Ansaldo STS’ track circuits

Ansaldo STS’ track circuits

Since deploying the world’s first AC track circuit in 1903, our commitment to product innovation remains unchanged. Today, Ansaldo STS and US&S’s track circuits have earned their place as technology standard throughout the world. No matter the rail network configuration, our extensive line of components provides dependable transmission of train detection data.

For territory with joint-less rail track circuits, the AF-800 Audio Frequency Train Detection and Wayside Cab SignalingSystemuses high frequency audio track carrier modulated at a low frequency track code rate to detect trains.

AF-900™ Series Digital FSK Track Circuit System
provides train detection and delivery of advanced train control data to moving vehicles, ideal for managing heavy mass transit traffic with close operating headway.

AF 1000 Track Circuit

AF 1000 W audio-frequency track circuits permit constant monitoring of track occupation to allow train movements in rapid mass transit systems to be managed in complete safety.
The special feature of these circuits is that they use only one pair of conductors for the connection to the electrical joint, with two different frequencies added together in the same pair (one transmission and one reception frequencies or two reception frequencies).

AF 1000 W track circuits also allow electronic equipment to be centralized in the stations, while the transmitter/ receiver units are installed along the trackside. This reduces the cost of both materials and maintenance work.

Application & Function

AF 1000 W audio-frequency track circuits do not require mechanical insulating joints (except at points) and can be implemented on both electrified (ac/dc) and non-electrified tracks.

A basic feature of AF 1000 W circuits is that they can have a central transmitter point and two receiver points. This makes it possible to:

treat the track circuit as two independent circuits using two distinct track relays (useful in sections with level crossing)
implement track circuits up to 1,400 m in length,

The shunt value is guaranteed for 0.25 Ω independently of: ballast conditions, length and configuration of the track circuit.

AF 1000 W track circuits are composed of a transmission system, way-side equipment and a receiver system.

AFO-IIC Track CircuitSystem
provides train detection for territories without insulated joint including dark territory and DC electrified LRT territories.

ATT-20 Audio Track Transceiver
an AF track circuit designed for 12-20 KHz, provides sharp block definition at highway crossings, island circuits, switch lock and release and for general train detection.

CI Impedance bonds for dc electrified lines

The present impedance bonds are non-resonating and non transformer type. They are used on d.c. electrified lines for carrying the traction return current to electrical substations, through the rails, in cases where a.c. type track circuits with isolating joints are used. A pair of impedance bonds are placed astride the insulating joints and are connected to the rails through the end terminals and between them through the mid-point of the respective windings.

The alternating currents feeding the two adjacent track circuits shall be confined in their respective track circuits, thanks to the high impedance encountered by the a.c. current towards the impedance bonds, while the d.c. return current will flow through the mid-point connection.Under these circumstances, each rail will carry one half of the traction return current. In cases when a difference between the two rails is verified, an unbalance is produced between the return currents that flow in the two rails and in the two halves of the impedance bond windings. This unbalance produces a drop in the impedance value of the impedance bonds. In order to avoid the unbalance to become excessive, thus introducing malfunctioning in th track circuits, and hence, in the signalling systems, a suitable air core is introduced in the iron core of the impedance bonds. New models 30/120/U and 50/220/U are standard versions for the Italian State Railways, conforming to their standards I.S. 416.

E-Code Coded Track Circuit System
is a powerful, cost effective solution that makes territory with ElectrodeTM coded track circuits compatible with the MicroLok® II Wayside Control System.

Hf 01 Audio-frequency circuit for short track sections

The HF01 is designed for use in superimposed short track circuit applications, to detect occupation of a short. clearly delimited section of track, e.g.:
superimposed short track circuits for level crossings
immobilization track circuits for switch points.

The HF01 is compatible with various types of existing ac, dc or pulse track circuits, does not require mechanical insulating points and can be used on ac and do electrified and non electrified lines.

Sections of track in the range 10 to 60 meters can be monitored. More than one track circuit can be implemented on the same track section by using different frequencies. Higher frequencies should be used where a more precise track occupation boundary localization is required ( 2 ¸ 10 m ).

MICROTRAX® Coded Track Circuit
programmable system controls wayside circuit applications in non-electrified territory. Track coding provides end-to-end rail integrity over long distances and operates over rail or line wire

Pulsat

PULSAT is a high voltage and high power coded pulse train detection system. The fundamental operating principle has stood the test of time. In this particular case, it is mainly based on the constant flow of high voltage, instant high power, polarized pulses emitted by a transmitter and detected by a receiver. Coded-current pulse track circuits can therefore be used for applications where particularly demanding services are required such as a high noise insensitivity, a considerable track circuit length and the elimination of problems deriving from a bad wheel/rail contact with an especially high resistance value due to rust or other causes.

