Single-phase transformers of the OSM series with power 0.063 - 4.0 kVA, execution U3, connected to an AC network with a frequency of 50 Hz and a rated voltage up to 660V, are designed to power control circuits for local lighting, signaling, and rectifiers assembled according to a two-half-period rectification scheme. The transformers are made on a split wound magnetic core made of cold-rolled electrical steel. Transformer coils are of a frame design made of copper wire with heat-resistant insulation. The assembled transformers are impregnated with moisture-resistant electrical insulating varnish in a vacuum impregnation unit. Transformers of the same type with different climate executions are identical in all electrical parameters and dimensions, differing only in protective coatings. Transformer contact terminals are located on plastic insulating blocks. OSM transformers are designed for operation in enclosed spaces under the following conditions: • non-explosive environment; • altitude - not more than 1000m; • ambient temperature from -45°C to +40°C. - resistance to impact loads and vibrations; - multi-purpose use; - protection against electric shock; - a split wound core made of electrical laminated cold-rolled steel is used as the magnetic core; - multiple design options.