Using first-principles theory, this work investigated the Cu-doping behavior on the N-vacancy of the C3N monolayer and simulated the adsorption performance of Cu-doped C3N (Cu–C3N) monolayer upon two dissolved gases ( H2 and C2H2). The calculations meant to explore novel candidate for sensing application in the field of electrical engineering evaluating the operation status of the transformers. Our results indicated that the Cu dopant could be stably anchored on the N- vacancy with the Eb of − 3.65 eV and caused a magnetic moment of 1 μB. The Cu–C3N monolayer has stronger performance upon C2H2 adsorption than H2 give the larger Ead, QT and change in electronic behavior. The frontier molecular orbital (FMO) theory indicates that Cu–C3N monolayer has the potential to be applied as a resistance-type sensor for detection of such two gases, while the work function analysis evidences its potential as a field-effect transistor sensor as well. Our work can bring beneficial information for exploration of novel sensing material to be applied in the field of electrical engineering, and provide guidance to explore novel nano-sensors in many fields.

이 논문은 절연유를 정제하여 SF6 가스를 용해시켰을 때 절연유의 수십 MHz대의 고주파 절연파괴 전압과 유전특성에 관해서 연구한 것이다. 1)절연유에서의 고주파 전류는 전압의 1/2승에 거의 비례하여 증가한다. 2)전원주파수가 증가함에 따라 고주파 절연파괴는 주파수의 제곱에 역비례하여 감소하는 현상을 나타내고 AC절연파괴의 전압때보다 약 35%정도가 감소한다. 3) 용해된 기체의 압력을 증가시킴에 따라 고주파 절연파괴 전압은 원만하게 증하한다. 4)전원주파수의 증가에 따른 유전정접(tan δ)은 거의 지수 함수적으로 증가하고 유전률(ε)은 [0.6% MHZ]의 기울기로 삼소하는 경향을 나타낸다. 5) SF6 가스를 용해시켰을때 절연파괴 특성은 Air 또는 Ar을 용해시켰을 때 보다 약 25% 정도 향상되는 특성을 나타낸다.

The formation potential and pathway of less-chlorinated PCBs, including mono- and di-chlorinated biphenyls, was investigated when PCBs contained in transformer oil were dechlorinated by commercial treatment. Potassium hydroxide with polyethylene glycol (PEG-600) was used for dechlorination of PCBs, and its destruction efficiency to whole 209 congeners of PCBs was 97.1% on average, ranging from 95.6% to 98.2%. Homologue of mono-CBs showed the negative destruction efficiencies, while those of highly-chlorinated ones through tri- to deca-CBs showed better efficiencies than about 99%. In particular, mono-chlorinated biphenyl in meta-position (#2) was about 34-47 times enriched after dechlorination, thus the reactivity seemed to be in the order of ortho-, para-, and meta-chorinated biphenyl. Co-planar PCBs' dechlorination efficiency was averaged as high as 99.4%, but 3,4,4',5-TeCB (#81) showed a relatively lower efficiency than others' in one case. Not only sodium metal but also alkaline metal such as potassium was thought of affecting the formation or enrichment of mono-chlorinated biphenyls produced by Wrutz-Fittig reaction as intermediates and products.

The dechlorination processes and efficiencies of PCBs contained in transformer dielectric oils were investigated on three commercial-treatment companies. Alkaline dispersion method was used for dechlorination of PCBs mainly using molten metallic sodium or potasium hydroxide with PEG, and its dechlorination efficiency to whole congeners of PCBs was 98.94% on average. Homologues of highly-chlorinated biphenyls showed better efficiencies than those of less chlorinated ones, especially mono-chlorinated biphenyl in para-position (#2) was about 37 times enriched after chemical treatment. Co-planar PCBs' dechlorination efficiency was averaged as high as 99.78%, but 3,3',4,4'-TeCB was relatively low as 96.5%. It was suggested for better dechlorination efficiency to remove the water in transformer oil prior to chemical reaction and to stir the reagents more rapidly when using alkaline dispersion method.

In this study, adsorption of polychlorinated biphenyls(PCBs) in transformer oil on powder activated carbon (PAC) and synthetic zeolite was evaluated. Adsorption characteristics of PCBs on the PAC and zeolite has been investigated in a batch system with respect to adsorbents amount and contact time. BET results showed 908 m2/g for PAC and 483 m2/g for zeolite. The adsorption capacity of PCBs increased with an increasing input amount of absorbent. The adsorption experimental results showed that PAC removed 90% of input PCBs in transformer oil while zeolite removed only 64%. Adsorption of PCBs to PAC and zeolite fit the Freundlich model well. The Freundlich parameter, Kf, for PAC and zeolite was 193.1 and 43.0 respectively, indicating that PAC is effect adsorbent for PCBs adsorption in transformer oil.

A practical and efficient disposal method for chemical dechlorination of PCBs (polychlorinated biphenyls) in transformer oil was evaluated. The transformer oil containing PCBs was treated by the PEG 600 (polyethylene glycol 600) and potassium hydroxide (KOH) along with different reaction temperatures(25, 50, 100 and 150oC) and times(30, 60, 240 and 480 min). The best disposal efficiency of PCBs in transformer oil was attained under the experimental conditions of PEG 600 (2.5 w/w%)/KOH (2.5 w/w%)/150oC/4 hrs, showing completely removal of all PCBs containing 3-9 chlorines on two rings of biphenyl. In studying the reaction of PEG/KOH with PCBs, it confirmed that the process led to less chlorinated PCBs through a stepwise process with the successive elimination of chlorines.