GB2548193A

GB2548193A - Methods for selecting a clear current threshold for a railway track circuit

Info

Publication number: GB2548193A
Application number: GB1700199.1A
Authority: GB
Inventors: Peter Myers Andrew; Harding Christopher
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2016-03-10
Filing date: 2016-03-10
Publication date: 2017-09-13
Anticipated expiration: 2036-03-10
Also published as: GB201700199D0; GB2548193B; GB2548141B; GB2548141A; GB201604121D0

Abstract

A clear current threshold for a track circuit is defined as a current above which a section of track is considered to be unoccupied. During periods of precipitation the current is reduced from a normal baseline even when the track is unoccupied which can lead to false alarms. The method includes receiving weather data for the vicinity of the track at a number of points in time, possibly from a simple rain gauge or online data over several days; and receiving corresponding current data from which a first level of current is identified that is likely to pass through the track circuit in the absence of a train and in the absence of precipitation. A clear current threshold is selected based on this data and the threshold may also be modified to take account of a drying track.

Description

Methods for selecting a clear current threshold for a railway track circuit

FIELD

Embodiments described herein relate to methods for selecting a clear current threshold for a railway track circuit.

BACKGROUND

Track circuits (TCs) are electrical devices used to monitor the absence or presence of trains on different sections of railway track. The output from these circuits is used to control signalling on the line and maintain a safe distance between trains travelling along the same line as one another.

The operation of a conventional track circuit can be explained by reference to Figures 1 and 2. As shown in Figure 1, the track circuit includes two circuits; a first circuit 101 and a second circuit 102. The first circuit 101 comprises a power source 103 and electrical connections which run along opposite rails 105 to a relay coil 107. The second circuit 102 includes its own power source 109 that supplies current to one of two indicators 111, 113, typically a red light and a green light. The second circuit includes a switch 115 that is operated by the relay coil and which determines which one of the indicators is powered at any one time.

As shown in Figure 1, in the absence of a train on the section of track, a current is supplied to the relay coil, causing the switch to adopt a first position and allowing current to flow through the first indicator. In this example, the first indicator is a green light, for showing approaching trains that the section of track is unoccupied.

Figure 2 shows the same section of track as a train passes through. Here, the train axle(s) 119 form an electrical connection between the opposite rails, effectively short circuiting the first circuit, such that current no longer flows to the relay coil. The switch 115 in the second circuit consequently switches to its second position, diverting current to the second indicator, in this case the red light 113. A driver of another train approaching the section of track will see the red light and so realise that the track ahead is occupied.

The condition of the track circuit may be assessed using a current monitor 121 to monitor the current flowing through the relay coil 107 as trains pass along the section of track. The current monitor may output data representative of the current passing through the relay coil, which may in turn be forwarded to a track operator, either directly, or over a communications network, for example. If the track circuit is functioning correctly, the current passing through the relay coil should follow a typical response curve, which will be reflected in the data output from the current monitor 121.

Figure 3 shows two example response curves 301, 303 for a track circuit such as that shown in Figure 1 as respective trains pass along the section of track (it will of course be understood that, although the two response curves are shown superimposed over one another, this is for comparison only, and in practice the trains will pass along the track at separate times from one another).

For both trains, the response curve indicates the current passing through the relay coil. Each curve can be divided into 4 sections: falling, occupied level, rising edge and clear level. In the “clear” section, the current passing through the coil is at a maximum, reflecting the absence of a train on the section of track. In the “occupied” period, the current passing through the coil falls to a minimum, as the train axles short the first circuit between the rails (as shown in Figure 2, for example). The “rising” and “falling” sections reflect the transition between clear and occupied states of the track.

It can be seen from Figure 3 that the current levels for the “occupied” and “clear” states may vary between trains; in the case of the first train 301, the current level in the absence of the train is somewhat higher than that for the second train 303. In order to accommodate these differences, thresholds are used to define whether or not the track circuit is in a clear or occupied state. For example, a “clear current threshold” is used to define the current above which the track circuit is considered to be clear / unoccupied, and an “occupied current threshold” is used to define the current beneath which the track circuit is considered to be occupied. The clear current threshold may be set, for example, by determining a mean clear current level for the track circuit, and defining the threshold as a percentage variation of the mean clear current level.

