Mineral insulating oils in service

There is precious little basic information openly available on how insulating materials in transformers behave over longer periods of time. However, such information is very important for ensuring that aging equipment works adequately. It is valuable both from the perspective of transformer maintenance/asset management, and as background information necessary for making informed choices on which type of insulating liquid to employ in new equipment

Insulating liquid properties impacting transformer performance

This paper briefly discusses the functions of a power transformer’s insulating liquid in achieving effective cooling and reliable performance under high voltage stress, and in having sufficient oxidation stability to maintain performance, as well as low maintenance. Low viscosity over operating temperature range, high oxidation stability and favourable streamer propagation behaviour characterized by high acceleration voltage are key aspects of a good insulating liquid. The efficiency of a power transformer can be partly improved by increased convective cooling, thanks to a lower viscosity of the liquid. Moreover, many established electrical design rules for oil/paper systems used in power transformers of today rely on the characteristics of “traditional” mineral oils, which typically have high acceleration voltage. Furthermore, the insulating liquid’s oxidation stability and ageing behaviour will have a direct impact on a transformer’s total cost of ownership for its operator

Insulating liquid properties impacting transformer performance

This paper briefly discusses the functions of a power transformer’s insulating liquid in achieving effective cooling and reliable performance under high voltage stress, and in having sufficient oxidation stability to maintain performance, as well as low maintenance. Low viscosity over operating temperature range, high oxidation stability and favourable streamer propagation behaviour characterized by high acceleration voltage are key aspects of a good insulating liquid. The efficiency of a power transformer can be partly improved by increased convective cooling, thanks to a lower viscosity of the liquid. Moreover, many established electrical design rules for oil/paper systems used in power transformers of today rely on the characteristics of “traditional” mineral oils, which typically have high acceleration voltage. Furthermore, the insulating liquid’s oxidation stability and ageing behaviour will have a direct impact on a transformer’s total cost of ownership for its operator

Manufacturing composite beams reinforced with three-dimensionally patterned-oriented carbon nanotubes through microfluidic infiltration

Functionalized single-walled carbon nanotubes (SWCNTs)/epoxy nanocomposite suspensions were prepared and injected into three-dimensional (3D) interconnected microfluidic networks in order to fabricate composite beams reinforced with patterned-oriented nanotubes. The microfluidic networks were fabricated by the robotized direct deposition of fugitive ink filaments in a layer-by-layer sequence onto substrates, followed by their epoxy encapsulation and the ink removal. Then, the nanocomposite suspensions prepared by ultrasonication and three-roll mill mixing methods were injected into the empty networks under two different controlled and constant pressures in order to subject the suspensions to different shear conditions in the microchannels. Morphological studies revealed that the SWCNTs were preferentially aligned in the microchannels along the flow direction at the higher injection pressure. The improvement of Young’s modulus of the manufactured 3D-reinforced rectangular beams prepared at the high injection pressure was almost doubled when compared to that of beams prepared at the low injection pressure. Finally, the stiffness of the 3D-reinforced beams was compared with the theoretically predicted values obtained from a micromechanical model. The analytical predictions give a close estimation of the stiffness at different micro-injection conditions. Based on the experimental and theoretical results, the present manufacturing technique enables the spatial orientation of nanotube in the final product by taking advantage of shear flow combined with dimensional constraining inside the microfluidic channels

Plasma emission spectrometry for determining germanium, tin, arsenic, antimony, bismuth, selenium and tellurium in geochemical samples

Imperial Users onl