جستجوی مقالات مرتبط با کلیدواژه "electrical resistance" در نشریات گروه "برق"

Graphene transfer from a metal substrate to the dielectric one is often the first step in graphene device fabrication. in order to achieve the proper performance of these devices surface cleanliness and maximum coverage of transferred graphene are crucial. In this paper wet transfer method and the effects of each stage of the process on transferred graphene quality have been investigated and also the reasons of tear formation and contamination during transfer process have been studied. In this research scanning electron microscopy images has been employed because of graphene surface morphology observation. by applying van der pauw method and measuring electrical resistance which itself depends on coverage percentage and contamination area , the quality of transferred graphene has been evaluated. The results are confirmed by raman spectroscopy in which spectra peaks display crystalline network defects and doping concentration. Finally an optimal process with 95% coverage level and 700 ± 50 ohm electrical resistance has been presented.

Moisture in oil-paper insulation system is one of the destructive factors which may cause power transformer failure. Decrease of dielectric strength, breakdown voltage and increase of partial discharges rate are some of the effects of moisture increment in the insulation system. Also, it is known that cellulose insulation decomposes in the presence of moisture and can decrease transformer’s lifetime. In the present study, the use of PDC method for estimating paper moisture content of an experimental insulation model have been investigated in three different temperatures. With every temperature increment step, moisture slowly migrates from paper to oil until the equilibrium condition be achieved. PDC tests were done at every temperature step. It can be seen from the results that value of the tail of polarization current, which is dominated by paper conductivity, decreases with moisture migration from paper to oil in a constant temperature. Thus, an effective method for estimating paper moisture by calculating paper electrical resistance from PDC measurements is presented. Test results demonstrate that paper moisture content can effectively be estimated from paper resistance when the effect of temperature has been eliminated and all of the results have been compared in a same temperature. NI LabVIEW 2013 was used to control the measurements procedure and to save measurements data. Further calculations were done using MATLAB 2016.