor Braking Resistor Chopping Transistor Converter DC Link Inverter L1 L2 L3 Control Logic M Regenerative Power Flow Regenerative Power Flow VFD Theory: 46

47 Power-Down Braking Keeps the motor under control even if supply power is lost. Improved safety for critical applications e.g. centrifuge, machine tool VFD Theory: 47

48 Optimum Excitation Control Greater energy savings at constant speed or during acceleration/deceleration Internal calculations are used to sense the motor current and apply the ideal output voltage for the load condition. VFD Theory: 48

49 Motor Peak Voltages & dv/dt Specializing in Motors, Drives, Generators, and Electrical Asset Management

50 dv/dt Reflective Wave Phenomenon Voltage wave reflection is a function of the voltage rise time (dv/dt) and the length of the motor cables. Impedance mismatches cause voltage pulses to be reflected back in the direction from which they arrive. As these reflected waves encounter incoming waves, their values add, causing higher peak voltage. As wire length or carrier frequency increases, the overshoot peak voltage also increases. This causes motor insulation degradation and failure. Resonant Circuit Phenomenon Electrical systems of every nature have a natural frequency. When system components have a resonant frequency that matches the natural resonant frequency of the system, peak voltages can quickly exceed standard reflective wave overshoots. VFD Theory: 50

51 Voltage Stress Vrated 600 Volts ALL MOTORS (NEMA MG1 Part 30) VFD MOTORS (NEMA MG1 Part 31) Vrated > 600 Volts Vpeak 1kV 3.1 * Vrated Rise time 2µs 0.1µs Vpeak 2.04 * Vrated 2.04 * Vrated Rise time 1µs 1µs Vrated is the line-to-line voltage Vpeak is a single amplitude zero-to-peak line-to-line voltage. For 480V: Recommend voltage spikes be limited to 1000V and dv/dt to 1000V/µs VFD Theory: 51

52 Typical Voltage Response at Motor Terminals NEMA MG-1 Vpeak Voltage 100% Steady-state voltage 90% V dv dt = V t 10% t Rise time Time VFD Theory: 52

53 Common mode voltage Common mode voltage occurs when the voltages on the three output lines of a drive do not sum instantaneously to zero. dv/dt filters slow down the rate of change of PWM switching as seen by the load. This reduction in the rate of change results in increased capacitive coupling impedance between bearings and bearing races. This increase in impedance, in turn, reduces the damaging Common Mode currents. Courtesy TCI VFD Theory: 53

54 dv/dt Courtesy TCI VFD Theory: 54

55 dv/dt Courtesy TCI VFD Theory: 55

56 dv/dt Is there another way? VFD Theory: 56

57 dv/dt (proprietary solution) Mitsubishi Soft PWM Changes acoustic motor noise from a metallic tone into an unoffending complex tone. Protects motors from dv/dt for longer lead lengths. PWM Frequency 1 hp and below 2hp 3 hp and above 2 khz 300 meters 500 meters 500 meters 3-15 khz 200 meters 300 meters 500 meters Note: Assumes NEMA MG1-Part 31VFD-rated motor insulation VFD Theory: 57

58 Soft PWM Noise Reduction VFD Theory: 58

59 dv/dt filter dv/dt filter Reduces voltage spikes to below 1000 Volts Slows down PWM dv/dt by a factor of 3 Reduces common mode currents by approximately 30% Protects both the motor and the cable insulation Recommendations Consider when VFD-to-motor cable length exceeds 100 ft Option: Leave room in VFD cabinet and install only if required Stay within filter manufacturer s recommendations for carrier frequency Use proprietary solution Hint If motor runs fine on sine wave power, but trips on VFD, then have the motor surge tested by a qualified motor rewind shop. Note: Keep the VFD to motor voltage drop to 2% or less VFD Theory: 59

