Vaisala DPT145 - Manual (Page 17)

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.