On occasion, the current may be observed to fall beneath the clear current threshold, without defining the characteristic response curve seen as a train passes along the section of track; this can give rise to uncertainty as to whether or not the track is occupied. An example of this is shown in Figure 4, which illustrates the observed current for a track circuit over a period of time. The initial part of the curve is characteristic of a train passing along the section of track, with the current level passing from above the clear current threshold to below the occupied current threshold and back again. However, in the subsequent period T1, the current is seen to fall beneath the clear current threshold without it being clear that a train is present on the track.

The signal seen in the period T1 could be indicative of a genuine fault in the track circuit; for example, it might indicate a failing battery charger. As a result, a “Low Clear Current alarm” will be triggered. If a number of such alarms are issued within a short space of time, it will be necessary to send a maintenance crew to the site as soon as possible.

In addition to genuine faults, a Low Clear Current alarm may be generated by other transient events, which do not require the intervention of maintenance crews. In particular, during periods of rainfall, the water on and between the rails may produce a similar effect to that seen when a train passes along the track, short-circuiting the first circuit 105 in Figure 1 and so reducing the amount of current that reaches the track circuit relay and attached current sensor. The current may remain at a lower level even after rain has stopped, since the resistance of the ballast will be reduced until such time as it fully dries out.

The need to investigate the cause of Low Clear Current alarms is costly, both in terms of time and finance, leading to train service delays. In addition, it exposes maintenance crew to risk, since there will always be danger present for men working on the line. It follows that it is desirable to distinguish low current events that are indicative of a genuine fault in the track circuit from those which are not, such as in the case of rainfall, for example.

In conventional systems, in order to reduce the number of false alarms (and the resultant despatch of engineers to non-defective track circuits), the clear current threshold may be set permanently at an artificially low level. However, doing so reduces the sensitivity of the whole system and could prevent maintenance personnel from being alerted to genuine issues fast enough to take the necessary preventative action to avoid asset failure.

SUMMARY

According to a first embodiment, there is provided a method for selecting a clear current threshold to apply to electrical current data received from a track circuit associated with a section of railway track, the electrical current data being indicative of electrical current passing through the track circuit and the clear current threshold defining a level of current above which the section of track will be taken as being unoccupied by a train, the method comprising: (i) receiving weather data indicative of weather conditions in the vicinity of the track circuit; and (ii) based on the weather data, selecting a clear current threshold to apply to the electrical current data.

In some embodiments, the method comprises: receiving electrical current data indicative of the current presently passing through the track circuit; determining whether the current is beneath the selected clear current threshold and if so, issuing an alert.

In some embodiments, the weather data is indicative of the amount of precipitation on or in the vicinity of the section of track.

In some embodiments, the step of selecting a clear current threshold comprises determining, based on the weather data, whether there is currently precipitation in the vicinity of the track circuit, or whether the track circuit is currently in a dry state; wherein in the event that there is precipitation in the vicinity of the track circuit, a first threshold is selected for the clear current threshold and in the event that the track circuit is determined to be in a dry state, a second threshold is selected for the clear current threshold, wherein the second threshold is lower than the first threshold.

In some embodiments, the step of selecting a clear current threshold further comprises: determining, based on the weather data, whether the track circuit is currently in a drying phase following a period of precipitation; wherein in the event that the track circuit is determined to be in a drying phase, a third threshold is selected for the clear current threshold, the third threshold being lower than the first threshold and greater than or equal to the second threshold.

In some embodiments, the steps (i) and (ii) are repeated at intervals.

In some embodiments, the method further comprises: receiving electrical current data indicative of the current passing through the track circuit at a number of points in time; receiving weather data indicative of the weather conditions in the vicinity of the track circuit at said points in time; identifying, based on the received electrical current data and received weather data, a first level of current that is likely to pass through the track circuit in the absence of a train and in the absence of precipitation in the vicinity of the track; and determining a clear current threshold based on the first level of current.

