GB2100902A - A static track relay system - Google Patents

Abstract

The system includes circuitry for controlling the output from a 20 KHz generator (14) to an electromechanical relay (13), as a function of the voltage, frequency and phase correlations of the track signal with the local reference signal. The circuitry basically consists of a phase comparator (31) for the controlled feeding of generator (14) on condition that any deviation of the track signal frequency and phase from the local reference signal be within pre-set values. The phase comparator (31) preferably controls the 20 kHz generator (14) through a first magnetic threshold, or magnetic AND gate (30), depending upon the track signal which is supplied through a 50 Kz semi- active filter (21) which delivers an alternating output current of a constant amplitude and or a frequency which is equal to the track signal. The output from the 20 kHz generator (14) to the final electro- mechanical relay (13) is preferably applied via a second magnetic AND threshold (101) which determines, along with the final relay itself, the energizing and de-energizing levels of this relay. <IMAGE>

Description

SPECIFICATION A static track relay The present invention relates to a track circuit block system for a railway system, and more particuiarly it has for its object a static track relay fed with alternate current.

The object of the invention is to provide an apparatus which is adapted for replacing the vane relay fed with alternate current which is presently used in railway systems for reliably detecting the presence of a train on a track section.

In fact, as it is known, the vane relay not only requires a periodic servicing, but is also sensitive to any noise (disturbance) frequency in the range of from 35Hz to 70Hz, with an increasing noise (disturbance) amplitude as the deviation from the normal 50Hz operation frequency is increasing.

Incidentally, it should be noted that the fundamental frequency of the traction choppers is set to 32.5Hz, that the auxiliary services of the locomotives and the carriages operate at 50Hz, and that any noise (disturbance) frequency is also affected by the filters on board of a train, the inductance and the capacity of the catenary-track system, and the sub-station filters.

The presently used vane relay (also called "disk relay") has a torque KlLlc sine, where 1L is a local current generated in the interior the cab by a 80V-50Hz voltage in phase with the 1 50V voltage supplying the track circuits, while Ic is the current produced by the voltage returning to the track, the so-called "track voltage". This voltage is leading of about 900 with respect to the local voltage, whereby it is obtained the maximum of the torque which is adapted for energizing the free track circuit relay.

The ratio L/R is the same for both of the windings of the relay. For the track circuits with only one stretch of insulated rails, the phase displacement is obtained in the conventional installations through a condenser located behind the relay counterplate and to a much lesser degree through the track, which is an electric line with distributed electric elements.

In the automatic block installations (track circuits in which both of the rail stretches are insulated) the phase displacement is obtained through the same inductive connections.

A drawback and a disadvantage of the vane relay (disk relay) reside in the fact that in the arc from 0 to 1 800 the torque is also dependent from the amplitude of the track voltage. The fact that in the arc from 1800 to 3600 the torque becomes negative is instead a sure advantage, since it produces an electric downward return of the vane.

A noise frequency fd ranging between 35Hz and 70Hz, and of a suitable amplitude, admitted on the track circuit, will therefore bring on beats at a frequency that derives from the combination of the 50Hz noise frequency fd with the frequency of the mechanical resonance of the vane.

The static track relay fed with alternate current, forming the object of the present invention, provides the following properties and advantages: a) a lower sensitivity to any noise frequency, as compared to the vane relay; b) "the phase transmission band", that is to say, the temporal phase difference of the track voltage with respect to the local voltage (Vc and VL, respectively), within which the regular operation takes place, has a value from 300 to 350, expressed in electric'degrees, or a higher value, whenever the variation that the ballast conditions determine on 0 becomes an appreciable variation.

The said narrowing of the phase transmission band becomes necessary also due to the fact that the relay fed with direct current, which is present in the apparatus as the final part, becomes deenergized owing only to gravity, and does not have a negative return torque.

The said relay moreover has another disadvantage, with respect to the vane relay: its de-energizing ratio is not higher than 0.6; whereas it is known.lhat a track circuit requires for a satisfactory shunt a ratio > 0.65. Hence the characteristic feature c) of the apparatus, as defined hereinbelow: c) a decrease of the hysteresis of the final part, and a shunt improvement.

