John_Perkowski wrote: ↑Sun Sep 22, 2024 9:15 pm
Please explain to me the multitude of catenary systems on the NEC and their/their substations state of repair.
Three different train companies built the overhead catenaries.
New Haven RR between NYC and New Haven hung 11kV 25 Hz power and was later re-hung 12.5 kV 60 Hz power.
Pennsylvania RR between NYC and DC hung 12kV 25 Hz power.
Amtrak between New Haven and Boston hung 25kV 60 Hz power.
So why was 25 Hz power used by the PRR? New Haven RR did first. Why did New Haven RR hang 25 Hz power?
During the beginning of the 20th century, 25 Hz power was much more readily available from commercial electrical utilities. The vast majority of urban subway systems used 25 Hz power to supply their lineside rotary converters used to generate the DC voltage supplied to the trains. Since rotary converters work more efficiently with lower-frequency supplies, 25 Hz was a common supply frequency for these machines. Rotary converters have been steadily replaced over the past 70 years with, at first, mercury arc rectifiers and, more recently, solid-state rectifiers. Thus, the need for special frequency power for urban traction has disappeared, along with the financial motivation for utilities to operate generators at these frequencies.
Principal advantages of motor generators include very high fault current ratings and clean output current. Solid state electronics can be damaged very quickly, so the microprocessor control systems react very quickly to over-correct conditions to place the converter in a safe, idle mode or to trip the output circuit breaker. Motor generators, being of 1930s design, are heavily overbuilt. These rugged machines can absorb large load transients and demanding fault conditions while continuing to remain online. Their output waveform is also perfectly sinusoidal without noise or higher harmonic output. They can actually absorb harmonic noise produced by solid-state devices, effectively serving as a filter. These attributes, combined with their high fault-current capability, make them desirable in a stabilizing role within the power system. Amtrak has retained two of the original converter plants and plans to overhaul them and continue their operation indefinitely.
So 25 Hz is likely to remain on the NEC between DC and NYC for a long time.