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The existing protection does not provide protective potential of traction substation grounding grid for the entire period of operation. This disadvantage is removed by improving of automatic drainage unit. The basis of the automatic drainage system is automatic control of drainage current by changing the pulse width of current. This method of current control allows the defined potential remain at the set value. The article presents a functional diagram describing the basic units of the improved automatic drainage unit. The results of the automatic drainage unit tests illustrate that the automatic drainage unit limits the current flowing through the grounding grid to the traction substation, allowing the potential remain at the set value Improved automatic drainage unit has great advantages in relation to existing and operated drain units at this moment and it can be recommended for introduction to the electrification infrastructure of the railway industry. Also this automatic drainage unit can be used for protection of other metal underground structures such as pipelines and other metal structures influenced by stray currents.

The paper is devoted to the calculation of the electrical quantities distribution in the system of three conductors. The first conductor is located on the surface of a uniform soil and the other two conductors are located at depths of h and h . As result, analytic expressions of current, potential and leakage current density in the first underground construction with considering the influence of the second construction was obtained. The influence of second construction increases the value of electrical quantities in the underground construction. The analytic expressions were obtained using Fourier transform method. The analysis showed the influence of the leakage current and insulation resistance of the second construction on the electric quantities distribution in the first construction

The paper deals with the protection of the buried structures under the influence of DC traction network stray currents. The paper presents an algorithm for joint operation of drainage units for simultaneous protection of the grounding grid and two isolated underground conductors with priority protection of the grounding grid. The proposed algorithm of joint drainage protection of buried structures allows providing the possibility of optimal protection: simultaneous keeping of the protective potential of buried structures with the minimum required drainage current, which allows reducing energy costs, reducing corrosion damage and extend the operating life of buried structures.

The paper deals with the influence of stray currents on underground metal structures located near the traction rail network. The paper presents a system consisting of a traction rail network, a grounding grid and two isolated underground conductors located under the stray currents influence caused by electrified railway transport. Analytical expressions for the calculation of the distribution of electrical quantities in underground structures with their mutual influence were obtained. The expressions were obtained using Hartley integral transform, which in contrast to the Fourier transform allows carrying out integral transformations only with real-valued functions. The obtained expressions allow determining the zone of dangerous influence of stray current and can be used in the design of underground structure protection.