Context: In the United States, 25 Hz, a once-common industrial power frequency is used on Amtrak's 25 Hz traction power system at 12 kV on the Northeast Corridor between Washington, D.C. and New York City and on the Keystone Corridor between Harrisburg, Pennsylvania and Philadelphia. SEPTA's 25 Hz traction power system uses the same 12 kV voltage on the catenary in Northeast Philadelphia. This allows for the trains to operate on both the Amtrak and SEPTA power systems. Apart from having an identical catenary voltage, the power distribution systems of Amtrak and SEPTA are very different. The Amtrak power distribution system has a 138 kV transmission network that provides power to substations which then transform the voltage to 12 kV to feed the catenary system. The SEPTA power distribution system uses a 2:1 ratio autotransformer system, with the catenary fed at 12 kV and a return feeder wire fed at 24 kV. The New York, New Haven and Hartford Railroad used an 11 kV system between New York City and New Haven, Connecticut which was converted to 12.5 kV 60 Hz in 1987.

Question: What frequency was typically used on US Amtrak?
Answer: 25 Hz

Question: What voltage does SEPTA system use?
Answer: 12 kV voltage

Question: What specification is similar for both Amtrak and Septa systems?
Answer: catenary voltage

Question: When was a 11kV system of NY, New Haven and Hartford was converted to 12.5 kV?
Answer: 1987

Question: The Northeast Corridor connects Harrisburg, Pennsylvania and what city?
Answer: Unanswerable

Question: The Keystone Corridor connects Washington, D.C. and what city?
Answer: Unanswerable

Question: What uses a 1:2 ratio autotransformer?
Answer: Unanswerable

Question: When was the New York, New Haven and Hartford railroad converted to a 11 kV system?
Answer: Unanswerable

Question: What uses a catenary fed at 24 kV?
Answer: Unanswerable