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Electromagnetic modeling of transformers is of paramount importance for the prediction of the transient behavior of the entire system during atmospheric overvoltages and switching transients. Time domain simulations and measurements have been performed to model the behavior of dry-type transformers under transient overvoltages in different configurations. This analysis and the developed method allow investigations of possible means of protection (or their possible redundancy) of the transformer against uncommon transients experienced in real circumstances that might exceed the dielectric stresses the transformer was designed for. For this purpose, an existing, detailed computational model has been further developed, and the results have been benchmarked against measurements. [ABSTRACT FROM AUTHOR]

This paper presents important results of the European HVDC Study Group founded on an initiative by the German Commission for Electrical, Electronic and Information Technologies in September 2010. The main task of the Study Group has been defining “Technical Guidelines for first HVDC Grids”: 1) to gain a common understanding of basic operating and design principles of HVDC grid systems, and 2) to prepare the ground for more detailed standardization work. The HVDC systems are moving from the stage of point-to-point (PTP) connectors to the stage of the transmission systems interconnecting more than two stations and utilizing multiterminal (MT), multivendor (MTMV) HVDC voltage-source converter (VSC) systems. The development will be modular, for example, in steps, starting with interconnecting PTP connectors and establishing three-pod, radial systems. Then, such simple systems may gradually be interconnected into radial and meshed HVDC–VSC systems comprising more HVDC lines and dc converter stations. This paper describes understanding, specification, and standardization of design and operation principles of the HVDC grids seen as the first needed steps toward such MTMV systems. [ABSTRACT FROM PUBLISHER]