Two real Mathcad 15 e-books exist with Transformer calculations.
Electrical and Electronic Engineering, and
Electrical Power Systems Engineering
I have no idea how to obtain them now. Perhaps someone in the community knows.
Here are some I have collected over the years. Hopefully they are a help.
I do have the Engineering Libraries (which i purchased) cite by the other responders but I do want to infringe on copyright material by posting them. There is also one by Hicks which has a lot of material found in the Engineering Handbook authored by Hicks.
"Mathcad Prime Worksheets Directory - Electrical Engineering": https://community.ptc.com/t5/PTC-Mathcad/PTC-Mathcad-Prime-Worksheets-Directory-Electrical-Engineeri...
Is there anyone who knows where these ebooks above mentioned can be found for free:
1. Electrical and Electronic Engineering
2. Electrical Power Systems Engineering
I think they were never available or free. You could buy them from Mathsoft, as an extra to Mathcad 14. Maybe this helps:https://www.mathcad.pl/?electrical-engineering-library,37"
Could it be that PTC converted those ebooks into Prime format and tried to sell it as new content of Prime 3?
Here you can see at least some pdf's of those files: