Page 17 - GuardII+ Series 4208 Platform PD User Manual

PD Card Operation

4. PD Card Operation

PD monitoring relies on measurements of electro-magnetic signals caused by sparking
inside or adjacent to electrical insulation, and effectively identifying and rejecting similar pulses
caused by other forms of sparking in the system such as tracking busbars, loose connections,
etc.

By monitoring PD, the condition of the stator winding can be determined. In high voltage
rotating machines, PD in stator windings is caused by the following degradation or failure
processes:
• Loose windings (looseness in wedges, side packing, ripple springs)

• Delamination due to load cycling or overheating
• Degraded semi-conductor coatings
• Degraded stress relieving coatings

• Electrical tracking caused by contamination
• Insufficient spacing in endwinding

• Voids in insulation due to poor vacuum pressure impregnation during manufacture
During normal machine operation, the PD from the winding and electrical interference
(noise) from the system is detected by the sensors. Each pulse captured by the sensor is
analyzed and classified by GuardII+ as either PD or system activity.

Each GuardII+ PD card decodes data from a single type of sensor installation, and each
GuardII+ monitor contains a single PD card. There are several behaviors that are common
to all GuardII+ PD monitors.

4.1. Online vs. Offline

While online, GuardII+ does not require user intervention for any basic functionality; it will
run measurements, evaluate Triggers and Alert levels, and produce measurement results via
Modbus. This is the normal mode of operation.
While offline, GuardII+ stops collecting data.
WARNING:
The monitor MUST be online for normal operation.
If GuardII+ is turned on, but has been offline for more than 24 hours, it will
automatically go online unless a USB drive is left inserted into the panel
(refer to Section 6.4.2 for details).

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