Rail oxidation monitoring system

Abstract

At present there is no evidence of fixed systems to verify the oxidation state of railway rails, even considering that the presence of oxide can inhibit the detection of the presence of rolling stock through the so-called Track Circuits whose operation is based on the alterations of currents due to the short circuits generated between the two rails by the axles of the trains themselves, In the general case of sections on continuous rails, delimited by two short circuits at their ends, the invention is composed of two different and cooperating subsystems, one of which is positioned centrally and the other positioned at the ends of the two short circuits mentioned above, asymmetries both of the currents impressed as a train advances along the section and with the comparison relative to other previous passages or calculated mathematically, can be interpreted as an index of the presence of a possible insulating layer of oxide.

Description

[0001] RAIL OXIDATION MONITORING SYSTEM

[0002] DESCRIPTION

[0003] - TECHNICAL FIELD:

[0004] The system covered by this patent application falls within the field of electronic systems used in the railway sector, positioned along the tracks and employed to ensure railway traffic control. In particular, the proposed system aims to monitor the presence of a possible oxide layer on the rails. This monitoring is especially important in areas where train localization systems operate through track circuits with injected currents. The invention is designed to function in fixed installations.

[0005] - BACKGROUND ART:

[0006] At present, there is no evidence of fixed automatic systems for verifying the oxidation state of railway tracks. This is despite the fact that most train localization systems rely on so-called Track Circuits (hereinafter CdB), where the presence of trains is detected through variations in the currents / voltages injected into the rails, which are altered by short circuits created between the two rails by the axles (axles and wheels) of the trains themselves. These short circuits could be masked by the possible presence of insulation oxide layers.

[0007] It is important to note that the failure to detect the presence of a train can easily lead to disastrous collisions between convoys.

[0008] Currently, the monitoring of rail oxidation is carried out through direct rail inspections, sometimes using diagnostic trains, at intervals that vary depending on the location (e.g., proximity to saltwater, tunnels with high humidity levels, etc.) and the frequency of train passages, as the passage of wheels itself contributes to the removal of thin oxide layers.

[0009] - DISCLOSURE OF INVENTION:

[0010] THE PROPOSED INVENTION AND ITS CONFIGURATIONS

[0011] The proposed system can be implemented in two configurations.

[0012] The first configuration consists of a single element, referred to as Subsystem A, which is repeated at appropriate intervals along the tracks. This setup is designed for situations where there are no short circuits between the rails — such short circuits can be found in various railway configurations, such as balancing short circuits or high- frequency track circuits. The second configuration consists of two elements, referred to as Subsystem A and Subsystem B. Subsystem B is necessary due to the sensitivity loss of Subsystem A in the vicinity of short circuits. This configuration is intended for use in environments where short circuits are present along the tracks.

[0013] Additionally, the integration of both subsystems with an Axle Counter Block (hereinafter referred to as BCA) can enhance and simplify their measurements. In cases where BCA systems are present, oxide detection can complement the BCA by integrating a system based on injected currents to verify the presence of rolling stock during potential restart procedures.

[0014] The solution is designed to allow the implementation of equipment capable of:

[0015] 1 ) Avoiding significant issues related to availability, maintenance, installation, and implementation.

[0016] 2) Maintaining a low production cost, enabling large-scale deployment across the railway network.

[0017] 3) Being applicable to both continuous rails and rails with insulating joints.

[0018] 4) Operating in environments with both DC traction (3000 V DC) and AC traction (2x25,000 V AC).

[0019] 5) Monitoring track sections with a minimum length of several kilometers.

[0020] 6) Detecting, with each train passage, the presence of excessive oxide on the rails that could compromise train detection based on short circuits created by train axles.

[0021] 7) Measuring the resistance imposed by the train axles.

[0022] 8) Easily integrating with BCA systems for axle detection and counting, simplifying system analysis or supporting restart procedures when necessary.

