©2004 Fluke Corporation Introduction to Motor Troubleshooting 1 Introduction to Motor Troubleshooting

©2004 Fluke Corporation Introduction to Motor Troubleshooting 2 Motors are the number one consumer of electrical power

©2004 Fluke Corporation Introduction to Motor Troubleshooting 3 Power consumption based on size

©2004 Fluke Corporation Introduction to Motor Troubleshooting 4 Standard motor operating conditions

©2004 Fluke Corporation Introduction to Motor Troubleshooting 5 Special purpose motor operating conditions

©2004 Fluke Corporation Introduction to Motor Troubleshooting 6 Motor failure

©2004 Fluke Corporation Introduction to Motor Troubleshooting 7 Troubleshooting fuses

©2004 Fluke Corporation Introduction to Motor Troubleshooting 8 Taking motor voltage measurements

©2004 Fluke Corporation Introduction to Motor Troubleshooting 9 Measuring motor voltage unbalance

©2004 Fluke Corporation Introduction to Motor Troubleshooting 10 Measuring motor control circuit transformer

©2004 Fluke Corporation Introduction to Motor Troubleshooting 11 Measuring motor current

©2004 Fluke Corporation Introduction to Motor Troubleshooting 12 Measuring temperature

©2004 Fluke Corporation Introduction to Motor Troubleshooting 13 Measuring motor insulation

©2004 Fluke Corporation Introduction to Motor Troubleshooting 14 Megohmmeter reading interpretation

©2004 Fluke Corporation Introduction to Motor Troubleshooting 15 Motor power measurements

©2004 Fluke Corporation Introduction to Motor Troubleshooting 16 Testing motor capacitors

©2004 Fluke Corporation Introduction to Motor Troubleshooting 17 Electrical measurements on adjustable speed drives

©2004 Fluke Corporation Introduction to Motor Troubleshooting 18 Voltage ratings Category ratings Safe practices De-energize circuits Use protective gear Do not exceed instrument voltage and category ratings Use 3-point test method Test known live circuit Test target circuit Test known live circuit again Avoid holding the meter Measurement category Working voltage (dc or ac-rms to gnd) Peak impulse transient (20 repetitions) Test source (Ohm = V/A) CAT I600V2500V30 ohm source CAT I1000V4000V30 ohm source CAT II600V4000V12 ohm source CAT II1000V6000V12 ohm source CAT III600V6000V2 ohm source CAT III1000V8000V2 ohm source CAT IV600V8000V2 ohm source Making safe measurements

©2004 Fluke Corporation Introduction to Motor Troubleshooting 19 Adjustable speed drive – theory

©2004 Fluke Corporation Introduction to Motor Troubleshooting 20 Theory of operation DC converter section supplies constant DC level Rms motor voltage is varied by the width of the PWM pulse Motor drive signal frequency is controlled by the modulation frequency Pulse-width modulated inverter

©2004 Fluke Corporation Introduction to Motor Troubleshooting 21 Motors – measurement 1: Low voltage Low voltages Check for voltage drops across connectors, or Check for heated connections Analog meters Reads the average voltage of the modulation frequency of the PWM drive Meter may not have IEC safety rating Digital multimeter Current DMMS read higher than analog meter on PWM drives because they responding to the entire frequency spectrum of the drive signal. These DMM are not giving inaccurate readings. Exception: New DMMs that include low-pass filters

©2004 Fluke Corporation Introduction to Motor Troubleshooting 22 Motors – measurement 1: Low voltage Using the ASD display 230 volts (calculated) Using a true-rms meter 247 volts 20 KHz B/W Using an averaging meter 230 5KHz B/W Using a voltage tester Hz B/W Using an oscilloscope255 (avg) 20MHz B/W Using a power 253 (avg) 20MHz B/W quality analyzer 243 3KHz B/W Hz Using an analog meter Hz

©2004 Fluke Corporation Introduction to Motor Troubleshooting 23 Max. Deviation (V or I) % (V or I) Imbalance =X 100 Average (V or I) = X 100 = 2.39 % 460 For example: Motors - measurement 2: Voltage & current unbalance Check for voltage unbalance (< 2 %) first, then Check for current unbalance (< 10 %) 123

©2004 Fluke Corporation Introduction to Motor Troubleshooting 24 Normal PWM waveform PWM waveform with reflected voltages Leading edge of normal PWM pulse Leading edge of PWM pulse with reflected voltage (ringing) PWM drives – measurement 3: Overvoltage reflections at the motor terminals

©2004 Fluke Corporation Introduction to Motor Troubleshooting 25 PWM drives – measurement 3: Overvoltage reflections at the motor terminals Overvoltage reflections at the motor terminals. Damages the motor windings Shorten cable if possible If motor is worth repairing, consider rewinding with better insulated wire such as TZ Q (by Phelps Dodge) If new motor is required, use one that meets NEMA MG Part 31 specifications (can tolerate sustained voltage peaks of 1600 V and rise times >100 ns) Use filtering if none of the above is feasible Try to mitigate overvoltages to <900 V for standard motors

©2004 Fluke Corporation Introduction to Motor Troubleshooting 26 Possible remedies for overvoltage reflections PWM drives – measurement 3: Overvoltage reflections at the motor terminals