In order to achieve such a performance, of the apparatus, two magnetic thresholds are used, the characteristic features and advantages of which will become clearly apparent in the following detailed description of the invention, may by way of a non-limiting example and with reference to the accompanying drawings.

Figure 1 shows the electric circuit of the static relay fed with alternating current, according to the invention; Figure 2 is a diagrammatic view of the operational arrangement of the magnetic threshold which is used in the wiring diagram shown in Figure 1; Figure 3 is a detailed view of the wiring diagram of the 20kHz generator which is used in the static relay shown in Figure 1; Figure 4 is a detailed view showing the arrangement of 50kHz semi-active filter which is used in the static relay shown in Figure 1; and Figure 5 shows in diagrammatic form the control signals in the static relay of Figure 1.

As an introduction to the detailed analysis of the static relay shown in Figure 1, the magnetic threshold shown in Figure 2 will be first broadly considered here.

When examining Figure 2, it appears that in the magnetic threshold 101, the permanent magnet 2 saturates the output transformer 3, since owing to the presence of the air gap 5, the flux of the permanent magnet 2 cannot get through the core 104 of the electromagnet 4.

Whenever through the electromagnet 4 there flows a current of such a sense as to produce a reverse magnetic polarity with respect to the polarity of the permanent magnet 2, and of such an intensity as to branch a portion of said magnet flux, the output transformer 3 commences to become released, thus enabling the flowing of a small quantity of energy between the primary 103 and the secondary 203.

As the current of the electromagnet 4 is increasing, the energy transmitted on the output 203 of transformer 3 increases, until at a given value of the control current through the winding 204 of electromagnet 4, the transformer 3 is completely de-saturated, and all the energy available at the input frequency (actually, 20kHz) is sent forth on output 203.

With control currents being higher than another value, it will be electromagnet 4 that starts to saturate the core of transformer 3 and, as a consequence, the energy sent forth to the output of the secondary 203 will be still more decreased.

The slope of the characteristic curve of the magnetic threshold 101, that is to say, of the curve that expresses the power transmitted by the transformer 3 as a function of the current for energizing the electromagnet 4, is substantially dependent from the intensity of the flux of the permanent magnet 2, and from the width of the air gap 5.

With regard to the reliability of its intervention, the magnetic threshold 101 exhibits the following features: 1) The change in the performance of the permanent magnet 2, along with a variation of temperature, is small, and the probability that it might become demagnetized is excluded, since it is "re-energized" every time through the electromagnet 4 there flows the current which is required for the operation of the apparatus.

2) The output transformer 3 has two ferrite cores 303, 403, which are set apart from each other. The primary winding is divided into two halves 6 and 7, which are wound in opposite directions, the one on the core 303, and the other on the core 403. The secondary winding similarly presents two halves 8 and 9 which are wound in opposite directions on the core 303 and on the core 403, respectively.

In default of energy to the primary winding 6, 7, any variation of the flux through the transformer 3, which is promoted by alternating currents flowing through the winding 204 of electromagnet 4, does therefore not produce any output signals on the secondary 203.

When for the transmission of energy a fairly high frequency is adopted, such as for example a frequency of 20kHz, the magnetic threshold 101 will be of a quite reduced size.

To recapitulate, a magnetic threshold affords the two following main characteristic features: 1) if there is a signal on the secondary 203 of the output transformer 3, this means that both a signal to the primary 103, and a signal on the control electromagnet 4 are simultaneously present. The threshold therefore acts like a logic circuit of the magnetic AND-gate type. 2) The transmission of energy on the output 203 starts only at a given, well defined and reliable value, different from zero, of the control current through the electromagnet 4, more precisely, through its excitation winding 204. Also the slope of the characteristic curve, apart from the slight deflexions due to temperature, is univocally defined.

This permitted as regards the magnetic threshold 101, we come now to describe the static relay fed with alternate current, according to the invention, by generally referring to the electric circuit shown in Figure 1.

