Investigation of factors influencing the operational characteristics of traction transformers

This article presents the results of visual inspections and a brief statistical analysis of the data obtained in order to identify the observed defects in traction transformers of ODTsE 5000 / 25 B and OTsR 5600/25 types in operation in the railway system. The analysis revealed that the main parameters that determine the operational characteristics of traction transformers are windings and insulation. Recommendations for the prevention of faults in traction transformers and increase their service life have been developed.


Introduction
Any device loses its performance over time, traction transformers too. Traction transformers are the main source of electricity for electric trains [1,[2][3][4].
Its malfunction or downtime leads to a lack of power supply to the rolling stock, which, in turn, leads to a downtime of the rolling stock and, as a result, to many other problems (late arrival of passengers and cargo at the destination, violation of traffic schedules, etc.).The uninterrupted and trouble-free operation of electric trains depends on the condition of the traction transformers [1,5,6]. Analysis of literature sources shows that [7][8][9][10][11][12][13][14][15][16] during the operation of transformers, malfunctions can be observed in the form of failure of the magnetic circuit, insulation failure, faults at the output of the transformer, oil leakage, cracks inside the transformer, excess of the permissible oil temperature, violations of oil circulation, loss of dielectric properties of oil, cracks in the rods, transformer operation with noise. Therefore, the study of factors affecting the operational characteristics of traction transformers is one of the most pressing issues in the power supply of the railway system.
The aim of the work is to study the factors influencing the operational characteristics of traction transformers and to identify the main factors.

Materials and methods
The data was collected on the identification of existing defects in them and the repair of traction transformers of types ODTsE 5000/25 B and OTsR 5600/25, operated in the railway network.
Defective traction transformers were examined. A brief statistical analysis of all the data obtained was carried out.

Results and discussion
Traction transformers of types ODTsE 5000/25 B and OTsR 5600/25 that are in operation on the railways in 2017, 2018, 2019 for various reasons (due to the fact that it is time to repair the rolling stock for malfunctions during operation ...) have been repaired.  Fig. 1 shows the number of traction transformers of ODTsE-5000 / 25B type repaired between 2017-2019 by months.      show that 34 % of all faults are related to insulation, 32 % -to windings, 18 % -to damage to the magnetic circuit, 8 % -to inputs, 5 % -to cooling system, 3 % -in the tank (Fig. 4). Visual inspection revealed insulation defects (Fig. 5). As can be seen from Fig. 5, the main faults are associated with the insulating part of the traction transformers. Research has shown that the most common failures in traction transformers are winding and insulation. To increase the integrity and service life of traction transformers, it is advisable to pay attention to the following recommendations. When repairing traction transformers, it is necessary to pay more attention to insulation and winding parts: a) Due to the fact that the main insulating function in traction transformers is oil, special attention should be paid to laboratory testing and oil purification when reusing used oil.
b) Review insulation technologies. c) It is recommended to pay attention to the potential of personnel repairing insulation and windings.
Following the above recommendations will prevent major failures of the traction transformers in the rail system and will increase the service life of the traction transformers, which in turn will provide energy and economic benefits for the railway system.