So How Does a Class 50 Work?
It is a popular misconception that class 50s are
complicated locomotives. It is perhaps true if compared to say a class 40, but
more modern designs such as the unique 89 or the classes 59 and 60 are orders
of magnitude more sophisticated.
So don't be put off the description below is designed not to be too
challenging even for the techno-phobic (if you don't understand any part of it
please e-mail the webmaster
with your question and we will try again).
The
Power Plant
A description of a diesel power plant works is
covered in this separate article.
The
Electrical System
Electricity can best be simply explained by analogy
with water. Water flows in pipes as direct current (d.c.) electricity flows in
cables. In electrical terms the voltage determines how much current flows, just
as the pressure on water will dictate how much will flow through a pipe.
The power plant on a Fifty turns three
generators each with its own particular role. The first generator (Main)
supplies power to move the train, the second supplies the train heating, and the
last supplies the auxiliary systems on the locomotive. An electrical generator
can be considered to be a pump, with its output current (volume of electricity
flowing) set by the strength of the magnetic field applied to it.
The output from the generator feeds three parallel
circuits each containing two motors (see simplified circuit diagram). One motor
in each arm of the circuit is mounted on each bogie. The volume of electricity,
or current applied to the motor dictates how much work the motor can do, in the
same way that the volume of water applied to a water wheel determines how much
work it can do. The work done by the motors causes the train to accelerate.
The
Control System
The control system on the class fifty is unique,
and it is this part of the locomotives that makes them more sophisticated than
their predecessors. When the driver moves his power controller on a class fifty
he is effectively setting the desired current he wants to draw from the
generator. He can select any one of an almost infinite number of possible
settings between minimum and full current.
The current output from the generator is measured
and compared with that requested by the driver in a current controller, this
outputs an error signal which is a measure of the difference between the
required current and the actual current.
The error signal is feed to the generator
field thyristor controller, this supplies the power to the magnetic field on the
main generator. If the current output from the generator is too low, the error
signal will make the field controller increase its output and thereby strengthen
the magnetic field so the generator will produce more current. If the generator
current is higher than requested by the driver, the generator magnetic field is
decreased, and hence less current flows.
The control system also prevents the driver
from overloading the main generator by preventing
the generator field being strengthened any further once maximum current is
reached.
This form of control gives the best possible
utilisation of the diesel sets’ power output as well as coping automatically
with varying gradients without overloading the generator, and with minimum
driver intervention.
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