Recent Trends in the Condition Monitoring of Transformers by Sivaji Chakravorti Debangshu Dey & Biswendu Chatterjee

Author:Sivaji Chakravorti, Debangshu Dey & Biswendu Chatterjee
Language: eng
Format: epub
Publisher: Springer London, London

It is useful to know the moisture equilibrium curves of oil-paper insulation system of transformer. Under equilibrium operating condition of a transformer, these curves provide a quick way of estimating the moisture content in paper by measuring the moisture in oil. Three steps need to be taken for this purpose [3], [12]: (i) Taking oil samples from in-service transformers, (ii) Measurement of water content in oil sample by Karl Fischer titration technique, and (iii) estimating moisture content in paper insulation with the help of oil-paper moisture equilibrium curves.

But, this approach suffers from several errors that may result into poor accuracy. Equilibrium depends on moisture adsorption capacity of solid insulation and oil and aging of insulation significantly changes the moisture absorption capacity. There is also possibility of moisture ingress from the atmosphere to oil during onsite oil sampling, transportation, and sample preparation during laboratory testing as transformer oil is highly hygroscopic in nature. The steep gradient of the equilibrium curves in the low moisture region increases error. An important point to be noted here is that the validity of oil-paper moisture equilibrium curves is restricted to the original materials that were used to prepare these curves [3, 12].

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