Rectifier Stations For Third Rail on The Nyc Subway

[rail10]

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

[Allan]

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.

http://www.mta.info/mta/museum/archiveguide.html

[kitn1mcc]

i would guess the AC is fed from a Con ed Substation using standard breakers at the station

i think DC is fused

[railfan365]

Somewhat related, but a bit different, my question is based on the fact that whle there is DC in the electric rails, there are a significant number of cars with AC traction in them, and there's due to be more. The third rail power is still DC because there's still a lot of equipment online with DC motors.

The actual question is whether anyone knows if third rail power will be changed to AC once the cars with DC motors will all be retired, and if the inverters on the R-142 cars onward will be disabled. I know that it should be upwards of 20 years for all of the R-62's and 68's to be replaced, but the fleet will eventually be changed over if NYCTA will continue to buy AC powered cars and scrap older DC powered cars.

[kitn1mcc]

i think it would take alot of covert the system to AC i dont even know if ac would work with the 3rd rail. one thing with ac is that they can then use just transformers plus they would have to add resistor banks for dynamic brakes

[railfan365]

i think it would take alot of covert the system to AC i dont even know if ac would work with the 3rd rail. one thing with ac is that they can then use just transformers plus they would have to add resistor banks for dynamic brakes

I'm not sure what you meant by adding resistor banks - to the railcars or to the power gride. All of the NYC subway cars from the R-142's on have AC traction with regenerative/dynamic braking already.

[kitn1mcc]

dynamic breaking on DC cars can be feed back onto the rail, with AC you can not back feed it with out matching frequency.

[farecard]

The actual question is whether anyone knows if third rail power will be changed to AC once the cars with DC motors will all be retired, and if the inverters on the R-142 cars onward will be disabled.

Unlikely....

The modern rolling stock uses 3-phase AC motors driven by variable-frequency drives [VFD]. The VFD generates AC to drive the motor at the desired speed. To do so, it must have a source of DC. That can come from a DC third rail, or a AC source that is rectified into DC. But given the system exists now; there's not a lot of justification for changing the third rail over; the VFD would not be any cheaper.

Plus, as others has alluded to... it's easier to dump regenerated power back onto a DC bus.

Another factor is it's trivial to parallel many DC power substations but doing so with AC from different AC sources takes more effort.

[farecard]

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
....
http://www.mta.info/mta/museum/archiveguide.html

No matter what link I try, I get shunted to the service advisory page.

[Backshophoss]

Untill almost full service is restored,the mta info site,"locks" in advisory mode,untill "reset" by MTA officals.
Have you tried to go to subchat(http://www.nycsubway.org)?

[MBTA3247]

I can tell you that there are a lot of arc rectifier substations all over the system - from what I understand nearly 200.

They're still using arc rectifiers instead of solid-state? Wow.

[farecard]

They're still using arc rectifiers instead of solid-state? Wow.

At least they retired the rotary converters....

[Disney Guy]

Mercury arc rectifiers are very efficient (around 95%), much more so than rotary converters (motor-generators). They have no moving parts and last a long time. I would think that they are less subject to damage from power surges caused by lightning compared with solid state rectifiers. I would say they fall into the category "if it ain't broke then don't fix it."

(reference: Dhogal, Basic Electrical Engineering Vol 2, pp 445, as seen in Google Books)

Feeding the traction power substations are standard transformers protected on the primary side with standard fuses, the latter similar to those protecting utility pole transformers. Such fuses consist of a fusible link (a wire) passing through a ceramic or plastic tube. The transformers are similar to those outside a "sub-substation" outside a factory, or maybe even as large as the transformers in a substation serving a small town. I think that subways of that vintage (going back to the early 20'th century) still use snap in cartridge fuses for the individual sections of third rail.

Early parts of the system had primary cables (11,000 volts 25 Hz) in conduits in the tunnel walls, from a central generating station going to the various substations. These cables are probably inadequate to carry enough 11,000 volt power needed for today's trains and schedule, tapped off of the Con Ed feed at a live substation uptown to a substation downtown without Con Ed power.

(Reference: Interborough Rapid Transit, The New York Subway, pp 93.)

[farecard]

Mercury arc rectifiers are very efficient (around 95%), much more so than rotary converters (motor-generators). They have no moving parts and last a long time. I would think that they are less subject to damage from power surges caused by lightning compared with solid state rectifiers. I would say they fall into the category "if it ain't broke then don't fix it."

I would doubt anyone has made them in decades. They were not cheap. They are a hazmat event waiting to happen; at manufacture, shipping, storage and operation. You have to preheat them for tens of minutes after moving them or they flash.

And they had forward voltage drops of 20-30 volts, as I recall. That's lots of wasted power vice a silicon rectifier's 0.6 volts.

But they do glow so pretty......