Third rail heater control system

A system for remotely controlling third rail ribbon heaters is provided for preventing the accumulation of ice and snow on the rails. The system includes a plurality of switching assemblies that control a flow of electric current from the third rail of a railway to ribbon heaters mounted on the third rail. A remotely located digital controller provides switching commands to the switching assemblies via a radio link. The switching assemblies include current and voltage sensors that continuously provide current and voltage information that allows the digital controller to accurately predict when a heater failure condition is likely to occur so that ribbon heaters may be preemptively and safely replaced before failure. Each of the switching assemblies is contained in a junction box that includes both a door panel and a safety switch that disconnects the switching assembly from third rail current when the door panel is opened for improved safety.

FIELD OF THE INVENTION

This invention relates to systems for controlling the electrical-resistance heaters used to prevent the formation of ice on the third rail of electrically-powered railways.

BACKGROUND OF THE INVENTION

Third rail heater systems are generally known in the prior art. The purpose of such heaters is to prevent the accumulation of ice on the third rail of an electrically-powered railway that would otherwise interfere with electrical contact between the contact plate of an electrically-powered train car and the 750 volt DC current that is conducted through the third rail.

In such systems, long strip-like electrical resistance heaters (known as “ribbon heaters” or “heat tape” in the art) are mounted flush along the outer side of the central flange of the “I”-shaped cross-section of the third rail. Each of the ribbon heaters is electrically connected to the third rail so as to be powered by the 750 volts DC that such rails conduct. Current flow to the ribbon heaters is controlled by switches contained within junction boxes positioned adjacent to the railroad tracks. In conditions where ice and snow are imminent, the control switches in the junction boxes are closed in order to actuate the ribbon heaters.

In older third rail heater systems, the control switches were manually closed at the beginning of the winter season and left on until spring. However, such systems are wasteful of electric power as there are often many days during the winter season when such third rail track heating is unnecessary. As a result, automatic systems were developed that allow a system operator to selectively and remotely close or open the ribbon heater switches on an as-needed basis during the winter months.

SUMMARY OF THE INVENTION

Electrically-powered railway tracks are an inherently dangerous environment. In addition to the 750 volts DC carried by the third rail (which only needs to be touched once accidentally to cause death), the other two running rails that the train wheels ride may also be electrified on an intermittent basis from, for example, the braking current generated by the motor of an electric train car, or an AC current applied by a code reading device used for train position monitoring. Such intermittent currents may have voltages high enough (e.g. ˜100 volts) to be life threatening. Additionally, many maintenance and repair operations (such as the replacement of a burned out ribbon heater, or components within a junction box) are carried out under conditions of snow and ice where the exact location of dangerous rails and connections is concealed, and where the terrain is slippery. Finally, most maintenance and repair operations are conducted at night, when railway traffic is at a minimum. On the plus side, such timing reduces the probability of the maintenance operator being struck by a moving train car. On the negative side, it greatly increases the chances of accidental contact with the 750 volts DC current on either the third rail itself, or on an exposed contact in the junction box. As a result of such hazardous conditions, electric train maintenance personnel are exposed to a very real danger of accidental electrocution.

