WO2001015930A1

WO2001015930A1 - A plant for feeding electric power to railway vehicles

Info

Publication number: WO2001015930A1
Application number: PCT/SE2000/001646
Authority: WO
Inventors: Jörgen GUSTAFSSON; Anders Frost; Thorsten Schütte
Original assignee: Balfour Beatty Plc
Priority date: 1999-09-02
Filing date: 2000-08-28
Publication date: 2001-03-08
Also published as: SE9903091D0; SE514156C2; AU7045800A; SE9903091L

Abstract

A plant for tansmitting electric power to railway vehicles (4) comprises a contact line (3) transmitting an alternating voltage and adapted to be in contact with the contact member (16) of the vehicle for feeding current to the latter. The contact line has an interruption (7) at at least one location along the railway with two separated contact line portions located on both sides thereof and an elongated element (8) bridging the distance between these portions. A resonance circuit (11) is connected to the element, which has portions (9, 10) overlapping the respective contact line portion and is adapted to be in contact with the contact member of the vehicle at the same time as with the respective contact line portion for applying a voltage to the element and charging the resonance circuit. The resonance circuit is discharged according to a damped harmonic oscillation for demagnetizing the transformer of the vehicle when the contact member of the vehicle leaves the contact with a contact line portion and is only in contact with the element.

Description

A plant for feeding electric power to railway vehicles

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a plant for feeding electric power to railway vehicles having an alternating voltage contact line adapted to be in contact with a contact member of the ve- hide for feeding current to the latter, said contact line having an interruption on at least one location along the railway with two separate contact line portions located on both sides thereof and an elongated element bridging the distance between these portions and adapted for bearing of the contact member of the ve- hide thereagainst over the entire said distance and to normally be electrically insulated with respect to said contact line portions, said plant being intended to feed vehicles provided with a transformer for transforming the voltage of the contact line to another level.

The word "contact line" is here to be given a broad sense and is intended to comprise a contact line suspended above the rail as well as a contact bar or so called third rail beside or between the rail. Neither is any restriction to determined levels and/or frequencies of the alternating voltage on the contact line made.

There are different reasons for arranging such an interruption having such a bridging elongated element along the contact line. When the contact line receives electric power from a three phase network, such as the public three phase network, this is achieved by connecting one phase of the three phase network, possibly through a transformer, to the contact line and this feeds power to the latter, but for avoiding asymmetric loads on the different phases of the three phase network the contact line is through said interruption divided into contact line portions, which are connected to mutually different phases of the three phase network for delivering a one phase alternating voltage to the contact line. It is then important that a said bridging element is there, since the contact member (voltage tapping member) of the railway vehicle, i.e. the engine, may otherwise be damaged through jumps and chocks. A dead section having a normal (electrically not conducting) contact line mechanically but not electrically overlapping the contact line carrying a voltage is in the practice used, so that the contact member may run past the interruption location as if there were no interruption, besides from the electrical point of view.

However, such interruptions may also be there in the case that the contact line is fed through a one phase alternating voltage in low frequency operation, i.e. normally 16 2/3 Hz or 25 Hz, since a division of the contact line in sections may then be needed for example at disturbances of the operation or for avoiding current transmission not desired through the contact line, and also then said bridging elongated element is arranged for ensuring a smooth running of the contact line member thereon.

A disadvantage which may sometimes have undesired consequences is adhered to plants of this type already known. When a vehicle with said contact member arrives to the dead region defined by said interruption the voltage supply to said transformer of the vehicle is abruptly interrupted, and the phase position of the voltage is then arbitrary. The voltage is also abruptly switched in in a likewise arbitrary phase position when the vehicle leaves the dead region downstream of the interruption and receives voltage from the contact line portion located down- stream. This could result in an unfavourable combination of phase positions, when for example the transformer is completely magnetized when the voltage is interrupted and then the phase position of the voltage switched in downstream is in such a position that it in that moment initiates tries to further magnetizing of the transformer, so that this is exerted to saturation effects, which in the worst case may be transferred to other vehicles along the railway resulting in sub-harmonic resonances and other undesired side effects. A very high current may then for example run out if the phase position of the contact line portion located downstream is wrong there, so that there is a risk for triggering over-current protections disconnecting some equipment or the entire feeding to the contact line. There is also a risk that said resonance oscillations which may knock out other railway vehicles may occur on said contact line portion located downstream.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a plant of the type defined above, which finds a remedy to the inconveniences mentioned above of such plants already known.

