T10 - Preventative Maintenance Techniques for Motor and Drives 12:00-12:50p

Transcription

1 T10 - Preventative Maintenance Techniques for Motor and Drives 12:00-12:50p Philip Mondro, SE Fluke IG Everett, WA Philip.Mondro@fluke.com

2 Where do we keep all the secrets: First a couple slides

3 Drive Trouble Shooting DV/DT Filter Overheat Cannot start, tripping After stop, cannot start Bearing damage Vibration 7/12/2018 Output fault Elevated motor temperatures Improper operation or Drive failure Damage to bearings includes spark erosion which can lead to vibration. Noisy motor Drive output voltage and current faults Breakdown of motor winding insulation. Tripping of overvoltage circuits, causing downtime. Life-shortening damage to shaft, bearings, drive, cabling, and motor. 3

4 Electrical + Mechanical Strategy Covered drive tests and measurements line side to load side. Input Power Quality with Fluke-435 Drive & Drive output with Fluke MDA-550, Motor Drive Analyzer II Mechanical Vibration with Fluke 810

5 Fluke Motor Drive Analyzer Sales Guide Nominal supply voltage, current and frequency Voltage and current unbalance Transients Harmonics Power factor 7/12/2018 DC Bus Voltage unbalance Current unbalance Sigma Current and PE Current Output reflections Disturbances Harmonics Volt to Hertz ratio Diagnostic shutdown Grounding Motor overload Single phasing Bearing failures Misalignment* Mechanical imbalance* Looseness Insulation breakdown Shaft voltage and bearing current Grounding *: Require Mech. tools 5

6 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Fluke Test Tool Line Logic Positioning Fluke-435-II Power Quality Analyzer Used by electrical engineers to test for power quality issues or discover energy consumption waste Fluke-438-II PQ & Motor Analyzer Used by plant and facility electrical engineers to test for PQ, Energy and check motor mechanical performance and efficiency Fluke MDA-550 Motor Drive Analyzer Used by field service engineers and plant equipment maintenance engineers to troubleshoot and maintain motor drive system. Comprehensive, guided drive measurements, cover system from end-to-end 6

7 Introducing Fluke Motor Drive Analyzer Fluke MDA 550 Simplify end to end testing and analysis of complex motor drive systems by; Providing users with guided setup, automatic measurements and context based help Simplifying the task of triggering on and capturing complex waveforms to discover drive failures Delivering new measurements not available in standard hand held oscilloscopes, eliminating the need for additional tools or complex data crunching

8 Fluke Motor Drive Analyzer Sales Guide Current State Workflow Using Existing Portable Oscilloscopes M&D Troubleshooting Workflow Challenges Complex connections & manually configuring lots measurements Difficult to trigger on complex Pulse Width Modulated waveforms Unfamiliar with drive test procedure with infrequent usage/testing Does not include all measurements needed Takes time to capture and assemble as-found, as-left report Leads To Potential miss-diagnosis Time consuming In consistent, unreliable measurements data Frustration 7/12/2018 8

9 Fluke Motor Drive Analyzer Sales Guide Workflow with Fluke Motor Drive Analyzer 1 2? 3 4 Pick Measurement Subsection Connect Test Tool Correctly Refresh knowledge Automatically see relevant measurements Document all measurements in one memory Fluke Motor Drive Analyzer Benefits Avoid mistakes, automatically setup relevant measurements Eliminate hassle of triggering on complex PWM waveforms Have information at your fingertips builds confidence and enhances reputation Covers all basic to advanced measurements that could ever be needed Easily and conveniently, with a press of a button, capture and assemble as-found, as-left report Leads To Isolating problem to root cause Reduce time spent on service calls Obtain consistent reliable measurement data Perform regular route based measurement efficiently Create reports for archiving and Predictive Maintenance 7/12/2018 9

10 Fluke MDA Capabilities 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Report Press F1 to Initiate or Close Report Create a single memory location for all screen captures Press F1 at each test point to accumulate all report data points in a single memory loc 10

