• Pantograph, phase gap, etc.

  • General discussion about locomotives, rolling stock, and equipment
General discussion about locomotives, rolling stock, and equipment

Moderator: John_Perkowski

  by tedklugman
I'm sure someone here can answer this rather quickly.

When an electric train goes through a phase gap, what happens? Does the engineer lower the pan or does it occur automatically? During the time that the pan is down, where does the aux power come from? batteries? How much aux power is available and for how long? enough to run the motors?

Sorry for the stupid questions :-)

  by Uzi-Cat
The pan stays up. Engineer cuts the throttle off so no power is drawn. Everything is pretty much automatic, triggered by magnets between the rails. That is the conductor explanation, somebody probably has a more thorough and meaningful explanation to add to this.


  by pgengler
While we're being inquisitive on this, is there some sort of posted sign/other notification that a phase gap is coming up, or is it something the engineer just knows (from having been qualified on the territory)?

  by BlockLine_4111
I always thought the train would blow through the PG with no change in throttle position.

Does the back EMF generated by the train have to be "in phase" with the juice on the other side of the PG ?

  by Uzi-Cat
A qualified engineer and conductor for that matter have to know where the plase gaps are. There are also "PG" signs posted as well as car markers hanging from the catenary. The gaps are really hard to miss.


  by nick11a
Oh, that's what it means. I always thought in meant "Parental Guidance." :wink: Sorry.

  by steemtrayn
Knowing where the phase gaps are can be fun. I clap my hands and the lights go out, I look at the passenger next to me and say "Oh, were you reading? I'm sorry..." and clap my hands twice, and the lights come back on.

  by timz
"During the time that the pan is down, where does the aux power come from?"

I've never watched a train pass a gap, but I'm guessing the pantograph doesn't lower-- nowadays, anyway. If it does, do Arrow pantographs lower sequentially?

It's been claimed here that the lights don't go out on Arrows (thru the gap) because the motors become generators to supply "HEP" to the cars for that three seconds or whatever. Sounds fairly incredible, doesn't it?

  by DutchRailnut
The lights are powered by the 64 volt(some 32 volt) car batteries during power outage.
The pantographs do not come down but travel tru a dead section about 90 feet long.
There are no magnets in the track, the engineer just coast tru the Gap or break and resumes powering after x amount of cars past the gap on MU's or Acela , but can resume imediatly with locomotive hauled trains.
yes powereing tru a gap or break gives one hell of buzz in train and usualy trips the overhead due to EMF in tranformer phased wrong.

  by Nasadowsk
The pans stay up through the gap.

Arrows will regenerate for HEP until they get below X speed. they also regenerate for HEP durring braking, and dump the excess energy via the roof grids

That's the source of the buzz noise as they come into a station...

  by timz
"The lights are powered by the 64 volt(some 32 volt) car batteries during power outage."

The emergency lights on Comets, you mean? He maybe was asking why the lights don't go out on Arrows.

"There are no magnets in the track"

Those yellow things in the gauge on either side of the gaps on tracks 5-6 (connecting the 12kV NEC/PRR with 25 kV NJT/DL&W) aren't magnets?

  by MBTA F40PH-2C 1050
the yellow squares in the tracks? those are the transponders

  by PRRTechFan
I believe that there is more than one correct answer to the original question; and "what happens" depends on what type of phase gap is being crossed.

A phase gap can be as simple as a gap where the voltage and frequencies are the same and only the phasing is different. Gaps will also exist where major changes in voltage exist (11-13kV to 25kV) and also where frequency changes exist (25Hz to 60Hz).

I believe that "phase" gaps where opposing voltages and frequencies are otherwise the same only require that the engineer release the throttle and coast through the gap. Examples of this on NJT on the North Jersey Coast Line are just south of Red Bank and at Laurel Avenue in Middletown. More about this later...

Where a phase gap separates circuits of significantly different voltages (11-13kV to 25kV), some form of switching must occur on board to adjust for the voltage change and avoid frying equipment due to severe under or over voltage. One way to accomplish this is by tripping the main circuit breaker on the train when crossing the gap. The circuit breaker cannot be "reset" until the gap is crossed and the voltage restored. The incoming voltage is compared to the primary voltage tap setting on the main transformer, and the circuit breaker can only be reset when the transformer is set to the "correct" voltage. It is my understanding that the circuit breaker is tripped by a magnet or some other type of acutator on the track. I believe that NJT uses this to accomplish the voltage change at the "Midtown Direct" connection with the Northeast Corridor. NJT is 25kV, 60Hz and the NEC is 11kV, 25Hz.

Something similar has to happen when frequency changes occur; the drive electronics absolutely are affected by line frequency; although resetting the drive electronics by using some sort of frequency sensing should be relatively easy.

"Powering through" a gap causes severe arcing at the point the connection is broken, which can cause excessive wear and damage to the catenary and pantograph. The situation caused when power is restored is that there is a sudden current inrush as the transformer and motors are re-energized; and yes; that can cause a caternary segment to trip.

I recall seeing signs on the catenary poles at the Midtown Direct phase gap and at the phase gap just north of New Haven; both of which jump from 11-13kV to 25kV.

