Page 13 - GuardII+ Series 4208 Platform Flux User Manual

GuardII+ Flux Card Operation

4. GuardII+ Flux Card Operation

Magnetic flux monitoring via permanently mounted air gap flux probes is a proven
technology in synchronous machines to determine if turn-to-turn shorts have occurred in the
rotor winding. Flux measurement provides the most direct means of monitoring the condition
of the rotor windings on-line, yielding information on the integrity of the coils’ interturn
insulation. This information is critical in planning maintenance, diagnosing abnormal
vibrations, and verifying new and rewound rotor integrity.

Flux monitoring relies on measurements of the local magnetic field from each rotor pole.
Factors affecting the magnetic field from each pole include:

• Change in the air-gap distance
• Rotor out-of-round or off-center

• Loose pole – key migration
• Stator migration
• Natural variations of the pole’s physical position

• Shorted rotor turns
During normal machine operation, the flux from each passing pole will induce a voltage in
the flux probe. The Flux card acquires the flux signal over several machine rotations and
analyzes these readings to identify shorted poles.

4.1. Online vs. Offline
While online, GuardII+ does not require user intervention for any basic functionality; it will
run measurements, evaluate flux data for Alerts, save measurements in the Archive, 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.

4.2. Flux Measurement Cycle
Flux measurements are performed every 30 minutes; on the hour and at half past the
hour. When performing flux measurements, the monitor will run through the following cycle:
• Collect and analyze flux data

• Update Operating Condition data.
• Check measurement data for new shorted turns; activate the Alert if necessary.

• Update Modbus slave flux data.

7
www.irispower.com