In some embodiments, the method further comprises: identifying, based on the received electrical current data and received weather data, a second level of current that is likely to pass through the track circuit in the absence of a train and in the presence of precipitation in the vicinity of the track; and determining a clear current threshold based on the second level of current.

In some embodiments, the received electrical current data is filtered to remove data that is indicative of the section of railway track being occupied by a train.

In some embodiments, the alert is issued by sending an electronic communication to a track operator. In some embodiments, the electronic communication message is sent as an email.

In some embodiments, the alert is issued as an aural sound.

In some embodiments, the alert is issued by updating a display on a track operator’s display screen.

According to a second embodiment, there is provided a computer readable medium comprising computer executable instructions that when executed by a computer will cause the computer to carry out a method according to the first embodiment.

According to a third embodiment, there is provided a computer system comprising one or more processors; and a computer readable storage medium comprising computer executable instructions that when executed by the one or more processors will cause the system to carry out a method according to the first embodiment.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows the configuration of a track circuit at a point in time in which there are no trains present on the section of track;

Figure 2 shows the configuration of a track circuit at a point in time in which a train is present on the section of track;

Figure 3 shows an example response curve for a track circuit as a train passes along the section of track;

Figure 4 shows an example of a track circuit response over a period of time;

Figure 5 shows the configuration of a track circuit according to an embodiment;

Figure 6 shows a flow chart of steps used in a method according to an embodiment;

Figure 7 shows a flow chart of steps used in a method according to another embodiment;

Figure 8 shows a flow chart of steps used in a method according to another embodiment; and

Figure 9 shows an example of track circuit data and weather data used to determine a base clear current threshold in an embodiment;

Figure 10 shows a flow chart of steps used in a method according to another embodiment; and

Figure 11 shows a flow chart of steps used in a method according to another embodiment.

DETAILED DESCRIPTION

In embodiments described herein, the clear current threshold level is adjusted dynamically, based on weather conditions in the vicinity of the track. Unlike conventional methods, which rely on the use of static thresholds, embodiments described herein can distinguish between genuine asset issues and temporary problems caused by changing weather conditions. In addition, the thresholds can be chosen to more closely align with the normal (mean) clear current level, thereby allowing for earlier detection of real issues with the clear current.

Figure 5 shows the configuration of a track circuit according to an embodiment. Features that are the same as those shown in Figure 1 are numbered accordingly. As shown in Figure 5, a processing system 501 is provided for defining the clear current threshold for the track circuit. The processing system receives data from the current monitor 121, and also receives weather data from a weather monitoring device 503 located in the vicinity of the track circuit. In the present embodiment, the weather monitoring device is a rain gauge provided alongside the track circuit.

The weather data provides an indication of the amount of precipitation on or near the section of track as a function of time. The amount of precipitation may be quantified (in mm of rain, for example), or in a more simple case may be split into different classes depending on its level, such as “high”, “low” or “absent”, for example.

It will be understood that, although the processing system 501 is shown as being located in the vicinity of the track circuit in Figure 5, the processing system may, in other embodiments, be located remote from the track circuit, with data from the track circuit being communicated to the processing system over a network connection, for example. Similarly, the weather monitoring device 503 of Figure 5 is presented by way of example only, and is not essential; in embodiments described herein, the weather data be obtained from one of a number of different sources, such as from a local weather station, or from an online weather service such as the UK metrological office, for example.

Figure 6 shows a flow chart of steps as carried out by the processing system in an embodiment. The method commences by setting a base clear current threshold for the track circuit (step S601). In step S602, the weather conditions at the location of the track circuit are considered, based on the received weather data. In particular, it is determined whether or not there is precipitation (for example, whether it is currently raining, snowing, or if there is hail or sleet in the region of the track) or if there has recently been precipitation, which has now subsided.