[0023] OPERATING PRINCIPLES

[0024] If we assume a section of track characterized by continuous rails and two short circuits positioned equidistantly from a generator capable of imposing coded currents on the rails, we will have an approximately equal distribution of the current applied along the two branches identified between the generator and the short circuits. In the absence of trains on the two branches, we can detect in both short circuits, although attenuated by the rails, a portion of the current imposed by the generator, identifiable with respect to different currents present on the rails thanks to the coding. If a train enters one of the two branches of the track, surpassing one of the two short circuits, the current imposed by the generator, before reaching the short circuit between the rails, will be short-circuited by the shorts between the rails imposed by the train’s axles. As a result, the current passing through the short circuit will experience a significant reduction. Furthermore, as the train approaches the generator, the distribution of the currents imposed by the generator will change, as the impedance of the branch with the train will decrease as it moves closer to the generator. This will lead to an increase in the current in the branch occupied by the train and a decrease in the second branch beyond the generator. After passing the generator, the current flow will follow an opposite trend.

[0025] As a consequence of the above, the almost total absence of current in one short circuit and the progressive decrease of current in the opposite short circuit clearly indicate the presence of a train and its approach to the generator. Meanwhile, the presence of discontinuities / asymmetries in the variation of current behavior when trains pass through the two branches or between successive vehicle passes is a clear indicator of anomalous changes in the contact between the train’s wheels and the rails, especially in the case of short trains and long sections where an insulating oxide layer is present.

[0026] In the case of electrically interrupted tracks, such as those equipped with insulated joints and BACC systems, there are obviously no short circuits delimiting the section, but rather open circuits. In this case, it is possible to place a generator at both ends of the section and compare the current at the approach of a train to the generator located at the exit of the section with the current provided by the generator at the entrance of the section as the train moves away.

[0027] Having clarified the underlying principle of the invention, we note that if the section is delimited by short circuits, even in the absence of oxidation, the presence of axles near the short circuit is difficult to detect when there is only a generator at the center of the two delimiting short circuits. The variation in current at the short circuits would indeed be minimal. To overcome this issue, it is sufficient to place a current generator between the two rails, in parallel with the short circuits, and to install a current meter on the short circuit to measure the portion of the generated current passing through it. The difference between the two is minimal in the absence of trains, while it becomes significantly meaningful when trains are nearby, even for a hypothetical vehicle with a single axle. By doing simple calculations, in fact, if we assume that the resistance of the short circuit is, for example, 10 milliohms and the resistance imposed by an axle placed exactly at the location of the short circuit is 250 milliohms, the presence or absence of the axle results in a variation of about 4% between the applied current and the current passing through the short circuit. Considering that there must be at least two axles, we will have a minimum variation of about 8%, which can be easily measured. Additionally, in this case, by looking at the current variation diagram when approaching and moving away from the short circuit, we can gain insights into a possible excess of oxidation near the short circuit.

[0028] The presence of a short circuit at the location of this second generator automatically ensures that the generated signals are, in the absence of other shorts caused by the presence of trains, confined to the area of the short circuit present.

[0029] The distribution between the generated current and the current passing through the short circuit is, of course, a function of the ratio between the resistance of the short circuit, which is known, and the resistance presented by the shorts generated by the axles and their distance from the short circuit. This value of the current distribution is used when a train passes to evaluate the resistance imposed by the axles between the two rails and, therefore, the possible oxidation of the wheels themselves. Meanwhile, its evolution and any non-linearity / asymmetry when the train approaches and moves away are clear indicators of the possible presence of an oxide layer on the rails near delimiting shorts on continuous rails. The presence of a BCA at the short circuit location allows for better characterization of both the expected current variation curves in the two short circuits when a train approaches and moves away, and a possible excessive oxidation state of the train's wheels.

[0030] Considering that the invention detects the presence of oxide only when trains pass, its indications are valid if the period between train passes is not so long that one could hypothesize a complete alteration of the oxidation state of the rails.

[0031] Considering the need to monitor long sections and keep costs low, in addition to ease of installation and maintenance, it is hypothesized to use frequencies lower than 250 Hz, where the attenuation due to passage through the rails is limited for generators placed at the center of sections delimited by short circuits. Meanwhile, for generators positioned at the short circuits, which are used for checks only in the adjacent sections, where it is practically impossible to make significant measurements using only the currents imposed by the generators placed at the center of the sections, signals in the range between 250 and 500 Hz are used, so as not to overlap with the signals from the central generators.

