3 phase Electric induction Motor Testing

Electric Motor Testing

1. (C) 2006, SUCCESS by DESIGN
Motor Testing (Motor Only)

2. (C) 2006, SUCCESS by DESIGN
Overview
•IEEE P1415: “Draft Guide for Induction
Machinery Maintenance Testing and
Failure Analysis”
•Key to Understanding Condition-Based
Monitoring and Troubleshooting is to
understand the capabilities and limitations
of testing technology

3. (C) 2006, SUCCESS by DESIGN
Overview
•Focus of This Presentation
–Stator Winding and Core
–Rotor Winding and Core
–Vibration and Noise
–Bearings and Shafts
–Structure and Frame
–Ventillation
–Accessories

4. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•AC High Potential
–2Ev + 1,000V for new
–125-135% of nameplate for existing
–Pass/Fail
•Acceleration Time
–Changes may indicate power supply problems
–Trending if conditions are identical
•Bearing Insulation
–Evaluate for reduced shaft currents
–Follow IEEE Std 43-2000 (up for re-affirmation in
October, 2005)
–Pass/Fail

5. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Bearing Temperature by RTD
–Thermocouple or Bulb-Type
–Temperature limits vary but generally fall in the range
of 90-100C for alarm and 105-120C for shutdown
–Higher temp limits for synthetics
–Trendable with temp correction
•Capacitance
–Trended value
–Surface contamination, high humidity, high
temperature or general insulation breakdown
–Effective for trending

6. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Core Loss (Loop Test)
–During motor repair to detect inter-laminar insulation
damage
–No hot spots greater than 10C from ambient core
temperature
–If value shown: <6 Watts/lb and no change from
before and after winding removal
–Pass/Fail
•Coupling Insulation
–Ensure no shaft currents into driven equipment
–IEEE Std 43-2000
–Pass/Fail

7. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Current, Demodulation
–Used in ESA and MCSA as a method of removing the
fundamental frequency from current FFT spectra
–Trendable
•Current, Running
–Indication of load
–Pulsating current, measured with an analog probe will indicate
rotor faults
–Not trendable
•Current, Signature Analysis
–Provides analysis of electro-mechanical condition and driven
equipment condition
–Analysis of current FFT spectra
–Trendable

8. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Current, Starting
–Inrush and starting current is evaluated for anomalies
–Trendable
•DC High Potential
–Trendable when leakage recorded
–(2Ev + 1000V) x 1.7 new insulation
–Value x 0.65-0.75 for used insulation
–A sudden increase in leakage current indicates a fault
–Trendable

9. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Dissipation Factor and Power Factor
–Utilize AC at the rated voltage of motor
–Trended value should not exceed a change of 2%
•Grease Analysis
–Used to trend and evaluate deterioration of lubrication
properties
–Trendable
•Growler (explain where name from)
–Used to evaluate the condition of rotor bars when the
rotor is removed from the electric motor
–Pass/Fail

10. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Insulation Resistance
–Measures insulation value (leakage converted to MegOhms)
–IEEE Std 43-2000
–Trendable
•Oil Analysis
–Used to evaluate the degradation of the lubricating properties of
oil
–Detect excessive mechanical wear
–Trendable
•Partial Discharge
–Measurement of capacitive discharges
–Generally trended on machines over 6kV
–Trendable

11. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Phase Angle
–The timed measurement between the peak voltage
and current at about 7Vac applied to a coil
–Compare two coils +/-1 digit from average
–Trendable
•Phase Balance (Z and L)
–Used to detect severe winding unbalances
–Detect inter-turn winding contamination
–Compare phase to phase patterns between
impedance and inductance
–Trendable

12. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Polarization Index
–Ratio of 10 minute and 1 minute insulation resistance tests
–A ratio of 2 or more is required on pre-1970 insulation
systems
–Trending required on newer insulation
•Single-Phase Rotor Test
–10% of motor nameplate voltage applied across one
phase of motor
–Rotor is turned and current values taken
–Variations of 3% or more over 360 degrees of rotation
indicate rotor bar fault
–Not trendable

13. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Shaft Grounding Current
–Measurement of shaft current
–Trendable
•Shaft Testing
–Magnetic particle, liquid penetrant and ultrasonic
examination used to evaluate condition of shaft
material
–Pass/fail
•Shaft Voltage
–Measurements taken from shaft of motor
–Variations may indicate problems with the motor
–Trendable

14. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Speed
–Uses measurements of motor RPM in order to
determine if potential motor or load problems exist
–Trendable
•Surge Test
–High frequency, high voltage impedance-based test to
check turn-to-turn dielectric strength
–Comparison of waveforms
–Not trendable

15. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Surge PD
–Variation of the surge test, evaluates partial
discharges that result from the high voltage, fast rise-
time test
–Trendable
•Thermography
–Utilizes an infrared camera to compare the ambient to
test component
–Defects can cause a high temperature rise at the
point of fault
–Trendable

16. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Torque Analysis
–Uses three phases of voltage and current in order to calculate torque
–Value is displayed and analyzed as torque FFT spectra
–Trendable
•Ultrasound/Ultrasonics
–Used to detect bearing and other electro-mechanical defects in motors
–Trendable
•Variable Frequency (I/F)
–Using about 7Vac, the motor current is measured then applied
frequency doubled and the resulting current compared to the first
current
–Displayed as a percentage, which should be no more than one or two
digits from average
–Trendable

17. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Vibration
–FFT spectra of vibration information is used to trend and
detect mechanical and some electrical faults
–Trendable
•Voltage Unbalance
–Voltage measurements detect voltage unbalance defects
in supply
–Less than 2% recommended, no more than 5%
–Trendable
•Voltage Distortion
–Harmonic content of voltage
–If value too high, rotor and stator heating occurs
–Trendable

18. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Voltage Drop
–Trended measurement of voltage drop when starting a large
motor
–Changes may indicate defects
–Trendable
•Voltage Level
–Measurements used to ensure that the supply voltage remains
+/-10% of nameplate
–Trendable
•Voltage Spikes
–Monitoring spikes allows the ability to evaluate supply and
control conditions
–Trendable

19. (C) 2006, SUCCESS by DESIGN
Condition-Based
Technologies
•Winding Resistance
–Used to detect broken wires and loose
connections.
–Trendable unbalance
•Winding Temperature
–Trended over time in order to determine if
overload conditions or insulation failure may
occur
–Trendable