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The use of twelve-pulse rectifiers instead of six-pulse rectifiers leads to increased efficiency and efficiency of traction substations of the underground. On the basis of experimental research and analysis of circuit solutions, the conclusion is made about the advantage of a twelve-pulse rectifier circuit of a serial type over parallel-type circuits. The use of rectifiers with a parallel type circuit is possible only if there is an equalization reactor, without which technical and economic indicators are reduced. The introduction of the most rational twelve-pulse bridge rectifier schemes of the sequential type can be carried out by upgrading the installed equipment, or by industrial development by manufacturers of dry transformers with different typical power and rectifiers with tablet avalanche valves with coolers based on heat pipes.

Various converters are operated at electric railways traction substations whose rectifiers design includes plug-in power rectifiers and pill ones. Such a variety of rectifiers design causes the problem of the power supply reliable operation unavailability both of volumes and of quality information concerning the characteristics and diagnostic parameters of power semiconductors rectifiers. For a possible prediction of the diodes and thyristors proper operation, new instruments as well as simple technologies of the preventive diagnostics, correspondent to the state and industry standards and instructions should be developed. One of the most accurate methods to determine not only the serviceability of rectifiers but also to forecast their wear - life, is the diagnostic method of recurrent peak backward current. This method is the basis for the design of a peak backward current meter which is used on the Western-Siberian railway. Using this device the screening of about thirty thousand rectifiers was carried out which resulted in the sorting of out-of-work rectifiers, predicting long term rectifiers conditions. The statistical analysis of the research allowed to determine the number of measures to improve the reliability of traction substations converters.

The article deals with the introduction of a twenty - four pulse rectifiers with various rectification circuits on direct current traction substations. The results of the operation of a twenty-four-pulse rectifier installed at one of the traction substations prove the expediency of using such a converter. The variants of the existing equipment modernization, which is a part of the six- and twelve-pulse rectifiers in order to use it in the creation of twenty-four-pulse rectifiers, as well as the requirements for the creation of such rectifiers in industrial design are given.