It was only a few years ago that the first generation of the German
Intercity-Express, the ICE1, was making headlines - but for the wrong
reasons. Problems due to overheating of the engine caused by ventilation
failures were frequently reported, and ensuing fires caused damage that
ran into several millions of pounds. Ventilators providing cooling air to
the traction power converters, are powered by auxiliary generators, which
themselves are self-ventilated. The fires were the result of failures of
this self-ventilation system.
A failure in the supply of cooling air can have several causes. Firstly,
the doors of the cabinets containing the power converter rectifiers must
always be closed. If this is not the case, the amount of cooling air will
not be sufficient to cool all the electronic components. Secondly, the
air exit shutters are closed during exterior cleaning to prevent cleaning
agent vapours coming into contact with the electronic components. After
cleaning, these shutters should open automatically, but if they remain
closed the auxiliary generator will overheat.
Deutsche Bahn's solution was to fit Turck Banner calorimetric type flow
controls* directly behind the ventilator to monitor the cooling flow. If
the flow remains below the set point for a certain period, the sensor
signals an alarm message to the control cab, the train driver receiving
both a visible and an audible error-message. The decision to opt for
calorimetric flow controls was based on their tolerance of deposit
build-up. They are also simple to mount and adjust, compared with
alternative arrangements such as differential pressure systems or
impeller flow meters. Indeed, the generally slow response of calorimetric
flow controls was an advantage in this case, because a more sensitive
system would tend to issue superfluous error messages in response to
standard air fluctuations.
The sensors are adjusted by means of a potentiometer, assisted by a dual
colour LED, which turns from green to red if the minimum flow is
under-ranged. If the flow stays below the minimum value for more than a
minute, the sensor's transistor output, which is coupled to a timer
module, sends an error message to the control cab. If the fault is
recovered and a sufficient amount of cooling air is supplied again, the
output transistor changes state and the LED illuminates green.
*Calorimetric flow control is based on the heat loss principle. The
sensing probe has two temperature-dependent measuring elements one of
which is heated electrically. When fluid moves over the outside of the
sensor, heat is conducted away from it and the temperature of the heated
sensing probe falls. The measuring element, that is not heated
electrically, assumes the temperature of the stationary or flowing
medium. The difference between the two temperatures is thus a measure of
the speed of flow.
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