I want to know the answer to the following question:
When was a 11kV system of NY, New Haven and Hartford was converted to 12.5 kV?
All the background I'm provided with is that "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.". Is that enough to answer the question?