Trolley pole, bow collector & pantograph

[melmerby]

Hi all

 

What were the advantages/disadvantages of the various OHE collection systems?

 

Obviously pantographs don't need to reverse but what of bow collectors?

Trolley poles need "pointwork" at junctions, the others don't.

 

What were the pros and cons of each type?

 

Cheers

 

Keith

Edited January 26, 2018 by melmerby

[Edwin_m]

Trolley pole more prone to dewirement. 

 

Bow collector and pantograph have much less lateral tolerance, so need more supports to keep the wire above the track on curves. 

 

Bow collector less tolerant to variable wire height?

 

I'm not sure how you reverse a bow collector, especially if it's somewhere the wire is quite low. 

[alastairq]

AFAIK.....trolley poles can have the contact wire displaced from the track centre line by quite a bit more, than with pans or bows.

 

Bows do need reversing, unless of the upright sort....which are rigid [sort-of]...

 

A sprung bow can be reversed automatically, by having a raised point in the wire.....the bow will spring up vertically, the vehicle is reversed, and the bow comes back down the other side.

 

A trolley can be automatically reversed by leading the overhead wire off to the side, at right angles. The pole and shoe are taken up the leg, until at right angles to the vehicle...... the vehicle is  reversed, and the pole comes back along the wire correctly.

 

Or, a triangle can be made in the overhead wire.....the pole is reversed up the leg, the vehicle keeps going, and the pole is brought back in line.

 

Unless one keeps the  overhead wire pretty much in line within the rails of the track....a pole really ought to have a swivelling shoe ....quite awkward in smaller scales?

[melmerby]

AFAIK.....trolley poles can have the contact wire displaced from the track centre line by quite a bit more, than with pans or bows.

 

Since starting the original thread I remembered a situation on the BCT network where the contact wire is lower than the height of the tram and offset to the side under a low bridge.

This was at Dudley Port where the track was singled and the contact wire was on the western side of the track.

Only a trolley pole can do this!

 

Some Birmingham services used bow-collector trams which I had understood was because of the curvature of the route (?)

 

Keith

[BR60103]

Pantographs need some special construction at right angle crossings so that they don't snag the other wirev-- not sure what but Toronto is converting from pole to panto.

Edmonton had an interesting bit of wire where the new (then) LRT system (pantograph) crossed the trolley bus system (poles) at 45 degrees or less. Complicated bit where the pantograph wire angles off parallel to the TB wire and there was another bit between the wires, all probably a few inches lower than the TB wires.

 

I think that pantographs may have a higher current rating than trolley poles.

[SRman]

Pantographs need some special construction at right angle crossings so that they don't snag the other wirev-- not sure what but Toronto is converting from pole to panto.

Edmonton had an interesting bit of wire where the new (then) LRT system (pantograph) crossed the trolley bus system (poles) at 45 degrees or less. Complicated bit where the pantograph wire angles off parallel to the TB wire and there was another bit between the wires, all probably a few inches lower than the TB wires.

 

I think that pantographs may have a higher current rating than trolley poles.

 

All of Melbourne's older trams that were originally equipped with trolley poles are now equipped with pantographs, while all subsequent builds and types have had pantographs from new. It is interesting where tram lines cross other routes at right angle intersections, but even more interesting where they cross railways with 1500V DC overhead - there has to be extra switchgear in place to ensure the trams don't get 2.5 times the voltage they should be on!

 

There are plenty of YouTube clips of Melbourne's trams, and some include railway level crossings as well. Here's one for starters (not my video, all credit to the owner of the video). This one is within earshot of the school I work in.

 

[melmerby]

Pantographs need some special construction at right angle crossings so that they don't snag the other wirev-- not sure what but Toronto is converting from pole to panto.

In last night's "Great American Railroad Journeys" MP travelled a bit on the Toronto network and the thing that stuck out was that even modern trams (5 unit articulated) had trolley poles.

SWMBO noticed that and she knows zero about trams & trains!

 

Keith

 

EDIT

In that vid of Melbourne it is noticable that the tram's pant bounces a bit over the junction of the wires

Edited February 3, 2018 by melmerby

[SRman]

...

 

EDIT

In that vid of Melbourne it is noticable that the tram's pant bounces a bit over the junction of the wires

 

The trams seem to cruise through at a reasonable rate of knots, while the trains always have to proceed at dead slow speeds.

[PhilJ W]

I read somewhere that where bow collectors were standard the overhead wire at terminals was slack so that the bow collectors would be able to swing over when the car reversed. Glasgow used bow collectors and when trolleybuses were introduced the routes chosen were those with the fewest crossings of the tram system. As an aside there were few places where trams and trolleybuses shared the same overhead but one was in South East London. In some places where trolleybus overhead had been installed the trams still ran on the conduit system the trams were forbidden from using the trolleybus overhead except in an emergency. This was because the negative return was through a second contact rail in the conduit instead of through the track.

