As a rule, if it is said about special-purpose transformers for tracking substations, it implies transformers for connection of contact line feeders. Characteristics of such transformers may differ depending upon the contact line type. As long as different types of contact lines are used at present — DC and AC and different voltage ratings.
DC contact line is connected to AC mains by means of rectifying device. In this case the transformer acts as converter transformer for rectifying unit, the design features and operation modes of which are described in section "Converter Transformers".
Transformers for AC contact line (25 kV and 3.3 kV) are reducing and/or isolating transformers in terms of functions. Description of features of these transformers is also given in the corresponding sections.
A specific feature of electrified transport — the possibility of energy recovery into the mains during the vehicle braking — shall also be considered for transformers of tracking substations. This mode is specific for tracking substations.
In general, taking into account the variety of tracking substations circuits, the transformers for them are special-purpose and their fabrication requires detailed agreement of specifications.