Behavior of transformer insulation under short-time overvoltage
This paper reports on a series of tests made on transformer insulation samples with automatically applied short-time a.c. overvoltages above the corona inception level to determine the conditions under which damaging corona occurs. Modified dielectric tests for power transformers are discussed.
EHV transformer dielectric specification improvements
EHV transformers have higher failure rates than lower voltage transformers. Many of these failures have been attributed to dielectric mechanisms. Therefore, the dielectric specification for these transformers has been enhanced by upgrading ratings, conducting comprehensive design reviews, performing voltage sensitivity analyses and proving the integrity of the transformer with improved dielectric tests. Most elements of the new specification have been applied to eight transformer designs, and the results are discussed. It is recommended that the industry further investigate insulation coordination and failure analysis of EHV transformers, and that standards be expanded to incorporate special requirements for these ratings. >
An analytical approach to the design of electrodes in high-power, fast-transverse-flow CO2 lasers
Abstract Usually, the design of the electrodes of fast-transverse-flow CO 2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrodes that achieves a quasi uniform gain distribution. The analysis, based on a two-temperature model and the gas-transport equations, computes the electron density that supports a flat gain pattern. Combining the desired electron density with the electron-balance equations, the model determines the required electric field. The results were used to design a new set of electrodes for a home-made fast transverse flow CO 2 laser. A stable, large volume discharge ( 4 × 8 × 90 cm 3 ) with very good uniformity was obtained. The resulting gain distribution was registered in a bi-dimensional map. The peak gain rose from 1.2 m - 1 , attained with the old electrode set, to 1.6 m - 1 with the new one and the gain showed a homogeneous profile.