While the prior art automatic third rail heater control systems substantially reduce power consumption and costs, the applicant has observed five shortcomings in the design of such systems that render the maintenance and operation unduly hazardous to the operators of such systems. First, there is no provision in such prior art systems for sensing, recording, and processing the type of data that could accurately predict when a failure condition of a ribbon heater is likely to occur. Such a capability would be far more advantageous than a system that merely generated an alarm signal when a failure condition was present, as it would allow maintenance personnel to routinely and preemptively replace or repair ribbon heaters or junction box components under favorable weather conditions when visibility is good and ice and snow is not present, as opposed to emergency conditions during a snowstorm at night. Second, the junction boxes containing the control switches often have exposed contacts carrying 750 volts DC from the third rail. While there may be an internal or external “kill” switch to break the connection of the third rail current to the switching components of the box, a hazardous shock condition will be present if the maintenance operator neglects to open such a switch. In the case of an internal “kill” switch, the need to locate and to manually operate the switch—which is necessarily close to open contacts carrying the750volts DC operating current—can be hazardous, particularly in snowstorm conditions at night. Thirdly, there is no provision in prior art systems for safely and conveniently powering up the switching assembly for diagnostic purposes when the 750 volts DC from the third rail is cut off. Fourth, while many prior art systems utilize radio links to communicate switching commands between a central controller and local junction boxes, the strength and reliability of such radio links can be compromised by the distances between the central controller and junction boxes, the EMI generated by the electrical activity in the train stations, and poor weather conditions. Accordingly there is a need for a design having wireless links that operates with the reliability of hard-wired links. Finally, there is no capacity in prior art systems to periodically self-diagnose in real time order to confirm that all critical components are performing normally.

To these ends, the third rail heater control system of the invention includes a digital controller, and a plurality of switching assemblies contained in junction boxes located proximate to the third rail of a railway and remotely from the digital controller. The switching assemblies control a flow of current from the third rail to a plurality of ribbon heaters mounted along the length of the third rail. Each switching assembly comprises (1) a plurality of electrically-controlled switches, each of which selectively switches electrical current from the third rail to one of the plurality of ribbon heaters; (2) a switch controller including a programmable logic circuit connected to a radio transceiver linked to the digital controller, the switch controller providing control signals to each of the plurality of electrically-controlled switches in response to switching commands received from the digital controller; (3) current sensors that continuously provide a signal indicative of current flow through each ribbon heater to the digital controller, and (4) a voltage sensor that continuously provides a signal indicative of the voltage applied to each ribbon heater to the digital controller.

The current sensors are sufficiently sensitive to provide a signal indicative of a difference in current draw when one of the heating elements within the ribbon heater being monitored ceases to draw power. In practice, this requires the current sensors to have a sensitivity of at least 0.2 amps, as the individual heating coils within commercially-available ribbon heater typically draw this much current at 750 volts DC.

In operation, the current sensors and the voltage sensor of each switching assembly continuously provide signals indicative of changes in the current flow as well as surges in the voltage applied to the ribbon heaters which, as explained in more detail later, are largely caused by the regenerative braking of trains along the tracks. This current and voltage information is continuously transmitted to and recorded by the remotely located digital controller. By monitoring the occurrence of initial heater element failures and the length and magnitude of voltage surges applied to each of the ribbon heaters, the digital controller can accurately predict when a particular ribbon heater will no longer have the capacity to effectively prevent the formation of ice on the third rail during freezing conditions, thereby allowing the ribbon heater to be pre-emptively replaced during favorable weather conditions.

The junction box includes a door panel that provides access to the switching assembly, and a safety switch that disconnects the switching assembly from third rail current when the door panel is opened, thus avoiding any danger of electric shock during maintenance operations of the switching assembly. The safety switch is linked to the handle of the door panel so that the 750 volts DC of the third rail is automatically disconnected from the switching assembly whenever the handle is operated. This configuration obviates the need for locating and operating a manual kill switch after the door panel has been opened.

The system further comprises a portable power supply for powering the switch controller during maintenance operations when the door panel has been opened and the incoming 750 volt current has been cut by the safety switch. In the preferred embodiment, the portable power supply is a battery pack. The switch controller of the switching assembly is advantageously designed to operate on less than 30 volts. Hence the portable power supply of the system needs to provide only a non-lethal 30 or less volt current in order to operate the switch controller when the door panel is opened and the safety switch is actuated.

The digital controller includes local relay units at railway stations and/or power substations, each of which includes a radio transceiver in communication with the transceiver of the switch controller, and a master control station located remotely with respect to the local relay units. The master control station is connected to the local relay units via an optical fiber cable. Such architecture minimizes the operational distance of the radio link between the wireless controller and the digital controller, thereby increasing the overall robustness of the communication links of the system.

