DC applied to primary of transformer

[Thaqalain]

I want to apply DC safely to the primary of a transformer,how can i
do?by
*When limiting resistance is in series.
*When limiting resistance is in parallel.
*when neither of above

 

[Thaqalain]

This was test question for ems comapny,they don't describe
Volatge/Current Source?here is original question:
DC is safely applied to the primary of a transformer:
*When limiting resistance is in series with primary.
*When -------------------------Parallel------------.
*When neither of preceding applies

 

[Thaqalain]

Thanks a lot Sir,I appreciate your detailed response due to that we get
some knowledge by these forums.I am civil engineer working for ems cos
in ON.