LAST EDITED ON Mar-31-03 AT 07:55 AM (EDT)
Hi Chris,let me dare to address your questions in length...1) Poles vs pantographs > After looking at some of the pictures of PCC cars posted earlier, I've noticed that most of the newer PCC cars, and also most new light rail systems use a pantograph. I was just curious, what is the advantage of using a pantograph as opposed to a traditional pole and pickup wheel? I would think that the contactor on the pantograph would wear out pretty fast from arcing and from abbrasion as it's dragged along the line.<First of course the "obvious" statement: Each type has its ups and downs...The trolley pole is actually an invention from early traction days, and many countries & systems that started electric service around 1890 / 1900 began with the pole. In my corner of the world, only the very first systems, such as two short trolley lines along Lake Geneva (Western Switzerland) used poles, or some but not all of the first trolley companies in the city of Zurich, before their competing routes were merged into one system. Most systems that came later started out with what we call the "lyra". This is basically a drag-style trolley pole, not a folding pantograph like later models. These lyra started to get replaced by pantographs, first the box-style ones (or however their name in English), later followed by the single holm models (see pix below). Please allow me to illustrate the topic with some pictures from various preserved and current trolley cars from Austrian, German and Swiss but also US systems, while we talk about the advantages and disadvantages of the various models, as far as a layman as me understands them. 
The classic trolley, as seen on PCC 1061 in use on the Market Street line in San Francisco, painted in PE scheme (yes, selected on purpose). Note how carefully the wire has to be laid through curves, to prevent the pole from derailing. Furthermore, trolley poles need aerial switches for the pole to take the right string of wire when the car underneath it travels over a switch or crossing. These switches do not only add up on your initial installation bill, but they also need (a lot of) maintenance, as they are the first part of the wire to suffer from tear and wear. While tear and wear on the pole may be limited when it uses a wheel, this model here is using a shoe. If the pole made direct contact with the wire (steel on steel), you’d have enormous problems with abrasion. Therefore, you will normally find a carbon collector inside the shoe which needs to be replaced occasionally. You can tell that the collector is almost used up when the pole starts to spark continously even while travelling along straight, unobstructed stretches of wire, with sparks in the colors of orange or green (depending on materials) – as opposed to the regular, blue type of sparks you always get when travelling over a circuit breaker, switch, intersection etc. 
Sacramento “Safety Car” 62 is a typical representative featuring a pole with wheel instead of contact shoe. While travelling along the wire, the wheels make a typical chirping sound, also referred to as “the singing wire” by many people.The upturn is that both types of poles are a rather easy piece of equipment as the pole moves in its entirety. Still, it needs to be mounted on a base that can swivel to the sides, as the pole needs to follow the wire when traveling around a curve. The narrower the turn, the better you can observe this. 
1902 built motor 2 of LSB, one of several suburban trolley lines later integrated into the City of Zurich’s transport agency. It is a typical example of the “lyra generation”. And the small trailer is actually a mail car (no joke)…From ca. 1900 onwards, many European systems opted for the lyra. “Car-side”, its construction is as easy as the pole – basically, it is a stiff piece of metal, mounted in a “harp-style” bow and held in place by springs at its base. Again, the contact bridge, i.e. the part of the lyra that makes contact with the wire needs occasional replacement. On some early models, the contact bridge was actually just “plain metal” touching the wire, with predictable results. Common sense dicdated to use carbonized collectors again, mounted onto (or into) the bridge or “bow” actually in contact with the wire. As the lyra is a little bumpy by nature, it rather scratches than slides along the wire. Abrasion is a persistent problem with lyra pantographs, both for the contact bridge as for the wire itself. Lyrae will actually damage the surface of the wire, almost like a rasp. Needless to say management does not like this, especially in times when copper supply became a problem (WW II!). Several atetmpts were made to reduce abrasion: On some early models, the contact bridge was actually just “plain metal” touching the wire, with predictable results. Common sense dictated to use carbon collectors again, mounted onto (or into) the bridge or “bow” actually in contact with the wire. Look at the following detail:
Furthermore, the wire was strung in a gentle “zig-zag” to ensure that abrasion did occur on the entire span of the contact bridge, not only in its centre.
Faced with the abrasion problem of the lyra, and the inherent need of copper for replacing worn out wires, lyra pantographs started to be replaced with the “classical” box-style type of pantographs from the 1920s/1930s onwards. An early example, again from the city of Zurich, is Motor 321 from 1931. For the record, 321 is one of three cars preserved into our days, representing a 50 car series of motorcars commonly referred to as the “elephants” for their excellent traction. Note how complicated this early model of a pantograph looks.While the pantograph is a much more complicated piece of equipment than the straight-forward lyra – all those moving parts need to be greased, otherwise a “frozen” panto can tear down your wire - its additional weight and need for maintenance is more than offset by the much smoother way it travels along the wire, thus reducing maintenance cost on the electrical installations of a system considerably. Regarding transition, one of the advantages of the lyra is that it could co-exist with the pantograph on the same system….
