The efficiencies of superconducting machinery are not clear-cut, but depend on
many different issues, such as, among other things, the properties of the chosen
HTS-material, the geometry of the superconducting tapes and the cooling system
which can be based on either LN2 or mechanical cryocoolers. All of these influence
the losses of the devices and thus it is not possible to precisely express the efficiency
figures of superconducting devices. A superconducting 30 MVA transformer, with
an efficiency of 99.97%, was designed by a French group [7], but in reality it is not
suitable to optimize the machines only for the lowest possible losses. In moving
systems, for example, the weight of the device plays a crucial role and optimization
should take that into account [7,8]. According to current knowledge, by utilizing
HTS windings in power devices it is possible to reduce losses to approximately half compared to that of the conventional devices [9,10]. The ratio, a, of the losses in the
HTS-device to the losses in the corresponding conventional one can be used to
express the efficiencies of HTS-devices, sc.