Electrical Motor Diagnostics Applications for Motors and Generators

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Kristian Burke
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Speaker BIO President MotorDoc LLC; VP MotorSight Corp; Treasurer SMRP; Web Editor in Chief IEEE DEIS; Managing Partner 2XL Powerlifting LLC Electrical Machinery and related systems condition,

VAD heart pump, Wind Turbines, specialty insulation systems application including nano dielectric materials SMRP advisor to Homeland Security on cyber physical and cybersecurity in relation to

1 Speaker BIO President MotorDoc LLC; VP MotorSight Corp; Treasurer SMRP; Web Editor in Chief IEEE DEIS; Managing Partner 2XL Powerlifting LLC Electrical Machinery and related systems condition, energy, power quality, repair/rewind and reliability programs and implementation Field service testing and vendor quality assurance Electrical Machinery research and design from hybrid vehicles, LEV VAD heart pump, Wind Turbines, specialty insulation systems application including nano dielectric materials SMRP advisor to Homeland Security on cyber physical and cybersecurity in relation to maintenance and reliability. 3 time World Champion Powerlifter, referee and gym owner. Member of Team Hope and Team USA Electrical Motor Diagnostics Applications for Motors and Generators Howard W Penrose, Ph.D., CMRP President MotorDoc LLC Lombard, Illinois Overview Offline Testing Low voltage motor circuit analysis High voltage motor circuit analysis Online Testing Electrical Signature Analysis (ESA) Relating ESA to Vibration Analyzing a Machine 1

2 What is a Motor System? Three-Phase Input Power The Electric Motor System Process Mechanical and Electrical Feedback Motor/Drive Subsystem Mechanical Subsystem 1200 rpm The Polyphase Induction Motor Stator Windings Stator Laminations Rotor Bearing Fan Interaction of Rotor Field and Stator Field Interaction of Two Magnetic Fields N Electrical Energy to Mechanical Torque Rotor Field Stator Field S 2

3 Rotating Fields Rotating Field and Rotor Cage Rotor Cage 3

4 Output Torque Operating Motor Coil Movement 4

Circuit Capacitance Changes due to charge Effects of atoms in Insulation medium.

5 STATOR LAMINATIONS Stator Failure Modes Turn to Turn Coil to Coil Open Circuit Phase to Phase Coil to Ground Insulation Diagram of Motor Phase A Ground Phase B Phase C Circuit Capacitance Changes due to charge Effects of atoms in Insulation medium. Dipoles are created As electric field crosses Atoms. As they align Capacitance increases. 5

6 The Dipole Neg Potential Pos Potential Dipolar Motion in Operation Capacitance High Wire Low GRND High Wire MegOhms High Ground Insulation Low Voltage High Dipolar Motion in DC Tests Neg Capacitance High GRND Low Neg Pos MegOhms High Meg Ohms Low Time 6

7 Basic Motor Circuit Resistance Inductance Capacitance Phase Angle Inductive Reactance X L Capacitive Reactance X C Impedance 2 2 R ( X L X C ) DC Armature 7

8 8

normally a DC electromagnet energized by either brushes/commutator ring or a dc generator

9 SYNCHRONOUS MOTOR Fixed pole magnet in rotor magnetic forces produced by the AC will induce the rotor to rotate at same speed as the stator supplied rotating magnetic field Rotating magnet normally a DC electromagnet energized by either brushes/commutator ring or a dc generator (excited) (c)2010, Dreisilker Construction: Stator Stator same as three phase machine (c)2010, Dreisilker 9

Rotor Power source to fields Excitation of fields determines power factor

10 THREE PHASE CURRENT Figure 7. Figure 8. Partially-Wound Induction-Motor Stator (c)2010, Dreisilker Construction: Rotor Power source to fields Excitation of fields determines power factor (leading, lagging or unity) Amortisseur Winding (c)2010, Dreisilker Synchronous Rotor (c)2010, Dreisilker 10

generator For Either Test rotor using impedance/inductance methods Change shaft position if fault found

