Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems. Группа авторов

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Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems - Группа авторов

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D1 3 Discharge (arc) with high energy D2 4 Mixture of electrical and thermal faults DT 5 Thermal faults of temperatures <300 °C T1 6 Thermal faults of temperatures between 300 and 700 °C T2 7 Thermal faults of temperatures >700 °C T3 8 Overheating O 9 Stray gassing S 10 Hot spots with carbonization of paper C

      where k = 1, 2, 3 as per the three gases mentioned above.

      (2.19)upper T o t a l upper G a s upper C o n t e n t left-parenthesis upper T upper G upper C right-parenthesis equals StartFraction StartLayout 1st Row upper V o l period o f g a s e x t r a c t e d left-parenthesis m l right-parenthesis times 2nd Row a t m period p r e s s u r e left-parenthesis c m right-parenthesis times 293 times 10 Superscript 6 Baseline EndLayout Over StartLayout 1st Row 76 c m times left-parenthesis t e m p period o f g a s e x t r a c t e d plus 273 right-parenthesis 2nd Row times q u a n t i t y modifying above upper A with caret o f modifying above upper A with caret o i l left-parenthesis m l right-parenthesis EndLayout EndFraction mu l slash normal l

      The H2 production is not very significant in both oils, but it is higher in the case of FR3. The insignificant concentration of H2 gas even after 2000 hours of aging makes the JAT less flammable compared with FR3. A few works show that the higher concentration of C2H6 may be due to faults at low temperatures below 150 °C. C2H4, which is the chief indicator for high‐energy thermal faults, is comparable for both oil types. The presence of solid insulation on reaction with the oil produces CO and CO2 in significant amounts, which indicates cellulose degradation. This happens because paper starts degrading at temperatures above 105 °C and the aging atmosphere influences the deterioration of oil [73]. The gas levels are quite substantial in the case of jatropha oil which might indicate that solid insulation is better safeguarded by FR3. Also, in general, the concentrations of all the gases in this oil increased with the aging duration. The small variations in gas concentrations can be ascribed to the different origination of these oils. The Duval Triangle 3 (recommended for non‐mineral oils) is used for both NEOs, as formulated by Michel Duval. The two NEOs are based on the different compositions of saturated and unsaturated oleic and fatty acids, which result in different patterns of gas generation. In the Duval Triangle 3, CH4, C2H4, and C2H2 are selected as the sides 3. The fault gas data are replaced into it, and it is observed from Figure 2.12c, that all of the data points for both oil types fall in corresponding thermal faults region. In some circumstances, the data points lie in the boundary regions and it becomes challenging to identify the actual faults. Also, many times stray gases are produced at temperatures below 200 °C in the PD, T1, or T2 zones, and consequently may affect the correct detection of these faults [22]. For analysis purpose of low‐temperature faults, Duval Triangle 6 uses the low‐energy gases (H2, CH4, and C2H6) as represented in Figure 2.12d. It is seen that stray gassing occurs in FR3 for all aging durations, however, for JAT, overheating is observed.

Schematic illustration of (a) DGA analysis of aged FR3 and JAT – ethane, ethylene, and hydrogen, (b) carbon monoxide and carbon dioxide, (c) Duval Triangle 3 for the aged FR3 and JAT oil samples, and (d) Duval Triangle 6 for the aged FR3 and JAT oil samples.

      Source: Baruah et al. [73] / with permission of IEEE.

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