[melmerby]

I read somewhere that where bow collectors were standard the overhead wire at terminals was slack so that the bow collectors would be able to swing over when the car reversed. Glasgow used bow collectors and when trolleybuses were introduced the routes chosen were those with the fewest crossings of the tram system. As an aside there were few places where trams and trolleybuses shared the same overhead but one was in South East London. In some places where trolleybus overhead had been installed the trams still ran on the conduit system the trams were forbidden from using the trolleybus overhead except in an emergency. This was because the negative return was through a second contact rail in the conduit instead of through the track.

In Birmingham there was a short section to access a depot where trolleybuses ran along a single wire tram route using just one trolley pole and had to drag a skate along the track to make a complete circuit for the current.

 

keith

[PhilJ W]

In Birmingham there was a short section to access a depot where trolleybuses ran along a single wire tram route using just one trolley pole and had to drag a skate along the track to make a complete circuit for the current.

 

keith

That also occured on other systems IIRC. Nottingham was one such system where the 'skate' was a bunch of chains dragged behind the bus.

[BR60103]

In last night's "Great American Railroad Journeys" MP travelled a bit on the Toronto network and the thing that stuck out was that even modern trams (5 unit articulated) had trolley poles.

SWMBO noticed that and she knows zero about trams & trains!

 

Keith

 

EDIT

In that vid of Melbourne it is noticable that the tram's pant bounces a bit over the junction of the wires

The new trams are dual equipped but the others are pole only. As routes are converted, the new ones are starting to use pantograph. Supposedly the last of the order (not sure if it's the last 100 or fewer) will not have poles.

 

When Toronto had trolley busses, there was a stretch of one block where the bus and tram overhead was integrated -- tram just used one wire of the two. There was an unusual switch at one end to separate the two types. It was not a regular tram route.  Other places the bus wires wire closer to the curb than the tram and there were separate wires.

 

I just checked: The TTC used bow collectors as a test in 1929. 7 cars were equipped. They were mixed with pole cars; then move to 2 routes that had modified overhead. The experiment may have been abandoned with the depression.

I also found pictures of 3 yard shunters -- 2 different bows and a pantograph.

[Lemmy282]

As has already been stated, bows and pantographs usually need the o/h wire near the centre of the tracks, whereas swivel head trolleys can have the wire some distance from the centreline, saving on traction poles etc. You would think pantographs were the least trouble to operate, and they probably are if over a bogie pivot which would keep them over the centre of the track, but as the current collector is usually in the centre of the tram this means the wire has to move all over the place to accomodate it.

The ten 1928 single deck Blackpool "Pullman" cars were originally equipped with pantographs, hence they became known as "pantograph cars", but by the mid 1930's they had been converted to trolleypoles,!

Bow collectors, as used in Leeds, Glasgow etc. have the advantage of not dewiring and can flip over when the tram reverses, so long as the wire is high enough and slack enough to allow. Trolleypole equipped vehicles, with either swivel, fixed head trolley wheels or skates are subject to dewirement, need more infrastructure if they are to turn automatically and need wheel/skate replacement as they wear out.

The tramway museum at Crich in Derbyshire operates all types except 'skates', so the overhead is a compromise to allow it to work with pantographs, bows, fixed head and swivel head trolleys.

[BR60103]

Bows and pantographs need to have the wire shifted regularly from side to side so as not to wear a groove in the pickup. Most pole systems keep the wire centered. I don't know if any N. American systems had swivelling shoes except on trolley busses. The TTC kept the wire on streetcars centered pretty well; there may have been a few curves with angled joints but most had a large collection of pull-offs. Trolley bus lines had pre-curved pieces inserted into the wire; 3 or 4 to a right angle turn.

 

When Edmonton opened their new LRT line, there was an acute angle crossing with the trolley bus line. They had a lot of heavy contact wire there to keep the pantograph below the trolley bus wires.

 

Recently, the TTC found the carbon inserts on the new cars were not lasting a full shift. They apparently had changed suppliers.

[RobClogs]

Short bows flipped over when the tram changed direction at the terminus, the higher wire allowing the bow to move to a vertical position and then back. As mentioned above.
 
Longer bows had to be turned horizontally. They were mounted on a pivot with a lock that was released at the terminus. When the bow had made its 180 degree turn, the pivot clicked into the lock again. Here's a 16 second video:


Beugelzwaaien-HTM2 by Tramweg Stichting, on Flickr