S&C Instruction Sheet 682-510 9
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. The gas pressure gauge includes four
distinct color-coded zones. See Figure 8.
If the needle is within a particular zone as described
below, it indicates the following:
Green zone:
The Vista unit is OK to operate.
Green/Yellow zone:
The Vista 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 SF
6
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 Electric
Company for assistance.
Orange zone:
The Vista 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 levels before operation of the
device. Contact S&C for assistance.
Gauge Needle Fluctuations from Rapid
Ambient Temperature Changes
When the Vista 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 cham-
ber filled with helium to compensate for ambient tempera-
ture 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 tempera-
ture 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.
Figure 8. Internal gas-pressure gauge for most Vista
switchgear models.
Components
Red
zone
Green/Yellow
zone
Green
zone
Orange
zone
