8 S&C Instruction Sheet 681-510
Components
Figure 6. Internal gas-pressure gauge for most Vista
switchgear models.
Red
zone
Orange
zone
Green
zone
Green/Yellow
zone
Understanding the Gas Pressure Gauge
Vista switchgear incorporates a temperature-compensated
gas pressure gauge inside the tank to provide indication
of the SF
6
-gas pressure gauge is in the green and yellow-
striped zone gas pressure. The gas pressure gauge includes
four distinct color-coded zones. See Figure 6.
If the needle is within a particular zone as described
below, it indicates the following:
Green zone:
The Vista switchgear unit is OK to operate.
Green/Yellow zone:
The Vista switchgear unit may have lost some gas but is still
OK to operate. The unit should be evaluated to determine
whether it needs to be refi lled with SF
6
gas and repaired
accordingly. Contact S&C for assistance.
Red zone:
The SF6 gas may be below the minimum operating
pressure for the gear.
Vista switchgear should not be
operated if the needle is in the red zone.
Contact S&C
for assistance.
Orange zone:
The Vista switchgear unit has been overfi lled in the fi eld
or has a defective pressure gauge. An external gauge can
be used instead to verify the gas pressure before operation
of the device. Contact S&C for assistance.
Figure 7. Internal gas-pressure gauge for Vista switchgear
models rated 15 kV, 12.5 kA sym. short circuit that have catalog
numbers ending with “-R1” suffix.
Green
zone
Red
zone
Green/Yellow
zone
Orange
zone
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 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 fi lled 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.
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 conditions to
stabilize to confirm that the needle has returned to its
nominal position.
