I do not have enough information on all of the pieces to give you definitive answers to all
of your questions, but I think I can get close to a general answer; there are other Forum contributors that may be able to fill in some of the missing pieces...
The Safe Harbor Power web site http://www.shwpc.com/facts_figures.html#station
indicates a total potential generation capacity (at 25hz, single phase) of 101,250KVA. (BTW: 101,250KVA = 101.25MVA) Direct generation from 25hz turbine generators: 2 x 35,000KVA; plus 31,250KVA from a rotary frequency converter that could convert some of the 60hz power generated at the dam to 25hz.
A Siemens web site http://www.sts.siemens.com/News/99_00/120199.html
indicates the rating of the Richmond (Philadelphia) electronic frequency converter as 180MW.
There is another rotary frequency converter station at Metuchen of unknown capacity. KenW2KB, can you or others help out on this one?
It was previously my understanding that these were the only sources of power for the ex-PRR NEC. I also do not believe that there are any other hydroelectric plants serving the NEC. However, while searching for information on the Richmond Converter, I found a related web site from Advanced Control Systems http://www.acsatlanta.com/pages/pr_amtrak.html
that indicates that there are also frequency converter stations located at Sunnyside Yard in New York and Jericho Park in Washington, DC. I have no other information about these converter stations.
If we add up these numbers:
101.25 (Safe Harbor) plus 180.00 (Richmond) = 281.25
and divide 101.25 (Safe Harbor) by the total 281.25,
=36% from Safe Harbor.
(To the engineers or technically-savvy readers out there; yes, I added MW and MVA. For the purposes of this question, it's easier to assume 1.0 power factor!)
Because we have not included the contribution from the Sunnyside, Metuchen or Washington DC converters, 36% is a "high" estimate.
As for Safe Harbor electricity "reaching" New Jersey, I would have to say yes. It would depend on how much power is being generated at each plant and where it is being consumed at any one moment. The Amtrak 25hz system is a small isolated "grid", but under normal cicrumstances, all of the generators and converters are synchronized and are run in parallel for redundancy, reliability and stability.
I believe that the 25hz facilities at Safe Harbor are operated and maintained by the utility on behalf of Amtrak. How and in what manner the "billing" takes place, I do not know...
...I can just imagine one of those little "postcard" electric bills.... To Amtrak, 30th Street, Philadelphia PA; 108,134,629 kwh used this month @ 032/c/kwh x 108,134,629 kwh; please remit $3,460,308.13. You may deduct $69,206.16 if paid by.....