Operation

PULSAT application is especially called for when, by the presence of insulating substances such as rust, traces of braking sand, grease or other, the wheel/rail contact assumes high initial resistance values; or in cases where the high speed of the trains in transit causes an accidental low wheel/rail adherence.

Pulse characteristics - high voltage (180 Vp max) and instant high power (2,500 Wp max) - are such as to guarantee that the insulation layer will be perforated, bringing the contact resistance value back to within correct operational limits.

The pulse repetition frequency (4 Hz) ensures that the power derived from the system's network is of a reduced value - 100 W max - while the pulse duration on the track guarantees that it won’t be dangerous to staff employed on it. Pulsat can monitor grom 18 meters of station track circuits to 2,000 meters of line track circuits.

This system can be applied equally to DC or AC electrified lines as it is sufficiently immune to the disturbance current deriving from the electric traction with chopper propulsion or pluriphase inverter. The polarized generation of the pulses permits instant and automatic checking of the insulating joints integrity. The presence of inverted polarity pulses (short-circuiting of joints) or breakage of the rail results in deenergization of the track relay.

Layout of Connections

The transmitter (feeding) and receiver boxes installed at the wayside allow the transmitter/receiver units to be installed far away from the monitored section, both of them in the same cabinet, together with other track circuit units, as well as other equipment. This arrangement can be used provided that the connection cable resistance between each single box and the relevant transmitter or receiver does not exceed the established value.

The cross section of cables must be selected according to their length. The cost of the system can be reduced by installing one transmitter only for the supply of more than one track circuit when they are of a limited length and the physical state of the track is not a hindrance to a good wheel/rail contact.

The PULSAT system can be applied to track circuits with single rail insulation, provided that both the length of the track circuit and the value of the return current (with either AC or DC traction) are compatible with the system's performance capabilities.

Configuration

Transmitter
It basically consists of a pulse generator circuit coupled to a code generator circuit which regulates the pulse emission frequency. By means of a step-up transformer, the pulses are sent, through the power supply box, to the track circuit in order to be monitored.

Receiver
It consists of an acceptance and threshold circuit system which constantly verifies the signal, in particular, the polarity and the ratio between the pulse's positive and negative amplitude. A delayed pick-up timer circuit and a signal amplifier circuit for relay control complete the receiver. The transmitter and the receiver are housed in plug-in boxes made of high quality plastic. Assembly on panels or frames is achieved by means of mounting bases, and electrical connections are achieved with plug-in connectors.
Coupling Boxes
The receiver and feeding boxes house matching transformer to the track, adjustment resistors for the calibration of the cable resistance values and wayside protection arrestors. The cases are made of aluminum alloy and painted against atmospheric elements.
Track Relays
Neutral type relays meeting the UIC, AAR, BS, and FS standards, with coil resistance values greater than or equal to 350 ohms can be used.


Single-Rail and Double-Rail Power Frequency Track Circuits
provide dependable train detection. Robust design and reliable components carry traction return and track signaling current on either single or double rail configurations.

SOLARTRACK Solar energy powered track circuits
Solartrack track circuits are powered using electricity generated by photovoltaic panels. Systems of this type are essential for lines where laying and maintaining track circuit power supply cables is considered too expensive.
Solartrack is particularly suited to track circuits in stations or other limited length applications.

UM 71 Track Circuit

An essential component of railway safety, the track circuit detects the presence or absence of any vehicle on a given stretch of track.

Jointless track circuits avoid the mechanical cutting of rails, the traditional insulating joints being replaced by tuned circuits.



UM 71 product line allows the use of jointless track circuits under a variety of conditions.
Non-electrified track
DC or AC electrified track with the traction current return circuit through both rails
version adapted to the “ cab-signal “ function
Operation

An UM 71 track circuit is generally terminated at each end by an electrical joint to a transmitter or receiver via a matching unit (Tad). An insulating joint may also be used in place of the electrical joint at each end or at both ends of the track circuit.

The length of track included in the electrical joint is terminated at each end by a tuning unit (BA) or (BU). Each tuning unit consists of an inductor and capacitors for obtaining:
parallel resonance with the track inductance (impedance pole) at the frequency of the involved track circuit
serial resonance at the frequency of the adjacent track circuit
This serial circuit shunts the track, thereby preventing propagation of the signal beyond the limits of the track circuit. A track air-core inductor connected (SVa or SVac) to the mid-point of the electrical joint optimizes performance and balances the return traction current between the two rails.

Ansaldo STS technology increases the maximum length of UM 71 track circuits. It consists in improving transmission along the track by connecting capacitors of appropriate values between the two rails and buried in the ballast at given intervals.

Since 1980, compensated UM 71 track circuits installed by the SNCF have proven their excellent reliability over thousands of kilometers of track.

The whole range of UM 71 track circuit complies with the EN 50121-4 standard

References

More than 30,000 track circuits in service throughout the world: Algeria, Australia, Argentina, Belgium, China, France, Korea, Morocco.