Tap-changer know-how: Enhancing the switching capacity of change-over selectors with minimized gas production

The article discusses methods to reduce the recovery voltages on the open change-over selector contacts. The generation of arcing or sparking gases can be minimized increasing the contact opening speed of the change-over selector. Using an additional snap contact, it can be assumed that the transformer DGA will not be influenced by the change-over operation

Common oil expansion tank for transformers and tap-changers

The connection of oil volumes of transformer and tap-changer offers several advantages and savings, such as a simplified piping construction and the omission of a second oil conservator. Combined oil volumes shall only be applied to vacuum type tap-changers, and the most simple, easy-to-apply and cost-effective solution is achieved by using the connecting bone

Tap-changer know how: Insulating liquids – Part II: Non-mineral insulating liquids

In this issue, alternative insulating liquids and their potential for being used with tap-changers is discussed, based on extensive research performed on various alternative liquids over the past 20 years, with the objective of qualifying selected tap-changer models to be used with these liquids

Common oil expansion tank for transformers and tap-changers

The connection of oil volumes of transformer and tap-changer offers several advantages and savings, such as a simplified piping construction and the omission of a second oil conservator. Combined oil volumes shall only be applied to vacuum type tap-changers, and the most simple, easy-to-apply and cost-effective solution is achieved by using the connecting bone

Tap-changer DGA: Uncovering an enigma

Gases dissolved in insulating liquids are generated by thermal deterioration of the insulating liquid or they are introduced by contact with a gaseous environment (air, for example). Gases can also be formed by normal ageing processes of the liquid or catalytic interactions with metals or paints. The analysis of these dissolved gases is called DGA. Electrical equipment suitable for DGA are power transformers, industrial and special transformers, instrument transformers, bushings, cables and switching equipment. DGA for transformers has been established more than 40 years ago and since then was continuously refined according to the proceeding technical development of liquid-filled transformers

Tap-changer know-how: Insulating liquids – Part I: Mineral oils

Tap-changers are complex mechanical devices which must also adapt to high-voltage conditions. This combination makes them unique components in energy supply technology. This article describes requirements for dielectric fluids for tap changers

Tap-changer know-how: Hermetical sealing of transformers and tap-changers

Oil-filled electrical apparatus must be able to handle a certain thermal expansion of the oil, which is caused by varying oil temperatures due to load changes and/or fluctuations in ambient temperature. This article provides an overview of sealing methods for transformers and tap-changers, discussing also appropriate tap-changer protection techniques

Elutriation of flotation products

Since the first application of the flotation process in ore dressing practice, engineers have been busy solving the most delicate relations of metal distribution in the minerals to be treated...The desire for more information was the reason for research concerning the mineral distribution in fine flotation material with particular attention to the development of a suitable laboratory method of hydraulic classification or, as it is especially called, elutriation --Introduction, page 1-4

Topography data harmonisation and uncertainties applying SRTM, laser scanner and cartographic elevation models

International audienceOnly a few studies have attempted to quantify topography-depending water fluxes, to evaluate retention and reservoir capacities and surface run-off paths within large river basins because data availability and data quality are critical issues to face this objective. It becomes most relevant if water balance has to be calculated in large or transboundary river basins. The advance of space based earth observation data offers a solution to this information problem. Therefore, this paper mainly focuses on weaknesses and strengths analyzing topography with SRTM (Shuttle Radar Topography Mission) digital height data and thus provides techniques for their improved application in river network derivation, floodplain analysis, watershed hydrology in large as well as in large river basins (>1000 km2). In the analysis different types of digital elevation models (DEM), terrain models (DTM) and land cover classification data (biotope map, Corine Land Cover 1994) have been used. The DHMs are generated from Airborne Laser Scanning (0.5 m), topographic maps (10.0/50.0 m) and SRTM at 30.0 m and 90.0 m spatial resolution. SRTM digital height models are generated by Synthetic Aperture Radar (SAR) and show a high spatial variance in urban areas, regions of dense vegetation canopy, floodplains and water bodies. As study area serve the Elbe basin (Czech Republic, Germany) with its sub-basins and the Saale river basin (Germany, different federal countries Saxony-Anhalt, Saxony and Thuringia)