13 Rotor (c)2010, Dreisilker (c)2010, Dreisilker Testing Synchronous Machines: Static Analysis If Static or Brush Excitation: Measure voltage and current to rotor If Brushless Excitation: Infrared of generator For Either Test rotor using impedance/inductance methods Change shaft position if fault found If readings rotate, the fault is in the rotor fields. If they stay in the same phase stator. (c)2010, Dreisilker 13

14 Testing Synchronous Machines: Dynamic RPM is synchronous Harmonics of synchronous are the same as power harmonics Trend when able Current higher than voltage harmonics (c)2010, Dreisilker A Few Simple (extra) Tests UV Flashlight 14

15 Motor Whisperer Microscope High and Low Voltage MCA 15

16 Ohm Testing A B C OHMab = 10.2 OHMac = 10.5 OHMbc = 10.7 Volt Ohm Standard Tolerance = 0.2 Ohms Milli-Ohm Meters = or better Micro-Ohm Meters = or better Temperature Correction K TC RC RH x K T H K TH RH RC x K T C Material K Aluminum 225 Copper R C = Resistance at Temperature T C (Ohms) R H = Resistance at Temperature T H (Ohms) T C = Temperature of Cold Winding (C) T H = Temperature of Hot Winding (C) Current Testing A B C Ia = 5.1 Amps Ib = 6.2 Amps Ic = 4.8 Amps 16

17 Insulation to Ground A B C 93.6 M Insulation Resistance Testing Results Winding Voltage IR DC Voltage < Correct Temperatures To 40 C Min Insulation Winding Being Tested Resistance at 1 min kv + 1 MegOhms Most windings made before MegOhms Form wound stators after MegOhms Random wound stators under 1,000 V after 1970 Adjust for Temperature 100 Winding Temp C Correction Factor Kt R40 = Kt x Rt

Dielectric Absorption Ratio of 1 Minute to 30 Second IR Testing Insulation DA Ratio Condition Dangerous < 1 Questionable 1.0 1.4 Good 1.4 1.6 Excellent > 1.

18 Dielectric Absorption Ratio of 1 Minute to 30 Second IR Testing Insulation DA Ratio Condition Dangerous < 1 Questionable Good Excellent > 1.6 Only accurate in insulation systems less than 5,000 MegOhms Polarization Index Ratio of 10 Minute to 1 Minute IR Testing Insulation PI Condition Dangerous < 1 Questionable Good Excellent > 4 Only accurate in insulation systems less than 5,000 MegOhms Insulation Resistance Profile Outlined in IEEE Std (Annex D) Been around a LONG time Review of 690 Vac, 4160 Vac and 13.8 kv machines Discussion of random wound machines 18

19 Evaluation of Wind Generator Winding (690 Vac) 800 hp 4160 Vac Motor 800 hp 4160 Vac Motor 19

20 800 hp 4160 Vac Motor IRP 13.8 kv 4500 hp Synchronous Motor Rotor Initial and New Data 20

21 It s Our Best Motor After Drying Rotor Discharge at lower end indicate dampness Higher end is aging Across entire curve indicates failing groundwall insulation system Degrading Rotor Insulation System After 4 months Identified excitation issues in addition to contamination Modifications arrested degradation 21

22 Post Repair Test Identical machine returned from rewind repair Evaluated rotor for insulation resistance profile What does this signify? Low Voltage MCA Before and After Defect Resistance Impedance Inductance Phase Angle I/F Ins Resist >99 MCA Result on 20 hp with contamination and slight phase to phase defect. Still running Resistance Impedance Inductance Phase Angle I/F Ins Resist >99 MCA test results following surge test from previous example. Trips on start. 22

23 Evaluation of Windings Winding Shorts Phase Angle and Current/Frequency Response Loose Connections Resistance Winding Contamination/Overheated Inductance and Impedance Rotor Condition and Severity Inductance and Impedance Waveforms Setting the Rules (MTME) Phase Angle and I/F readings Both Fi and I/F > +/ 2 Shorted Turns Fi > +/ 1, I/F Balanced Shorted Coils in the same phase Fi Balanced, I/F > +/ 2 Shorted Phase to Phase Rules stand regardless of motor size Resistance ~ +/ 5% Setting the Rules (Cont.) Impedance and Inductance If impedance and inductance are parallel, phase unbalance is most likely due to rotor position If impedance and inductance are not parallel, phase unbalances are most likely due to winding contamination or overheated winding. 23