11 Fluke Motor Drive Analyzer Sales Guide Fluke MDA Features & Benefits Feature Benefit Quantified Customer Value Measure key motor drive parameters Provides guided measurements Simplified measurement setup Quickly and easily create reports Measure additional electrical parameters Improve diagnostics with comprehensive suite of specific drive measurements to test the complete drive Reduce risk of setup errors when connecting the voltage leads and current probes and indicates areas where users should be troubleshooting. Setup complex measurements without having to understand how to configure difficult to use test tool like an oscilloscope Use reports to capture, document and archive data for predictive maintenance purposes or obtaining signoff after repairs or commissioning. Use ScopeMeter test tool to troubleshoot beyond the drive, for example drive control signals, feedback sensors or digital communications Effectively troubleshoot drive, get to root cause. Lower cost of repairs and in-warranty claims Reduce turn around time. Labor cost $/hr Extend lifespan of drive system, avoid failures. Reduce capital expenses Increase maintenance effectiveness, reduce downtime. 7/12/

12 Fluke MDA Capabilities Fluke Motor Drive Analyzer Sales Guide Motor Drive Input Automatic Measurement Options Measurement and Analysis Combinations Test Point Sub Group Reading 1 Reading 2 Reading 3 Reading 4 Motor Drive Input Voltage and Current Phase-Phase Voltage and Current Phase-Ground Voltage Unbalance Current Unbalance V-A-Hz V AC+DC A AC+DC Hz V Peak V Peak max V Peak min V pk-to-pk Crest Factor A Peak A Peak max A Peak min A pk-to-pk Crest Factor V-A-Hz V AC+DC A AC+DC Hz V Peak V Peak max V Peak min V pk-to-pk Crest Factor A Peak A Peak max A Peak min A pk-to-pk Crest Factor Unbalance V AC+DC V AC+DC V AC+DC Unbalance Peak V pk-to-pk V pk-to-pk V pk-to-pk Unbalance A AC+DC A AC+DC A AC+DC Unbalance Peak A pk-to-pk A pk-to-pk A pk-to-pk 7/12/

13 Fluke Motor Drive Analyzer Sales Guide Voltage and Current Measurements Connection Points Nominal Drive Input Measurements Compare RMS voltage against nominal voltage. More than 10% out of range means there is a supply voltage problem. If voltage is out of range: Check if current is within local current capacity Check if conductor size is within specification for the current. Compare frequency against the specified frequency. More than 0.5Hz difference could cause problems. Measurement can be repeated for the other phases. 7/12/

14 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Supra Harmonics F3=Scale Options 1-9 khz or KHz band Harmonics Supra Harmonics bands of 1-9kHz and 9-150kHz band can be viewed as FFT/Spectrum Indicative only!! May show e.g. switching frequency of other motor drive with active front end (energy feed back) 14

15 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Voltage Unbalance Connect 3 Voltage Probes 3 Waveforms shown simultaneously Unbalance is highest percentage difference of one of the phase vs average voltage Used to check if there are voltage levels differences between the phases and if the phase displacement is 120 degrees. High voltage unbalance reading can indicate phase failures. Even a reading of over 0.3% can lead to voltage notching and can cause tripping the drive`s overload fault protection or disturb other equipment. 15

16 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Current Unbalance Connect 3 Current Clamps 3 Waveforms shown simultaneously Unbalance is highest percentage difference of one of the phase vs average current Use Current Unbalance to check if there are current level differences between the phases and if the current phase displacement is 120 degrees. Current Unbalance reading of over 6% is potentially problematic. Excessive current unbalance can point to voltage unbalance or drive rectifier problems. 16

17 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Motor Drive DC Bus Connection Points DC Bus Measurements DC Level Check the value and stability of the internal DC-bus and influence of power feedback and braking (if supported by the drive). Except for controlled rectifiers (IGBT) inputs, the voltage should be about 1.31 to 1.41 times the RMS line voltage. A low DC voltage can trip the drive. This can be caused by a low input mains voltage or the input voltage is distorted by flat topping. Use the RECORD function to check the DC voltage variations over time. AC Ripple After the AC to DC conversion a slight AC ripple component will remain present on the DC-bus. The shape will depend on the conversion principle. If the peaks of the ripple have a different repetitive level, one of the rectifiers could be malfunctioning. Ripple voltages above 40V can be caused by malfunctioning capacitors or undersized drive for the motor and load. Use the RECORD function to check the ripple voltage variation over time. 17

