Designation of the concept
Stray currents are charged electrical particles with a specific trajectory of movement that appear in the ground, which is a conductor. The term wandering appeared due to the fact that it is impossible to predict the localization of particles and the beginning of the process. The impact of stray electrical particles is very bad on iron products present above and below the ground.
The same processes appear due to the growing number of electrified objects that are the basis of modern countries. And since the soil is a conductor for electricity, there is a mutual action between the elements.
Wandering particles akin to electric ones appear, the mutual action of which requires a comparison of the potential difference at 2 arbitrary points; exclusively for the wandering version, the conductor is the ground. As a result, the iron material located near the process collapses faster due to corrosion.
Causes
The cause of electric current is the potential difference between two points of a conductor. The same happens when a stray current occurs. Only in this case the soil itself serves as a conductor.
In total, there are four reasons for the occurrence of stray current:
- As mentioned above, the ground serves as a conductor (this reason is most often found in areas where there are railroads or large power plants).
- Poor wire insulation (result of poor maintenance).
- Installed television tower. A high-power radio signal generates a stray current and is the cause of its occurrence.
- Electric vehicles. The main reason for the occurrence of stray current in the above example is the curvature of the routes.
Formation process
The basis for the appearance of stray currents is a countless number of equipment operating from an electric charge, as a result, possible sources are the following elements:
- the presence of chargers in such objects as substations, overhead lines with a neutral conductor, distributors;
- the appearance of activity, ultimately destruction of the insulation layer of wires carrying current in cables and overhead lines, where the neutral is insulated;
- the presence of an innovative connecting link between the conductor and the soil in structures with a grounded neutral and rail vehicles driven by current.
The mechanism of the appearance of spontaneous discharges can be considered using the example of one of the above points.
One end of the neutral wire is connected to the power station charger, and the other is connected to the PEN bus consuming energy, which has a connection to the charger. It follows that the potential difference in electrical value between the terminals forms stray currents, since the energy will be transferred to the charger, which in turn will form a circuit.
In this case, the volume of losses does not have a high percentage, since it will pass along the path of the least resistance, but a specific part will fall into the ground.
Energy leakage occurs in the same way if the wiring insulation is damaged.
In this case, a constant, uninterrupted leak does not occur, since its occurrence is signaled by the system and the area is automatically localized, and according to the standards, there is a specific time period allotted for the removal of breakdowns.
Important! According to statistics, the central places for the formation of electrical energy leakage and the formation of stray currents are in urban and suburban areas, where there is ground transport that depends on the power grid.
Currents on the rails
When operating urban electrified transport, voltage is supplied from the substation to the traction system, which is transferred to the rails and completes the reverse cycle. If the rails as a metal base are not stable relative to the conductor, this leads to the appearance of stray currents in the soil, then every metal structure that appears in their path, for example, plumbing products, acts as a conductor.
Important! This mutual action occurs due to the fact that the current, as it moves, selects the path of least resistance, which is less for the metal than for the ground.
All this leads to accelerated destruction of metal products.
Stray current protection
To prevent damage caused by stray currents, equipment is protected from them using cathodic protection . The principle of its operation is based on eliminating the formation of anodic zones on the protected object, leaving only cathode zones. To do this, use an additional direct current source, the negative pole of which is connected to the protected object (rails), and the positive pole to additional electrodes (protective anodes) located along the protected object. The current source is a cathodic protection station .
Connecting the cathode station
As a result of cathodic protection, destruction is transferred from useful metal structures to auxiliary anodes, also called “ sacrificial ”. Additionally, protective coatings are applied to prevent corrosion.
Operating principle of cathodic protection
But cathodic protection has disadvantages :
- overprotection – when the protective potential is exceeded, corrosion of the protected object occurs;
- If the protection is incorrectly calculated, accelerated corrosion of nearby pipelines and cables is possible.
Additional protection measures against stray currents are:
- the use of cable lines made of cross-linked polyethylene, covered with a non-conductive protective sheath;
- the use of pipelines consisting of or coated with non-conductive materials;
- use of the TN-S grounding system, in which the neutral working conductor is isolated from the ground on the receiving side. This eliminates the chain of formation of stray currents due to the potential difference on the grounding circuits of objects due to the flow of zero operating current.
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Relationship between currents and corrosion processes
Any water-measuring unit located in the soil is damaged by corrosion due to the influence of moisture and salts on it, but if current activity is also added here, an electrolytic process appears. In this case, the rate of electrochemical reaction is affected by the charge flowing between the anode and cathode. It follows that the activity of damage to metal products will be influenced by the resistance of the soil to the movement of charges, as well as the complexity of the flows present in the anodic and cathodic zones.