From the track circuit 10, the track voltage Vc is applied to the primary of the reception transformer 11, the secondary of which feeds the magnetic threshold 101 through the rectifier 12.

The magnetic threshold 101, together with the final relay 13, determines the energizing and deenergizing levels of this relay, and permits the increase of the de-energizing ratio thereof.

When the quantity of energy taken in by a relay fed with direct current, and the condition of the highest transfer from the generator to the load are known, the optimum values are determined for the resistance R1, which is needed in order to prevent the short circuit of the 20kHz generator 14, and for the ratio of the turns in the output transformer 3.

Thus, it is possible to make the permanent magnet 2 of such a size that it can be neutralized by a power on the electromagnet 4 that in the worst conditions of ballast, is thought to be not higher than half a watt.

The 20kHz generator 14 is shown in detail in Figure 3 of the accompanying drawings.

Referring to this Figure, the generator 14 consists of the two sections in series 11 4 and 214.

The second 114 operates at signal level and is fed only when the track voltage has a frequency and a phase within the desired values. This is the basic principle of the apparatus.

The section 214 of the generator is formed by a 20kHz selective amplifier with no selfoscillations, since it is tuned only on the collector, and by four transistors 1 6, 17, and 18, 19 which supply only the required current.

The 20kHz filter designated by the reference numeral 20, is needed for controlling the frequency generated in section 114. In fact, the voltage on the secondary of the output transformer 3 of the magnetic threshold 101 would increase when, due to the breakdown, the generated frequency should increase, with adverse results as regards a safe operation.

Simultaneously, the track voltage Vc is sent to the semi-active 50Hz filter designated by the reference numeral 21, through a step-down transformer 22 which on the primary has a capacitor 23 acting as phase regulator, since it leads the track voltage Vc with respect to the local voltage VL.

The photocoupler 24 comprises a photodiode 1 24 which is fed from the output of transformer 22, while its light energizes a photoelectric transistor 224 which supplies an alternate current of a constant amplitude and of a frequency which is equal to the frequency of the alternate input current.

With such a coupler, in order to obtain an efficient filtering, only one cell L, C (25, 26), Figure 4, is sufficient, where the coil needs obviously to have a high figure of merit Q=1 5+20. A filter consisting of two cells, one in series and the other in parallel, although affording the advantage of a higher selectivity and of a better wave-form, would however guarantee a lesser degree of safety due to the fact that, since it must not supply an appreciable amount of active energy, any possible decrease of one of the capacities should not prevent the operation of the apparatus, and should generate a double-tuned filter, with an uncontrolled widening of the filter pass band as a whole.

The output voltage from the 50Hz filter designated by 21 is leading with respect to the input voltage, and this output voltage controls a transistor 27 acting as a switch, and thus producing in correspondence of the positive and negative fronts of the square wave existing at the terminals of resistance 28, a series of very shortlasting pulses on the output transformer 29 of the magnetic threshold 30 of the phase comparator which is for checking the phase correlation between the track voltage V0 and the local voltage V,.

The result is the generation of pulses at the zero level of the track voltage Vc, and these pulses, which are amplified by transistor 131 , will be conveyed to feed the first section 114 of the 20kHz generator 14, however on condition that they are produced, for example, not before 5 milliseconds and not after 7 milliseconds from the starting of the local voltage V, negative halfwave.

Owing to the pulse amplification, only the positive pulses are important. Thus, a definite restraint is created on the phase of both voltage and with the above data, there is a time lag of 2ms, corresponding to a "phase transmission band" of about 360.

Therefore, the final relay 1 3 will be energized only when the track voltage V0 is leading, with respect to the local voltage VL, by an angle ranging, for example, between 1000 and 640, or between 900 and 540, or else between other intervals of a same width, depending upon the particular moment of time in which the time lag is created, that is to say, the threshold is released.

The control circuit 31 of the electromagnet 32 for driving the magnetic threshold 30 will be now examined. In this circuit, the part which serves for triggering the silicon controlled rectifier (SCR) 33 has the property of supplying only one positive pulse to the interior of the negative halfwave of the local voltage VL.

