Chapter 3 ______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 17
CHAPTER 3
FUNCTIONAL DESCRIPTION
This chapter describes the primary application and the sensor
technology of DPT145.
Measurement Needs of SF
6
Insulation
Sulphur hexafluoride (SF
6
) is used as an insulating gas in
transmission and distribution equipment such as switchgears and
circuit breakers. It effectively prevents arcing during switch-offs and
protects equipment from failures.
In order to maintain SF
6
insulation properties and to reduce the
formation of unwanted secondary decomposition products, the
amount of water vapor in the gas insulated system (GIS) should be
kept to a minimum. Also, the SF
6
system needs to be pressure tight
for best insulation performance and safe operation of the equipment.
There is always some diffusion of water molecules from high ambient
water vapor pressure to low vapor pressure inside the system. The
more connection points the higher the diffusion rate. DPT145 is
ideally suited to the online monitoring of dewpoint, pressure, and
temperature in such a system. Sudden and minor leakages are
immediately detected by the direct normalized pressure measurement,
while online dewpoint measurement alerts the user to moisture issues.
With online monitoring, on-site visits can be kept to a minimum. The
long calibration interval of DPT145 means practically service-free
operation.
