Vaisala DPT145 User's Guide download pdf (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

Insulation

Sulphur hexafluoride (SF

) 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

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

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.

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Vaisala DPT145 User's Guide Page 17