Page 15 - GuardII+ Series 4208 Platform EV User Manual

GuardII+ EV Card Operation

4. GuardII+ EV Card Operation

A rotating machine’s stator endwinding is at high-voltage potential and requires support
against mechanical vibration driven by electrical and mechanical forces. Machine
endwindings are designed so that under normal circumstances these mechanical stresses are
controlled enough to prevent damage. However, the endwinding can be damaged due to:

• Looseness of the endwinding support and tie structure due to mechanical aging and
thermal expansion

• Poor design of the endwinding bracing with resonance conditions close to the primary
forces of the rotational frequency and twice line frequency

• Abnormal operating events such as short circuits resulting in stress and deflection of
components beyond their mechanical limits

• Relative motion between one component and another which can abrade the high
voltage insulation on the coils

The purpose of endwinding vibration monitoring is to directly measure if the stator
endwindings are vibrating during normal operation, so that any incipient vibration can be
detected (and corrected) at an early stage, well before failure. The monitoring system consists
of four components:

• Non-metallic EVA sensors mounted at critical locations in the endwinding
• Non-metallic fiber optic cable to connect the sensors outside of the motor or generator
frame
• An EOD to convert the optical sensor signals to electrical signals which are
proportional to the acceleration of the sensor
• The GuardII+ monitor to digitize, process and store the vibration spectra

4.1. Online vs. Offline

While online, GuardII+ does not require user intervention for any basic functionality; it will
run measurements, evaluate EV data, save measurements in the internal GuardII+ 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. EV Measurement Cycle

EV measurements are performed repeatedly; as soon as a measurement is completed
and analyzed, another is started. When performing EV measurements, the monitor will run
through the following cycle, taking approximately 6-10 seconds to complete each
measurement cycle:

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