This object is according to the invention obtained by the fact that in such a plant the elongated element is electrically conducting, that the plant comprises a resonance circuit connected to the element and having at least a capacitance and an inductance, that the element has portions overlapping the respective contact line portion and being adapted to be in contact with the contact member of the vehicle at the same time as the respective contact line portion for connecting the element to a voltage and charging the resonance circuit, and that the resonance circuit is adapted to be discharged according to a damped harmonic oscillation for demagnetizing said transformer when the contact member of the vehicle has left the contact with the contact line portion located upstream of the element with respect to the direction of movement of the vehicle and only is in contact with the element. The resonance circuit will hereby as soon as the vehicle is located in said interruption region ensure a demagnetizing of the transformer of the vehicle, so that the transformer will when a voltage is supplied to the vehicle again through the contact line portion located downstream of the interruption be in such a state that no saturation effects may be obtained irrespectively of the phase position of the voltage of the latter contact line portion. No problems of sub-harmonic resonances with the potential to knock out other vehicles or high currents which may trigger over current protections will by that occur. Thus, it does not matter any longer in which relation the phase positions of the voltage on the contact line portions located on the respective side of the interruption is.

According to a preferred embodiment of the invention the resonance circuit is dimensioned to enable at least oscillations at said discharging thereof irrespectively of the magnitude of the load of the vehicle on the contact line. It is by this ensured that also at a very high load of the vehicle on the contact line the resonance circuit may absorb so much energy that it may turn around and oscillate back and not only be slowly damped towards zero, which would not mean any demagnetizing of the transformer.

According to another preferred embodiment of the invention the resonance circuit also has at least one resistor adapted to ensure a damping of the oscillation of the resonance circuit at discharging thereof and a substantial tuning away of this oscillation before the vehicle with the contact member thereof reaches the contact line portion located downstream as seen in the direction of movement. Energy which has to be burned away may be burned away either in the engine or in the resistor by the arrangement of such a resistor, and if a minimum load of the vehi- cle on the contact line would be there, the resistor will still ensure that the oscillation of the resonance circuit is substantially tuned away before the engine leaves the interruption region, accordingly even if the engine does not consume any power.

According to another preferred embodiment of the invention the resonance circuit is dimensioned with a resonance frequency in the order of the frequency of the voltage intended to be transmitted by the contact line, and the resonance circuit is advantageously dimensioned with a resonance frequency being slightly higher than the frequency of the voltage to be transmitted by the contact line. Higher frequencies mean a less expensive resonance circuit and that the demagnetizing procedure will be accelerated, but the risk of only damping, i.e. no oscillation able to demagnetize the transformer, increases simultaneously. Moreover, the resonance circuit functions as a harmonic filter if the frequency is in the order of the frequency of the voltage which the contact line is intended to transmit.

Other advantages as well as advantageous features of the invention appear from the following description and the other de- pendent claims.

BRIEF DESCRIPTION OF THE DRAWING

With reference to the appended drawing, below follows a spe- cific description of a preferred embodiment of the invention cited as an example.

In the drawing:

Fig 1 is a very simplified schematic view of a plant for feeding electric power to a railway vehicle according to a preferred embodiment of the invention,

Fig 2 is a graph illustrating the development of the voltage across the resonance circuit in the embodiment in Fig 1 over the time when a railway vehicle is in contact with a dead element through the contact member thereof, and

Fig 3 is a view corresponding to Fig 1 of a plant for feeding electric power to a railway vehicle according to a further development of the embodiment according to Fig 1 .

DETAI LED DESCRIPTION OF A PREFERRED EMBODIMENT OF TH E I NVENTION

It is very schematically illustrated in Fig 1 how two different phases 1 , 2 of a public (general) three phase alternating voltage network, which may conduct an alternating voltage of for example 25 kV having a frequency of 50 Hz, may be connected to a contact line 3 for feeding electric power to railway vehicles 4. The two phases 1 , 2 are connected to a contact line portion 5, 6 each, which are electrically insulated with respect to each other by an interruption 7. The distance between the two contact line portions 5, 6 at the interruption 7 is bridged by an elongated element 8 being electrically conducting in the form of a short contact line section , which also has portions 9, 10 for overlapping the respective contact line portion on both sides of the interruption.

Furthermore, the plant comprises a resonance circuit 1 1 having a capacitance 12, an inductance 13 and a resistance 14, which is connected between the element 8 and the rail 15 onto which the vehicle 4 is intended to move. This resonance circuit has a resonance frequency in the same order as the frequency of the one phase alternating voltage on the respective contact line portion 5, 6, which may for example be 50 Hz or 60 Hz.

