- it is the electric device which is intended for transformation of alternating current of one tension to alternating current of other tension for food by the electric power of consumers. It is the most important and obligatory element of any electric network since any use of the electric power in life and on production assume its transformation that is impossible without power transformer.
- depending on quantity of phases: single-phase and three-phase;
- by quantity of windings: dvukhobmotochny and trekhobmotochny;
- on an accuracy class, i.e. on the allowed values of errors;
- on a way of cooling: transformers with oil cooling (oil), with natural air cooling (dry and with cast isolation);
- by the nature of installation: for internal installation, for external installation and for the complete distributing devices (CDD);
- to destination: lowering and raising.
Besides, power transformers are distinguished on groups of connection of windings. Also at selection of transformers consider climatic conditions.
The oil transformer consists of a magnetic conductor, windings, a tank, a cover with inputs. The magnetic conductor is collected from isolated from each other (for reduction of losses by vortex currents) sheets of holodnokatany electrotechnical steel. Windings produce from a copper or aluminum wire. For regulation of tension the winding of a high voltage has the branches connecting to the switch. Two look switching of branches are provided in transformers: under loading - RUL (regulation under loading) and without loading, after disconnection of the transformer from a network - SWE (switching without excitement). The second way of regulation of tension as the simplest is most widespread.
Except the specified transformers with oil cooling (TM) transformers in tight execution (TMG) in which oil is not reported with air are issued and, therefore, its accelerated oxidation and moistening is excluded. Oil transformers in tight execution are completely filled with transformer oil and have no dilator, and temperature changes of its volume when heating and cooling are compensated by change of volume of corrugations of walls of a tank. These transformers are filled with oil under vacuum owing to what the electric durability of their isolation increases.
The dry transformer as well as oil, consists of a magnetic conductor, windings of the high and low tension concluded in the protection cover. The main isolating and cooling environment is atmospheric air. However air is less perfect isolating and cooling environment, than transformer oil. Therefore in dry transformers all insulating intervals and ventilating channels do big, than in oil.
Dry transformers have a little big overall dimensions and weight, and smaller reloading ability, than oil, and no more than 80% are used for work in the enclosed space with relative humidity. Refer their fire safety (lack of oil), comparative simplicity of a design and rather small costs of operation to advantages of dry transformers.
In distributive networks use, as a rule, the three-phase dvukhobmotochny lowering transformers transforming voltage of 35/10/6 kV to voltage of 0,4 kV.