Hi,
My career was with British Rail for 41 years working in the C.M.& E.E.Department,at various times in my career I was responsible for sub station maintenance,and involved in new build projects,what do you wish to know about traction substations and what area are you interested in ie Sussex,Kent,London area, Wessex as the equipment and design of buildings are different although of course the electrical principals are the same.
You may have trouble obtaining drawings as they are restricted issue and there could be a security risk.
Regards
Yeovil