24 Setting the Rules (Cont.) Inductive Rotor Tests Measurements of inductance due to rotor position will present an idea of the condition of a rotor due to casting voids or broken rotor bars. Measurements of impedance matched to inductance provides a relative severity of rotor condition. Rotor tests should be symmetrical and not necessarily perfect sine waves Example: Bad 15 HP (Garlic Mill) T1-T2 T1-T3 T2-T3 R Z L Fi I/F Megger >99M Note that both Fi (Phase Angle) and I/F (Current-Frequency Response) are bad. This Motor was still operating but tripping intermittently. The test results show that this Winding is shorted (most likely turn-to-turn shorts). Garlic Mill Motor Condition Phase 1 Phase 2 Phase 3 Resistance Impedance Inductance Phase Angle Note that the impedance and inductance are not parallel. This would indicate That the winding short was most likely the result of contamination or winding Overheating (burned insulation). 24

25 8,000 HP Synchronous Motor Case Study 8,000 HP, 200 RPM Synchronous Motor 36 rotor coils and 244 stator coils Failed on start up but unable to determine cause of fault over two days with surge testing and other winding test technologies 25% of compressed air capacity for chemical plant unavailable during downtime Motor circuit analysis applied in two tests rotor position 1 and rotor position 2 (next slide) which identified faults within the rotor (note winding faults show in both readings, but rotate with new position). Four rotor coils found to be directly shorted, causing a fault in the motor secondary circuit. Repaired and returned to service (See Case Study Synchronous ). Equipment Size Limits? 8,000 hp, 200 RPM, 13.2 kv, Synchronous T1-T2 T1-T3 T2-T3 Resistance Impedance Position 1 Inductance Phase Angle I/F Insulation #.# T1-T2 T1-T3 T2-T3 Resistance Position 2 Impedance Inductance Phase Angle I/F Insulation #.# 400 HP Motor with Bearing Problems 400 HP, 3600 RPM motor with continuous bearing faults Current Signature Testing shows non specific rotor fault MCA rotor test shows combination of casting void severe resulting in rotor heating, and eccentric rotor note curve of sine waves over time. Most likely combined casting void and eccentric endshield bearing fits. See next slide for rotor test results. 25

Rotor Analysis 400 hp, 2-Pole 1.2 Inductance 1.1 1 0.9 0.8 1 4 7 10 13 16 19 22 25 28 Position Impedance/Inductance Rotor Motor with rotor casting void.

26 Rotor Analysis 400 hp, 2-Pole 1.2 Inductance Position Impedance/Inductance Rotor Motor with rotor casting void. Will not severely impact operation (see indentations In side of sine-waves instead of peak) but will result in some twice line frequency Electrical vibration. Faults that will impact the motor s ability to produce torque will Impact peak or valley of sine-wave. Inductance (mh) Rotor Position Impedance (400Hz) Rotor Position 50 HP, 3600 RPM 400 HP Fault at Steel Mill High electrical vibration that increases as the motor heats up 26

Test Results Winding Test Rotor Test T1-T2 T1-T3 T2-T3 Resistance 0.

009 Impedance 6 6 6 Inductance 1 1 1 Phase Angle 53 52 53 I/F -40-40

27 Test Results Winding Test Rotor Test T1-T2 T1-T3 T2-T3 Resistance Impedance Inductance Phase Angle I/F Insulation #.# T1 T2 T3 Findings High Voltage MCA 27

