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A new biodegradable dielectric fluid for transformers, palm fatty acid ester (PFAE), with better cooling performance and oxidative stability than conventional mineral oil (MO) was developed in 2008. In this report, the thermal aging characteristics of Kraft paper (KP) in PFAE and MO were compared in air sealed tanks, in order to evaluate the applicability of PFAE to pole transformers. The degradation of paper impregnated in PFAE and MO was compared with degree of polymerization (DP) and tensile strength (TS). The electrical properties of PFAE and MO after aging were determined.The DP of the KP aged in MO is nearly half of that in PFAE after 365-day aging at 105°C. The TS of the KP in PFAE after 365-day aging at 105°C decreases to about 78% of initial strength, while the TS for the paper in MO drops to 15%. After 365-day aging at 105°C, the breakdown voltage of aged PFAE is 76 kV, while that for aged MO is 20 kV; the dissipation factor of aged MO increased over 100 times, while that for PFAE kept the similar value. The production of sludge in aged MO makes it black, while aged PFAE keeps its transparence. Additionally, the mechanism on the suppression of KP degradation in PFAE is proposed.

Two cases of massive gangrenous inflammation of the colon proximal to obstructive carcinomatous lesions, the so-called obstructive colitis, are reported. Because of the rarity of this condition, the etiological factors responsible for this entity are not yet clear. The detailed pathological and microbiological studies at the time of operation are essential to their further clarification.