©2004 Fluke Corporation Introduction to Motor Troubleshooting 27 PWM drives – measurement 4: Motor shaft voltages Bearing currents: occur when shaft voltages exceed insulating capability of the grease Higher breakdown voltages of V occur due to the fast edge of the PWM pulse First signs of this problem = noise and overheating caused by pitting and loosened metal fragments Use an oscilloscope to view shaft voltages measured between the motor shaft and the grounded frame using stranded wire or a carbon brush

©2004 Fluke Corporation Introduction to Motor Troubleshooting 28 Bearing currents: occur when shaft voltages exceed insulating capability of the grease Make the measurement after the motor has heated up Simplest solution is to lower the carrier frequency to less than 10 kHz, or down to 4 kHz if possible Shaft grounding devices, bearing insulation, faraday shield in the motor, conductive grease or filtering between the ASD and the motor PWM drives – measurement 4: Motor shaft voltages

©2004 Fluke Corporation Introduction to Motor Troubleshooting 29 Bearing currents: occur when shaft voltages exceed insulating capability of the grease Make the measurement after the motor has heated up Simplest solution is to lower the carrier frequency to less than 10 kHz, or down to 4 kHz if possible Shaft grounding devices, bearing insulation, faraday shield in the motor, conductive grease or filtering between the ASD and the motor PWM drives – measurement 4: Motor shaft voltages

©2004 Fluke Corporation Introduction to Motor Troubleshooting 30 PWM drives – measurement 5: Leakage currents (common mode noise) Leakage currents flow in capacitive coupling between the stator windings and frame ground. The faster rise times and switching frequencies of the PWM pulse can increase leakage Interferes with 4-20 ma control signals and PLC communications Increased leakage currents pose potential safety problems and may cause ground fault protection relays to trip

©2004 Fluke Corporation Introduction to Motor Troubleshooting 31 To measure, place current clamp around all three motor conductors at the inverter output Use an oscilloscope to examine the CMN waveform Possible solutions: special EMI suppression cables, isolation transformers on the line input, or a common mode choke PWM drives – measurement 5: Leakage currents (common mode noise)

©2004 Fluke Corporation Introduction to Motor Troubleshooting 32 PWM drives – measurement 6: Testing the IGBT output waveshape 1.Connect the scope common lead to the dc+ bus and measure each of the three phases at the inverter’s motor output terminals. Check for clean-edged square waves with no visible pulse noise. Verify that all three phases have the same appearance. 2.Check the negative conducting IGBTs by connecting the common lead to the dc- bus and performing step 1 on each phases at the inverter’s motor output terminals.

©2004 Fluke Corporation Introduction to Motor Troubleshooting 33 PWM drives – measurement 7: Testing the IGBT outputs for leakage Measure voltage from earth ground to the inverter’s motor output terminals with the drive powered on and speed set to zero (motor stopped). If leaky, the voltage will be elevated 3 or 4 times normal. Perform this measurement on a known good drive to determine what is normal for that drive.

©2004 Fluke Corporation Introduction to Motor Troubleshooting 34 PWM drives – measurement 8: ASD “trip” problems – overloading Cause of overloading = too much motor current Verify motor load is not causing the problem Check for excessive current unbalance (possible shorted phase windings) Verify ASD trip points are set correctly Is dc bus voltage being regulated properly? Leaky capacitors (too much ripple, too little inrush current) Link inductor OK? (waveform different or same on both sides?)

©2004 Fluke Corporation Introduction to Motor Troubleshooting 35 PWM drives – measurement 9: ASD “trip” problems – overvoltage Check for high line voltage and/or long term variations Check for line transients Lightening protection in place? Proper wiring and grounding? Isolation from transient producing loads? Verify ASD trip points are set correctly Is load regenerative (cranes, elevators)? If so, is dynamic braking installed and working properly? Is dc bus voltage being regulated properly? Leaky capacitors (too much ripple, too little inrush current) Link inductor OK? (waveform different or same on both sides?)

©2004 Fluke Corporation Introduction to Motor Troubleshooting 36 Overvoltage transient capture with a power quality analyzer. PWM drives – measurement 9: ASD “trip” problems – overvoltage

©2004 Fluke Corporation Introduction to Motor Troubleshooting 37 PWM drives – measurement 10: ASD “trip” problems – undervoltage Check for low line voltage and/or long term variations Verify ASD trip points are set correctly Is dc bus voltage being regulated properly (dc link capacitors and/or reactor) Check for voltage sags

©2004 Fluke Corporation Introduction to Motor Troubleshooting 38 Check for flat topping of the input voltage PWM drives – measurement 10: ASD “trip” problems – undervoltage

©2004 Fluke Corporation Introduction to Motor Troubleshooting 39 Check for V THD < 5 % at the point of common coupling (PCC), not the ASD Check power factor. Utilities may start charging for distortion power factor. Check for I THD < ? % at PCC, not the ASD (% depends on short circuit current ratio of PCC) PWM drives – bonus measurement: ASDs and IEEE-519 measurements

©2004 Fluke Corporation Introduction to Motor Troubleshooting 40 Series resonant tuned LC shunt filter. Series resonant tuned LC shunt filter with series line reactor. PQ troubleshooting: Transformer solutions – Three phase filter traps

©2004 Fluke Corporation Introduction to Motor Troubleshooting 41 Samples load current for harmonic content Generates harmonic frequencies demanded by load Source supplies 60 Hz only Current distortions typically less than 5 % PQ troubleshooting solutions: Active harmonic compensation devices

©2004 Fluke Corporation Introduction to Motor Troubleshooting 42