18 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Connection Points Drive Output Measurements Measures voltage between 2 of the phases and current on one of the phases. Check if the drive output voltage and current are within the limits for the motor. If the output current is too high, the motor may run hot and could result in decrease of stator insulation life. Check if the voltage/frequency ratio (V/Hz) is within specified limits for the motor. If V/Hz too high the motor may overheat, if V/Hz too low the motor will lose torque. Stable Hz, unstable V points to DC bus problems. Unstable Hz, stable V points to IGBT problems. Unstable Hz and V points to speed control circuits. 18

19 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Connection Points Drive Output Measurements Phase to phase is mainly used to check for high voltage peaks. These may damage the motor insulation and drive output circuit and cause the drive to trip. Voltage peaks higher than 50% of nominal voltage are often problematic. Phase to ground is mainly used to measure switch frequency and identify high voltage peaks to ground that could damage the motor insulation. Phase to DC or DC+ is also used to measure switch frequency, identify IGBT problems or when signal is floating up and down this may indicate system grounding problem. 19

20 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Connection Points Drive Output dv/dt Measurements Check if the steepness of the switching impulses indicated by the dv/dt reading, is within motor insulation specification. Risetime can be shown as PEAK per IEC or LEVEL per NEMA MG1 Part

21 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Voltage Unbalance Connection Points Output 3-Phase Waveforms Perform this measurement preferably at full load. Voltage unbalance should not be more than 2%. Voltage unbalance causes current unbalance that will eventually result in excessive heat in the motor windings. Possible causes are: one of the phase drive circuits is faulty one of the output currents is so large that it overloads the drive output. This can point to shorted motor windings or phase(s) shorted to ground. When one of the phases shows a failure this is called 'single phasing'. It can cause the motor to run hot, not start after stopping and loose efficiency. A phase failure may be due to drive output malfunction or bad connection between drive and motor. 21

22 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Current Unbalance Connection Points Output 3-Phase Waveforms Generally, current unbalance for three phase motors should not exceed 10%. Large current unbalance, while voltage unbalance is low, could point to shorted motor windings or phase(s) shorted to ground. Large current unbalance can cause drive tripping, high motor temperatures and burnt windings. When one of the phases shows a failure this is called 'single phasing'. It can cause the motor to run hot, not start after stopping and loose efficiency. A phase failure may be due to drive output malfunction or bad connection between drive and motor. 22

23 Fluke 7/12/2018 Motor Drive Analyzer Sales Guide Connection Points Motor Input Measurements Same Measurements as Motor Drive Output Saved to Report stores measurements separately Measuring on output of motor shows influence of cable Fluke MDA-550 beta test customer proved their was issue at input of Motor Overshoot of >100% Caused by 80 Meter cable not suited for application Leads to breakdown of winding insulation 23

24 Fluke MDA Capabilities 7/12/2018 Fluke Motor Drive Analyzer Sales Guide Automatic Measurement Options Measurement and Analysis Combinations Test Point Sub Group Reading 1 Reading 2 Reading 3 Reading 4 MDA 550 Only Motor Shaft Events off V pk-to-pk Shaft Voltage Events on Delta V Rise/Fall time Delta V/s Events/s The gap between the Stator Winding and Rotor Bars behave as capacitor, allowing current to flow due to higher PWM carrier frequency. Small electrical charge builds up in the rotor, until eventually it exceeds the insulation between the bearing surfaces, discharging to earth ground causing flashover. Bearing grease gradually fails and surfaces 24 exhibit phenomena called fluting

25 Connection Points Motor Shaft Measurements Uses the carbon brush probe to measure the voltage between motor chassis and drive shaft. Detect bearing flashover currents that may damage motor bearings. Fast edges of the switching voltage from a drive may result in shaft voltage. MDA-550 proved issue with electrical discharges More than 100 events per second More than 15V and faster than 50 ns 7/12/2018 Fluke Motor Drive Analyzer Sales Guide 25

26 Copy report to USB drive Document all measurements as saved for one motor drive and create report on PC Copy to USB drive results in series of PNG files Directory name is name of the Report Filenames automatically created PNG files can be directly opened or included in eg. Word file USB drive limited to 2GB Max, included in MDA-550 FlukeView 2 can Open Report as stored on USB drive All PNG files opened at once Can be printed at once 7/12/2018 Fluke Motor Drive Analyzer Sales Guide 26

27 Transfer Report to PC Document all measurements as saved for one motor drive and create report on PC FlukeView 2: Support 190 Series II in addition to 120B Important Reports from MDA directly or open from USB drive FV1 FV2 7/12/2018 Fluke Motor Drive Analyzer Sales Guide 27

28 Fluke MDA 510 and Fluke MDA 550 Motor Drive Analyzer and ScopeMeter test tool Simplify end to end testing and analysis of complex motor drive systems

29 Interpreting the thermal signatures of key components in the motor drive input Use a thermal imager to scan the component and look for irregular and nonuniform thermal patterns or anomalies. Diagnostic benefit: Identify hot spots, cold spots, or unexpected conditions faster and safer than contact measurements alone. Arrive at problem resolution faster. Avoid damage to the motor drive.