As for the back EMF of the motor acting as a generator when the power comes back; I think this would strongly depend on the type of "drive" controller and whether the actual motors are AC or DC. The Acela's drives actually can regenerate energy back into the catenary while using the motors as generators to accomplish braking. If the drive removes the voltage from the motor field, the back EMF will rapidly drop off.

However, there is one thing about the NJT phase gaps on the North Jersey Coast Line that I do not understand. As the train approaches the gap (...noted by day-glo painted catenary poles!), the engineer backs off the throttle. The train passes the gap, which appears to be very short, several feet at most; and all the power to the train goes out. About 10 seconds later, power is restored and acceleration is resumed. This happens at Red Bank and Middletown, which are simple phase gaps; and I believe it also happens at the gap south of Matawan, which is a 25Hz-60Hz gap. The engineer tells me that all they do is drop back the throttle, that the 10 second power loss is not something that the engineer does, nor does the length of the actual phase break coincide with the length of break in power. It seems to be something that is originated at the local substation(s). Does anyone have an explanation for this sequence of operation?

Knowing where the phase gaps are can be fun. I clap my hands and the lights go out, I look at the passenger next to me and say "Oh, were you reading? I'm sorry..." and clap my hands twice, and the lights come back on.
Very good! LOL!

Any engineers out there with better information?

  by Ken W2KB
Pure conjecture, but electrical equipment often has a time delay built in of a few seconds so that it does not turn on immediately to avoid a current surge. Compressor motors for instance, may need a few second delay.

  by Sirsonic
The actual workings of what happens at a pahse gap can be explained simply.

There are 6 pahse gaps on electrified lines where I am qualified, two of which involve a voltage change. On the other 4, I have been told that the phase gaps allow for different suppliers of electricity on either side. There are also 3 on the Coast Line, I of which involves a voltage change. They are:
M&E --
Meadows (Between Meadows interlocking and Kearny Jct)
Kearny Jct (On tracks 5&6, with a voltage change from 25Kv on the M&E to 11Kv on Amtrak)
Cape (On the singe track Waterfront Connection, with a voltage change like that at Kearny Jct.)
Maplewood (Behind the Pathmark in Maplewood, and right by the detector)
Morristown (About a mile west of Morristown station)
Gladstone --
Sterling (MP 29, just west of Sterling station)
Aberdeen (Just west of Matawan station, this also has a voltage change from 11Kv east of to 25Kv west of. Additionally, power east of there is provided from Amtrak as the catenary is connected at Union)
Laurel (West of Hazlet, near the Laurel Ave undergrade bridge)
Red Bank (Just west of Red Bank station)

Anyone qualified on the physical characteristics of the railroad will know exactly where these are located, however, they are also marked by two signs on the catenary poles, or in the catenary itself. One cat pole from the actual dead section of the phase gap, which is about 10 feet long, there is a PG sign, which is an indicates an approaching phase gap. At the actual dead section, there is a phase gap marker, which is a white triangle, with a black dot in the center of it. This is where if you are operating an MU train you must have the controller back to off.

Now, lets say I am operating an ALP-44, or 46 east towards the phase gap at Kearny Jct. As I approach the phase gap, I will back off the throttle so that once I reach the PG signs, I have the throttle back to "O", which is the same as idle on a diesel. Located between the rails, usually near the PG signs, but sometimes a little farther back, are two yellow magnets. There are two magnets just in case one gets stolen, knocked out of position, or for some reason fails to do its job. The magnets are detected by an "antenna" (their term, not mine) located underneath the locomotive which causes the main circut breaker (MCB) to open or close, depending on its current position. Whatever position it is in now, it will do the oppisite, if possible. This has the same effect as the pan being dropped. This is also why the lights go out on the train when passing through a phase gap. Once the locomotive clears the dead section, once again, a set of magnets will be encountered. Before the MCB closes, the locomotive will check the line voltage, and make sure the transformer is set up to operate under that voltage, changing the transformer setup if required. Once that is done, the locomotive will power up, the engineer may bump for power, that is, open the throttle rapdily to get a bump, to make sure the locomotive is come totally back. Sometimes, you will not get traction power after passing through a phase gap, although you will get the HEP back, this allows you to make sure. Bumping for power is only done on the cab car as the locomotive has an amp meter to show if the traction motors are taking power, and the cab car does not.

Now on MU's, they do not open the MCB prior to a phase gap, and so an engineer must have the controller back to off so as not to draw an arc across the dead section of the phase gap, which would blow the line behind the train. When the pan of the MU gets to the dead section of wire, the equipment automatically switches to dynamic brake to supply power to keep the lights lit, and the rest of the systems operating. In the even that the line goes dead, they will do the same thing, until the train stops.

In an ALP it is not required to shut off the throttle, as the magnets will open the MCB anyway, although this would make for a very rough ride, and could damage the electronics on the ALP.

Finally, as to why the cat poles just on either side of a phase gap on the coast line are painted lime green, there is a simple answer. When the E60's were running, it was necesscary to manually open the MCB at phase gaps. To remind engineers of this, the cat poles just before the phase gaps, as well as the button on the control stand were painted lime green.