A superconducting transformer brings savings in weight, loss and to a lesser degree, in volume. A transformer uses a magnetic circuit in order to decrease the no-load current. The magnetic circuit can operate either at the same temperature than the superconducting windings or at room temperature. In the first case the cryostat is simple and can be metallic but the iron losses must be multiplied by the refrigeration system coefficient of performance (about 30 W/W at 77 K). With a magnetic circuit at 300 K, there is no multiplying coefficient for the iron losses but the cryostat is more complicated and requires electrical isolating materials which are problematic in cryogenics. We have reviewed several magnetic materials and measured their iron losses at 77 K and compared the latter to the one obtained at 300 K. Scratched Fe-Si steel show reasonable iron losses and could be used in a cold iron HTS transformers. Amorphous materials offer good opportunities. Transformers with a rating of 30 MVA were designed. With PIT (powder in tube) conductors the AC losses are relatively high and a cold magnetic circuit can be considered. However with Y coated conductors a cold magnetic circuit penalises the transformer efficiency a lot.

Considerations about HTS superconducting transformers

Amorphous ribbon exhibits low power loss. However, core loss of amorphous ribbon based toroidal cores is about twice as large as that of the ribbon even after field annealing under an optimum condition. In the present work, effects of residual strain and inter-laminar eddy-current loss on loss increase were examined for toroidal cores based on recently developed Metglas 2605 HB1 alloy which has a high saturation induction Bs of 1.64 T. The results show that: 1) with increase in residual strain, core loss and hysteresis loss are increased and no significant change in excess eddy-current loss was observed, and 2) there is no significant difference for frequency dependence of eddy-current loss by varying packing factor from 83% to 87%. This implies that there is no loss increase due to inter-laminar eddy current.

Core Loss in Toroidal Cores Based on Fe-Based Amorphous Metglas 2605HB1 Alloy

Reducing the core loss of amorphous cores for distribution transformers

Amorphous metal core dry-type distribution transformers have a significant place in today power market since they exhibit 60–70% lower no-load losses when compared to the standard steel based transformers. At typical loading regimes these losses are the most significant ones for a distribution transformer. In order to improve the design and to shorten significantly the time to market of such products numerical analysis of the no-load as well as of the load tests are of paramount importance. The present manuscript describes the FEM based numerical analysis performed on a 1 MVA unit, in an industrial environment, with the emphasis on the importance of non-linear and anisotropic magnetic modeling as opposed to isotropic for the accurate computation of no-load losses. The choices for the analysis regime and the specific analysis tools are described in details - and results are given to prove the salient points of this particular design of a transformer.

Investigations of no-load and load losses in amorphous core dry-type transformers

Publisher Summary This chapter discusses the anisotropy in iron-based soft magnetic materials. The production of soft magnetic materials in a form of electric sheets on an industrial scale includes cold-rolling. Thin amorphous ribbons or tapes are produced by rapid quenching of the liquid alloy changing its liquid state into an amorphous or microcrystalline state. 6.5% silicon microcrystalline tapes are manufactured by chemical vapor diffusion. Electrical sheets are characterized by anisotropy of magnetic parameters resulting from the crystalline structure of the material as well as from the type and degree of orientation. Oriented transformer sheets display the Goss texture and the anisotropy resulting from this texture is smaller than in the case of a Fe–Si single crystal. Isotropic silicon sheets with weak Goss texture and isotropic silicon-free sheets with mixed texture possess grain orientation that is an order of magnitude smaller. Determination of the anisotropic properties of the materials depends on improved measurement methods. This concern mainly the lamination stacking technique applied in the Epstein frame and a method for quantitative determination of sample demagnetisation.

Chapter 4 Anisotropy in iron-based soft magnetic materials

The need for more efficient transformer core materials, due to increased recognition by electric utilities of the costs of system losses, has spurred the development of amorphous alloy usage in power transmission and distribution transformers. Amorphous alloy core fabrication, as it relates to single-phase distribution transformer operating characteristics, is discussed. The effects of winding tension, a superior core annealing technique, and other annealing parameters are included. The potential use of Powercore??? consolidated amorphous alloy strip in three-phase stacked core transformers is also discussed in terms of the magnetic and physical characteristics of this newly developed amorphous core material. The most recent data on the thermal stability of amorphous core alloy magnetic properties are also summarized. These data confirm that core loss degradation is not expected to occur under typical transformer operating conditions and life.

David M. Nathasingh

Papers

Transformer Applications of Amorphous Alloys in Power Distribution Systems