Track circuits are railway safety installations, with an automatic and permanent operation, their basic function is to inform about the “free” or “busy” state of the insulated railway sections. This function is based on the fact that the wheels – axle assemblies of the stationary or moving rolling stock have a very low ohmic resistance (under 0.01 ohm) between the contact areas with the roller tracks. For each track circuit with operating current, there exist’s one or several stationary or moving axles, being in firm electric contact with the railway tracks of the insulated sections (controlled by means of voltage level) does no longer allow the transfer of electric power from one of the (emission) extremities to the other extremity of the reception track circuit (that may be singular or multiple), as a result of the achieved ohmic shunt effect.
Track circuits are railway safety installations, with an automatic and permanent operation, their basic function is to inform about the “free” or “busy” state of the insulated railway sections. This function is based on the fact that the wheels – axle assemblies of the stationary or moving rolling stock have a very low ohmic resistance (under 0.01 ohm) between the contact areas with the roller tracks. For each track circuit with operating current, there exist’s one or several stationary or moving axles, being in firm electric contact with the railway tracks of the insulated sections (controlled by means of voltage level) does no longer allow the transfer of electric power from one of the (emission) extremities to the other extremity of the reception track circuit (that may be singular or multiple), as a result of the achieved ohmic shunt effect.
The C4-64-type track circuits can operate on the non-electrified sections of the Infrastructure,generally with steam or diesel traction, as well as on 25 Kv/50Hz electric traction sections, using both the station line as well as the running line, this can be with any kind of rail and with any type of connections. The maximum length of the insulated sections is 2,500m in the bifilar usage variant and 1,100m in the unifilar usage variant, with a maximum speed of train traffic of up to 200 Km/h. They may adjacently operate with other types of track circuits provided they are separated from these by using separation joint coils. For the busy state of the C4-64 insulated sections, the equipment must furnish the “busy” information when a standardized 0.06 Ω shunt is applied from any point of the controlled track circuit.
The „C-4-64”-type track circuits operate continuously, with 75 Hz Alternating Current impulses, numerically codified in four sequences. The insulated railway sections that are controlled by means of voltage level, are separated by insulating joints for delimitation and informational protection.
The apparatus specific to these track circuits is mounted in:
•the relay room; • the stakes on the ground; • the apparatus cabinets placed on the ground.
The EEC 4-64 electronic code transmitter,
• the TIS 4 and/or TIS 2 synchronisation impulses transmitter; • the BDEF-4-type electronic decodifying blocks; • the ASA 4 and ASA 5 supply surveillance adaptors; • the PIC 1 or IMVS-type impulses relays;• the CS16 or CS10 static power relay switches; • as well as the B-75 Hz-type track filters; • the C-type track relays are mounted in the Electrodynamic Interlocking Installation relay room of the station.
The following are mounted in the stakes on the ground:
• the D or L-type power and regulating transformers; • the MCC-3 or LIC 3-type current limiters ;• the 2.2 Ohms adjustable rezistors; • the CFR-type fuse plugs;• as well as the condensers required for compensating the line’s inductive effect and for the extra protection against track power surges.
Both sets of equipment for the local deco-dification of reception-impulses and equipment for generating emission – impulses, as well as subassemblies specific to the C4-64 track circuits required for the operation of the equipment on the running line may be provided in the apparatus cabinets that are placed on the ground. BP4E-type protection – emission blocks and BP4R-type protection – reception blocks are also mounted in apparatus cabinets. They have the role to decodify the ±120 V distant synchronization sequences used on the running line.
The transfer of impulses to the railway tracks is made by means of the BJ-250-type joint coils, these are placed at each bifilar reception.
The C4-64 track circuits equipment is power supplied from the electrodynamic interlocking installation’s own network, at an alternating voltage with a rated value of 220V and a rated frequency of 75 Hz. The EEC4-64-type code electronic transmitter subassembly is unique for the C4-64 track circuits equipment these correspond to a station and the adjacent running lines. The line sequences are transmitted to each power supply at the end of the insulated sections in the station according to an allocation plan, that is set up by design. This is made by means of the CS16 or CS10-type static relay switches. The sequences’ distribution is made depending on the requirements, so as to ensure the informational protection between the track circuits corresponding to the neighbouring adjacent or parallel insulated sections.
The interconnection of the indoor equipment with the outdoor ones is provided by both power and signalling cables. The links between the joint coils and the stakes are made by means of ropes and their own fastening systems, these are protected by the conductors, which should have a maximum total resistance of 0.5 Ω.
The composition of the C4-64 equipment is made so that any flaws of the component, by interruption or short-circuiting, should result in the de-energization of the C-type relay. It is also protected against the influence of any disturbing electrical signals that are likely to come from the neighbouring track circuits, from the 50 Hz traction current or from other disturbing sources regardless of their frequency. Also under disturbing conditions, the amplitude of the voltage that occurs at the output of the B-type track filter is in continuous rating or in impulses that are under 2 V.On the Romanian railways network, the C4-64 track circuits have been implemented on numerous traffic sections and this also incorporates the associated stations such as:
• Bucharest – Constanta,
• Cluj – Oradea,
• Bucharest – Brasov,
• Galati – Tecuci,
as well as in many other stations:
• Arad, Timisoara, Brasov, Simeria, Drobeta Turnu-Severin, Constanta – Palas, the Bucharest Complex.
The average time for the operating condition of the equipment is 90,000 h > 10 years. The manufacturer ISAF S.A. guarantees the C4-64 equipment for 3 years after their delivery.
ISAF S.A. have been manufacturing the C4-64 track circuit equipment for over 20 years, having a strong and established background in this field.
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