Top-oil temperature modelling by calibrating oil time constant for an oil natural air natural distribution transformer

© The Institution of Engineering and Technology 2020. Integration of low carbon technologies poses a technical challenge on distribution transformers due to the dynamic loading and potentially frequent overloading scenarios. Transformer dynamic thermal rating is hence required, which is the most economical approach to tackle this challenge and ensure a safe operation. To reach the aim, it is important to enhance the accuracy of the dynamic thermal model, where the top-oil temperature is a key thermal parameter. In this study, a wide range of constant load temperature-rise tests were carried out on an 11/0.433 kV distribution transformer to study the dynamic thermal behaviour of the top-oil temperature. A model based on the IEC 60076-7 thermal model but with an improved oil time constant calibration was deduced for top-oil temperature modelling. The oil time constant calibration was inspired by IEEE C57.91 and verified by eight temperature-rise tests with load factors ranging from 0.7 to 1.4 pu. In addition, the improved top-oil temperature modelling was further verified in experiments under multiple load profiles

A single immunization with HA DNA vaccine by electroporation induces early protection against H5N1 avian influenza virus challenge in mice

<p>Abstract</p> <p>Background</p> <p>Developing vaccines for the prevention of human infection by H5N1 influenza viruses is an urgent task. DNA vaccines are a novel alternative to conventional vaccines and should contribute to the prophylaxis of emerging H5N1 virus. In this study, we assessed whether a single immunization with plasmid DNA expressing H5N1 hemagglutinin (HA) could provide early protection against lethal challenge in a mouse model.</p> <p>Methods</p> <p>Mice were immunized once with HA DNA at 3, 5, 7 days before a lethal challenge. The survival rate, virus titer in the lungs and change of body weight were assayed to evaluate the protective abilities of the vaccine. To test the humoral immune response induced by HA DNA, serum samples were collected through the eye canthus of mice on various days after immunization and examined for specific antibodies by ELISA and an HI assay. Splenocytes were isolated after the immunization to determine the antigen-specific T-cell response by the ELISPOT assay.</p> <p>Results</p> <p>Challenge experiments revealed that a single immunization of H5N1 virus HA DNA is effective in early protection against lethal homologous virus. Immunological analysis showed that an antigen-specific antibody and T-cell response could be elicited in mice shortly after the immunization. The protective abilities were correlated with the amount of injected DNA and the length of time after vaccination.</p> <p>Conclusion</p> <p>A single immunization of 100 μg H5 HA DNA vaccine combined with electroporation was able to provide early protection in mice against homologous virus infection.</p

Improved lumped parameter model for transformer fast transient simulations

To accurately simulate fast transient phenomena in transformer windings, a turn-to-turn-based multiple transmission line (MTL) model is regarded as the best approach because it is valid in a wide frequency range and capable to describe discontinuity of capacitive coupling among the turns of a non-uniform winding. However this MTL modelling approach also means that a series of large dimensional equations characterised by fully coupled admittance matrices need to be numerically dealt with, when simulating a winding typically having thousands of turns. In this study an improved lumped Resistor-Inductor-Capacitor (RLC) model is presented, which has lower computational complexity than but almost equal accuracy to the MTL model. Firstly, both the MTL and conventional lumped RLC model were compared and it was concluded that the conventional lumped RLC model is only valid in the frequency range below 2 MHz. Secondly, an improved lumped RLC model was derived in which a negative-value capacitive branch is added in parallel with the inductive branch to compensate the decrease of susceptance with the increase of frequency. Both numerical analysis and laboratory measurements were conducted on large power transformer windings, and it is confirmed that the valid frequency range of the improved lumped RLC model can be extended to about 4 MHz with no significant increase of computational cost