THE by-products of oxidation of mineral transformer
oils, such as acids, ketones, peroxides, alcohols and
aldehydes [1, 2], lower their insulating efficiency and in turn
lead to electrical failures. Antioxidants added to insulation
transformer oils neutralize peroxy radicals responsible for the
formation of polar oxidation by-products and minimize acid
formation [3]. Since antioxidant concentrations deplete
significantly over time they need to be monitored and if
necessary replenished to maintain their effectiveness.
Several methods are available to determine the levels of
the oxidation by-products in insulating oil. ASTM 3487 [4]
includes tests for dielectric breakdown, the neutralization
number, interfacial tension, the dielectric dissipation factor
and resistivity. Some tests may not be sensitive enough to
provide a definite conclusion regarding the amount of polar
oxidation compounds in the oil, while others like interfacial
tension and the neutralization number are highly sensitive
and may produce a rejection value for the oil quality [5].
However, the above mentioned parameters do not give a
direct statement about the oxidation stability profile. In the
THE by-products of oxidation of mineral transformeroils, such as acids, ketones, peroxides, alcohols andaldehydes [1, 2], lower their insulating efficiency and in turnlead to electrical failures. Antioxidants added to insulationtransformer oils neutralize peroxy radicals responsible for theformation of polar oxidation by-products and minimize acidformation [3]. Since antioxidant concentrations depletesignificantly over time they need to be monitored and ifnecessary replenished to maintain their effectiveness.Several methods are available to determine the levels ofthe oxidation by-products in insulating oil. ASTM 3487 [4]includes tests for dielectric breakdown, the neutralizationnumber, interfacial tension, the dielectric dissipation factorand resistivity. Some tests may not be sensitive enough toprovide a definite conclusion regarding the amount of polaroxidation compounds in the oil, while others like interfacialtension and the neutralization number are highly sensitiveand may produce a rejection value for the oil quality [5].However, the above mentioned parameters do not give adirect statement about the oxidation stability profile. In the
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