[0032] The use of similar systems at higher frequencies is possible but not recommended due to the greater complexity and cost compared to low-frequency systems.

[0033] Let us recall that, although there may be significant noise in the aforementioned frequency band, both theoretically and experimentally it has been found that this noise is not continuous in frequency. It typically consists of distinct spectral lines, although they vary over time, especially depending on the speed of the trains. Therefore, there are almost always frequencies with very little noise where signals can be applied to monitor their behavior over time. One system that could be used is transmitting a set of non-multiple frequencies that do not coincide with those typically used in the railway sector. An analogous system is to analyze the spectrum of the signals present on the rails and transmit in the bands most free from them.

[0034] In relation to the safety of the analyses, it relies on the coding of the applied signals. For this purpose, it is useful to consider that the probability of code misinterpretation is related to both the signal-to-noise ratio, the type of code, the type of modulation used, and the potential simultaneity of multiple coded carriers.

[0035] In the case that, during the progression of the oxidation processes, they develop asymmetrically relative to the rails, there may be noticeable variations in the presence of currents in the devices responsible for rebalancing the return of the traction current during the advancement of a train. These devices can be either short circuits between the rails in the case of both DC and AC traction, or rebalancing coils in the case of DC traction.

[0036] Therefore, if rapid variations in the rebalancing currents are observed during the advancement of a vehicle, they may indicate the presence of oxide layers.

[0037] PROPOSED SYSTEM

[0038] The device is composed, in the case of positioning on continuous rails and in the presence of short circuits, of two interconnected subsystems (hereinafter called subsystem A and subsystem B), subsystem A at the centre of the section and subsystem B on the two delimitation shorts. In the case of sections delimited by electrical separations, where there are no short circuits, only A subsystems positioned at one end of the section are used, capable of verifying the variations in current as the position of the rolling stock changes as it approaches or moves away depending on its direction of travel; if two A subsystems are positioned at the two ends of the section, anomalous situations can be observed more easily by comparing the trend of the current detected by the two subsystems. Even if not absolutely necessary, it is advisable that the subsystems are able to communicate with each other and, in the case of BCAs, also with them for any additional functions such as having simple numerical and temporal references relating to the passage of the axes.

[0039] The invention has the following characteristics:

[0040] 1 . The system found is able to identify situations of presence of oxide on the rails. This check can be carried out at the passage of each convoy.

[0041] 2. In the case of continuous rails the system is formed by the two subsystems A and B.

[0042] 3. The subsystems are able to communicate with each other, with the ACC control network and, if present, with BCA systems.

[0043] 4. The invention complies with the directive of having wired connections in minimum number. The measure is important to reduce costs and times of installation and maintenance and reduce the possibility of tampering with the systems (copper theft).

[0044] 5. The system has no particular installation problems.

[0045] 6. The invention also works in the presence of strong electrical noise (due to traction) without having to make any modifications to the rolling stock and does not imply the need for expensive traction filters such as those generally necessary in BACC track circuit systems nor the need to use frequencies higher than approximately 500 Hz due to obvious problems of cost and complexity..

[0046] 7. The invention designed for use on continuous rails also works in the presence of insulated joints, in a simplified version, i.e. without subsystem B placed in parallel to the short circuit, which does not exist in this case and considering only the evolution of the current emitted by the generators placed in the subsystems A, as the train approaches. Greater precision can be obtained if 2 subsystems A are placed for each section so as to be able to compare the current emitted by the generator exiting the section with that supplied by the generator present at the entrance to the section when the train passes.

[0047] 8. The invention is able to operate in a context where there is strong electrical noise due to the return of the traction currents. The traction currents present a discontinuous and unpredictable spectrum as it varies with the speed of the train and presents various spectral lines, some also due to harmonic and intermodulation distortion, and is applicable whether the power supply is direct or alternating.

[0048] 9. The invention can coexist in contexts where traction current rebalancing devices are present (short circuits or rebalancing coils).