The master control station automatically runs a self-diagnostic procedure every time it is started up. Upon initial actuation of the local control units, the master control station first determines whether or not an electrical current is present in the third rail connected to the junction box. Next, it proceeds to test the operability of other components of each of the switching assemblies. Finally, the master control station connects the strip heaters to the electrical current from the third rail in sequential fashion such that the electrical load on the third rail is gradually applied. The master control station also is equipped with precipitation and temperature sensors that monitor the outside weather conditions for ice and snow and will automatically energize the heat tape system. These sensors may be located in multiple places along the rail tracks and operate only the heater sections needed based on the local weather conditions. This provides for fully automatic operation as well as maximum energy savings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference toFIG. 1, the third rail heater control system1of the invention generally comprises a master control station3remotely located from the railway stations, a plurality of local relay units5located in the railway stations (which together form the digital controller of the system), and a plurality of trackside junction boxes13.

The local relay units5each include a transceiver7connected to a programmable logic circuit (PLC)9. The local relay units5are optically coupled to the master control station3via an optical cable10, and are radio linked the relatively short distances to the junction boxes13via an antenna11connected to the output of the transceiver7. Such an architecture advantageously obviates the need to install a communications cable in the relatively harsh trackside environment where the junction boxes13are mounted, while keeping the length of the radio link short, thereby minimizing the chance that the radio link will be degraded or rendered inoperative by outside electromagnetic interference. The local relay units5further include ice and snow sensors12connected to their respective programmable logic circuits9via a cable as shown. Each snow and ice sensors12is ground-mounted in an open area near the railway station. In the preferred embodiment, the snow and ice sensors are LCD-8 type model number24619snow switches manufactured by ETI located in South Bend, Indiana. In operation, the local relay units5relay instructional commands between the master control station3and the junction boxes13, as well as data collected by sensors in the junction boxes13to the master control station3for storage. The local relay units5further relay a snow condition signal to the master control station3in the event that its respective snow and ice sensor12detects whether a snow condition is present, whereupon the master control station3automatically issues a ribbon heater start-up command to the junction boxes13within the particular zone serviced by the local relay unit5.

With further reference toFIG. 1, each of the junction boxes13houses a switching assembly15that will be described in detail hereinafter. An antenna17radio-links the switching assembly15to one of the local relay units5as previously indicated. An input cable19connected to the750volts DC third rail21of the railway is connected to an input terminal of the switching assembly15. Input cable includes a shoebox fuse23as indicated. A connecting cable27in turn connects the third rail21to a 750 volt DC source25via a circuit breaker29. A ground cable31, which forms the other pole of the 750 volt DC current applied to the switching assembly15, is connected between an output terminal of the switching assembly15and one of the running rails33of the railway. Finally, each of the junction boxes13includes output cables35a,35bconnected to a ribbon heater37. While only one set of output cables35a,35bis shown inFIG. 1, each junction box13preferably has four pairs of such output cables in order to control electric power to four different ribbon heaters37a-d.

With reference now toFIGS. 2 and 3, the ribbon heaters37controlled by the system1of the invention included a pair of conductive bus wires39a,39b.One bus wire39ais connected to the 750 volt DC current from the third rail21, while the other bus wire39bis connected to the ground cable31. A plurality of heating elements41are serially arranged along the 500 foot length of the ribbon heater37. Each heating element41is spirally wound around a layer of insulation covering the pair of conductive bus wires39a,39b,with opposite ends of the heating elements41connected respectively to the pair of conductive bus wires39a,39b.The heating elements41are covered over by a thermally-conductive jacket43formed from a silicone compound. In this example of the invention, each of the heating elements41draws about 0.2 amps. As is indicated inFIG. 3, one of the flat sides of the jacket43of the ribbon heater37is attached to the central flange45of the third rail21in order to keep ice from accumulating on the upper electrical contact surface46.

