S&C Instruction Sheet 682-510 11
Components
Gauge Needle Fluctuations from Rapid
Ambient Temperature Changes
When the Vista switchgear tank experiences rapid changes
in ambient temperature, the gas-pressure gauge needle may
temporarily move to indicate a higher gas pressure when
the tank is rapidly cooled or at a lower gas pressure when
the tank is rapidly heated. This phenomenon may occur, for
instance, with sudden, direct exposure to intense sunlight.
The gas-pressure gauge uses a small reference gas
chamber filled with helium to compensate for ambient
temperature and altitude without applying correction
factors. The gauge indicates tank pressure by measuring
the pressure differential between the gas in the tank and
the gas in the gauge. When the tank experiences rapid
ambient temperature changes, the smaller volume of gas
inside the gauge can change temperature more quickly
than the larger volume of gas in the tank, which can lead to
temporary movement of the needle. When the temperature
stabilizes, the needle will return to its previous position
within 1-2 hours.
For SF
6
units: If a sudden drop or increase in pressure
is seen on the gauge, S&C recommends checking with an
external gauge or waiting for ambient temperature condi-
tions to stabilize to confirm that the needle has returned
to its nominal position.
Vista Green switchgear models are hermetically
sealed. The gas-ll port is not accessible in the
eld as standard. Contact S&C for assistance.
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