[0049] DESCRIPTION OF THE PROPOSED INVENTION: To address the challenges and opportunities outlined above, the system we have developed consists of two subsystems, A and B, each associated with a single axle counter system.

[0050] Along the rails, subsystems of type A and B alternate, paired with the respective axle counters that follow one another along the railway line.

[0051] Subsystems of type B should be placed near the short circuits between the rails, which are used for traction current balancing, while subsystems of type A are positioned at the center of the sections bounded by the short circuits.

[0052] Subsystem Type A

[0053] The Type A subsystem, as shown in Figure 1 , consists of the following components:

[0054] 1. A generator block, illustrated as G1 in Figure 1 , operating at frequencies below several hundred Hz (for example, 250 Hz). This generator is capable of generating one or more modulated carriers, appropriately encoded, and is equipped with sufficient power and an interface suitable for connection to the rails. The system is designed to transmit signals to the adjacent short circuits with a sufficient signal-to- noise ratio, ensuring that the signals can be reliably read (SIL4) by the sensors of the Type B subsystems positioned there.

[0055] 2. A current sensor, illustrated as S7 in Figure 1 , to measure the output current from the generator G1 described above.

[0056] 3. Sensors on the rails on both sides of the generator, represented by blocks S5 and S6 in Figure 1 , to detect the distribution of the currents imposed by the generator. It should be noted that while sensor S7 is highly accurate, as it fully encloses the cable carrying the current to be measured, these two sensors cannot completely enclose the rail for obvious reasons. As a result, their absolute output values may be less precise, but they are sufficiently reliable for determining the ratio between the currents they measure. Additional sensors, whose number and position may vary, can be used to better characterize the evolution of the currents as trains approach and move away.

[0057] 4. A voltage sensor, illustrated in Figure 1 (block V), to characterize variations in impedance as trains move forward, thereby normalizing the variations in the measured currents and facilitating their comparison.

[0058] 5. An optional axle counter pedal, represented as CA in Figure 1.

[0059] 6. A general control block (block SC1 in Figure 1 ) whose function is: to control and coordinate all the previous blocks; to connect to Type B subsystems, adjacent BCA systems, and remote control systems; Compare the consistency of current variations when trains approach or depart, using both the sensors in the subsystem and the readings from sensors positioned in the adjacent Type B subsystems; to compare the differences between the currents observed during the approach and departure of trains with those recorded in previous train passes; Send alarm messages reliably (SIL4) if the variations in the currents (approaching, departing, and archived) can be interpreted as indicating the presence of oxide on the rails.

[0060] Subsystem B

[0061] The type B subsystem, to be positioned near short circuits between rails illustrated in figure 2 is made by:

[0062] 1 . A short circuit, represented as C in Figure 2. This short circuit can also utilize any pre-existing short circuits already installed for traction current equalization.

[0063] 2. current generator block, represented as G2 in Figure 2, connected to the rails at the previously described short circuit C. It operates at frequencies typically ranging between 250 and 500 Hz, capable of generating one or more simultaneously modulated carriers. The generator is designed with sufficient power and an appropriate rail interface to ensure that signals reach adjacent short circuits with a sufficient signal-to-noise ratio, allowing them to be reliably detected (SIL 4-certified) by the sensors of the Subsystem B units positioned there.

[0064] 3. A current sensor for monitoring the current emitted by G2, represented as S2 in Figure 2.

[0065] 4. A current sensor for monitoring the current circulating in the short circuit C, represented as S1 in Figure 2, with a bandwidth sufficient to accurately acquire currents generated either by the local generator G2 or by generators G1 from adjacent Subsystem A units. This sensor must not saturate in the presence of possible traction return currents and could also be designed to measure them if necessary.

[0066] 5. Sensors on the rails at both sides of the generator, represented by blocks S3 and S4 in Figure 2, are used to highlight the distribution of currents impressed by the generator. It is important to note that, while sensors S1 , S2, and S7 are very precise, as they completely surround the cable through which the current to be measured flows, these two sensors (S3 and S4) cannot fully encompass the rail for obvious reasons. As a result, they may be less precise for the absolute values provided at their output, but they are sufficiently accurate to provide a reliable indication of the ratio between the currents they measure. Additional sensors, whose number and positioning may vary, can be used to better characterize the evolution of currents as trains approach and depart.

