Vaisala HUMICAP MMT310 Guía de usuario descargar pdf (Pagina 57)

Appendix 1 _____________________________________________________________ Applications

VAISALA _______________________________________________________________________ 55

APPENDIX 1

APPLICATIONS

Transformer oils

The determination of moisture in oil is an essential part of a

comprehensive transformer maintenance program. Oil immersed

transformers rely on the oil for cooling, protection from corrosion and

as an important component of their insulation. Excessive moisture

contents in oil causes accelerated ageing of the insulation materials

and reduces their dielectric strength. In extreme cases this can result in

arcing and short circuits within the windings. Accurate moisture

measurements can also warn about leaks in the oil system, as water is

absorbed from the surrounding air.

Heating and cooling of a transformer effect moisture levels in oil. This

is due to the fact that the water solubility of oil is temperature

dependent. In general, water solubility increases as temperature raises

(see Figure 1). Changes in temperature affect also on water desorption

of the paper insulation around the transformer windings. Desorption of

water from the insulation increases as temperature raises and the

surrounded oil absorbs desorbed water. Moisture level in oil is thus a

true indicator of moisture present in the paper insulation.

In addition, it must be noted that capacity of oil to absorb water

depends both on the chemical structure of the oil and the additives.

The water concentration of transformer oil is usually 0...80 ppm and

the temperature range of the oil 0...100ºC.

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Vaisala HUMICAP MMT310 Guía de usuario Pagina 57