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On-line motor circuit evaluation (all testing is non-destructive).
Tests include: a)
Current signature analysis is performed through a combination of
frequency versus dB amplitude spectrums (graphs) and software automation to
identify rotor bar defects and or static or dynamic eccentricity. b)
Start-up in-rush tests (if possible) are performed by recording
graphically the amperage versus time from start to finish.
Changes in start-up characteristics can be attributed to rotor or stator
faults. Also, like motors /
equipment can be compared for evaluating which is in better condition. c)
Power analysis (480 volt systems ONLY or higher volt systems if
current transformers and potential transformers are installed and available on
all three phases) provides invaluable insight into incoming power quality, power
circuit condition, stator health, and motor efficiency. Utilizing a combination of unbalance
parameters and harmonic analysis, our Emax test unit examines the power signal
for indications of defects. Power
quality is diagnosed using total harmonic distortion (THD) and crest factor
calculations. Distortion, which is
often the result of non-linear loads, produces additional heat within the motor
that will reduce life if not corrected. The power circuit and stator are evaluated through the use of unbalance
parameters and impedance sequence data. Unlike
positive impedance sequence currents that produce useful torque, negative
sequence currents are caused by high resistive connections within the motor or
circuit and generate heat producing counter torque.
Rising negative sequence currents couple with high impedance imbalance is
indicative of developing stator faults. |