[0067] 6. A possible axle counter pedal, represented as CA. in figure 2.

[0068] 7. A general control block, represented as SC2 in Figure 2, whose functions are: controlling and coordinating all the previously mentioned blocks; connecting with adjacent Subsystem A units, nearby BCA systems, and remote control systems; Discriminating, through codes and frequencies, the currents imposed by the G2 generator from those imposed by the G1 generator of a neighboring Subsystem A, as well as from background noise present on the rails; Comparing the consistency of the variations in the current imposed by G2 in the short circuit C, both with respect to the approach and departure of trains and to the recorded passages of previous trains; emitting a SIL 4-certified alarm message if this comparison indicates the presence of oxidation on the rail; communicate to Subsystem A any changes in the currents in the short circuit C, previously described, imposed by Subsystem A while trains are moving between the opposite short circuit and Subsystem A.

[0069] - BRIEF DESCRIPTION OF DRAWING

[0070] For further clarification of the drawings in relation to the previously described invention, we provide the description of each individual figure below.

[0071] In Figure 1 , R represents the rails near the application point of a generator positioned centrally between two short circuits that delimit a section of the track. The various elements constituting Subsystem A of our invention are depicted. These elements are:

[0072] G1 : Generator equipped with power output and an interface to the rails.

[0073] V: Voltage sensor.

[0074] S7: Sensor for current output from the generator.

[0075] S5 and S6: Current sensors to verify the distribution of current across the rails relative to the generator.

[0076] SC1 : Control system.

[0077] CA: Optional axle counter pedal.

[0078] In Figure 2, R represents the rails near the application point of a circuit, where the various elements constituting Subsystem B of our invention are depicted. These elements are:

[0079] R: Rails.

[0080] S1 : Current sensor in the short circuit.

[0081] S2: Current sensor at the generator output.

[0082] S3 and S4: Current sensors to verify the distribution of current across the rails relative to the short circuit.

[0083] G2: Current generator equipped with a power output and an interface to the rails.

[0084] SC2: Control system.

[0085] CA: Optional axle counter pedal.

[0086] - BEST MODE FOR CARRYNG OUT THE INVENTION:

[0087] Like all electronic systems, the system we propose can be designed by selecting the various components, which must necessarily be custom-built, in contrast to the parts that can be realized through software or programmable electronics (e.g., gate arrays, FPGAs, etc.).

[0088] From the previous description, it is clear to any designer that the following components must be custom-made or purchased from the market: the sensors (S and V), the axle counter blocks (CA), at least concerning the sensors, and the hardware parts of the generators (G1 and G2).

[0089] The remaining open possibilities are for the two control systems (SC1 and SC2) and the low-power section of the aforementioned generators. However, considering that the system must meet the requirements set by railway standards, and that currently there are only a few examples of systems of this type designed with programmable electronics (FPGA, etc.), along with the complexity of the functions performed by the two control blocks and the low-power section of the generators, which makes custom electronic design less advisable, it seems evident that it would be more efficient to implement these blocks using dedicated software on general-purpose programmable boards, potentially already certified for use in railway applications.

[0090] - INDUSTRIAL APPLICABILITY:

[0091] From the previous descriptions, it is clear that equipping the rails, especially in sections where standard axle counter systems are already in place, with the proposed system allows for an economical method of monitoring the potential presence of excessive oxidation on the rails.

[0092] It is important to note that in a simplified version, the system described above can also function in sections with insulated joints, consisting solely of Subsystem A, as there are no short circuits for section separation. If axle counter pedals are also absent, signals from the BACC system can be used to detect the presence of rolling stock in the section of interest.

[0093] Implementing the above system results in only a minimal cost increase for sections where BCA or BACC systems are already in place and does not require wired communication connections if wireless techniques (loT, etc.) are used.

[0094] The use of frequencies not exceeding a few hundred Hz (around 500) avoids all the issues related to audio-frequency track circuits, and the ability to function on continuous rails regardless of the power supply type (DC or AC) suggests the potential for widespread adoption.