28 Different Types Some do both high and low voltage MCA Resistance Low Voltage Tests 28

29 Insulation Resistance and HiPot IRP HiPot 29

30 Failed HiPot PD Surge Test ESA Analysis ESA Interpretation 30

31 Electrical Signature Analysis Impact of Current During Operation Benefit of ESA 31

32 Motor Faults Type of Fault Stator Mechanical Rotor Indicator Static Eccentricity Mechanical Unbalance Dynamic Eccentricity Stator Electrical (Shorts) Pattern (CF) CF = RS x Stator Slots LF Sidebands CF = RS x Rotor Bars LF Sidebands CF = RS x Rotor Bars LF and 2LF Sidebands CF = RS x Rotor Bars LF Sidebands and 2LF Signals CF = RS x Rotor Bars LF and 2LF Sidebands with Running Speed Sidebands CF = RS x Stator Slots LF Sidebands with Running Speed Sidebands Rotor Fault Sideband Values db Rotor Condition Assessment Recommended Action 60 Excellent None Good None Moderate Trend Condition High Resistant Connection or Cracked Bars Broken Rotor Bars Will Show in Vibration Multiple Cracked/Broken Bars, Poss Slip Ring Problems Increase Test Frequency and Trend Confirm with Vibration, Plan Repair / Replace Repair/Replace ASAP <30 Severe Rotor Faults Repair/Replace Immediately Good Airgap 32

33 Static Eccentricity Dynamic Eccentricity Effect on Shaft 33

Line Frequency Amplitude Modulation (LF = Carrier) 1 1 S

Twice Slip Frequency Safety Considerations PPE LOTO Test

Nameplate Horsepower (or kw) Voltage Current RPM Nice to

34 Line Frequency Amplitude Modulation (LF = Carrier) 1 1 S Cos ct bcos( c m) t bcos( c m) t 2 2 c m Sidebands: Intensity proportional to strength! RPM RPM PPF 2( RPM s r ) s xlf Rotor fault sidebands: Twice Slip Frequency Safety Considerations PPE LOTO Test for Power Equipment Information Minimum (For ESA) from Nameplate Horsepower (or kw) Voltage Current RPM Nice to have Rest of Nameplate Number of Rotor bars and stator slots Bearing information 34

35 Software Database and US DOE s MM+ Can Help Collect MCSA Data Connect Check Connections Check Voltage and Current At least 1 phase current at a minimum Take Data Compare/Trend as Necessary Before Repair After Repair 35

36 Driven Load and Coupling Belted Fan Motor sheave = 3, Sheave center to center = 30 inches, Driven Sheave = 12 FS (Fan Shaft Spd) = PF x FS = RS x PMd FS = 29.5 Hz x (3/12) = Hz or RPM BL (Belt Length) = 30 x2x1/2(cir[pf+pm]) = 60 x ½( x 3 + x 12) = CIR = πdpm = π x 3 (assume 1770 RPM) = (π x 3 x 1770)/60Sec = in/sec Driven Load and Coupling Belted Fan Since the belt length = then: BS = /83.55 = Hz (RPS) Note: Sidebands of BS = Belt flapping As V = Rw where R1 = 1.5 and R2 = 6 and w1 = 1770 FS = (1.5/6) x 1770 = RPM Blade Pass Frequency (BPF) = 6 x FS = 6 x / LF (3600 rpm in Current Spectrum) Or = 6 x 442.5/60 Hz in demod spectrum Driven Load and Coupling Direct Fan RS (Motor Speed) = FS (Fan Speed) Assume RS = 1170 RPM FS = 1170 RPM (19.5 Hz) BPF = Assume 10 Blade Fan = 10 x 19.5 Hz (demod) = 195 Hz 36

37 Driven Load and Coupling Direct Fan GM = Gear attached to motor drive (10 teeth) GF = Gear attached to fan (100 teeth) Motor = 3570 RPM = 59.5 Hz FS = RS x (GM/GF) = 3570 x (10/100) = 357 RPM = 5.95 Hz Gear Tooth Mesh Freq = RS x GM = 10 x 3570 = 35,700 +/ 3600 Or = 595 +/ 60 Hz Static and Dynamic Eccentricity +/- 180 Hz Figure 2: Dynamic Eccentricity +/- 60 Hz +/- 180 Hz +/- 60Hz CF = Hz Figure 1: Static Eccentricity +/ Hz CF = Hz Stator Winding Problems CF = Hz +/ Hz 37