30 Correcting misalignment In the case of misalignment, use a laser shaft alignment tool to quickly check and correct misalignment.

31 Interpreting looseness measurements Fluke 810 Using an extensive database reference it does the interpretation for you

32 Tools for ma loop troubleshooting What can be measured or sourced Measure 4 ma to 20 ma signals Source 4 ma to 20 ma signals Simulate 4 ma to 20 ma signals Measure 24 V loop voltage Supply 24 V loop voltage Source 0 V to 10 V, 1 V to 5 V Continuity measurements Measurement and sourcing tool DMM. Loop calibrator, ma clamp, ProcessMeter Loop calibrator, ma clamp, ProcessMeter Loop calibrator, Fluke 772 or 773 ma Clamp, ProcessMeter DMM, Loop calibrator, Fluke 773 ma Clamp, ProcessMeter Loop calibrator, ma clamp, Fluke 789 ProcessMeter Loop calibrator with voltage source (715) or specialized ma Clamp (773) DMM, ProcessMeter, some multifunction process calibrators What it tells the technician If the measured ma value is the expected value If the I/O or other ma input device is working correctly If the power supply, wiring and I/O is working correctly, perform transmitter substitution test If the full 24V supply available, if it is defective or being loaded down? If a substitution test for installed supply fixes the problem If the I/O or other voltage input device is working correctly Find open circuits, bad terminations, resistive connections and mis-wires

33 773 ma loop measurement test Measure a ma signal without breaking the loop 1. Power on the 773, zero and connect to wire shown from the pressure span indicator 2. Compare the % of span of the 773 to the trainer indicator, should be close to agreement. 3. Disconnect 789 and reconnect wire from #10 to #6 1

34 Common problems in control loops Wiring and termination problems Loop power supplies Control system I/O Transmitters Sensors Temperature transmitter Temperature input Current output Percent of span 0 C 4 ma 0 % 75 C 8 ma 25 % 150 C 12 ma 50 % 225 C 16 ma 75 % 300 C 20 ma 100 % Pressure transmitter Pressure input Current output Percent of span 0 psi 4 ma 0 % 25 psi 8 ma 25 % 50 psi 12 ma 50 % 75 psi 16 ma 75 % 100 psi 20 ma 100 %

35 Causes of errors in ma control signals Defective or mis-adjusted transmitter Defective pressure or temperature sensor Clogged input to pressure transmitter Resistive wiring or wiring connections Bad wiring insulation Overloaded or defective power supplies

36 Causes of a noisy signal Bad insulation Cable shielding breakdown Ground loops Marginal power supplies Cable routing errors

37 Troubleshooting for signal noise Measure noise View with a scope Troubleshooting step: Measure AC voltage with DMM View with a scope Should only be a few millivolts ACV

38 Testing insulation Leakage test Troubleshooting step: Disconnect wires on both ends and ensure not touching each other or ground Test against each other and cable shield Measureable resistance indicates cabling leakage problems

39 Where do we keep all the secrets: In the Library! Visit us today Booth 89

40 13 common causes of motor failure Application Note What to look for and how to improve asset uptime Motors are used everywhere in industrial environments and they are becoming increasingly complex and technical, sometimes making it a challenge to keep them running at peak performance. It s important to remember that the causes of motor and drive issues are not confined to a single domain of expertise both mechanical and electrical issues can lead to motor failure and being armed with the right knowledge can mean the difference between costly downtime and improved asset uptime. Winding insulation breakdown and bearing wear are the two most common causes of motor failure, but those conditions arise for many different reasons. This article demonstrates how to detect the 13 most common causes of winding insulation and bearing failure in advance. Power quality 1. Transient Voltage 2. Voltage Imbalance 3. Harmonic Distortion Variable frequency drives 4. Reflections on drive output PWM signals 5. Sigma current 6. Operational overloads Drive and drive output Mechanical 7. Misalignment 8. Shaft imbalance 9. Shaft looseness 10. Bearing wear Improper installation factors 11. Soft foot 12. Pipe strain 13. Shaft voltage Motor and drive train From the Fluke Digital