Claims

CLAIMS1 - SYSTEM FOR MONITORING OXIDATION ON RAILS based on the analysis of the variations in the trend of currents in the rails between those mathematically calculated when a rolling stock passes on rails in the absence of oxide layers and those measured when real trains pass, the invention is able to verify the presence of oxidation both on continuous rails and on rails with insulated joints and both in the presence of direct current and alternating current traction, it uses frequencies lower than the range of audio frequency systems; the invention consists of two subsystems: a type A subsystem positioned far from the short circuits present between the rails and a type B subsystem that injects currents in correspondence with the short circuits;Type A subsystems are characterized by being composed of: an electric generator block connected to the rails with, maximum frequencies lower than a few hundred Hz capable of generating one or more contemporary coded carriers and equipped with an interface towards the rails and with adequate power in relation to the length of the section, which is delimited at its ends either by short circuits or by electrical interruptions such as those presented by insulated joints, at least one current sensor at the output of the generator described above, at least one voltage sensor applied to the rails, a general control block equipped with: reading interfaces for the sensors described above, communication interfaces with remote systems, communication interfaces with type B subsystems, communication interfaces to axle counter block systems;This control block is configured to: control and coordinate all other blocks of subsystem A, read sensor outputs, acquire the currents and impedances read from neighboring B subsystems, acquire the number of wheels entering and exiting the sections under its jurisdiction if axle counter block systems are present, verify whether there are asymmetries or unexpected elements such as sudden variations in current not attributable to the advancement of the convoy between the currents detected in approaching I moving away, such as to be able to hypothesize the presence of variations in the wheel-rail contact attributable to insulating oxide states verify whether the differences in the current patterns related to the passage of trains both compared to those mathematically calculated inthe presence of ideal rails and to those stored from previous passages do not exceed predefined values, a situation that could indicate the presence of oxide, use during the analysis of currents, external data such as times and number of axes coming from Axle Counter Block systems and currents and impedances coming from type B subsystems, store the value of the current relating to previous passages, send alarm messages, in case the trend of the detected currents / voltages may deviate from that expected in the case of a normal electrical contact between wheels and non-oxidized rails;Type B subsystems located at short circuits between rails, to be used in conjunction with type A subsystems, are characterized by being composed of: a current generator connected to the rails at the points where the short circuit is applied, at least one sensor to detect the current emitted by the generator, at least one sensor to detect the current present in the short circuit, a general control block equipped with: reading interfaces for the sensors described above, communication interfaces with type A subsystems, communication interfaces to Axle Counting Block Systems;This control block is configured to: control and coordinate all other blocks of the type B subsystem, read sensor outputs, acquire the number of wheels entered and exited on the sections under its jurisdiction if axle counter block systems are present, verify whether there are asymmetries or unexpected elements such as sudden variations in current not attributable to the advancement of the convoy between the currents detected in approaching I moving away, such as to be able to hypothesize the presence of variations in the wheel-rail contact attributable to insulating oxide states verify whether the differences in the current patterns related to the passage of trains both compared to those mathematically calculated in the presence of ideal rails and to those stored from previous passages do not exceed predefined values, a situation that could indicate the presence of oxide calculate the impedance presented by the axles of the trains as they pass over the short circuit using the value of the ratio between the current emitted by the generator and that present in the short circuit,use external data such as times and number of axes coming from Axle Counter Block systems during the analysis of the current data, send the values of the read currents to the type A subsystems, store the value of the current relating to previous passages, send alarm messages, in case the trend of the detected currents / voltages may deviate from that expected in the case of a normal electrical contact between wheels and non-oxidized rails2 - Subsystems A and subsystems B as per claim 1 which also have sensors on the rails on both sides of the generator to highlight the value of the distribution of the currents impressed by it.3 - Subsystems A and subsystems B as per claim 1 which also have at least one sensor configured to read the imbalance of the traction current whether it is direct or alternating, and logic capable of evaluating whether the trend of the imbalance current as a train advances can be attributed to the presence of oxide layers predominantly on one of the two rails..

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