38 Mechanical Analysis Bearings NTN 6305 Brg BPOR = BPIR = xBSF =.372 FTF = BPOR BPIR xBSF FTF Hz Hz Faulty outer Race of bearing Line Freq. Sidebands Driven Equipment Analysis Belts 880 RPM (14.67 Hz) 1760 RPM (29.33 Hz) 40 C-C 4 Diameter 8 Diameter Driven Equipment Gear Mesh 352 RPM (5.87 Hz) 100 Teeth 20 Teeth 1760 RPM 38

39 Driven Equipment Blade Pass Six Blades (88Hz) Shaft speed = Hz The Bringing It Together Case Motor Info 1750 RPM 40 Rotor Bars 48 Stator Slots 50 HP, 58 A, 460 V 2x NTN 6310 brgs Fan 12 Blades 2 x NTN 6315 brgs Motor Operating Info 1755 RPM 57, 59, 56 Amps 464, 470, 466 Volts 6 inch inch Determine Rotor Bars and Static and Dynamic Eccentricity Frequencies Fan -20dB 3 Hz Sidebands 12 Blades 60 Hz Motor Mtr Run Freq = Hz Eccentricity CF = 1170 Hz Stator CF = 1404 Hz 6 inch inch 39

40 Determine Motor Bearing Frequencies and Mechanical Unbalance Motor NTN 6310 Brgs BPOR = BPIR = xBSF =.384 FTF = BPOR BPIR xBSF FTF Mechanical Unbalance CF = 1170 Hz Belt Speed Frequencies and Driven Speed 1755 RPM Hz RPM 9.75 Hz 6 inch 18 inch Belt length = inches Conveyor Speed = inches per second Belt Frequency = 3.74 Hz Fan Bearing and Blade Pass Frequencies Blade Pass Frequency = 117 Hz NTN 6315 Brgs BPOR = BPIR = xBSF =.385 FTF = Fan 12 Blades BPOR BPIR xBSF FTF

41 Consolidation and Review of Data Motor Calculated Values Nameplate 1750 Operating RPM 1755 Line Freq 60 Hz Driven Freq 9.75 Hz RPM Rotor Bars 40 Operating 57,59, 56 Motor Running Hz Belt Length Amps Freq Rotor Stator Slots 48 THD N/A CF 1170 Hz Conv Freq IPS HP, Amp, 50hp, 58A, Operating Volts 464,4704 Volt 460V 66 Stator CF 1404 Hz Belt Freq 3.74 Hz Mtr Brgs NTN 6310 Fan Brgs NTN 6315 Blade Pass 117 Hz Bearing Frequencies NTN BPOR BPIR xBSF FTF NTN BPOR BPIR xBSF FTF Evaluation of FFT Data Fan 12 Blades Motor , SUCCESS Frequency by DESIGN Evaluation of FFT Data Fan 12 Blades Motor One time and three time line frequency CF 120, 240, 120 Mechanical Unbalance Amps Frequency 41

ESA of Synchronous Motor Electric Motor Shaft Failures New design 800 and 600 horsepower, 480 Vac motors and VFDs Motors are

purchasing separate VFD and installation of VFD No direct communication between vendors or end user Problem started in May, 2013,

failed data was tampered with Additional issues yet another third party was brought in to perform additional balancing Weights

42 ESA of Synchronous Motor Electric Motor Shaft Failures New design 800 and 600 horsepower, 480 Vac motors and VFDs Motors are designed and run to 125% of load with a slow down to 45Hz Annealing oven manufacturer assembled machine, end user saved money by purchasing separate VFD and installation of VFD No direct communication between vendors or end user Problem started in May, 2013, finally resolved in March, 2015 Initial Investigations Drive tuning claimed (discovered in October, 2014, never performed) When failed data was tampered with Additional issues yet another third party was brought in to perform additional balancing Weights placed 180 from where they should have been Welds not sure where grounded Discovery First time machine was never prototyped Emotions and Egos 42