…and still can do so today. This wouldn’t be easy with poles. Many of the installations on a wire used by trolley poles – such as the switches – would have to be amended with protecting flanges to direct the contact bridge of a lyra or pantograph away from the fragile installation for the poles. Such an effort was not necessary for systems that used lyrae, as these were also just dragged along the wire.This inter-operability also ment that a transit company did not have to change from pole to pantograph in one systemwide step. Cars could simply be updated to new models of pantographs whenever they were due for maintenance or a rebuilt, as the following example illustrates:
Zurich motor 2 as it exists today, preserved in an early state featuring a lyra.
Preserved sister motor 1009 is basically of the same type of car, restored into a state after the installation of a pantograph and the introduction of a new numbering scheme. 
The almost ornamentalistic style of the first panto’s used on the “elephants” soon made way to a functional design that remained in use for the next 50 years. Zurich motor 1392, a representative of the “Unified Type” adopted by 5 cities – making it the Swiss counterpart to the PCC in the US – has been restored into the original state these cars were in when deliveries started in the 1940’s. 
Motor 427 is of the same type of car and shows the “Unified’s” as used by the Basel transit authority from 1948 until 2001. I added this picture because you can see that the shiny new contact bridge has just replaced the previous one which had obviously worn out. This had to happen for safety reasons, despite the decision to withdraw and scrap the car a few weeks after that picture. The imminent withdrawal was a fact at the time of the photo already, as the billboards on the rooftop and all ads inside 427 are gone already, probably transferred to a new car.
Historic motor car 19 of the Austrian city of Innsbruck. Note the typical contact bridge that German and Austrian trolleys used from the 1950s to the 1980s. It is not mounted stiffly on the top of the pantograph, but it tilts backwards when the car moves forward, further reducing tear and wear.
Modern cars such as articulated motor 2034 of San Diego, use single holm style pantographs which started to appear around the 1970’s. They offer the advantage of a considerable reduction in weight and space eaten up on the roof. It’s stability is no issue, and with fewer moving parts it has become the favourite pantograph not only for trolleys but also for conventional locomotives on electrified mainlines as well as for high speed trains. 
Despite all those pantographs, the trolley pole is not dead with many European transit agencies: As bus 104 of the small town of La Chaux-de-Fonds shows, many cities have electrified some of their bus routes. While the current on trams flows from the wire into the ground through the traction motor, its associated resistors and the steel tracks, buses need to overhead wires as those rubber tires on asphalt provide quite an efficient isolation towards the earth. So on the trolley bus, the current flows from the wire with a positive charge to the earth via traction motor and the wire with a negative charge. Neither the two wires nor the pantographs are to touch each other at any time or those 600V will be making a short circuit of a dimension which will have everybody within one block jumping. Therefore, two trolley poles are the ideal means to make contact with the two wires. 2) AC versus DC> Also, are modern PCC and light rail systems still using DC, or are they running on AC now? I would think that it would be more efficient to use AC, especially on longer lines, because then you could increase the voltage to overcome voltage drops.<To my knowledge, almost all transit systems still use DC world wide, simply for the fact that:
a) lines are short
b) wires and supporting installations can be built much lighter and cheaper. AC systems with their high voltage tend to need massive installations, down to the poles, isolators and the wire itself. > But then I guess traction motors still run on DC, so you would have to have an onboad transformer to step down the voltage and rectifiers to convert it to DC. Who knows?<The German city of Karlsruhe did some pioneering steps when it introduced by-modal motor cars about a decade ago. The system uses standard gauge, and (me thinks) 600V DC overhead. The German Railroad "DB" which was about to withdraw from operating some commuter lines in the region uses standard gauge, but 15 kV AC overhead. The transit system dared to offer to take over the exploration of the commuter services by building "on/off-ramps" from the city's rail network to the mainlines, plus by developing a set of cars that could run under both systems with the simple flip of a switch.
That is Karlsruhe 823 travelling on the city streets towards the main station. After calling in front of the buildnig, it will continue to the access ramp, enter DB tracks, and travel on to the city of Baden Baden, some 40+ (estimate) miles away from Karlsruhe…OK, I hope I could shed some light on those questions, Chris. Kind regards, and cheers Lukas a.k.a Swissie
(Updated for the persistent typo)
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Route Building 1% Completed
Note the two neighbouring circuit breakers within the red box. Another pair would be behind the trainset, to the right of the picture. The short stretch of wire inside each of the two pairs is the permanently insulated wire, the train itself is under the part of wire that can be switched to either voltage. Bound for the city centre under 600 V DC, it is just leaving from the plattform where the transition from 1200 V to 600 V has taken place while passengers were loading/unloading, in MSTS slang...From the picture, you can easily see why that layout was chosen. The transition point is in quite a steep grade! Having to idle the uphill trains (those that come from 600 V to 1200 V) through the transition point on their own momentum would be quite unreliable, and given the fact that there is a stop in the area anyways, the layout chosen is the best solution for this specific situation.Lukas a.k.a Swissie
