Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
1999-04-22
2001-06-26
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
Reexamination Certificate
active
06252408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an arrangement for the monitoring of a resistance between adjacent rail-ends of a section of railway track, to a rail end-post for use in such an arrangement, and to a method for monitoring such a resistance.
2. Description of the Related Art
Railway tracks are conventionally divided into sections of track which are separated by an insulating member. The insulating member may be located between one rail of a section and the corresponding rail of the next section, or between both sets of rails of the two sections. Insulation is provided in order to enable the presence of a train on a particular track section to be detected.
FIG. 1
shows a typical track signaling arrangement comprising three adjacent sections of track, namely sections n−1, n and n+1. The sections are insulated from each other on one rail
10
by so-called insulated block joints
12
and
13
. The other rail
11
is, in this example, not provided with such block joints. Connected across the rails at one end of section n (similar arrangements apply to the other sections too, but are not shown) is a DC source
14
and a resistor
15
. Across the rails at the other end of section n is a relay
16
whose contacts
17
are connected to suitable signaling circuits. When the track section n is clear, current I flows from the DC source
14
through the resistor
15
, the rails
10
and
11
and through the relay
16
, thereby operating the relay. Under these circumstances the signaling circuits give a “track clear” indication to the railway signaling system or to railway personnel. When, however, a train is situated on the section n, the axles and wheels of the train serve to provide a low-impedance shunting path for the current I so that the relay
16
de-energizes, thereby changing the signal from “track clear” to “track occupied”. In some systems track signaling is effected by AC currents rather than DC.
The insulated block joints
12
,
13
are normally constructed as in FIG.
2
. In
FIG. 2
it can be seen that two main items of insulation are provided: a so-called “end-post”
20
between the ends of the opposing rails
10
n
and
10
n
-
1
and “skin” insulators
21
between the two adjacent rails and the fishplates
22
(only one is shown) which connect the rails. In addition, and not shown, insulating bushes are provided separating the fishplate bolts
23
from both the fishplates
22
and the rails
10
n
-
1
,
10
n
. (In an improved form of construction known as a “glued joint”, the assembly described above is encapsulated in epoxy resin for extra strength.)
A common cause of track-signaling failure is a short-circuit failure of an insulated block joint which can cause the signaling circuit to show “occupied” instead of “clear”. While this failsafe condition ensures the safety of the public and railway personnel traveling on the rolling stock, it does create unnecessary disruption to rail traffic so that throughput is needlessly reduced.
There are two potential short-circuit paths in an insulated block joint: firstly, a path via a single short-circuit from one rail-end to the next, adjacent, rail-end and, secondly, two simultaneous short-circuit paths from each of the two adjacent rails to the same fishplate. While it is known to monitor for short-circuits between the rails and the fishplate, there is a need to be able to predict a potential short-circuit (or low-impedance) between the rail-ends.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention there is provided an end-post for the interfacing of adjacent rail-sections of a railway track, comprising an electrically insulating material having an electrically conductive laminar part disposed therein at an intermediate point between rail-interfacing ends thereof.
In particular, the electrically conductive part is disposed between two portions of the electrically insulating material, which insulating portions comprise rail-interfacing ends of the end-post.
It may be advantageous if the conductive part extends slightly beyond a profile of said insulating material over at least a part of the periphery of the end-post, this being for the purpose of providing an electrical contact means of detecting unwanted “creep” movement of the adjacent rail sections towards each other.
The two portions of insulating material may be formed separately and affixed to each other by way of said conductive part. However, alternatively and preferably, the end-post may be a molded component with said conductive part embedded in said molded component, the conductive part being incorporated in the end-post as an insert during the molding process. For this purpose, the conductive part may advantageously be a laminar perforate having a plurality of holes therethrough, the insulating material filling at least some of the holes therein such that the conductive part is thereby embedded in the insulating material and is inseparable therefrom except by disruption of the insulating material.
Alternatively stated, the preferred form of molded end-post for the interfacing of adjacent rail-sections of a railway track, comprises an electrically conductive part disposed between two portions of electrically insulating material, which insulating portions comprise rail-interfacing ends of the end-post, the conductive part being a laminar perforate having a plurality of holes therethrough such that the insulating portions are joined to each other through the holes and the conductive part is effectively embedded in the insulating material.
Preferably, the above-mentioned laminar perforate is a conductive mesh and the insulating material fills at least some of the holes in the mesh.
The conductive part is preferably disposed in the insulating mate rial approximately parallel to the rail-interfacing ends and approximately midway therebetween.
The conductive part may be provided with a peripheral extension for connection with external measurement circuitry.
The invention also provides a method of manufacturing a molded endpost constructed as described above, comprising the steps of holding the conductive part inside a mold cavity shaped to reproduce the external profile of the end-post, injecting the mold cavity with insulating material in a moldable state to achieve incorporation of the conductive part into the end-post, solidifying the insulating material by curing or cooling, and separating the end-post from the mold.
In accordance with a further aspect of the invention, a monitoring arrangement for the monitoring of a resistance between adjacent rail-ends of a section of railway track comprises a pair of adjacent rails, an end-post as described above disposed between opposing ends of said rails, and a resistance-measuring device connected to said conductive part and to at least one of said rails, whereby said resistance measuring device is arranged to provide an indication of an undesirably low resistance between a respective rail and said conductive part.
The resistance-measuring device may be connected to both rails such as provide said indication for both rails independently, or it may be connected to said both rails in a bridge configuration such as to provide an indication for both rails in combination. The resistance-measuring device may take the form of a computer-based monitoring system in which the resistance measurements are evaluated and compared with reference resistance values under the control of a software program. Such a program may also provide an indication of the derived resistance values.
In yet another aspect of the invention there is provided a method for monitoring a resistance state between adjacent rail-ends of a section of railway track, said rail-ends being separated by an insulating medium, the method comprising monitoring the resistance between respective said rail-ends and a conductive plane disposed in said insulating medium at an intermediate point between said rail-ends.
This method may include the further step of providing an indication of an undesirable de
Alstom UK Limited
Kirtschstein, et al.
Leroux E P
Metjahic Safet
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