The situation when the controller’s scoreboard or the station duty desk lights up a red signal of the site’s employment, although in reality the rail space is free, is one of the most stressful for railway workers. This phenomenon is known as false-employmentIt instantly paralyzes traffic or requires transfer to telephone communication, which significantly reduces the throughput of the highway. A driver who has received permission to follow may face an unexpected stop before a closed traffic light, which disrupts the schedule and creates an emergency situation.
The nature of such failures lies in the complex interaction of electric circuits, weather conditions and the technical condition of the rolling stock. Rail chainThe main element of autolocking works on the principle of track integrity control: as long as the current flows from the source to the receiver through the rails, the section is considered free. Any factor causing rail filament bypass or circuit break is interpreted by system logic as the presence of a train, even if it is just a fallen branch, snow porridge or insulation defect.
It is important for the specialist to understand that ignoring the primary signs of false employment can lead to more serious consequences, including false inclusion of routes or, conversely, the inability to build them. In this article, we will analyze in detail the physical and technical prerequisites for the occurrence of anomalies in the operation of alarm, centralization and locking systems (SCB), as well as algorithms for the prompt restoration of normal traffic mode.
Physics of the process: how the rail circuit works
The basis of any automatic locking system is rail-chain. The principle of its operation is based on the transmission of electric current of a certain frequency and voltage along rail threads. At one end of the plot is installed power supply, and at the other - track relay. When the path is free, the current passes unimpeded through the joints and reaches the relay winding, keeping it in an elevated state, which signals the freedom of the site.
When the train enters the section of the wheel and the axles of the carts close the rail threads between themselves, creating the so-called "Wheel" shunting. The resistance of the wheel pair is much lower than the resistance of the track relay winding, so the main current goes through the wheels, without reaching the receiver. The relay releases the anchor, and at the traffic lights a prohibitive signal is lit. False employment occurs when this mechanism works without the actual presence of rolling stock.
The critical parameter here is ballast. Under ideal conditions, the current should flow only on the rails. However, if a conductive medium appears between the rails (water, dirt, metal debris), some of the current begins to go to the ground or flow between the threads, without reaching the receiver. If this leak current becomes too large, the voltage on the relay falls below the release threshold and the system records the occupancy.
⚠️ Note: Operation of rail circuits in conditions of high humidity or ballast pollution requires special control of insulation parameters. Exceeding the permissible leakage currents can lead to unstable alarm operation even with proper equipment.
It is worth noting that modern systems use tonal rail circuits that are less susceptible to traction current and interference, but the physics of bypassing remains unchanged. Any extraneous connection of rail threads with a resistance below the normative (usually 0.06 Ohms for shunt sensitivity) causes the protection to actuate.
External factors and environmental impacts
The most common cause of automation failures is climatic conditions. Rain, snowfall, snow melting or extreme heat can drastically change the electrical characteristics of the path. For example, when there is heavy rainfall ballast It decreases sharply, which leads to an increase in leakage currents. In such conditions, even a serviceable rail chain can turn into a state of employment.
In winter, the problem is created by snow porridge and anti-icing reagents. A mixture of snow, salt and dirt, stuffed into the subrail space, creates excellent conditions for current flow. The situation is especially critical in places of switches, where pollution occurs more intensely due to the mechanical impact of moving parts.
In summer, the main threat is high temperature, causing thermal expansion of the rails. This can lead to a change in gaps in the joints or, conversely, to the occurrence of compressive stresses that affect the contacts. Also in dry weather, the accumulation of static electricity or dust on insulators is possible.
Influence of vegetation on the work of the SSC
Sprawling grass and shrubs, touching rails or insulating joints, can create additional ways of leaking current. It is especially dangerous when wet vegetation connects the sole of the rail to the ground or a neighboring thread. Regular cleaning of the withdrawal lane is a mandatory requirement for stable operation of automation.
It is important to take into account that during transition periods (spring, autumn), the combination of factors can be unpredictable. The dirt carried by the train wheels is mixed with moisture, creating a conductive layer on the surface of sleepers and ballast. In such cases, it is not just waiting for the weather to improve, but active actions to clear the path or temporarily change the alarm mode.
Technical malfunctions of equipment and infrastructure
Along with external factors, a significant proportion of problems are technical defects. Wear of the insulating joints is one of the frequent causes of false testimony. If the insulation between the ends of the rails is broken (breakdown, crack, pollution), the current begins to flow through the joint, bypassing the receiver, or, conversely, close the chain where there should be a break.
Defects in throttle transformers can also cause failures. These devices are used to pass traction current and separate signal currents. A throttle shoulder symmetry violation or turn-to-turn circuit may distort the signal that the system perceives as site occupancy.
Mechanical damages include:
- 🔩 Breaking or weakening of contact connections in relay boxes.
- 🔨 Mechanical damage to the cable going to the track equipment.
- 🔌 Corrosion of contacts in the places of connection of wires with the rail.
- 📉 Degradation of insulation gaskets under the sole of the rail.
Particular attention should be paid to the state of track-relay. Sticking of contacts, weakening of springs or mechanical wear of moving parts of the relay can lead to false positives. Regular inspection and lubrication of the machinery, as well as monitoring of the electrical parameters of the coils, prevent many of these problems.
⚠️ Attention: If mechanical damage to the insulating joints or cables is detected, it is forbidden to repair under voltage. It is necessary to call the electromechanic of the SSCB and arrange the work with the appropriate outfit.
Often the cause is the human factor in construction or repair work. Accidental damage to the cable by an excavator, a metal tool left in the way or a violation of sleeper laying technology can instantly disable the site. Therefore, monitoring of third-party organizations operating in the security zone is critical.
