Through the merger of several small factories producing electrical equipment, electric motors and transformers, creating high voltage factory "Vasil Kolarov".
During the period 1951-1953, altering the structure of the plant. Created three main workshops - electric devices, electric motors, transformers, and four auxiliary workshops.
During 1958-1961 creating three main directorates - Electrical appliances, transformers, electric motors. This enables a later stage of production units to be converted into individual plants
In 1975 the name of the factory was changed to ELPROM-energy. In the same year the Research Institute of electric power engineering, which is the successor of the previous Research Institute introduction and development of electric power equipment.
In 1991 plant ELPROM-Energo is divided into five new independent companies: - ELPROM-TRAFO - Sofia - ELPROM-TRAFO - Kyustendil - (manufacturer of distribution transformers) ELPROM-ZEM (manufacturer of electric motors and generators) ELPROM-SIU - Plant in tooling - Institute of electric power equipment. In 1994 The Institute of electric power engineering was closed and its activities related to the production of transformers and electrical equipment is transferred to ELPROM-TRAFO JSC.
In 1997 the plant was privatized company Hyundai Heavy Industries Co. Korea, which became the main owner of the company shares. The name of the Bulgarian company was changed to "Hyundai Elprom Trafo" JSC.
The name of the factory was changed to "Hyundai Heavy Industries Co. Bulgaria ".