In the event that there is precipitation, or there has recently been precipitation in the vicinity of the track circuit, the processing system sets the clear current threshold at a level beneath the base clear current threshold, in order that the reduced resistance between the rails will be taken into account when the current flowing through the track circuit is analysed. If the weather conditions are good, and there is no recent precipitation in the vicinity of the track circuit, the system reverts to the base clear current threshold (step S604). The process is then repeated in the next time interval.

Figure 7 shows an example of how the method of Figure 6 can be extended to issue a Low Clear Current alarm, in accordance with an embodiment. Here, steps S701 to S704 correspond to steps S601 to S604 of Figure 6, respectively. Once the clear current threshold has been selected to be either the base clear current threshold (step S704), or an adjusted threshold (step S703), the selected threshold is used to determine whether or not current readings received from the track circuit monitor are a cause for concern. In step S705, the processing system receives track circuit data from the current monitor 121, reflecting the amount of current that is passing through the track circuit at the present time. In step S706, it is determined whether or not the amount of current passing through the circuit is beneath the clear current threshold. If not, no action is taken until the next time interval.

If the amount of current passing through the track circuit is beneath the clear current threshold, the method proceeds to step S707. The fact that the amount of current passing through the track circuit is beneath the clear current threshold could be indicative of a fault in the track circuit, but equally could signal that the circuit is in an occupied state, or is in a transition from an occupied state to an unoccupied state (or vice versa). Therefore, before deciding whether or not to issue a Low Clear Current alarm, the processing system determines whether or not there is a train passing through the section of track. In order to do so, it is first determined whether or not the current level is beneath the occupied state threshold (see Figure 3). If the current is beneath the occupied state threshold, the circuit is most likely occupied by a train. In order to rule out a transition between occupied and unoccupied states, the rate of change of current is considered, by comparing the present current reading with other, recent readings. The rate of change in the current level provides a means for distinguishing between a transition from an occupied state to an unoccupied state (or vice versa) and a reduction in clear current caused by rain, because the rate of change in current associated with a transition between occupied and unoccupied states is significantly greater than the rate of change in current seen as the track transitions from a dry phase to a wet phase. If it is determined that no train is present on the track, then a Low Clear Current alarm is issued (step S708). Otherwise, the method returns to step S702 in the next time interval and repeats.

The Low Clear Current alarm may take one of a number of different forms. In some embodiments, an alert is issued by sending an electronic communication to a track operator. The electronic communication message may be sent as an email, for example. In another embodiment, the alert may be issued as an aural sound, or as a visual alert by updating a display on a track operator’s display screen.

The steps involved in obtaining the base clear current threshold in an embodiment will now be described with reference to Figure 8. In a first step S801, track circuit data is received from the current monitor 121. The track circuit data comprises a sequence of current levels as measured at different time points. In step S802, the track circuit data is filtered to remove current measurements that correspond to an occupied state of the track, or a transition between a clear and occupied state. The remaining data then represents measurements of clear current alone.

The filter employed in step S802 works by determining the mean current level for the series (including both occupied and unoccupied states) and identifying those data points in the series that lie above the mean. The filter then determines the rate of change between successive points in the data series that lie above the mean, in order to identify the presence of occupied states. The data points that correspond to occupied states are then excluded from the series. As discussed above in relation to Figure 7, the filter is able to distinguish between changes in the clear current value that reflect a transition from an occupied state to an unoccupied state (or vice versa) and changes that are caused by rain, because the rate of change in current associated with a transition between occupied and unoccupied states is significantly greater than the rate of change in current seen as the track transitions from a dry phase to a wet phase.

In step S803, it is determined whether or not there is sufficient data to calculate the base clear current threshold. In the event that more data is required, determination of the clear current threshold is deferred until such time as sufficient track circuit data has been received. Once sufficient data has been collected to calculate the base clear current threshold, the method proceeds to steps S804 and S805. Here, the track circuit data is compared alongside received weather data to identify periods of time in which there has been precipitation on or near the track circuit. By observing the clear current level during periods in which precipitation is absent, it is possible to derive suitable current level to use as the base clear current threshold (step S806).