41 Power quality 1 Transient voltage Transient voltages can come from a number of sources either inside or outside of the plant. Adjacent loads turning on or off, power factor correction capacitor banks or even distant weather can generate transient voltages on distribution systems. These transients, which vary in amplitude and frequency, can erode or cause insulation breakdown in motor windings. Finding the source of these transients can be difficult because of the infrequency of the occurrences and the fact that the symptoms can present themselves in different ways. For example, a transient may appear on control cables that don t necessarily cause equipment damage directly, but may disrupt operations. Impact: Motor winding insulation breakdown leads to early motor failure and unplanned downtime Instrument to measure and diagnose: Fluke 435-II Three-Phase Power Quality Analyzer Criticality: High 2 Voltage imbalance L1 L2 L3 L3 L2 L1 Three-phase distribution systems often serve single-phase loads. An imbalance in impedance or load distribution can contribute to imbalance across all three of the phases. Potential faults may be in the cabling to the motor, the terminations at the motor, and potentially the windings themselves. This imbalance can lead to stresses in each of the phase circuits in a three-phase power system. At the simplest level, all three phases of voltage should always have the same magnitude. Impact: Imbalance creates excessive current flow in one or more phases that then increases operating temperatures leading to insulation breakdown Instrument to measure and diagnose: Fluke 435-II Three-Phase Power Quality Analyzer Criticality: Medium 2 Fluke Corporation 13 common causes of motor failure

42 3 Harmonic distortion Simply stated, harmonics are any unwanted additional source of high frequency AC voltages or currents supplying energy to the motor windings. This additional energy is not used to turn the motor shaft but circulates in the windings and ultimately contributes to internal energy losses. These losses dissipate in the form of heat, which, over time, will deteriorate the insulation capability of the windings. Some harmonic distortion of the current is normal on any part of the system serving electronic loads. To start investigating harmonic distortion, use a power quality analyzer to monitor electrical current levels and temperatures at transformers to be sure that they are not overstressed. Each harmonic has a different acceptable level of distortion, which is defined by standards such as IEEE Impact: Decrease in motor efficiency results in added cost and an increase in operating temperatures Instrument to measure and diagnose: Fluke 435-II Three-Phase Power Quality Analyzer Criticality: Medium Variable frequency drives 4 Reflections on drive output PWM signals Tolerance envelope Captured waveform Voltage waveform Variable frequency drives employ a pulse width modulation (PWM) technique to control the output voltage and frequency to a motor. Reflections are generated when there is an impedance mismatch between the source and load. Impedance mismatches can occur as a result of improper installation, improper component selection or equipment degradation over time. In a motor drive circuit, the peak of the reflection could be as high as the DC bus voltage level. Impact: Motor winding insulation breakdown leads to unplanned downtime Instrument to measure and diagnose: Fluke ScopeMeter fast sampling 4 channel portable oscilloscope. Criticality: High 3 Fluke Corporation 13 common causes of motor failure

43 5 Sigma current du/dt = 3 kv/µs PE I = C.dU/dt = = 3A pp C = 1 nf = 10-9 As/V Sigma Current M Current flow through rotor caused by dv/dt Sigma currents are essentially stray currents that circulate in a system. The sigma currents are created as a result of the signal frequency, voltage level, capacitance and inductance in conductors. These circulating currents can find their way through protective earth systems causing nuisance tripping or in some cases excess heat in windings. Sigma current can be found in the motor cabling and is the sum of the current of the three phases at any one point in time. In a perfect situation, the sum of the three currents would equal zero. In other words, the return current from the drive would be equal to the current to the drive. Sigma current can also be understood as asymmetrical signals in multiple conductors that can capacitively couple currents into the ground conductor. Impact: Mysterious circuit trip due to protective earth current flow Instrument to measure and diagnose: Fluke ScopeMeter isolated 4 channel portable oscilloscope with wide bandwidth (10kHz) current clamp (Fluke i400s or similar). Criticality: Low 6 Operational overloads Motor Load Motor overload occurs when a motor is under excessive load. The primary symptoms that accompany a motor overload are excessive current draw, insufficient torque and overheating. Excessive motor heat is a major cause of motor failure. In the case of an overloaded motor individual motor components including bearings, motor windings, and other components may be working fine, but the motor will continue to run hot. For this reason, it makes sense to begin your troubleshooting by checking for motor overload. Because 30 % of motor failures are caused by overloading, it is important to understand how to measure for and identify motor overloading. Impact: Premature wear on motor electrical and mechanical components leading to permanent failure Instrument to measure and diagnose: Fluke 289 Digital Multimeter Criticality: High 4 Fluke Corporation 13 common causes of motor failure

