HOW THEY WORK - STANDARD CARS
Electricity is supplied from the overhead wires and passes to the PANTOGRAPH on the roof at 1500 volts DC. Back in the 1920s, the only way in which motor speeds could accurately be controlled was to use DC electricity. DC motors use a set of BRUSHES and a COMMUTATOR to provide the change in current direction needed to drive the motor ARMATURE around.
Left: An "Airmate" pantograph, of modern design, attached to specially welded bars to allow it to be fitted onto the earlier Standard cars. The original pantographs had two pans and were manufactured by Dorman Long, the same company who built the Harbour Bridge.
Having BRUSHES and an ARMATURE means that the motors need more regular maintenance than the AC type motors found in most factories and industry. Only very recently has the advent of high tech variable frequency electronic controllers permitted use of AC motors in electric trains, the most recent Tangara and Millennium cars employing this motor type.
The traction motors under the standard cars are a series interpole wound DC motor. This means the field coils (the
electro-magnets affixed to the outside "fixed" part of the motor) are wired in series with the brushes and the armature. Somewhere in there too are also a set of interpole windings which act against the main windings and are used to prevent sparking on the commutator.
This small (but rare!) photo above is the Metropolitan Vickers switchgroup under C3102, snapped just as the driver shut off power after accelerating from stand. The large "Splat" spark inside Nos 1 and 4 switches can clearly be seen. The arcing horns are designed to draw the arc out into the low pressure atmosphere, aided by a magnetic "blowout" coil built into the switch.
DC motors are strange beasts. Their speed INCREASES as the magnetic field WEAKENS. That means a series connected motor runs FASTER as the CURRENT flowing through it gets SMALLER, the opposite of what most people would think. If we simply connected the motor directly to 1500 volts on a stationary train, thousands of amps of current would flow, blowing many fuses and probably destroying the motor.
So we must find a way of limiting the current through the motors,and until the advent of thyristors in the '70s, the only way of doing this was to connect RESISTORS in series with the motors and "cut them out" as the train speed increased, a process similar to changing gears in a motor car.
Resistors get HOT when current flows through them, and this wastes energy. So the standard cars are wired so that the
resistors are only used for a short while when the train is accelerating from rest. Early locomotives (and even the 46 class) had complicated controls where the driver manually "cut out" the resistors as the train sped up. The Sydney standard cars were amongst the first to "automate" this process by including an "accelerating relay" which does this stepping automatically.
Left : A cab shot of car C3218 in operation. The Driver's left hand rests on the brake stand, in the "release and running" position. The Master Controller (in the foreground) is being held in "full parallel" position and the train is doing about 80kPh. The special spanner - like key is the reversing control, the key is removed by the driver when the train is unattended and the control locked in the centre "OFF" position. The handle on the controller must be held down at all times by the driver (the "Dead Man Switch" otherwise the power will instantly be removed and the brakes will activate. The amount of pressure needed to hold the handle down is the stuff of volumes of engineering data and has often been of considerable interest to unions, insurers and alike.
A standard power car "master controller" has four positions. When the driver moves the controller to the first position, the motors and all resistors are connected to the pantograph in series. This is enough to get the train moving to around 10kPh. The controller is then moved to the second position, where the accelerating relay begins to "cut out" each resistor as the train accelerates. Finally the controller is moved to the third position, which connects the motors to the overhead in parallel again with the resistors in circuit, whereby the accelerating relay again "cuts out" the resistors as the train accelerates further, when the motors have a full 1500 volts across them from the overhead.
Originally the standard cars had a fourth notch which "weakened"the field current in the motors further, to allow acceleration to higher speeds. This was progressively disabled in the '70s due to shortage of spare parts. It was ultimately found that the disabling of the weak field resulted in only a four percent overall performance loss in the train operations. Nowadays for special tour workings this loss can be easily overcome by using more motor cars than trailers in the train.
Above : A section of resistance grids from underneath parcel van C3773.
Above : The original type of pantograph as installed atop C3102.
Left : The original type of motor bogie, the "A" type, with plain bearings and fabricated construction. The axles have no journal collar, and are instead held in place by the bogie frame itself which needs to be twice as strong in the lateral direction as a result. This particular one is pictured underneath C3082.
This means that even though the overhead has only 1500 volts, the voltage across the switches can reach well over this voltage when the driver "shuts off" the motors. This creates a large fat and very hot "SPLAT!" spark at the switch, as the excess energy is burnt off. The switches are specially designed to "draw out" this spark from the contacts to the lower pressure atmosphere, and that's why you often see large sparks come from underneath the standard cars. A poorly maintained pantograph will "bounce" too much, and cause regular sparks on the contact wire at high speeds. In actual fact the sparks are a continuation of the current flowing to the motors across the air gap. Careless driving can cause
serious damage to the overhead, even to the extent that the wire may "burn through" and fail, causing the inevitable delays to traffic.
Maintenance of high energy DC electric equipment such as the single deckers requires a special dedication to high quality workmanship.