The railway vehicle 4, i.e. the engine, has in a conventional way a contact member 16 for contact with the contact line for trans- ferring electric power to the vehicle 4 and a so called main transformer 17 adapted to transform the voltage of the contact line down to a level suitable for the operation of an asynchronous motor 18 for driving the vehicle. The voltage of the secondary side of the main transformer 17 may for example be in the order of 300-600 V. The secondary side of the transformer 17 is connected to the entrance of a static converter 19, which in conventional way firstly rectifies the alternating voltage and then through a direct voltage intermediate link filtrates disturbances in the form of harmonics created by the conversions of the converter away, whereupon an inverter produces a three phase al- ternating voltage for the asynchronous motor 18.

The function of the plant according to the invention is as follows:

When the vehicle 4, which as seen in Fig 1 is assumed to move to the right, reaches the overlapping portion 9 of the element 8 the contact member 16, i.e. the voltage tapping member, will bear against both the contact line portion 5 and the overlapping portion 9 and thereby electrically connect these to each other, so that a voltage is applied to element 8. This will mean that the resonance circuit 1 1 is charged. When the contact member 16 then reaches the interruption at 20 and changes to only being in contact with the element 8 the connection of the contact member 16 and also of the element 8 to the feeding voltage disappears, and the resonance circuit 1 1 begins to be discharged according to a damped harmonic oscillation 21 as shown in Fig 2 while demagnetizing the transformer 17. The resonance circuit is then so dimensioned that it enables oscillations also at the highest conceivable load from the engine on the contact line, i.e. it may also then oscillate back and not only a damping is obtained, and the resistor 14 connected to ground ensures a minimum load, so that the oscillation has substantially tuned away before the engine leaves the interruption 7, i.e. arrives to the overlap located downstream at 22.

When the vehicle now with the contact member 16 thereof reaches the location 22 and enters into contact with the contact line through the contact line portion 6 again it does not matter in which phase position the alternating voltage on the contact line portion is located, since the transformer has been demagnetized and there is no risk for occurrence of saturation effects therein.

Should the railway vehicle come from the opposite direction the same will of course take place when passing the interruption 7.

A further development of the plant according to Fig 1 is illus- trated in Fig 3. Parts of this plant corresponding to parts in the plant according to Fig 1 have been provided with the same reference numerals. This plant differs from the one shown in Fig 1 by the arrangement of an additional overlapping portion 23 and 24, respectively in the form of an elongated element being elec- trically conducing on both sides of the interruption 7 along the respective contact line portion 5, 6. This additional overlapping portion extends along the contact line in the direction away from the interruption further than the overlapping portion arranged on the same side and belonging to the elongated element 8, which means that a railway vehicle 4 approaching the interruption will establish electric contact with this additional overlapping portion before electric contact is established with the overlapping portion in question of the element 8. The additional overlapping portions 23, 24 are through a resistor 25, 26 each connected to the resonance circuit 1 1 on the side thereof connected to the element 8.

The function of the plant according to the invention shown in Fig 3 will differ in the following way from the one shown in Fig 1 : We assume that the vehicle 4 as shown in Fig 3 approaches the interruption 7 from the left. When this with the contact member 16 thereof enters into contact with the additional overlapping portion 23 the resonance circuit 1 1 will be connected to the contact line portion 5 through the resistor 25. Thereby a charging of the resonance circuit 1 1 through this resistor begins so that the resonance circuit is at least partially charged when the contact member 16 reaches the element 8 and connects the resonance circuit 1 1 directly to the contact line portion. Thus, the arrangement of the resistors 25 and 26 results in a smoother charging of the resonance circuit 1 1 .

The invention is of course not in any way restricted to the preferred embodiment described above, but many possibilities to modifications thereof will be apparent to a man skilled in the art without departing from the basic idea of the invention as defined in the claims.

It is shown above how different phases 1 , 2 of a three phase alternating voltage network are connected, possibly through transformers, to different contact line portions, but as mentioned above the contact line portions may just as well be connected to one and the same one phase alternating voltage.

