Information Technology Reference
In-Depth Information
The protection system against hot axles boxes (also called as
hot box
)is
one of these systems that are based on knowledge and existing rules. We pro-
pose to illustrate our method by evaluating this particular protection system.
The first part of this paper presents the system for detecting hot boxes
and risks associated with the lack of detection. The second part of this paper
presents the model proposed. Finally, a probabilistic evaluation and results
obtained for high-speed lines are shown.
2
Presentation of train hot boxes
2.1
Definition and frequency
In railway systems, a
hot box
is an axle box that has reached a overheating
temperature. According to [2], the axle temperature can rise to 900
◦
Cor
1000
◦
C and can break the axle. Fortunately a broken axle is quite rare on
the European network. The ERA safety performance report [3] shows, in
Europe, 100 broken axles for 4225 million tr.km in 2007. Given the disparity
in reporting, these results should be taken with caution. In fact, they are not
completely reliable but they give an indication of the number of broken axle
per million tr.km: between
10
−
2
and
10
−
2
broken axle per million
1
,
15
.
2
,
36
.
tr.km.
Scientific literature also provides further informations on the number of
broken axle in the United Kingdom: 1-2 broken axles per year on the U.K.
network as reported by [4], an average of 1,6 broken axle per year over the
past 25 years (between 1975 and 2000) on a population of 180000 axles as
reported by [5]. If these numbers are reported in million tr.km in the U.K.,
it can be estimated, with the assumption of 20 millions kms travelled, that
there are about
10
−
2
broken axle per million tr.km.
8
.
2.2
General risks and consequences
An overheated axle box can lead to several consequences for the train:
- it can cause a fire (but it seems unusual),
- it can lead to a rupture of the axle which give rise to two major possibil-
ities of serious injury:
•
a derailment of the train (which is the most frequent case),
•
a loss of braking capability for the train.
2.3
Train protection systems against hot boxes
As previously shown, consequences of an overheating axle has significant
consequences. The STEM (supervisory of running trains) agents [6] intend
to monitor trains in order to detect overheated axles as soon as possible.