It will be understood that the steps shown in Figure 8 will need to be performed before the method of Figures 5 and 6 can proceed; in other words, the processing system will need to build up a store of track circuit data and weather data before it can establish a base clear current threshold and then apply that base clear current threshold to subsequent measurements of electrical current data received from the current monitor 121.

Figure 9 shows pictorially how the steps of Figure 8 may be implemented. Figure 9A shows the raw track circuit data as received from the current monitor 121 over a period of 10 days. As can be seen, the raw track circuit data comprises a plot of electrical current at different time points throughout each day. At certain points in the graph of Figure 9A, the current level is seen to fall to zero (or very close to zero); these points reflect the occupied states in which a train is present on the track. Figure 9B shows the track circuit data once it has been filtered to remove the occupied states (step S802 in Figure 8). The current level is seen to dip intermittently throughout the time course of measurements; after each dip, the current gradually returns to close to the same value.

Figure 9C shows precipitation levels recorded in the vicinity of the track circuit. As discussed above, the precipitation levels may be obtained from a local weather station, for example, or may be retrieved from an online weather service such as the UK metrological office, for example. It can be seen from Figures 9B and 9C that the dips in the clear current level coincide with higher levels of precipitation in the vicinity of the track circuit. By filtering the data in section 9B to remove those portions that coincide with higher precipitation, it is possible to obtain current measurements for periods in which the track is both unoccupied and unaffected by precipitation; these current measurements can then be used to define the base clear current threshold for the track circuit.

The track circuit data can also be used to derive a clear current threshold to be used in the event that there is precipitation on the track; in this case, the clear current threshold can be selected by considering the minima in the graph of Figure 9B that coincide with the periods of rainfall in Figure 9C. These minima can provide an indication of the expected clear current level in the event that there is precipitation on the rails.

As an example of how embodiments described herein can reduce occurrence of false alarms, Figure 9B shows the clear current threshold as a function of time, for both the case where a dynamic threshold is used (in accordance with embodiments described herein) and for the case of a conventional (static) threshold. As shown by arrows 901, 903, the dynamic threshold is reduced at times when the precipitation is at a high. As a result, the reduction in the size of the clear current seen during those periods will not give rise to a (false) Low Clear Current alarm. By comparison, in the case where the conventional (static) threshold is used, the fall in clear current that accompanies a rise in precipitation will result in an alarm being issued.

The rise in the clear current level that is seen in periods immediately after the precipitation has ended can also be used to determine a clear current threshold to use during a drying phase of the track. As will be clear from Figure 9B, the clear current does not return immediately to the base level when precipitation stops, but rises over a period of time - this lag may be attributed to the time taken for the ballast to dry out and return to its original (dry) level of resistance. In some embodiments, therefore, the clear current level may be set by determining whether or not the track is currently in a drying phase, following a period of precipitation.

Figure 10 shows a flow chart of steps as used in an embodiment in which the drying phase is also taken into account. Steps S1001 to S1003 of Figure 10 are identical to respective steps S801 to S803 in Figure 8, so will not be described in detail here. Referring to steps S1004 and S1005, the method proceeds by identifying periods in which there has been precipitation, using the received weather data. The weather data is also used together with the trend in the (filtered) track circuit data, to identify periods in which the track is in a drying phase; typically, these “drying periods” will be identified by a gradual rise in the current level, following a bout of precipitation. The portions of the track circuit data that correspond to periods of precipitation, and drying periods, are then used to select appropriate thresholds for the clear current level.

Figure 11 shows an example of an embodiment in which the thresholds determined in Figure 10 may be implemented to dynamically adjust the clear current threshold in line with current weather conditions. The method of Figure 11 commences as before by setting the base clear current threshold (step S1101). In step S1102, it is determined based on received weather data, whether or not there is currently precipitation in the vicinity of the track circuit. In the event that there is precipitation, the clear current threshold is adjusted to a lower value, to accommodate the expected reduction in the amount of current reaching the current monitor 121 (step S1103). In the event that there is no precipitation, the method proceeds to step S1104, in which it is determined whether or not the track is in a drying phase, following a recent period of precipitation.

