• Trolley Poles
• Pantographs
• Bow Collectors

Toronto's streetcars to this day use the trolley pole, but we may see a new generation of streetcars and LRVs using pantographs, so this page will discuss only those two. For information on Bow Collectors, see this page.

TROLLEY POLES

A trolley pole is mounted with springs on the roof of the vehicle. The springs maintain the tension to keep its shoe in contact with the wire. Wooden poles have a cable to carry the electrical current down to the vehicle. A similar cable is used with a metal pole, either inside or outside the pole. Modern trolley poles may also be made of a fiber glass type of material with an insulated copper cable through the centre of the pole.

The trolley pole must always be pulled behind the car and not pushed, or dewiring is very likely, and possible damage to the overhead wiring may occur. On systems using double ended cars that reverse direction at the end of the line instead of using a loop, either the pole at one end of the car is lowered and one at the other end is raised, or in some cases, the pole may be turned around for the opposite direction.

Modern trolley poles installed on Vancouver's low-floor trolley buses.
Trolley poles are the only practical device on trolley buses due to the need for two power contacts.

Trolley poles are usually raised and lowered manually by a rope from the back of the vehicle, though in some cases the poles may be lowered from the driver's seat. The rope feeds into a spring reel mechanism, known as trolley catcher. The trolley catcher is designed to "catch" the rope to prevent the trolley pole from flying upward if the pole is dewired.

Advantages of trolley poles:

• simpler construction

• simpler overhead wiring

Disadvantages of trolley poles:

• dewiring is more common with trolley poles, especially as speed increases

• speed is limited due to dewiring issues

• raising is a manual task, and lowering can also be a manual task

• the end of a line must raise and lower poles or use loops that require a substantial amount of real-estate as well as turns

PANTOGRAPHS

Single arm pantograph on Minneapolis LRV (Bombardier Flexity Swift)

Double arm pantographs are usually heavier, require more power to raise and lower, but may also be more fault tolerant. Regardless, the single arm pantograph is more common with light rail vehicles.

On the end of this LRV in Minneapolis, carbon dust deposits can be seen, especially due to the light colour of the roof of the vehicle.

Operator's display on a Citadis LRV from Alstrom showing pantograph position.

Advantages of pantographs:

• at lower speeds, may use non-catenary wiring

• more stable at higher speeds, little chance of dewiring

• may be automatically raised and lowered

• wire frogs are not needed where tracks diverge

Disadvantages of pantographs:

• high speed lines require catenary wiring

• generally cannot run under trolley pole wiring at higher speeds

• carbon dust tends to deposit on roof and ends of vehicle

OVERHEAD WIRING

This simple wiring supported by a centre pole is used on the downtown section of Minneapolis' LRT.

SIMPLE OVERHEAD

A simple installation will have the contact wire suspended from support arms or from support wires strung across the right of way, or all the way across a road where the line exists. This wire is tensioned, and not simply hung, but not tensioned in the same way as with catenary overhead (see below).

In Pittsburgh, some of the Library Branch (left) and the
Beechwood Branch (right) use simple overhead wiring.

CATENARY OVERHEAD

A more complex installation will have the contact wire suspended from above by means of a second wire known as either a messenger wire or catenary. This wire is allowed to follow the natural path of a wire strung between two points, which is known as a catenary curve, hence the use of catenary to describe this wire or sometimes the whole system.

This wire is attached to the contact wire at regular intervals by vertical wires known as droppers or drop wires. Effectively, the contact wire is supported at numerous points. The messenger wire is supported regularly at structures either by means of a pulley, link, or clamp. The whole, system is then subjected to a mechanical tensioning system using either weights or hydraulics.

Catenary provides two benefits. First, it dampens any waves generated in the contact wire from the movement of the trolley pole or pantograph. Second, it can provide better support for the contact wire - where a longer span between suport poles is necessary, catenary can support a heavy contact wire.

 
This tensioning system maintains a constant tension despite changes in temperature.

As a new section of overhead catenary begins, another section comes
to an end with tensioning cable connected with an insulator. The tensioning
cable can be seen in the left photo passing through a pulley to a set of weights.

The pantograph contacts both sections of catenary during the overlap.

Trolley poles can use catenary wiring, but tensioning must be done differently.

As the LRT in Minneapolis enters downtown streets west of the Downtown East/Metrodome station, the overhead transitions from catenary to simple contact wire.

