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PD Investigations
7.3.3.4 High level disturbance
Sometimes, sources external to the machine can produce such a high level of electromagnetic energy and induce disturbances in
the stator winding that exceed the typical PD activity by orders of magnitude. One typical example would be an air gap between
the bus-bar and the bus-bar support. The intense sparking at this location will induce high frequency pulses that will travel to the
PD couplers and be detected there. If such external disturbances occur close to the machine, they may be classified as PD.
Measurements in low (for PD) and high (for disturbance) sensitivity ranges may be required to distinguish between the two.
Additional instrument counters (Between Activity, for example) can also assist in these complicated cases. Please note that
although external disturbance is not in the scope of machine PD monitoring, high external discharge could be associated with
malfunctions of connected auxiliary equipment and it could lead to a ground fault.
Figure 53: External Disturbance in Machine PD Plot That Is Clearly Not Winding PD
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