HOW THEY WORK - STANDARD CARS  
     
  Electricity is supplied from the overhead PANTOGRAPH 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.
  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.		 Above : 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.
  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.
  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		 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.
  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.		 Above : A cab shot of car C3218 in operation. The Driver's left hand rests on the brakestand, in the "release and running" position. The Master Controller (in the foreground) is being held in "full paralell" 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.
Above : A section of resistance grids from underneath parcel van C3773.
 

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.
   
  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 part, causing the inevitable delays to traffic.
Above : The original type of pantograph as installed atop C3102.
  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 switchgroups must be neat and tidy, to prevent undue
strain on any terminals. Cables must not be able to rub up
against each other.

 

 Above : 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.
  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.
Above : A closer view of the "A" type axlebox. The large centre mounted adjustment screw is an adjustment to take up play in the axle due to the journal-less design.
 

 

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 stop, the motor current increases and trips the car out. The driver has to reset the car before it can re-motor .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.

Above : 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 startup. 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.

Above : The original "G" type plain bearing trailer bogie under C3082. This type predates electrification, and once saw steam service under these same vehicles.
  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.
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.
 

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
airpipe 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.

 
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.
 

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.

Above : 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.
 

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.
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.
     
 

 

 

  
     
   

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