Claims

1 . A plant for feeding electric power to railway vehicles (4) having an alternating voltage contact line (3) adapted to be in con- tact with a contact member (16) of the vehicle for feeding current to the latter, said contact line having an interruption (7) on at least one location along the railway with two separate contact line portions (5, 6) located on both sides thereof and an elongated element (8) bridging the distance between these portions and adapted for bearing of the contact member of the vehicle thereagainst over the entire said distance and to normally be electrically insulated with respect to said contact line portions, said plant being intended to feed vehicles provided with a transformer (17) for transforming the voltage of the contact line to another level, characterized in that the elongated element is electrically conducting, that the plant comprises a resonance circuit (1 1 ) connected to the element and having at least a capacitance (12) and an inductance (13), that the element has portions (9, 10) overlapping the respective contact line portion and being adapted to be in contact with the contact member of the vehicle at the same time as the respective contact line portion for connecting the element to a voltage and charging the resonance circuit, and that the resonance circuit (1 1 ) is adapted to be discharged according to a damped harmonic oscillation for demagnetizing said transformer (17) when the contact member of the vehicle has left the contact with the contact line portion (5) located upstream of the element with respect to the direction of movement of the vehicle and only is in contact with the element (8).

2. A plant according to claim 1 , characterized in that it comprises two resistors (25, 26) connected to the side of the resonance circuit (1 1 ) connected to the elongated element (8) and means (23, 24) adapted to switch in the respective resistor through the contact member (16) of the vehicle between the respective contact line portion (5, 6) and the resonance circuit before the contact member enters into contact with the respective overlapping portion (9, 10) of the elongated element (8) when a vehicle (4) approaches the interruption (7) for at least partially charge the resonance circuit through the respective re- sistor before that happens.

3. A plant according to claim 2, characterized in that said means comprise two additional overlapping portions (23, 24) in the form of elongated conducting elements extending along the contact line portions (5, 6) on each side of the interruption (7) further away from the interruption than said overlapping portions (9, 10) and adapted to be in contact with the contact member of the vehicle at the same time as the respective contact line portion for applying a voltage to the respective additional overlap- ping portion (23, 24), and that the resistors (25, 26) connect the additional overlapping portions (23, 24) to the resonance circuit (1 1 ).

4. A plant according to any of claims 1 -3, characterized in that the resonance circuit (1 1 ) is dimensioned to enable at least two oscillations at said discharging thereof irrespectively of the magnitude of the load of the vehicle on the contact line (3).

5. A plant according to any of claims 1 -4, characterized in that the resonance circuit (1 1 ) has also at least one resistor (14) adapted to ensure a damping of the oscillation of the resonance circuit upon discharging thereof and substantial tuning away of this oscillation before the vehicle by the contact member (16) thereof reaches the contact line portion (6) located downstream as seen in the direction of movement of the vehicle.

6. A plant according to any of the preceding claims, characterized in that the resonance circuit (1 1 ) is dimensioned with a resonance frequency in the order of the frequency of the voltage intended to be transmitted by the contact line (3).

7. A plant according to any of the preceding claims, characterized in that the resonance circuit (1 1 ) is dimensioned with a resonance frequency being slightly higher than the frequency of the voltage intended to be transmitted by the contact line (3).

8. A plant according to any of the preceding claims, characterized in that the resonance circuit (1 1 ) connects the element (8) to ground.

9. A plant according to claim 8, characterized in that the resonance circuit (1 1 ) is adapted to connect the element (8) to the rail (15) on which the vehicle is intended to move.

10. A plant according to any of the preceding claims, charac- terized in that it is intended for feeding of vehicles having a said transformer (17) adapted to transform the voltage of the contact line down to a lower level on the secondary side.

1 1. A plant according to claim 10, characterized in that the contact line (3) is adapted to transmit an alternating voltage having an effective value between 6 and 50 kV.

12. A plant according to claim 10 or 1 1 , characterized in that the voltage of the secondary side of the transformer (17) is be- tween 300 and 600 V.

13. A plant according to any of the preceding claims, characterized in that said contact line is adapted to be fed with a voltage of one phase (1 , 2) of a three phase alternating voltage network.

14. A plant according to claim 13, characterized in that the two contact line portions (5, 6) located on each side of the element (8) are adapted to be fed with a voltage from different phases of a three phase alternating voltage network.

15. A plant according to claim 13 or 14, characterized in that the frequency of the alternating voltage of the contact line (3) is about 50 Hz or about 60 Hz.

16. A plant according to any of claims 1 -12, characterized in that the contact line (3) is adapted to be fed with a voltage from a one phase alternating voltage network.

17. A plant according to claim 16, characterized in that the fre- quency of the voltage of the contact line (3) is about 16 2/3 Hz or about 25 Hz.