This is one of the many substations Amtrak owns to supply power to their electrified rail lines. These step 138kv down to the 12kv catenary voltage. This system operates at a 25hz frequency rather than a 60hz frequency, which explains the single phase, 2 wire circuits. The substation was built in 1937 when the Pennsylvania Railroad electrified their main line from Paoli to Harrisburg and their low grade freight line. Most of the equipment in this one is original, like the big Westinghouse transformers and the insulators with grading rings.