Baker D30R, User'S Manual & Operating Instructions

Page: 99 / 142

D30R Users Manual
99
Do Not Touch Test Leads while test is in Progress!
71-023 Rev C 5/8/2007
Fig 8-6: Seconds/Div set too far CW Seconds/Div adjusted CCW
To correct for this display condition turn the Seconds/Div control counter-
clockwise, slowing the sweep rate. The correct surge wave pattern will always
extend below the zero line. Observe the natural ringing to the right of the point
where the wave pattern crosses the zero line in a positive (upward) direction.
Good practice is to start with the Seconds/Div control turned to its counter-
clockwise limit to begin when testing high voltage AC machines.
Notes and Tips for Large AC Stator/Motors
•
Large AC motors with parallel windings may show little, if any
separation of wave patterns when shorted or open windings are present.
The inductance change caused by these faults is often not detectable.
Instances have been noted where an end turn of a winding “has a hole
blown in it,” and yet surge wave pattern comparisons show no
separation.
As a result, it is critical to perform a winding resistance test with a
milli-ohmmeter or micro-ohmmeter whenever evaluating the condition
of a motor winding.
•
The surge test must be done on each of the parallel windings
individually for the highest degree of fault sensitivity.