EATON ELECTRICAL
19
Predictive Diagnostics
metering device. RTD and it’s wires also operate as a local RF antenna for PD. High
frequency signals can be filtered out and used to for PD representation. Common noise
disturbing PD signals from RTD comes from temperature metering system wires. A
possible source of noise can be the operation (switching pulses) of the temperature
metering system itself and/or pulses cross-coupled to wires from another wire at the
same tray.
CHPD produces RTD PD sensor board with embedded filters, suppressing external
noise. RTD PD sensors are designed as a single board replacing the existing RTD
terminal board at the motor frame. It does not affect temperature measurements, and
produces PD signals for InsulGard. RTD PD board is designed to handle six RTDs. If, in
a particular application, the number of RTDs is greater than 6, additional boards might
be needed. An RTD PD board can be installed online, disabling temporarily temperature
alarm or relay system.
Winding temperature, load current, and humidity in a terminal enclosure are the three
most important parameters to correlate. Use one of the winding RTDs for temperature.
It can be difficult to bring a load current signal to the InsulGard enclosure from some
distant CT (frequently in switchgear cubicle). In this case you can consider installing a
FlexCore CT around a cable of the phase A in the motor terminal enclosure. The
FlexCore CT is installed over the shielded part of a cable and, therefore, is under
ground potential and does not endanger insulation integrity. Cable shield should be
grounded through CT.
Note: One InsulGard device is required for a motor.
2.1.8 Application Specific for Large Generators
The application for large generators is, in general, similar to one on a motor or small
generator. Some specifics include:
•
Coupling capacitor (IPDS) is commonly used as a sensor at line terminals.
Generator equipped with iso-phase bus duct might produce sparking in bus
supporting insulators.
The later firmware versions (02-14-03 and higher) have built in software
filters. The older versions may require two sets of IPDS for noise suppression.
•
Certain generators do not have RTDs embedded into a stator winding. For example,
large Westinghouse hydrogen cooled machines have RTDs near the hydrogen outlet
from the winding. These RTDs cannot be used as PD sensors. Check RTD location
in a winding.
•
Large generators may have very long signal wires from RTD to the first RTD
terminal board. Frequently, these wires are also placed into a spiral armature. These
factors significantly affect high frequency signal propagation attenuating PD pulse
.
In
order to minimize signal attenuation; install the RTD PD board at the generator
gland, where the RTD wires come out of generator.
