The team of researchers from Russian University of Transport, Irkutsk State Railway University and Irkutsk National Research Technical University together with their colleagues from “Angel Kanchev” University of Ruse explored if traditional overhead power transmission lines (OHPL) feeding traction substations at railways could be replaced with gas-insulated lines. Such gas-insulated lines are metallic pipes with a conductor inside filled with insulating gas.
Standard traction substations are connected to the grid via 110-220 KV overhead lines. However, in this case the reliability of OHPL to a great extent depends on climate conditions, as the cables are prone to strong wind and glaze ice. Besides, lengthy zones of electromagnetic exposure are formed along the OHPL routes affecting people and sensitive electronics. Broad protective zones are needed to mitigate such risks, hence, significant areas of land are excluded from agricultural and business use.
Gas-insulated lines, where the current-conducting elements are contained in sealed metallic shell, are to a great extent resistant to such problems. They are compacted, weather resistible and due to the screen effect of the shell practically do not generate external electromagnetic field. However, for railway applications, where the loads are not stable and differ significantly from the standard design mode, it was necessary to understand how such lines will be operating in real conditions.
This was the task the researchers were trying to resolve. They developed detailed computer simulations of the energy system feeding a group of traction substations with account of the real cargo trains traffic up to 6.8 kt along the complicated profile section of the tracks. Such modes are often accompanied by violent fluctuations of the consumed capacity and current, and electric locomotives with single-phase rectifiers introduce significant harmonic distortions to the grid violating the ideal sinusoidal form of the current. To account correctly for all these factors, specialized software Fazonord AC-DC was used based on the phasal bearings method. It allows for simulating not only asymmetry and ultra-harmonics, but also physical effects specific for gas-insulated lines, in particular, skin-effect and affinity-effect in massive aluminum conductors.
In the process of a virtual experiment, the scientists compared the operation of one and the same 110 KV grid in two modes – feeding traction substations via OHPL and via gas-insulated line. The results proved that using gas-insulated line noticeably improved the quality of electricity. The non-symmetric voltage coefficient at the substation bus lines in the scenario with gas-insulated line did not exceed 2% and was within the norms, while as it was several times higher in the scenario with OHPL. The harmonic distortions of voltage in the grid fed by gas-insulated lines decreased by 70-88% vs the traditional option directly affecting the reliability and the resource of transformers and other high-voltage equipment.
The most obvious differences manifested themselves during calculation of electromagnetic fields. The simulation showed that gas-insulated lines formed the magnetic field six times weaker than an overhead line of the similar capacity, and the electric field was dozens of times weaker. At the distance of 2 meters from railway axis the magnetic field intensity of the gas-insulated lines was approximately six times lower, and of OHPL – almost 40 times. Even peak currents emerging when heavy trains are passing by caused only moderate fluctuations of the field around the gas-insulated line, while as the amplitude of such fluctuations around the overhead line was significantly higher.
Based on the outcome of the study the scientists propose to use the developed simulations and the methodology of calculations when designing and upgrading the systems of supplying electricity to railways, primarily in the areas with high-density development and heightened requirements to electromagnetic safety. The next stage they are planning will be propagation of this approach to the direct-current mains feeding traction substations with even more agile modes.
If the proposed solutions are implemented, railways will become more reliable, and the energy system along the transportation corridors and adjacent to residential communities will stop creating problems for the residents.
