LumaSMART
®
User Manual
Installation of Probes and Accessories
•
32
Single Phase Transformers—Autotransformer and GSU
It is recommended that each transformer have an FOT installed in the hottest spot in the hottest winding. If the
autotransformer has a tertiary winding and it will be loaded, there should be an FOT installed in all three windings
as overloading is possible in each winding.
Top Oil Measurement
In the above applications, measurement of the top oil is easily done by using the FOT mounted in a holding device
near the top of the transformer tank at a location that will always be below the oil at its lowest possible level.
Caution:
Do not mount the top oil FOT too close to vents from the core or coils so that higher than
actual temperatures are not indicated.
For transformers with On Load Tap Changers (OLTC), the top oil temperature of the OLTC Compartment may also
be measured for use in comparing main tank oil to OLTC compartment oil. Redundant top oil FOTs are often
specified by users.
3.3
Handling the Fiber
The fiber used for the internal transformer probe is double-jacketed with Teflon
®
PFA and wrapped with Kevlar
®
in
between the Teflon
®
jackets for extra strength. The fiber can be handled normally without breakage. However, the
fiber is formed from a single filament of fused silica, making it breakable.
Caution:
Avoid sharp bends, shocks, or impacts to the fiber optic cable; silica fiber is brittle and
breaks more easily under impact than metallic wire.
In planning the fiber route, and when handling the fiber, allow for relatively gradual bends of
51 mm (2.0 in) radius or more, so that sudden shocks or continued stress over long periods of time do not lead to
the fiber being fractured. Bending a fiber reduces its light transmission; therefore, do not bend the fiber further
than absolutely necessary.
Fused silica fiber, while brittle if bent beyond its elastic limit, is quite flexible and resilient. Unlike metallic wires, it
can be flexed endlessly without fatiguing.
If a probe connector end requires cleaning, wipe it with a cotton swab moistened with spectrograde methanol or
isopropyl alcohol. Use the yellow Teflon
®
cap to cover the connector ends when probes or extensions are not in
use.
