History of electrification

That was mainly due to the increased share of industry, mainly due to the high energy-intensive character of metallurgical and chemical industries.

Industry

The other economic branches, such as transport, communications, agriculture and construction, had a small share in electricity consumption. The Bulgarian railways electrification started in 1963 and all main railways were electrified during the years that followed.

It is worth noting that by the end of the period reviewed (1970) all settlements in the country had been electrified. 5298 population centers (93.9%), giving residence to 99.6% of the Bulgarian population, were electrified.

In terms of operation, at the beginning of the fifties a dis-patching service was created. Over the years that fol-lowed, it developed at three levels: National Dispatching Center in Sofia, regional dispatching centers (Sofia, Plovdiv and Gorna Oryahovitsa), and district dispatching units at the electricity supply enterprises and their branches. An automatic dispatching service and a telecommunication system covered 35 of the most important sites. Automatic frequency control system and exchange capacity control system were modeled.

By 1970, with the overall electrification of the country, the daily load curve of the electrification system consid-erably changed by seasons and time of the day.

The ratio between maximum and minimum loads signifi-cantly increased. In December 1970 the average monthly load minimum was 48°/o of the maximum, and the average annual load was about 40%. That necessitated the construction of load-following power plants, including pumped-storage hydro power plants.

Load curves on typical days in August and December I 971

During the reviewed period 1948-1970 the electrification in Bulgaria developed at a considerably high rate thanks to the following four main factors:

1.Nationalization of electrification.

2.Increasing the number of graduates of the State Technical University-engineers and architects of all specialties, as well as opening of technical schools for technicians training.

3.Faster development of national electrical industry in order to meet the requirements of the country and exports to other countries.

4.Establishment of Energoproject in 1948 – research institute of project investigations and engineering design. This institute became the center for training experts not only for the Bulgarian electrification, but for project engineering and construction abroad, as well. A number of other specialized research institutes also appeared in that field, closely connected with electrification, such as the Research and Design Institute of Electrical Industry, Techenergo.