44 Mechanical 7 Misalignment Angular misalignment Parallel misalignment Misalignment occurs when the motor drive shaft is not in correct alignment with the load, or the component that couples the motor to the load is misaligned. Many professionals believe that a flexible coupling eliminates and compensates for misalignment, but a flexible coupling only protects the coupling from misalignment. Even with a flexible coupling, a misaligned shaft will transmit damaging cyclical forces along the shaft and into the motor, leading to excess wear on the motor and increasing the apparent mechanical load. In addition, misalignment may feed vibration into both the load and the motor drive shaft. There a few types of misalignment: Angular misalignment: shaft centerlines intersect but are not parallel Parallel misalignment: shaft centerlines are parallel but not concentric Compound misalignment: a combination of parallel and angular misalignment. (Note: almost all misalignment is compound misalignment, but practitioners talk about misalignment as the two separate types because it is easier to correct a misalignment by addressing the angular and parallel components separately.) Impact: Premature wear in mechanical drive components that leads to premature failures Instrument to measure and diagnose: Fluke 830 Laser Shaft Alignment Tool Criticality: High 8 Shaft imbalance VdB The large peak of 124 VdB at 1X running speed is caused by the imbalance The other peaks are caused by different pheomena in the machine Orders Imbalance is a condition of a rotating part where the center of mass does not lie on the axis of rotation. In other words, there is a heavy spot somewhere on the rotor. Although you can never completely eliminate motor imbalance, you can identify when it is out of normal range, and take action to rectify the problem. Imbalance can be caused by numerous factors, including: Dirt accumulation Missing balance weights Manufacturing variations Uneven mass in motor windings and other wear-related factors. A vibration tester or analyzer can help you determine whether or not a rotating machine is in balance. Impact: Premature wear in mechanical drive components that leads to premature failures Instrument to measure and diagnose: Fluke 810 Vibration Tester Criticality: High 5 Fluke Corporation 13 common causes of motor failure

45 9 Shaft looseness Looseness occurs when there is excessive clearance between parts. Looseness can occur in several places: Rotating looseness is caused by excessive clearance between rotating and stationary elements of the machine, such as in a bearing. Non-rotating looseness happens between two normally stationary parts, such as a foot and a foundation, or a bearing housing and a machine. As with all other sources of vibration, it is important to know how to identify looseness and resolve the issue to avoid losing money. A vibration tester or analyzer can determine whether or not a rotating machine is suffering from looseness. Impact: Accelerated wear on rotating components resulting in mechanical failure Instrument to measure and diagnose: Fluke 810 Vibration Tester Criticality: High 10 Bearing wear Damage Bearing race A failed bearing has increased drag, emits more heat, and has lower efficiency because of a mechanical, lubrication, or wear problem. Bearing failure can be caused by several things: A heavier load than designed for Inadequate or incorrect lubrication Ineffective bearing sealing Shaft misalignment Incorrect fit Normal wear Induced shaft voltages Once bearing failure begins, it also creates a cascade effect that accelerates motor failure. 13 % of motor failures are caused by bearing failure, and more than 60 % of the mechanical failures in a facility are caused by bearing wear, so learning how to troubleshoot this potential problem is important. Impact: Accelerated wear on rotating components resulting in bearing failure Instrument to measure and diagnose: Fluke 810 Vibration Tester Criticality: High 6 Fluke Corporation 13 common causes of motor failure