With reference again toFIG. 1, the master control station3is preferably a supervisory control and data acquisition (SCADA) network system that includes a server section50having a server51, an Ethernet switch52, and an uninterruptible power supply (UPS)53as shown. The server section50is connected to the local relay units5via the optical cable10. The master control station3further includes a server display monitor54connected to the server51of the server section50for maintenance of the server51, as well as a work station55having a display monitor56connected to a personal computer57.

Turning now toFIGS. 4A and 4B, each junction box13has a door panel60with a door handle62that affords access to the switching assembly15contained therein. The door handle62is mechanically linked to both a latch mechanism63that includes upper and lower latches64aand64b,and a safety switch66that disconnects the input cable18from the switching assembly15. In particular, a pivot rod68connects handle62to a rotary switch mechanism in safety switch66such that when the handle62is turned 90°, the upper and lower latches64a,64bbecome unlatched and the safety switch66becomes open, thereby breaking all connection between the 750 volt DC input cable19and the interior of the box13. In the preferred embodiment, safety switch66includes four pairs of contacts to suppress arcing. As is shown inFIG. 4A, the door panel60also includes indicator lights70a-dthat indicate that current is flowing through each of the ribbon heaters37a-d.Also included on the door panel60is a push-button test switch74that tests whether or not the light bulbs used in the indicator lights70a-dare operative.

FIGS. 5 and 6Aillustrate the details of the switching assembly15contained within the junction box13. The previously-discussed safety switch66includes an input terminal connected to the 750 volts DC input cable19, and an output terminal, to which four output cables79a-dare connected which in turn carry 750 volts DC when the safety switch66is closed. Output cables79a-dare in turn connected to manual switches81a-d,respectively. The provision of such manual switches81a-dallows the 750 volts DC current to be turned off with respect to a particular ribbon heater power circuit to allow such maintenance operations as the replacement of one of the ribbon heaters or the replacement of fuses downstream of the manual switches81a-d.The manual switches81a-dare connected to the programmable logic circuit (PLC)99as shown provide an electrical signal to the PLC99as to whether they are open or closed. The PLC99in turn conducts a 24 volt DC current to the indicator lights70a-dwhen the switches81a-dare closed, but does not conduct such a current to a particular indicator light70a-dwhenever its respective manual switch81a-dhas been opened. The output terminals of the manual switches81a-dare in turn connected to fuses83a-dwhich prevent an over-current condition from damaging components downstream thereof. In the preferred embodiment, fuses83a-dhave a 40 amp capacity even though their respective ribbon heaters37a-dhave about a 30 amp operating draw in view of the fact that the current draw of such heaters in an initial “cold” state is substantially more than their draw during normal operation after reaching a thermal steady state. The current output from each of the fuses83a-dis in turn connected to the inputs of electrically-controlled switches85a-d.As will be explained in greater detail hereinafter, the closed or open state of the switches85a-dis determined by the switch controller95which includes a transceiver97a programmable logic circuit99. Switches85a-dare preferably vacuum-type switches to avoid arcing which could otherwise occur during the opening or closing of their internal contacts.

Cables79a-dconduct the current flowing out of the electrically-controlled switches85a-dthrough current sensors87a-d,respectively. In the preferred embodiment, each of the current sensors87a-dis a MCR-SL-CUC-100-U universal current transducer (model no. 2308108) manufactured by Phoenix Contact located in Middletown, Pa. Preferably, to enhance the sensitivity of the current sensors87a-d,the cables79a-dare looped around the ring of the sensors in the manner indicated inFIG. 5. Such current sensors87a-dare capable of detecting a change in current of 0.2 amps or lower, which means they are capable of detecting when a single one of the dozens of heating elements41ceases to operate in its respective ribbon heater33a-d.Each current sensor87a-dhas an output wire88a-d,respectively, that is connected to an input of the programmable logic circuit99of the switch controller95which relays this current information to the memory of the master control station3via its transceiver97.

