Baker D30R, User'S Manual & Operating Instructions

Page: 65 / 142

D30R Users Manual
65
Do Not Touch Test Leads while test is in Progress!
71-023 Rev C 5/8/2007
Determination of a Fault
If a fault exists in a motor, the wave pattern on the display will collapse in
amplitude and a distinct shift to the left will occur, signifying an increase in
frequency (a decrease in inductance). When inductance decreases, the
frequency of the wave pattern will increase according to the formula above.
This is illustrated in the figure below. This type of fault is generally one that
indicates a failure of the turn-to-turn short.
Fig 6-2: Good vs Bad Coil Waveform
If any wave pattern becomes erratic and/or flickers during testing, intermittent
shorting or arcing is probably occurring in the windings under the voltage stress.
Arcing is often accompanied by audible sounds. It may be desirable to store the
wave pattern by this arcing for reference if the operator can release the TEST
(this freezes the wave pattern) at the moment when the wave pattern appears the
most affected by the fault (reduced amplitude and increased frequency or shift to
the left).
Motivation for Surge Testing
Motors are subjected to high energy, high voltage transients in their everyday
operating environment. These transient pulses can damage the insulation in the
motor and, given enough time, cause a catastrophic failure in the motor. The
causes of high energy, high voltage transients are:
•
Motor start-up inrush current coupled with
contact bounce
in the
MCC.
•
Lightening
strikes in the power system.