To achieve good high speed current collection, it is necessary to keep the contact wire geometry within defined limits throughout the length of the overhead line. This requires the catenary installation. It is this reason and the fact that there is a near zero chance of dewiring with pantographs that they are the preferred current collector for high-speed, high-reliability, systems.

In Minneapolis, the main line has catenary overhead while
the yard it is passing uses simple overhead wiring.

The one thing that does differ between overhead wiring for trolley poles and pantographs is the alignment.

Trolley pole wiring must stay relatively centred above the rails on tangent track and shifts to the outer side of curved track. Some small left-to-right adjustment is made to reduce vibration generation from the trolley pole. By having a minimal amount of lateral movement of the trolley pole, chances of dewiring is decreased. At lower speeds, pantographs may operate under wire aligned this way.

At higher speeds, this wiring would cut a groove on the pickup surface of a pantograph. For pantograph use, the contact wire is usually pulled slightly to the left and right by successive supports, so that the contact wire staggers on the pantograph as the vehicle moves along.

View from the front of a Route 75 tram in Melbourne heading towards Vermont South in the median of Burwood Hwy. The staggering of the overhead from one support to the next can be clearly seen in its shadow between the rails.

In this photo of the overhead installation north of Melbourne on Plenty, the hangers on each support alternate from left to right.

Much of Melbourne's tram network has overhead wiring with little or no staggering, just like this example on Riversdale Road.

Only newer portions of the network in outlying areas on separate ROW designed for higher speed operation has staggered overhead.

Another misconception about the wiring used with pantographs is that intersections where different lines meet, especially with connecting turns, can be very difficult.

In fact, the opposite is true since wire frogs are not required for pantograph use. They are needed with trolley poles in order to ensure the pole follows the correct route with the vehicle. Simple wiring (non-catenary) is used in Melbourne with many instances of intersections with and without connecting turns.

No wire frogs needed: these photos show the overhead at each end of the south track in Melbourne at St. Vincent's Plaza. The first is at the east end where the track goes east and branches north; the second is at the west end where the track goes west and branches south.

Melbourne tram passes through the intersection of Flinders
and Market where two lines intersect with no connections.

In Melbourne (Glen Eira), intersection of Hawthorn and Balaclava
has a Grand Union where both tracks turn in all four quadrants.

Melbourne route 70 tram crossing level railway crossing at Riversdale Station

THE FUTURE FOR THE TTC

The next generation of streetcars that the TTC will acquire will be single-ended vehicles (driver position at one end and will use a trolley pole for power pickup). For new Transit City LRT lines, the same model vehicle will be ordered in a bi-directional model (driver position at both ends with doors on both sides) with pantographs for power pickup.

A significant amount of the TTC's overhead wiring may be used with pantographs, with speed restrictions. Long runs where streets run basically straight have a contact wire hung from a span wire and are strung straight above the track. Pantographs can operate under this wiring, but the faster the operation, that greater the possibility exists of this overhead wearing a groove on the pantograph in short time. As we are discussing the TTC's current network in mixed traffic, the speed is naturally limited by traffic conditions throughout most of the day.

That said, a pantograph-equipped vehicle currently won't travel very far before running into problems. Where the track curves, the overhead is hung using a hanger that does not leave the contact wire lower than the span wire. The two photos to the right show these hangers. A pantograph would snag on these, not to mention that it would provide a way to make the span wires live with power.

Pantograph-equipped vehicles will not be able to pass through an intersection or a curve until the overhead has been upgraded to be pantograph friendly. Ultimately, all wiring will likely be altered to introduce a slight stagger to reduce groove wear on pantographs, but initially the hangers on curves will have to be changed.

In preparation for the future use of pantographs in Toronto, new overhead wiring now follows a specification that makes it pantograph friendly.

The photos to the left show the new overhead constructed as part of the track rebuilding on Fleet Street. The hangers are designed so that the contact wire is held below the span wire. Looking closely, these hangers are not symmetrical, and their orientation on alternate spans face in opposite directions so that there will be a slight staggering to the overhead to avoid groove wear on pantographs.

Another change to the wiring practices is not so obvious in these photographs. It is expected that larger vehicles will require some higher power demands, so instead of using 2/0 gauge contact wire, this new installation uses 4/0 gauge

The capital budget for the TTC contains a project for converting the entire network of overhead wiring by 2012.

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This page last updated October 06, 2009