In fact, during the positive half-wave, the transistor 34 is saturated, and the voltage Ve at the terminals of the local condenser Cl is at zero level, whereas during the negative half-wave, the transistor 34 is cut off, and the local condenser Cl can be charged through the resistances 35 and 36.

Whenever the voltage Vci at the terminals of the local condenser Cl is equal to the addition of the voltage Vz of the Zener diode 37 to the baseemitter voltage Vbe of transistor 38, this transistor comes to be saturated, and generates a positive pulse on the secondary 139 of the transformer 39 for turning on the silicon controlled rectifier 33.

This rectifier thus enters into its conductive state, so that a direct current flows through the load resistance 40. The previously charged threshold condenser 41 can now be discharged through the winding 132 of threshold 32 and through the rectifier 33, while it can be charged in the opposite direction, owing to the circuit L-C and the separation from the ground of the base of the controlled rectifier 33.

The threshold current is now tends to flow in the direction which is opposite to the preceding one and to the undirectional current of load 40.

When these two currents are balanced, the silicon controlled rectifier 33 is turned out, and the threshold capacity 41 is charged through the load resistance 40, according to the exponential law.

Typically, the positive half-cycle of the threhsold current 1S is of about 2ms.

Insofar as safety is concerned, it is believed that a safe operation is required only for the circuit for turning out the controlled rectifier 33, and not for the trigger circuit.

In fact, it is sufficient that the time lag produced by the half-oscillation of the unit LC (132, 41) connected in parallel to the silicon controlled rectifier 33, does not grow longer, and it is known that the reactive elements can only decrease.

The continuous feeding of the silicon controlled rectifier 33 cannot in any way effect the threshold which is released by a current of the reverse sense. When due to the breakdown of any component of rectifier 33, ail the alternating voltage of the network should flow through the unit R2mLCs (40, 132, 41), the flowing current would be quite insufficient, owing to the resistance 40 and the impedance of unit LCs, to release the threshold. The failure of the other components of the apparatus can be easily conceived. The increase or decrease of the local voltage brings about very small effects, since the duration of the half-oscillation is not dependent from the said voltage.

The said voltage is however selected of such a value that sufficiently steep pulses of Ig are generatwed, whereby the threshold is promptly and fully released.

If a transformer should be used to replace the whole unit for generation of the local comparator pulse, its performance during the positive alternating current half-wave, would be definitely of an inferior quality and could be also much more influenced by the amplitude of the local voltage Vt, owing to the trigger characteristic of the notsteep threshold.

As to the circuit for triggering the silicon controlled rectifier 33, the variation of the latching voltage of the Zener diodes 37, 42 or a change in the time constant R-C(40, 41) will have the only result of shifting the particular moment in which the silicon controlled rectifier 33 is turned on; as already pointed out, this is not detrimental to safety since with a relay fed with direct current the fact of creating the phase time lag of about 5ms (1/4 of a period) from the starting of the negative voltage of the local voltage V1, may be deemed merely discretional.

In order to increase the safety of the system, a condenser CA (43) with four terminals on the 24V DC power supply may be provided, so that the ripple is not allowed to promote in any way the infeed (possibly a negative infeed) of the generator, due to a short circuit of transistor 131 (Q3).

The sequence of the threshold signals is evident from the diagram shown in Figure 5.

Of course the invention is not limited to the embodiment just described and shown by way of example, but can be widely changed and modified, the more so in connection with the various requirements of each single case in the art, without however departing from the widest limits of the leading principle of the invention, as set forth hereinabove, and as claimed hereinafter.

Claims (20)

Claims

1. A static track relay fed with alternate current, for the driving of a final electromagnetical relay which is set through a 20kHz controlled generator, characterized in that it comprises an apparatus in form of a circuitry for controlling the output from said generator as a function of the track signal and of its voltage-frequency-and phase-correlations with the local reference signal, the said apparatus basically consisting of a phase comparator circuit for driving the said generator, according to the condition that any deflexion of the track signal frequency and phase from the reference signal be within pre-set values.

