Baker D30R, Руководство пользователя

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Surge Test Applications
12/3/2009 | 71-022 V6
D30R 59
wave pattern for 7 bars spanned may sometimes match that for 11 bars spanned. In
addition, the patterns may show a rhythmic shift consistently throughout the 360
degrees of rotation. For instance, as the armature or fixture is rotated, every third bar
shifts slightly left. This is due to the equalizers and does not indicate faulty windings.
Testing large AC stators/motors
Due to the physical non-symmetry of the input area, high capacitance, and inductance on
some large AC high voltage machines, care must be exercised when evaluating the
waveforms.
The screens below show wave pattern comparisons for a typical 4160V stator. The first wave
pattern is produced when the Seconds/Div control (sweep rate) has been turned clockwise too
far, expanding the display of the wave pattern. The sweep rate is set too fast. This wave
pattern is actually the first half cycle of the full wave. Distortion is caused by the non-
symmetrical, distributed capacitance in the input portion of the winding.
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
Fig 8-6: Seconds Div set too far CW Seconds/Div adjusted CCW
Fig 8-5: Wave pattern comparison for motor with rotor in place.