43 Data Data Data Pointed to materials Pointed to manufacturing Pointed to the phases of the moon Installed a different 600 hp (same manufacturer) no failure Discovery run at half load All failures occurred in full load conditions Used to say aha but no conclusions Kept adding additional components to motor Ignored data Vibration/Torsional/Driverelated First and Second Tuning of Drive Return in February,

44 VFD 1 VFD 2 VFD 3 44

45 Low Frequency Data (High Resolution) High Frequency Data Torque Ripple 45

high still in ESA and vibration under full load Additional drive adjustments are necessary to soften torque and

46 Discussion A combination of high torsional vibration/ Torque Ripple with side load Failure close to 90 degrees as a result 45 degrees would have identified immediately Tuning of the drive dropped level significantly Extremely high still in ESA and vibration under full load Additional drive adjustments are necessary to soften torque and prevent drive from reacting too fast Gain Turn off energy saver Electrical Signature Analysis Misalignment or Unbalance 46

47 Gearbox Fault Classic Rotor Bar Punch Press 47

48 Fan Belt Issue Loose Coils Static Eccentricity 48

National Labs) Industry Assumption magnetic wedges June 2015 (C) 2015

49 Machine Failures Generator insulation systems failing at an alarmingly high rate Previously was gearboxes as second in failure only to blades As solutions became available for fracturing bearings in gearboxes, generators were found to account for 7% unavailability of turbines (CREW Sandia National Labs) Industry Assumption magnetic wedges June 2015 (C) 2015 MotorDoc LLC 145 Winding Failure 146 (C) 2015 MotorDoc LLC June 2015 (C) 2015 MotorDoc LLC

slot Wedges brittle so vibrate and crack/fail June 2015 (C) 2015 MotorDoc LLC 151 Stripping Process Approach Stripping process 410F or less Maintains an intact insulation system The intact

51 Evaluation of Machines Evaluated a series of generators across 690V to 12.4kV All failures occurred at top edge of slot where wedge was missing All failures direct to ground Iron dust present throughout stator in all cases Previous Assumptions: Failure blew wedge out of slot Wedges brittle so vibrate and crack/fail June 2015 (C) 2015 MotorDoc LLC 151 Stripping Process Approach Stripping process 410F or less Maintains an intact insulation system The intact insulation system allows for analysis of materials Interesting Notes: Following ignition of on brand of generator at these temperatures (coil end insulation systems caught fire) Discovered that the coils could be removed cold with a few exceptions June 2015 (C) 2015 MotorDoc LLC 152 Winding Analysis 153 (C) 2015 MotorDoc LLC 51

Evaluation of Materials Reviewed coil materials Abrasion on coil materials in slots Peeled back layers and reviewed materials underneath in both

system Found packing systems on many models were inexpensive matting type June 2015 (C) 2015 MotorDoc LLC 157 Findings/Discussio n Primary Issue

possible, not always using space heaters Design consideration Hey folks environment is 360 degrees!

53 Evaluation of Materials Reviewed coil materials Abrasion on coil materials in slots Peeled back layers and reviewed materials underneath in both areas with wedges and without Found top edges where wedges were missing (in direction of rotation) had iron filings migrating through insulation system Found packing systems on many models were inexpensive matting type June 2015 (C) 2015 MotorDoc LLC 157 Findings/Discussio n Primary Issue Manufactured with coils relatively loose in slots counted on global VPI Thermal shock especially in colder climates/times of year Online as fast as possible, not always using space heaters Design consideration Hey folks environment is 360 degrees! Use of different packing materials from rigid to ripple springs Tighter coils in slots Others are manufacturerspecific. June 2015 (C) 2015 MotorDoc LLC 158 Moving On June (C) 2015 MotorDoc LLC 53

Application of Electrical Signature Analysis. Howard W Penrose, Ph.D., CMRP President, SUCCESS by DESIGN

Application of Electrical Signature Analysis Howard W Penrose, Ph.D., CMRP President, SUCCESS by DESIGN Introduction Over the past months we have covered traditional and modern methods of testing electric