If the track is determined to be drying, the clear current threshold is adjusted accordingly (step S1105). If there is no precipitation, and the track is dry, the system reverts to the base clear current threshold (step S1106).

In some embodiments, the clear current threshold that is set in step S1103 may differ from that which is set in step S1105. Specifically, the clear current threshold that is selected during periods in which there is precipitation (step S1103) may be lower than the clear current threshold that is set when the track circuit is determined to be in a drying phase (step S1105); this takes into account the fact that the mean clear current observed during a drying phase will tend to be higher than that seen when there is precipitation. In other embodiments, the same threshold may be used in both steps S1103 and S1105 i.e. the low threshold that is used during periods of precipitation may also be used during periods in which the track is drying.

It will be understood that the method of Figure 11 may be extended in a similar way to Figure 7, such that the selected clear current threshold may be applied to received track circuit data in order to determine whether or not to issue a Low Clear Current alarm.

Embodiments described herein can help to reduce the number of false alarms associated with the clear current level. As a result, embodiments can improve the efficiency of condition based maintenance, allowing better resource allocation to solve actual problems associated with rail assets. The reduction in false alarms can also reduce the frequency of trackside visits by maintenance personnel, hence reducing the exposure of workers to potentially dangerous situations.

Embodiments described herein can be implemented without the need for any additional trackside circuitry, beyond the standard data logging systems routinely implemented on most track circuits. The data can be processed using a central system, thereby helping to keep the need for additional infrastructure to a minimum. In some embodiments, the system may operate as a post-processing system, whereby events marked as “Low Clear Current” are subsequently reviewed and re-designated as “non-alarm” events; in other embodiments, the method may proceed in real or quasi-real time, with the thresholds being updated in real-time in accordance with received weather data.

While certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the invention. Indeed, the novel methods, devices and systems described herein may be embodied in a variety of forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope of the invention.

Claims

1. A method for selecting a clear current threshold to apply to electrical current data received from a track circuit associated with a section of railway track, the electrical current data being indicative of electrical current passing through the track circuit and the clear current threshold defining a level of current above which the section of track will be taken as being unoccupied by a train, the method comprising: receiving electrical current data indicative of the current passing through the track circuit at a number of points in time; receiving weather data indicative of the weather conditions in the vicinity of the track circuit at said points in time, wherein the weather data is indicative of the amount of precipitation on or in the vicinity of the section of track; and identifying, based on the received electrical current data and received weather data, a first level of current that is likely to pass through the track circuit in the absence of a train and in the absence of precipitation in the vicinity of the track; and selecting a clear current threshold to apply to the electrical current data based on the first level of current.

2. A method according to claim 1, comprising: receiving electrical current data indicative of the current presently passing through the track circuit; determining whether the current is beneath the selected clear current threshold and if so, issuing an alert.

3. A method according to claim 1 or 2, comprising: identifying, based on the received electrical current data and received weather data, a second level of current that is likely to pass through the track circuit in the absence of a train and in the presence of precipitation in the vicinity of the track; and determining a clear current threshold based on the second level of current.

4. A method according to any one of claims 1 to 3, wherein: the received electrical current data is filtered to remove data that is indicative of the section of railway track being occupied by a train.

5. A method according to claim 2 or any one of claims 3 to 4 as dependent on claim 2, wherein the alert is issued by sending an electronic communication to a track operator.

6. A method according to claim 5, wherein the electronic communication message is sent as an email.

7. A method according to claim 2 or any one of claims 3 to 4 as dependent on claim 2, wherein the alert is issued as an aural sound.

8. A method according to claim 2 or any one of claims 3 to 4 as dependent on claim 2, wherein the alert is issued by updating a display on a track operator’s display screen.

9. A computer readable medium comprising computer executable instructions that when executed by a computer will cause the computer to carry out a method according to any one of the preceding claims.

10. A computer system comprising one or more processors; and a computer readable storage medium comprising computer executable instructions that when executed by the one or more processors will cause the system to carry out a method according to any one of claims 1 to 8.