When working on high energy DC gear, special care must be taken to ensure all connections are properly tightened and not
corroded. Lugs must be crimped securely and insulated. Cable layout in switch groups must be neat and tidy, to prevent undue strain on any terminals. Cables must not be able to rub up against each other
As explained elsewhere, 2 motor type Standard cars can develop "wheelslip" when they accelerate from rest. The
presence of the accelerating relay makes this situation worse,and the driver must exercise skill in starting a set from rest especially in wet weather. The Accelerating relay operates by measuring the current taken by the motors as it accelerates and normally this allows the controls to estimate what speed the carriage is travelling at. However if a "Wheelslip" develops, the driving wheels begin to rotate faster than the car is actually travelling. The current drops, and the relay steps the motors into the next highest speed which makes the wheels spin even faster, whereby the current drops more and.. well the rest is history. Eventually the wheels regain traction. If a driver steps into parallel (Notch 3) too early, a wheelslip can be made much worse. Many factors affect wheelslip and include the curvature of
the track, the condition of the wheels and the presence of water or grease on the track.
In wet weather, Standard 2 motor cars can sometimes develop severe wheel slip on acceleration from rest. In many places around Sydney, stations are near overhead bridges and as the spinning wheels reach the dry track under the overhead bridge the spinning stops, the motor current increases and trip the car out. The driver has to reset the car before power can again be applied. The loss of the power car would then slow the train, putting more strain on the other cars and eventually lead to a failure if the driver did not pay attention to the situation.
Left : A closer view of the "A" type axle box. The large centre mounted adjustment screw is an adjustment to take up play in the axle due to the journal-less design.
Left : The much - more modern "F87" type bogie, so called because they were manufactured by Bradford Kendall in the late '80s to facilitate the "Redfern Overhaul" program. The cast construction, roller bearings and coil springs can be clearly seen. The same motors (MV172) are used inside, which could be up to 50 years older than the bogie! .
Many references are made by traction fans to the "sound" that electric cars create. This is not made by the motors, but the pinion gear system which transmits the motion to the wheels. Until 1972, all Sydney electric stock utilised "axle hung" traction motors which used the gear transmission. The double deck "S" type power cars (and most cars made after that time) use bogie frame hung motors and a flexible gear drive to the wheels, which removes the "whine" traditionally associated with the older electric trains.
The 2 motor standard cars have a unique sound due to the very high power on one bogie, as well as the larger diameter wheels and low gear ratio used as a result. The sound tends to be much "lower", literally shaking the car on start-up. Over the decades, the motor pinion tooth profiles have worn, leading to pronounced gear whine. Unlike road vehicle differentials, the gear profiles on electric trains are not matched and so cars tend to become noisier as motors are swapped for maintenance.
The standard cars use a 36 volt system to provide auxiliary power, which is used to provide emergency lighting in
case of blackout in tunnels. The auxiliary supply also operates the electrical unit switches which accelerate the main motors,and all the other various electrical apparatus on the train. Each power car has a "motor generator (MG)" set under the floor, which is like a small 1500vDC motor coupled directly to a 36vDC generator. Originally, a switching system was provided to permit the driver to switch on and off the saloon lighting. Originally the trains used nickel-iron batteries in single 2 volt cells - an advanced concept even today. However due to economies lead acid batteries are now used.
Above : The original "G" type plain bearing trailer bogie under C3082. This type predates electrification, and once saw steam service under these same vehicles.
Above: The more modern "MR" type bogie (above) now used under most of the heritage vehicles, is a cast construction and uses roller bearings, and dates from the mid '50s.
Above : Interior of U 1955 vintage "U" Boat" cabin showing brake stand and master controller. The "U" Boats were originally designed with regenerative braking but this was soon disabled due to repeated problems and the complexity of using it.
The brakes on the standard trains operate as a standard Westinghouse arrangement but with one slight addition. With
normal Westinghouse brakes, each car is fitted with a special "triple valve" coupled to an airbrake reservoir and brake piston cylinder, which operates the clasp brakes on the wheels. An air pipe is provided throughout the train called the "brake pipe". As the train operates normally, the brake pipe is charged with high pressure from the driver's brake valve. This air passes through the triple valves and into the airbrake reservoir on each car, filling them with high pressure air.
When the driver makes a brake application, a REDUCTION in pressure of the brake pipe occurs. When the triple valves detect this reduction, they shut off the flow of air from the brake pipe to the airbrake reservoir, and let the air from the airbrake reservoir into the brake cylinder, applying the brakes. In the event that a train breaks in half, or for some reason the brake pipe through the train is broken, the train will immediately stop because the air from each airbrake reservoir on each car will apply the brakes on each car. To release the brakes, the driver again charges the brake pipe with air and the process repeats itself.
We also have to be careful not to leave a "Westinghouse braked"
train standing too long, otherwise the pressure in each carriage can "leak off", releasing the brakes and causing a runaway. For this reason handbrakes are provided and must be applied if the train is to be left standing for any length of time unattended.
The Standard cars feature a refinement of the Westinghouse system by fitting an "Electric Holding Valve. This consists of an electrically controlled air valve attached to the exhaust port of each car's triple valve. When this valve closes, it is impossible for the air to be released from the brake cylinder, so the brakes remain applied at the pressure set by the driver. Because the control is on each car, it allows the driver to smoothly bring the train to a stand at a station, and also maintain air in the brake reservoir of each car.
Left : The "M.G." (or Motor Generator) set, which converts 1500vDC to 36vDC needed for cabin lighting and control circuitry. The 1955 cars' MG sets develop 132vDC, while more modern cars such as the Tangara use electronic static inverter rectifier sets to carry out this task.
Fellow H.E.T. Member Driver Geoffrey "Whoosh" Watling at the controls of preserved W set car C3708. As can be seen, the master controller on the "W" sets has been converted to a Hitachi "Double Deck Type", to Geoff's right hand side. The original controllers were very compact and proved too difficult for the drivers to hold down for extended periods.