IOR810 ABB distributed control system industrial DCS module card

Description

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Insulation systems composed of ester liquids and
cellulose materials have been shown to operate
with lower moisture content in the insulation
system and endure higher temperatures than those
composed of mineral oil and cellulose materials,
making them an ideal choice [5].
There are three factors that contribute to the
lower aging rate and longer lifetime of ester-filled
transformers:
• The moisture content in the mineral-oil-filled
system increases with time, while that of the
ester-filled system declines. An ester-filled
cellulose insulation system operates with lower
cellulose insulation moisture content than one
filled with mineral oil →3.
• The solubility of water in ester liquids is several
times higher than in mineral oil at typical
transformer operating temperatures. This
means more water is drawn out of the paper
into the ester liquid.
• Cellulose polymers change when aged in natural
ester liquids. The chemical reaction of water
generated during the cellulose aging process
with natural esters produces free fatty acids
that attach to the cellulose structure through
a reaction called trans-esterification, thus
forming a barrier to water ingress, leading to
a decline in the rate of deterioration of the
cellulose insulation [5].
The practical result of the combined effect of all
these phenomena is that cellulose insulation has a
20 °C thermal advantage when aged in ester liquids
[5-6]. Specifically, for the same life expectancy,
cellulose impregnated with ester liquids can
be designed with a 20 °C higher hottest spot
temperature than one with mineral oil.