Generally speaking, equivalent circuits are used to simplify a complex circuit into terms that are solvable with known relations. For example, in a transformer equivalent circuit you can account for...
Isolation transformers are used to isolate one circuit from another. Highly sensitive circuits may require isolation from high power circuits, for example.
If you are saying that the secondary (output) winding on a transformer seems to be a short circuit, it is very likely to be low resistance and may only be a few ohms if you measure the resistance...
If you want to know a printed circuit board is designed here is the explanation in simple terms. 1. First you decide on the components which are in the design. 2. Need a software in which you can get...