To complement the monitoring and diagnostic function of the current sensors87a-d,the junction boxes13each further contain a voltage sensor90that is likewise shown inFIGS. 5 and 6A. Voltage sensor90is located immediately downstream of the safety switch66and is connected between the input cable19and the ground cable31. Voltage sensor90has an output wire90.5that is in turn connected to the input of the programmable logic circuit99of the switch controller95. In the preferred embodiment, the voltage sensor90is a Swartz model C4280-901 voltage transducer manufactured by SMC Electrical Products located in Barboursville, W.Va. and having a website at www.smcelectrical.com. The voltage sensor90continuously monitors the voltage of the input cable19that is connected to the 750 volts DC third rail21of the railway, and continuously relays this information to the memory of the master control station3via the transceiver97of the switch controller95.

The combination of the data relayed by the current sensors87a-dand the voltage sensor90from each of the junction boxes13enables the personal computer57of the master control station3not only to immediately detect malfunctions such as the burning-out of a heating element in a particular ribbon heater33a-d,(and to generate an appropriate alarm signal) but further allows the personal computer57to accurately predict the expected lifetime of the heating elements of a particular ribbon heater33a-d.For example, a baseline lifetime of each of the ribbon heaters33a-dmay first be determined from the recorded data generated by the current sensors87a-d.Specifically, if the first set of ribbon heaters lasted, for example, for five years before heating element failure began occurring, then the baseline lifetime of each of the ribbon heaters33a-dwould be set at five years. This baseline lifetime can then be modified from the data generated by the voltage sensor90. To understand how such a modification might be made and why it is important, some background is necessary.

Most electric trains employ regenerative braking to slow down or stop at a particular train station. When regenerative braking is used, the function of the electric motor of the train is changed to that of an electric generator that applies drag to train in order to slow or to stop it. Hence, instead of receiving power from the 750 volt third rail, the electric motor of the train generates and conducts electric current to the third rail. This in turn results in a power surge that substantially raises the voltage of the third rail from 750 volts to well over 1000 volts. If the ribbon heaters33a-dare on at the time that a nearby train uses regenerative braking, they are subjected to the power surge generate by the electric motor of the train, which in turn applies lifetime-shortening thermal stresses to the individual heating elements of the ribbon heaters. Hence the collected voltage data supplied to the personal computer57of the master control station3by the voltage sensor90can be used to modify the baseline lifetime determined by the data collected from the current sensors87a-d.Specifically, the baseline lifetime can be shortened into a more accurate lifetime in proportion to the duration and magnitude of all the power surges the ribbon heaters33a-dare subjected caused by the amount of rail traffic employing regenerative braking traveling through the train yard.

In addition to the power surges created by regenerative braking, the ribbon heaters33a-dmay also be subjected to intermittent voltage surges due to the AC current applied by code reading devices used for train position monitoring. Such intermittent voltages may be high enough (e.g. ˜100 volts) to further shorten the lifetime of the ribbon heaters33a-d.Again, the data provided by the continuous monitoring of all such surges by the voltage sensor90allows the personal computer57to consider such data and to generate an even more accurate projected lifetime for each of the ribbon heaters33a-d.

Downstream of the current sensors87a-dthe cables79a-dare connected to an input of a terminal block89which contains a32amp fuse for each ribbon heater circuit. Ground cable31is also connected to the terminal block89via the safety switch. From the out of the terminal block89four pairs of heater circuit wires91a-dare formed. Each of these pairs of circuit wires91a-dare connected to one of the ribbon heaters37a-das is most easily seen inFIG. 6A.