2. A static track relay fed with alternate current, according to Claim 1 , for the driving of a final electromechanical relay within pre-set frequency and phase values of the track signal with respect to the reference signal, characterized in that the said phase comparator controls the said 20kHz generator through a first magnetic threshold, or magnetic AND gate, according to the track signal which is supplied through a semiactive 50Hz filter with its output delivering an alternate current of a constant amplitude and of a frequency which is equal to the frequency of the track signal.

3. A static track relay fed with alternate current, for the conditional driving of a final electromechanical relay within pre-set frequency and phase values of the track signal with respect to the reference signal, according to the preceding Claim 2, characterized in that the output from the said 20kHz generator to the said final electromechanical relay is conditioned by a second magnetic AND threshold, the said threshold, together with the final relay itself, determining the energizing and de-energizing levels of this relay, and therefore the correlative, commensurate increase of the de-energizing ratio.

4. A static track relay fed with alternate current, according to the preceding Claim 3, characterized in that the said phase comparator which is operatively associated with the correlative semiactive filter of the track signal, lowers the static relay sensitivity to any noise frequency down to a level which is below the level of the vane (disk) relay, this being achieved by locating the operating range of the static relay within a frequency response band not wider than 1 OHz, more precisely within the band of 50Hz + 5Hz.

5. A static track relay fed with alternate current, according to the preceding Claim 3, characterized in that each of the said magnetic thresholds, or magnetic AND gates, comprises a permanent magnet to which an output transformer and a driving electromagnet with an air gap are magnetically connected, the said permanent magnet normally saturating the transformer, while a gradual driving of the electromagnet, which is discordant with respect to said permanent magnet, progressively releases the transformer up to a maximum degree of transfer of energy, and therefore up to a possible latching of same in the reverse sense, which leads to the result of a decrease in the hysteresis of the final electromechanical relay, and a consequent shunt improvement, which is normally obtainable only with a de-energizing ratio not lower than 0.65, as against a de-energizing ratio of the normal relay not higher than 0.60.

6. A static track relay fed with alternate current, according to the preceding Claim 1, characterized in that for the same a phase pass or transmission band is provided, for example within the said interval of from 300 to 350, which is sufficiently narrow for counterbalancing the deenergization due only to gravity, without any negative return torque, of the electromechanical relay included in the apparatus as the final part thereof.

7. A static track relay fed with alternate current, according to the preceding Claim 3, characterized in that in each magnetic threshold thereof, the output transformer comprises two ferrite cores which are magnetically separated from each other, the primary and the secondary of said transformer being wound in opposite directions, for one half on the said first core, and for the other half on the said second core, so that in default of input energy to the primary of the said transformer, any flux variation in the transformer cores, which is produced by alternating current flowing through the driving electromagnet, does not generate any output signal on the secondary of the transformer.

8. A static track relay fed with alternate current, according to the preceding Claim 3, characterized in that in each magnetic threshold, or magnetic AND gate, included in said relay, an output signal to the secondary of the correlative transformer is generated whenever a signal to be supplied to the primary of the transformer and a control signal on the associated driving electromagnet are simultaneously present, the transfer of energy to the output of said transformer being started only at a well defined and sure value, different from zero, of the control current, while the slope of the characteristic curve of the threshold is univocally defined, apart from any slight deflexion due to any temperature variation.

9. A static track relay fed with alternate current according to the preceding Claim 1, characterized in that a high frequency generator, more particularly a 20kHz generator, is provided for supplying the final electromechanical relay through the magnetic threshold, whereby a correlative and commensurate reduction in the proportioning of the threshold components is achieved.

10. A static track relay fed with alternate current, according to the preceding Claim 9, characterized in that the said 20kHz generator comprises a first section acting as a signal, and a second selective amplifier section, the said first section being driven by the local signal through the said phase comparator and the associated magnetic threshold which is controlled by the track signal through the said semi-active filter, this filter being associated to a phase regulator condenser, so that the said section acting as a signal is fed only when the said track signal, with respect to the local reference signal, has a frequency and a phase within the desired preset values.