The problem of poor bypassing of rolling stock
Paradoxically, sometimes false employment of neighboring areas or unstable signal operation is associated with a problem. bypass. This phenomenon occurs when the train's wheel pair does not provide reliable electrical contact with the rail thread. As a result, the system “does not see” the train where it is, or, in an attempt to compensate for the instability of the signal, it fails, which is interpreted as a false occupancy of the free section.
The main reasons for poor bypass surgery:
- 🚂 Pollution of the wheel rolling surface (oil, sand, rust).
- 🍂 Leaf fall in the autumn period, creating a dielectric film on the rail head.
- 🛤️ Use of composite brake pads that do not clean the wheels as efficiently as cast iron.
- 📉 The light weight of the axis of empty wagons, insufficient for the oxide film to be pressed.
When a train with poor bypass travels along a distillation, it can be "lost" to the rail circuits. The autolock system, losing control over the location of the train, can transfer adjacent areas to the employment mode for security purposes. This creates a domino effect where one poorly shunted car stops movement in a whole direction.
To combat leaf fall and wheel pollution, the use of sandboxes of locomotives in the sand supply mode before entering problem areas is effective, as well as the use of special cleaning trains.
There are special measures to combat this phenomenon, including the installation of additional portable shunts or the use of “follow with caution” regimes. Drivers should be instructed about the possibility of losing control of the train by the SSC and act according to the regulations.
Algorithm of actions in the detection of anomaly
If there is an indication of false employment, the driver or station officer must act clearly and quickly. The first step is always to confirm the actual freedom of the site. Visual control, data from CCTV cameras or survey of track workers make sure that there is no train on the site.
The nature of the malfunction must be assessed. If employment has arisen at the adjacent distillation, it may be a problem in the throttle transformer or insulating junction. If the whole area is burning, it is most likely the ballast or cable. It is important to record the time of occurrence and previous events (thunderstorm, train passage, construction work).
The standard sequence of actions includes:
- Report to the dispatcher and adjacent stations.
- Checking the readings of the instruments (voltmeter, ammeter) in the relay room.
- Calling the electromechanic of the SSC for measurements.
- If necessary, transfer to telephone communication or issue warnings to drivers.
In some cases, with confirmed freedom of path and malfunction of technical means, the method of artificial bypassing or disconnecting the damaged rail circuit can be used (only on the instructions of the work manager and with observance of safety measures). This allows for a temporary recovery of traffic, although it reduces the level of automation.
☑️ Actions in false employment
The key point is the inadmissibility of independent interference in the work of relay devices by persons who do not have the appropriate admission. Any manipulation of wires and relays can lead to electric shock or aggravate the situation.
Comparative table of causes and methods of diagnosis
To systematize knowledge about possible causes of failures, it is convenient to use a summary table, which helps to quickly classify the problem by external signs and choose a diagnostic method.
| Cause of failure | Appearances | Method of diagnosis | Elimination |
|---|---|---|---|
| Low ballast resistance | Employment during rain/snow | Measurement of insulation resistance | Clearing the track, drying, circuit shutdown |
| Defect of the insulating joint | Permanent or floating employment | Measurement of junction voltage | Replacement of insulating pads, cleaning |
| Foreign subject matter | Sudden employment of the site | Visual inspection of the path | Removal of the object (metal, wire) |
| Relay malfunction | Blinking signal, clicking | Checking the relay, measuring the current | Replacement or adjustment of the relay |
The use of such tables in the instructional materials allows staff to navigate the situation faster.
Accurate diagnosis of the cause of false employment requires a comprehensive approach: analysis of weather conditions, checking the technical condition of the equipment and visual inspection of the path.
Modern methods of preventing failures
The railway industry is actively implementing new technologies to minimize the impact of human error and external factors. One of the promising areas is the use of diagnostic systems based on artificial intelligence, which analyze the current profiles of rail circuits in real time. Such systems can predict equipment failure before it causes a stoppage.
Implementation digital-rail-chain with frequency selection allows to significantly reduce susceptibility to interference from traction current and vagus currents. These systems are able to distinguish between a useful signal and noise, ignoring short-term bypasses caused, for example, by a spark skipping or short-term contact with a foreign object.
Automatic insulation monitoring systems are also being developed. Sensors installed along the path constantly transmit data on ballast resistance and integrity of the insulating joints. This allows you to move from scheduled and preventive repair to repair on the actual condition, eliminating (hidden hazards) before they manifest.
However, no amount of automation can replace the vigilance of the staff. Regular bypassing of the path, timely cleaning of debris and snow, monitoring of the mound condition remain the foundation of safety. Engineers and station workers who know the signs of false employment and the algorithms of actions are the last and most important barrier to the occurrence of emergency situations.
What if false employment occurs at night?
At night visibility is limited, so first of all it is necessary to use technical means of control (cameras, sensors). If visual control is not possible, movement through the site is prohibited until the station duty officer or track monitor arrives for physical inspection. The use of lights and thermal imagers can help in detecting foreign objects or animals on the way.
Could a thunderstorm cause false employment?
Yes, lightning discharges can create powerful electromagnetic pulses that bring currents to rail circuits and SCB cables. This can result in a short-term but strong voltage surge, which the relay interprets as a bypass. Modern systems are equipped with lightning protection devices, but near the epicenter of a thunderstorm failures are possible.
How does the length of the train affect the likelihood of false employment?
The length of the train does not directly affect the occurrence of false employment of free sections. However, long trains create a large load on the contact network and can cause voltage drawdowns, which indirectly affects the operation of electrified sections. The problem of false employment is more often associated with the condition of the last axes of the long composition (bad bypass) than with its length.