rail10 wrote:Where are these located and what type of fuse and breaker system is used to protect them on both ac from the transformer and dc side
While I could not get into the technical part of your question (because I don't know that answer), I can tell you that there are a lot of arc rectifier substations all over the system - from what I understand nearly 200. Some are in older substation buildings (where the rotary converters have been removed and replaced) and others are located just below the street and all you see are the sidewalk vents.
There is no specific list of these but there is a list of NYC Substations here: http://www.mta.info/mta/museum/pdf/Powe ... %20Aid.pdf
This list is actually an inventory of records of the construction and maintenance of the electrical supply systems for the New York City subway and elevated lines, from 1898-1998. and contain all substations in the system (including ones that are no longer in existence or have been abandoned - some of the street names have been changed over the years - the list has the original name of the substation location). There are no indicators as to whether they are above ground in a building or below ground.