In this environment, the water supply system is prone to ordinary corrosion under the influence of leakage currents. The influence forms a galvanic couple, accelerating the development of corrosion. There are a large number of factors in history when the pipeline being laid was supposed to last 20 years, but in reality the destruction occurred after 2 years.
Options for proposed protection
To protect metal products from bad influences, various methods are used, divided according to the nature of their use into inactive and energetic.
Passive option
This option is considered to be the use of different insulation materials that form protection between the conductor and the metal. How insulation is applied:
- epoxy resin mixtures;
- inclusion of polymer materials;
- bitumen coating.
However, if you make do with only this option, then full protection will not work, since the insulation material is not considered a 100% barrier due to the presence of diffusion permeability. Thanks to this, isolation occurs in a selective manner. In addition, in the process of moving pipes, such a layer can be damaged, which causes significant scratches, cuts, through holes and other defects.
Important! Due to this, the passive method of protection can only be used as an addition.
Vigorous Defense
Indicates the use of an active method of localizing the source of influence using cathodic polarization, where a negative charge displaces a natural one.
To implement such protection you need to use one of 2 tools:
- Galvanic method - the effect of a galvanic couple, the destruction of the sacrificial anode is carried out, thus ensuring protection of the metal structure. The method is effective when soil resistance is up to 50 Ohms per meter; if the resistance is lower, the method is not effective.
- Continuous current source – ensures avoidance of dependence on the soil resistance force. Electrochemical protection against corrosion is used, the source of which is contained in the formed converter connected to the electrical circuit. Since the source was formed by regulating it, you can set the desired level of current protection, depending on the prevailing circumstances.
Vigorous insulation
A similar method can also provide adverse effects:
- overprotection - exceeding the required potential, ultimately causing destruction of the metal product;
- incorrect calculation of protection - leading to accelerated corrosive destruction near the located iron objects.
The above options can be considered on the protection of such a product as a coil.
The processes associated with corrosion on such products or other terminal plumbing products have never occurred, but this was true before the use of metal-plastic pipes, where there is contact with aluminum in the middle of the wall. As a result, the formation of wandering components occurs not only due to the use of plastic pipes in the immediate room, but also in others, since in a house with several apartments they can be used by a neighbor on another floor.
Important! To avoid the adverse effects of emerging currents on your structure, you need to equalize the potentials by equipping the towel dryer, battery and water pipes with a grounding element.
In this case, the application of the much-needed grounding occurs in relation to any communication that is made of pipes made of metal, for example, a gas pipeline to the ground.
Rules for taking measurements
To assess the full extent of the resulting situation with leakage of electrical charges, a number of measures need to be taken:
- voltage measurement and current flow through the sheaths of main cables;
- designation of the potential difference between the contact rails and pipelines located in the soil;
- checking the level of insulation of rails from the ground covering, using a section of the track for the experiment;
- assessment of the density of energy leakage from the cable sheath into the soil.
To take measurements, a specialized device is used; if activities are carried out on railway tracks, the peak hour of transport traffic should be selected.
Measuring tools
To check, they use electrical energy converters and substations near the traffic line - the electrode connected to the device is combined with a charger and plugged in 10 meters from the substation. Any difference that appears is recorded by the device.
If a line of pipes for water supply is to be laid, it is important to detect the location of stray currents; for this purpose, the potential difference between 2 sample points on the earth's surface, located perpendicular to each other at an equal distance, is determined. It is important to carry out this designation systematically at intervals of a kilometer.
In this case, the devices used must certainly have an accuracy class of at least 1.5, and the equipment resistance must be from 1 MOhm. Use of measuring electrodes with potential differences above 10 mV. The time for one measurement primarily lasts within 10 minutes, and the gap between processes is 10 seconds.
Measurement methods
Stray currents are calculated by measuring the potential difference between points on the earth's surface that are perpendicular to each other and located at a distance of 100 meters. Such measurements are carried out every kilometer. They require special devices that must have an accuracy class of at least 1.5 and have an intrinsic resistance of 1 ohm.
Copper sulfate reference electrodes are also used for these measurements. Their design includes non-metallic housings, inside of which there are red copper rods and a saturated solution of copper sulfate. It is worth noting that measurements must be carried out at each point for at least 10 minutes, with manual or computer recording of the results every 10 seconds. If the largest swing of potential fluctuations exceeds 0.4 V, then this confirms the presence of stray currents.