60 VFD s & Motor Bearings Specializing in Motors, Drives, Generators, and Electrical Asset Management

61 Electric Motor Design 460 VAC 60Hz = Most electric induction motors were designed for operation on 3 phase sign wave power either 50 or 60 Hz. The input power was balanced in frequency, phase (120 degrees apart) and in amplitude. Common mode voltage the sum of the 3 phases would always equal zero volts. Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 61

62 Electric Motor Operation by VFD + = When operated by VFD, the power to the motor is a series of pulses instead of a smooth sign wave. The input power is never balanced because the voltage is either 0 volts, positive, or negative with rapid switching between pulses. The Three phases of voltage pulses ensures that the common mode voltage is never equal to zero and instead is a square wave or 6 step voltage. Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 62

63 What effect does this have on the bearings? Voltage builds up until it exceeds the insulation level of the bearing s oil film layer the break-down voltage of the bearing. The voltage then arcs through the bearing creating an electrical discharge machining (EDM) pit. Thousands of pits per second may be created and over time the ball rolling over the disturbed surface can cause fluting damage. Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 63

65 Bearing Discharge Voltage Pattern Bearing Discharge ~50 nano sec. Creates EDM pitting Voltage Increase & drop Signifying Current flow through Bearings Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 65

67 Motor Bearing Damage from Electrical Currents Electrical Discharge Machining (EDM) Bearing Pitting Damage Electron Microscope (SEM) Image 1000x Magnified Bearing Fluting Damage EDM Pit EDM Pitting 67 Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved

68 Mitigation Techniques VFD Waveform Mitigation Bearing Insulation Alternate Discharge Paths Sine Wave Filter Bearing Insulating Sleeve Ceramic Bearings Conductive Grease (Not in current use) Grounding Brush Shaft Grounding Ring Expense, produces heat Expense, does not protect driven equipment, capacitive coupling may allow currents to pass through insulation, contamination Expense, does not protect driven equipment Conductive particles would increase mechanical wear, rendering lubricants ineffective. Expense, wear, contaminants, oxidation, maintenance Expense (lower than others above), contamination Sine-wave filter Ceramic Bearing Ceramic Insulated Bearing VFD Theory: 68

69 New Conductive Microfiber Shaft Grounding Technology Uses several methods to transfer electrical currents* Direct Contact Conduction Electrical Contact without mechanical contact by field emission *IEEE paper, September 2007: Design Aspects of Conductive Microfiber Rings for Shaft Grounding Purposes, by Dr. Annette Muetze et. Al. Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 69

70 Micro Fiber Shaft Grounding Ring Discharges shaft voltages to ground Easy to install Maintenance free Improves VFD motor bearing reliability Best ROI - Small investment Addresses the root cause of the problem (shaft currents) Diverts the shaft current away from the motor bearings Protects motor with highly reliable solution Longest lasting protection Wear rate less than 1 mill per 10,000 hours operation Lasts for over 200,000 hours operation 2 million direction reversals - Zero fiber fatigue or broken fibers Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 70

71 AEGIS SGR Bracket Mounted Shaft Grounding Ring Fits most motor end brackets Drill and tap for mounting brackets and small screws Ring slides over shaft Easy Installation Applications OEM installations All VFD driven Motors HVAC Industrial Process Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved

72 Standard Mounting Brackets Shaft diameters: to 6.02 (8mm to 153mm) Ships with mounting brackets, screws and washers Quick and easy installation to most surfaces Split Ring Shaft diameters: to 6.02 (8mm to 153mm) 4 to 6 mounting brackets, screws and washers Installs without decoupling motor Bolt Through Mounting Shaft diameters: to 6.02 (8mm to 153mm) M3 x 14 socket head cap screws and lock washers 2 mounting holes up to shaft size 99mm 4 mounting holes for larger sizes Press Fit Mounting Shaft diameters: to 6.02 (8mm to 153mm) Clean dry 0.102mm press fit Custom sizes available NEMA-IEC Mounting Kits Shaft diameters: see chart for standard kits Custom kits available for other shaft diameters Clears any slinger, shaft shoulder or protrusion Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved

73 AEGIS SGR Conductive Epoxy Mounting Split ring or solid ring Installs with Conductive Epoxy to clean metal surface No drilling holes or tapping for screws Best solution for field installation Applications Pump motors Fan Motors Mechanical Rooms Coupled Equipment Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved

74 AEGIS CS015 Colloidal Silver Shaft Coating Enhances shaft surface conductivity lowers residual shaft voltage Can be used in all AEGIS Bearing Protection Ring installations Required for vertical motors and roller bearings Helps prevent oxidation Applications For shaft grounding ring installations in harsh areas Included in all ipros Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved

76 Large Low and Medium Voltage Motors over 100 HP AEGIS Shaft Grounding Ring on DE Insulated bearing on ODE Stator Shaft Rotor V F D Ground Copyright 2010 Electro Static Technology-ITW Patented Technology All Rights Reserved 76

77 TM GE Automations Systems MV ASD & Systems School ASD Fundamentals & MV Drive Evolution M IEGT Voltage Controlled Gate Driver Equipment IEGT Gate Drive Board IEGT 4.5kV-4kA IEGT = Injection Enhanced Gate Transistor Copyright TM GE Automation Systems March 2011 Slide #77 We drive industry

78 TM GE Automations Systems MV ASD & Systems School ASD Fundamentals & MV Drive Evolution Building Block for MV PWM Drives M Q1 Q1 Q1 E E E Q2 Q2 Q2 +E 0V -E E Q3 E Q3 E Q3 Q4 Q4 Q4 NPC: Neutral Point Clamped Configuration Multiple supply voltage levels allows good waveforms Compatible with IGBT, GCT, IEGT Devices Copyright TM GE Automation Systems March 2011 Slide #78 We drive industry

79 TM GE Automations Systems MV ASD & Systems School ASD Fundamentals & MV Drive Evolution Complete 3 Level Circuit, Neutral Point Clamped M 3 Level inverter is M 2 times higher output voltage 2 times larger capacity Twice as clean waveform +E 3 Level 3 Level Inverter 0V -E Q1 Q1 Q1 E E Q2 Q3 E E Q2 Q2 +E 0V -E E E Q3 Q3 Line to Line 3 / 5 levels Including zero Q4 Q4 Q4 3 Level phase output voltage Copyright TM GE Automation Systems March 2011 Slide #79 Output voltage of 3 Level Inverter We drive industry

80 TM GE Automations Systems MV ASD & Systems School ASD Fundamentals & MV Drive Evolution M Progress of Inverter Circuits to High Capacity 5 Level Inverter 3 Level Inverter 2 Level Inverter 3 Low voltage application 460V, 690V Large capacity 3kV - 15MVA 6kV~7kV, 8MVA~120MVA High voltage, large capacity, clean waveform Copyright TM GE Automation Systems March 2011 Slide #80 We drive industry

81 TM GE Automations Systems MV ASD & Systems School ASD Fundamentals & MV Drive Evolution M MV IGBT Drive with Integral Transformer INCOMING POWER INVERTER SECTION BYPASS CONTACTOR [option] TRANSFORMER & DC CONVERTER DRIVE CONTROL Copyright TM GE Automation Systems March 2011 Slide #81 We drive industry

82 TM GE Automations Systems MV ASD & Systems School ASD Fundamentals & MV Drive Evolution M Line up of Large Capacity Inverters kv, 5 level output 5 Level IGBT Inverter Capacity: 6kV - 8MVA 5 Level IEGT Inverter Capacity: 7kV - 30MVA up to 30MVA x 4 = 120 MVA 5 Level IEGT Inverter Capacity: 6kV - 20MVA, up to 20MVA x 4 = 80 MVA Copyright TM GE Automation Systems March 2011 Slide #82 We drive industry

83 VFD Custom Assembly Shop VFD Theory: 83

84 VFD Repair Area VFD Theory: 84

85 VFD Inventory VFD Theory: 85