With reference again toFIGS. 5 and 6Bthe transceiver97of the switch controller95is connected to the antenna17shown inFIG. 1, and to the PLC99via an Ethernet switch98. Output wires101a-dof the PLC99are connected to control inputs of the switches85a-dsuch that the open or closed state of the switches85a-dis determined by the electrical signals generated by the PLC99via the wires101a-d.Isolating relays101a-dare interposed between the PLC99and the electrically controlled switches85a-dto prevent any possibility of a damaging current surge from the switches85a-dbeing transmitted to the PLC99. A terminal block103facilitates connection between the outputs of the isolating relays101a-dand the control inputs of the electrically-controlled switches85a-d.A power supply105supplies power to the transceiver97and the PLC99. As is schematically shown inFIG. 6B, the power supply105converts the 750 volts DC power from the input cable19to a non-lethal24volts DC current appropriate for the operation of the components of the switch controller95, and conducts the converted current to the transceiver97and PLC via an output cable107shown inFIG. 5. As is best seen inFIG. 6B, a power input connecter109is provided at the output of the power supply105. In the event that the power supply105ceases to provide power to the components of the switch controller95(as would happen for example when the door panel60were opened and the safety switch66actuated) a power output connector110of an auxiliary power supply111(which may be a portable battery pack) may be connected to the power input connector109, thereby providing operable power to the transceiver97and PLC99of the switch controller95.

FIG. 6Cillustrates the connections between the24volts DC power supply105and the transceiver97, the PLC99, the indicator lights70a-d,and the test switch74. Normally, when the PLC99transmits a “close switch” command to the electrically-operated switches85a-d,each of the isolating relays101a-dare closed to relay 24 volts DC to the inputs of not only the switches85a-d,but also the indicator lights70a-d.As is evident inFIG. 6A, push-button test switch connects the 24 volt DC current to the indicator switches70a-deven when the isolating relays101a-dare open, which would occur when the door panel60has been opened and the safety switch66actuated.

FIGS. 10A and 10Bare a flowchart generally illustrating the operational steps taken by the operator to start the system1. The operator first checks if the third rail21is energized. If not, he checks to see if the substation circuit breakers are closed and if the shoebox fuse23is conductive. If so, the operator then checks to see if the safety switch66is closed. If so, he inquires whether all of the components of the switching assembly are receiving a flow of the 750 volts DC power from the third rail21. If so, he then powers up the local relay unit5located at the railway station, and inquires whether all of the components of the unit5are receiving power. In the remaining steps illustrated inFIGS. 10A and 10B, the operator powers up the master control station3and likewise inquires whether all of the components of the station3are receiving power. After the booting up and component checking of the switching assembly15, the local relay units5and the master control station3has been completed, the system1proceeds to conduct the 750 volts DC power from the third rail to its specific ribbon heaters37a-d.

FIG. 11is a flowchart illustrating the specific operational steps taken by the PLC99to initiate actuation of the ribbon heaters37a-dpowered by its particular switching assembly15. While not specifically indicated in this flowchart, the master control station sequentially actuates the ribbon heaters37a-dso as not to apply too great a load on the third rail21would might otherwise interfere with the smooth operation of any trains near the junction box13.

FIGS. 12A-12Eare a flowchart illustrating in detail the operational steps taken by the system1after the ribbon heaters have been actuated. Upon the actuation of all of the ribbon heaters37a-d,the current sensors87a-dand voltage sensor90continuously send a signal to the PLC99indicative of the real-time current draw and voltage experienced by each of the ribbon heaters37a-d.This current draw and voltage data is periodically relayed from the PLC99to the memory of the server51via the radio link between the transceivers97and7of the switching assembly15and local relay unit7, respectively, and the optical link via the optical cable10.

Although the invention has been described in detail with particular reference to a preferred embodiment, it will be understood that variations and modifications can be effected within the spirit and scope of the invention. Other modifications, variations, and additions to the invention will become apparent to persons of skill in the art, and all such modifications, variations, and additions are intended to be within the scope of this invention, which is limited only by the claims appended hereto and their various equivalents.