EATON ELECTRICAL
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Predictive Diagnostics
2.1.9 Application Specific for MV Switchgear
Three types of PD sensors can be used for switchgear lineup: coupling capacitor
(IPDS), RFCT and RFVS.
Preferred option is IPDS
.
•
Three IPDS sensors (one per phase) are installed, commonly in every third cubicle.
Therefore, each set of three IPDSs assess the cubicle, where it is installed, and on
each sides. Increasing a distance between IPDS sets might cause some distant PD
to be missed. Keep in mind that PD signals attenuate approximately twice from
cubicle to cubicle due to energy splitting in every T-connection. IPDS can be
installed on a bus side or load side of a breaker. In the case of a load side, the
sensor will not measure PD while the breaker is open. In general, one InsulGard can
handle up to 15 cubicles.
•
An RFCT sensor is installed on incoming and outgoing feeder shield grounding
conductors; commonly, one per cubicle. Phase to phase signals can be missed in
such a configuration. Installing three RFCT sensors in every cubicle looks very
difficult. RFCT sensors on cable shields are susceptible to any ground noise. Noise
level should be checked before deciding to use an RFCT.
•
An RFVS sensor is connected to C0 (common point) of a metering CT and to V0
(common point) of PT. Constructive capacitance of CT or PT to a bus is used as a
small coupling capacitor. This sensor is the easiest to install, however, it is
susceptible to many noises produced by modern metering and relaying electronics.
These sensors work very well on older lineups without modern electronics.
Two main factors, temperature and humidity, should be considered to correlate with PD.
Plan on installing temperature and humidity sensors with InsulGard. You may also
consider voltage signal, if expected voltage variation can /-5%.
In indoor installation InsulGard can be mounted without NEMA-4 enclosure in one of the
cubicles. Check for available space before ordering a device. In some cases, the bus
and breaker structure is very complicated. Consult with a Cutler-Hammer application
engineer before ordering sensors.
2.2 Installation
InsulGard
TM
is normally shipped in one of the following options:
•
In NEMA-4 (4X) enclosure. In such a case, all ordered options (modem, cellular
modem, radio-modem and power supplies and so on) have already been installed
onto internal mounting panel. The enclosure has two entries for power and signal
cables in the bottom.
•
On the mounting panel. This option is identical to the first one, except that mounting
panel is not mounted into enclosure.
•
Flash mount option. This option is used for panel mount predominantly in switchgear
line up. InsulGard comes with Sensor Interface Board installed on it’s back cover.
Communication options (modems and their power supplies) are separate items.