46 Improper installation factors 11 Soft foot Machine based Parallel soft foot Angular soft foot Foundation based Soft foot refers to a condition in which the mounting feet of a motor or driven component are not even, or the mounting surface upon which the mounting feet sit is not even. This condition can create a frustrating situation in which tightening the mounting bolts on the feet actually introduces new strains and misalignment. Soft foot is often manifested between two diagonally positioned mounting bolts, similar to the way that an uneven chair or table tends to rock in a diagonal direction. There are two kinds of soft foot: Parallel soft foot parallel soft foot occurs when one of the mounting feet sits higher than the other three Angular soft foot angular soft foot occurs when one of the mounting feet is not parallel or normal to the mounting surface. In both cases, soft foot can be caused either by an irregularity in the machine mounting feet, or in the mounting foundation upon which the feet rest. In either case, any soft foot condition must be discovered and remedied before proper shaft alignment can be achieved. A quality laser alignment tool can typically determine whether or not there is a soft foot problem on a particular rotating machine. Impact: Misalignment of mechanical drive components Instrument to measure and diagnose: Fluke 830 Laser Shaft Alignment Tool Criticality: Medium 12 Pipe strain Pipe strain refers to the condition in which new stresses, strains, and forces, acting on the rest of the equipment and infrastructure transfer backward onto the motor and drive to induce a misalignment condition. The most common example of this is in simple motor/pump combinations, where something applies force to the pipeworks such as: A shift in the foundation A newly installed valve or other component An object striking, bending, or simply pressing on a pipe Broken or lack-of pipe hangers or wall-mounting hardware Those forces can put an angular or offset force on the pump, which in turn causes the motor/pump shaft to be misaligned. For this reason it is important to check machine alignment more than just at the time of installation precision alignment is a temporary condition that can change over time. Impact: Shaft misalignment and subsequent stresses on rotating components, leading the premature failures. Instrument to measure and diagnose: Fluke 830 Laser Shaft Alignment Tool Criticality: Low 7 Fluke Corporation 13 common causes of motor failure

47 13 Shaft voltage When motor shaft voltages exceed the insulating capability of the bearing grease, flashover currents to the outer bearing will occur, thereby causing pitting and grooving to the bearing races. The first signs of this problem will be noise and overheating as the bearings begin to lose their original shape and metal fragments mix with the grease and increase bearing friction. This can lead to bearing destruction within a few months of motor operation. Bearing failure is an expensive problem both in terms of motor repair and downtime, so helping to prevent this by measuring shaft voltage and bearing current is an important diagnostic step. Shaft voltage is only present while the motor is energized and rotating. A carbon brush probe attachment allows you to measure shaft voltage while a motor is rotating. Impact: Arcing across bearing surfaces create pitting and fluting resulting in excessive vibration and eventual bearing failure Instrument to measure and diagnose: Fluke ScopeMeter isolated 4-channel portable oscilloscope, with AEGIS shaft voltage carbon brush probe. Criticality: High Four strategies for success Motor control systems are being utilized in critical processes throughout manufacturing plants. Equipment failure can result in high monetary losses both from potential motor, or parts, replacement and from equipment downtime for the system the motor powers. Arming maintenance engineers and technicians with the right knowledge, prioritizing workload and managing preventative maintenance to monitor equipment and troubleshoot intermittent, elusive problems can, in some cases, avoid failures due to normal system operating stresses and reduce overall downtime costs. There are four key strategies that you can undertake to restore or prevent premature failures in motor drive and rotating component: 1. Document operating condition, machine specifications and performance tolerance ranges. 2. Capture and document critical measurements at installation, before and after maintenance and on a routine basis. 3. Create an archive reference of measure ments to facilitate trend analysis and identify change of state conditions. 4. Plot individual measurements to establish a baseline trend. Any change in trend line of more than +/- 10 % to 20 % (or any other % determined, based on your system performance or criticality) should be investigated to root cause to understand why the issue is occurring. Fluke. Keeping your world up and running. Fluke Corporation PO Box 9090, Everett, WA U.S.A. Fluke Europe B.V. PO Box 1186, 5602 BD Eindhoven, The Netherlands For more information call: In the U.S.A. (800) or Fax (425) In Europe/M-East/Africa +31 (0) or Fax +31 (0) In Canada (800)-36-FLUKE or Fax (905) From other countries +1 (425) or Fax +1 (425) Web access: Fluke Corporation. Specifications subject to change without notice. Printed in U.S.A. 11/ A_EN Modification of this document is not permitted without written permission from Fluke Corporation. 8 Fluke Corporation 13 common causes of motor failure