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See Facts & Figures for dimensions and other statistics.
When public service started the light rail vehicles were quickly called trams by people in Manchester, the shorter name has stuck.
At the time phase one was planned most of the proposed system was to be converted rail lines with the short City Centre connecting lines. Low floor car technology was in its early stages so it was decided to use high floor cars which match the height of British main line platforms.
A fleet of 26 double ended high floor T68 trams were provided for phase 1, with a further 6 T68a trams for phase 2. The 6 phase 2 and 3 modified phase 1 trams can operate throughout the network. Unmodified vehicles are not allowed to run on the Eccles line. At first single vehicles were operated. A limited number of double sets operate on the Altrincham and Bury line in the peak periods. In an emergency, four vehicles can be controlled by a single driver.
The tram bodies are of a welded steel construction. The floor is made from composite wood sheets mounted on stainless steel and has an abrasion–resistant rubber covering. The saloon walls are lined with laminate materials which are moulded to form window recesses. The ceiling is lined with light alloy panels which are shaped to accept two rows of semi–recessed fluorescent light fittings and to provide central air distribution ducts. Thermostatically–controlled heaters are provided at floor level along the side walls of the vehicles. The main saloon windows include a hopper–type opening section at the top of the window with sealed windows next to the articulation and in the doors.
The driver’s cab has a deep windscreen and long side windows giving excellent vision all around. Self–retracting mirrors, which are heated and adjustable from the cab, on each side of the vehicle allow the driver to see the length of the tram when it is in a station. To provide clearance for vehicles passing on 25m curves, the vehicle ends are tapered for almost the length of the cab. The driver’s position is on the cab centre line with a wrap–around console carrying the various controls (radio, public–address, heating, ventilation, lighting etc).
Four wide doorways are provided each side, with externally–hung double sliding door leaves. At stops the driver releases the doors which are opened by passenger–operated push buttons mounted at each doorway. At low level platforms (when the second of two units) a retractable step operates automatically with the doors. Floor height relative to the platform is maintained nominally constant by the air suspension system. Drivers must close all open doors before the tram can depart.
Two areas (adjacent to the centre doors) have been specially set aside for wheelchairs and a further two areas are allocated for parcels/luggage. Fold down seats provided there can be used by other passengers if the spaces are not required for their prime purpose. The articulation gangway is wide enough to allow wheelchairs to move freely from one section to the other.
Propulsion equipment
Each tram has three bogies, the two outer bogies are powered. The unpowered centre bogie supports the articulation gangway. Under full–load conditions almost 70% of the weight is on the powered bogies, which assists the hill–climbing ability of the trams. The powered bogies each have two 105kW motors, separately–excited dc on phase 1 and three–phase ac on phase 2.
Each pair of dc motors is fed from independently controlled choppers utilising gate turn off (GTO) thyristors. The separate field control is provided by 4 quadrant inverters with insulated gate bipolar transistor (IGBT) technology. The choppers are microprocessor controlled operating at an interlaced chopping frequency of 600 Hz. A frequency monitoring circuit prevents chopper frequency deviating into signalling frequencies.
The three–phase ac motors are lighter, more reliable, require less maintenance and are more cost effective. They use IGBTs in the power control circuits, thus minimising the power electronic components and allow cooling techniques that insulate the high voltage electric components from dust and moisture.
Another 4–quadrant IGBT inverter is the ac source for the transformer/rectifier which produces the 110V dc supply used for battery charging, also providing control and auxiliary supplies.
The line filter performs three functions: it presents a low impedance source to the chopper; it presents a high impedance to the ac voltage component in the overhead 750V supply and it filters out chopper–generated ripple.
A programmable logic controller is used to reduce the number of control relays, thus providing space savings and giving greater flexibility of operation.
Traction and Braking Control (TBC)
The driver’s left hand is used to operate a joystick–type controller for acceleration and braking. This has a “T” shaped handle which, when released, is sprung to return back to the full emergency brake position with its top bar in a fore/aft alignment.
The TBC is made active by a key–operated switch. To move, the driver turns the TBC handle clockwise to a left/right alignment and moves it forward past the midway “Coast” position applying power. At the required speed the TBC is held in the “Coast” position. To brake the TBC is drawn back from the midway position. If the TBC is allowed back past the slight detent which marks normal service braking, the emergency brake is applied; this is the driver’s safety device. A thumb operated button on the TBC sounds the horn.
The braking system is fully–blended, using regenerative/rheostatic electric brakes on the motored bogies and pneumatic brakes on all bogies. Energy which the line cannot absorb is dissipated from naturally–cooled resistors mounted on the roof of the tram. Electric track–brakes fitted to all bogies provide a significant additional braking force under emergency conditions, allowing the tram to operate safely with normal road traffic. Emergency braking is applied by pulling the Traction Brake Controller one notch beyond the service brake position. On phase 2 units, and modified phase 1 units, the emergency brake system consists of both air brakes and the electromagnetic track brakes. It can be released and reapplied as required.
Auto Couplers & Exterior Appearance Differences
Unmodified phase 1 tram couplers are fixed, phase 2 and modified phase 1 tram couplers are retractable. Extension and retraction — using a ‘scissors’ mechanism — is pneumatically operated. It is controlled by push button in the cab and includes a locking mechanism in both the extended and retracted positions. Manual operation of the auto coupler is possible by use of a steel bar housed on the scissors arm. The coupler head consists of the mechanical connection, a pneumatic air line valve and an electrical head containing 130 contacts protected by a retractable cover. Retracted couplers are covered by front fairings.
On the phase 2 and modified phase 1 trams all three bogies are fully covered with protective side panels/skirts. This and the retractable auto couplers are required as the Eccles route is almost entirely at street level and beyond Broadway will share the carriageway with other road users
From the start phase 2 trams had their external doors coloured contrasted — both inside and out — to make them more visible. Note that after mid–life refurbishment, the phase 1 tram doors are also colour contrasted on the outside.
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This page was written by Tony Williams, Manchester Area Officer, Light Rail Transit Association. Contact manwebm@lrta.org if you have any comments, ideas or suggestions about these pages.