11. A static track relay fed with alternate current, according to the preceding Claim 10, characterized in that the said second section of the 20kHz generator is formed by a selective amplifier with a 20kHz tuning filter, the said amplifier being tuned on the collector, whereby any self-oscillation is avoided, the said 20kHz tuning filter being provided for controlling the frequency generate by the said first section of the generator, in order to prevent any improper voltage increase on the magnetic threshold output transformer, as a consequence of any abnormal increase in the frequency of the generator itself.

1 2. A static track relay fed with alternate current, according to the preceding Claim 2, characterized in that the said 50Hz semi-active filter receives the track voltage through a stepdown transformer and a capacity for regulating the phase of the track signal with respect to the reference signal, the said semi-active filter comprising a photocoupling transducer, which supplies an alternate current of a constant amplitude and of a frequency which is equal to the frequency of the alternate input current to a filter having one single cell L C, with a coil having a high figure of merit (0=1 5+20).

1 3. A static track relay fed with alternate current, according to Claim 12, characterized in that the output from the said 50Hz semi-active filter, which is leading with respect to the input voltage, is sent to control a transistor switch of the DC power supply for said 50Hz generator, through the output transformer of the said phase comparator magnetic threshold, subordinatively to the consent lag of the comparator, which drives the electromagnet for controlling the magnetic threshold.

14. A static track relay fed with alternate current, according to Claim 13, characterized in that the said pulses on the output transformer of the magnetic threshold between the 50Hz semiactive filter and the phase comparator, are generated at the zero level of the track voltage and are directed to drive the power supply for the said first section of the 20kHz generator, the comparator setting the condition that the said pulses fall within a predetermined time interval of the local voltage period, such as for example a time interval ranging from 5ms before the starting, to 7ms after the starting of the negative half-wave of said local voltage, and with such an interval there being time lag of 2ms, corresponding to a "phase transmission band" of about 360.

1 5. A static track relay fed with alternate current, according to Claim 14, characterized in that with a given correlation of the components of the said phase comparator, the final electromechanical relay will be energized only when the track voltage is leading, with respect td the local voltage, by an angle ranging between 1000 and 640, or between 900 and 540, or else between other intervals of a same width, depending upon the particular moment of time in which the time lag is started, that is to say, the magnetic threshold is released.

1 6. A static track relay fed with alternate current, according to the preceding Claim 1, characterized in that the said phase comparator comprises a silicon controlled rectifier circuit which through a transformer with multiple secondary winding is fed by the 80V, 50Hz local voltage, the said rectifier supplying only one positive pulse to the interior of the local voltage negative halfwave, the said pulse output being obtained by means of a transistor switch driven by the alternating charge and dishcarge of a local signal condenser.

1 7. A static track relay fed with alternate current, according to the preceding Claim 16, characterized in that in the said phase comparator circuit, whenever the voltage at the terminals of the local condenser is equal to the addition of the voltage of the Zener diode to the base-emitter driving voltage of a latching transistor, this transistor comes to be saturated, thus generating a positive pulse on the secondary winding of the transformer for turning on the silicon controlled rectifier, which enters into its conductive state and causes a current to flow through the correlative charge resistance, whereby it enables the series-connected condenser discharge towards the winding of the threshold-controlling electromagnet and through the silicon controlled rectifier, the said condenser being finally charged in the reverse sense, owing to the inductance and L C capacity branch, and to the separation from ground of the silicon controlled rectifier itself.

1 8. A static track relay fed with alternate current provided with two magnetic thresholds, or magnetic AND gates, and with a voltage comparator for a "phase transmission band" operation, the whole or in part substantially as shown, as described, and for the aforementioned purposes.

19. A static track relay system comprising input means for receiving a track signal having a first incoming frequency; comparator means for comparing the frequency and phase of the incoming track signal with a reference signal to produce a control signal when substantial identity is determined; and frequency generator means dependent on said control signal for generating a second signal of different frequency to said first frequency for driving the relay.

20. A system as claimed in Claim 1, wherein additional control means are provided for controlling the passage of the relay drive signal to the relay in dependence on the signal received from the track.