There are not any additional libraries for proteus , there are only the ones sold by labcenter, I hope you are not asking for them :evil:.
From time to time a see a post about custom components in proteus but not libraries with many components.
there are several transformers in proteus but they are not named transformers.
Open the component dialog and write TRAN-, you will see four models, also add VSINE in the project as the AC voltage source for the transformer
double click the transformer and change the transformer ratio, or since the default is 1/1 use a 12V AC source in the primary and also set the source frequency to 60Hz
there are several transformers in proteus but they are not named transformers.
Open the component dialog and write TRAN-, you will see four models, also add VSINE in the project as the AC voltage source for the transformer