1) You can specify the impedance. The farther away from a "standard" impedance you specify, the higher the probable cost of the transformer.
2) Start with industry "standard" impedances. In the U.S., they are found in the C57.12.xx series of standards (the product standards). Each of...
If they are two paralleled wye-wye transformers and one phase is lost on one of the transformers, then the capacity of the one phase will be halved and the capacity of the other two phases will still be full rated. Assume A-phase fuse blows on one transformer. A-phase capacity on that...
