History of Sofia Trams

In the end of 19 century, the horse-drawn omnibus known to people in Sofia as the “tram” was introduced in Sofia and started to operate permanent services from Gurkovo Square (Sveta Nedelya (Sabbath) Square) to the train station, Gorna Banya and Knyazhevo.


The history of the electric tram dates from 01.12.1898 when the Municipality contracted the French company – Marseille, and the Belgian company – Electric Trams SA, to supply the city with electricity and to construct tram lines.

The start of tram operation in Sofia was marked by an opening ceremony on 01.01.1901. The fleet consisted of 25 tramcars and 10 coaches on 6 tram services over a total of 23 km of single track. The track gauge was 1,000 mm. Sofia entered the new 20th century in possession of a tram network operating the following services: from the train station via the Shareniya (Lavov) Bridge to the square known today as Slaveykov; Tsarigrad Service; Knyazhevo; Poduene; Alabin, etc. 

The first tram carriages were small, had two axles, two 18-kW motors and open platforms, fenced with metal grids. The salon was divided into first and second class. The carriages were open with the passengers boarding and alighting from the side and the conductor going round on a special raised platform.


With the increase in passengers in 1908 new trams were supplied:                                                                                                                                                

12 Siemens two-axle motor streetcars divided into two classes and 6 Zeppelin four-axle motor streetcars with two 33-kW motors. In 1916 the Municipality of Sofia started a procedure on withdrawal of the trams’ operation from the Belgian company, with the final transfer of the company continuing until 18.02.1927.

By a decision of the Municipality of Sofia from 1916, the company was reformed as the Directorate for Trams and Lighting with two departments – Trams and Lighting, led by a director and two heads of departments: Traffic and Technical Workshop.

This method of management was kept until the end of 1948 when the Department of Lighting was separated and the Sofia Urban Passenger Transport Business Enterprise (trams, trolleybuses and buses) was established at the Municipality.

In 1927 a Main Technical Workshop was set up and equipped on the grounds of Maria Luiza Depot. That year – 1927 – is agreed to be the year of establishment of a company for repair, restoration and reconstruction of streetcars and carriages.

From 1924 to 1938, when the last imported trams were supplied, the tram lines were serviced by: two-axle motor streetcars with carriage bodies from the Ringhoffer plants in Prague; two-axle motor streetcars, series with baskets from Franko-Belge and electrical parts from the Austrian branch of BBC; four-axle with baskets from Atelie metallurgic dyo Nivel and with electrical parts from ACEC; Energy carriages from Belgium; motor streetcars with structure made entirely out of iron, manufactured by MAN-EAG; motor streetcars from MAN-Siemens, carriages with one middle door from the plants Urdingen and Vegman; motor streetcars from the plant Ernesto Breda – Milano with electrical parts from Ansaldo Marelli.

In 1931, based on the experience accumulated in repair, and under the management of Eng. Kardalev, the first Bulgarian carriages were manufactured out of the chassis of decommissioned trams and in 1935 12 carriages were constructed from scratch.

In 1934 in Krasno Selo Depot was constructed a modern, spacious and bright building where the Main Technical Workshop was moved to after the end of the Second World War. In 1936 began the manufacture of the first Bulgarian two-axle motor streetcars with imported controllers and motors. In the end of 1951 the technical workshop was separated as an independent plant.

In 1952 the Urban Passenger Transport Company was divided into two: Sofia Autotransport Company and Sofia Urban Electric Transport Company . In 1956 the tram repair and trolleybus activities were undertaken by the Sofia Urban Electric Transport Company. In 1959 the operational transport companies were united under the name Urban Passenger Transport Company and on 01.07.1964 Electric Transport was restructured as Branch 1 of the Urban Transport company. 


According to our construction design the first four-axle Bulgarian motor streetcars of the Republika type were built in 1951.


From then to the present the following types of motor streetcars have been manufactured in the tram plant: in 1959 – the Komsomolets four-axle motor streetcar ; in 1961 – the Kosmonavt articulated six-axle motor streetcar ; in 1965 – the Sofia tram – single-articulated and on 01.05.1970 the double-articulated Sofia 70; in 1979 – Sofia 100 – single-articulated and in 1981 to mark the 1,300 year anniversary from the creation of the Bulgarian country – the Bulgaria 1300 tram, double-articulated and with eight axles.

In the next years, after the defects of these trams had become apparent, began a preparation for the construction of a new type of cardan drive shaft structure, and in 1986 the first motor streetcar of the T6M-700 type was put into operation. Based on this tram, the manufacture of T6MD-1000 motor streetcars for track gauge of 1,435 mm was started in 1987.

On 01.07.1987 the Electric Transport Company was divided into several companies: Tram Transport, Trolleybus Transport, Transenergo, Transremontstroy and Vazheni Linii.

In 1987 a new tram depot named Iskar was created for track gauge of 1,435mm and the first tram line for this track gauge was put into operation. In 1989, 37 Czech T6B5 trams were imported. 

For the period 1990-1991, 40 Czech T6A2 trams (1009 mm) were imported. In the same year, based on the single-articulated T6M-700M, was built one double-articulated tram – T8M-900, and then the manufacture of Bulgarian trams was stopped.

In 1995 the new No. 22 tram line was launched from the Iztok Quarter Mladezhki Teatar. For this reason 29 second hand Duvag trams were imported from Germany.

 In 1998 was started the modernization of T6M-700M trams. In December 1999 was started the manufacture of T8M-900 trams with a low floor on one side and changed external design.


In January 2000 two T4D second hand trams were imported from Germany. Since April 2000 17 Czech trams of the new modernized T6A2-BG type have been put into operation, and since July 2001 – 16 second-hand T4D trams. 

Concurrently with the increase of the tram fleet continued the construction of the tram network. The total length of the track in 1944 was 79.3 km (single track). During the period until the end of the Second World War was built the foundation of the current tram network in Sofia. 


On 19.05.1998 was established SKGT Elektrotransport EAD, which since 08.12.1992 has been an independent joint-stock company that manages the tram and trolleybus transport in the City of Sofia..

In December 2002 the company was restructured into an independent joint-stock company – Stolichen Electrotransport.

As at 2002 trams transport passengers on 16 lines of 221km length in total on a single track at average operational speed of 13.8 km/h. A total of 190 trams are operated by 380 drivers on workdays. As at 2006 trams transport passengers on 17 lines of total length of 308 km on a single track at average operational speed of 12.56 km/h. A total of 176 trams operate on workdays. 

ELECTRIC ECONOMY.

Rectifier stations. 

After the first electric tram was put into operation power was supplied by the Pancharevo hydroelectric power plant and backup power was generated by steam machines until 1925. With the increased consumption, Sharleroa motor generators with power of 400 kW were delivered and installed consecutively in 1904 and Oerlikon generators were installed in 1906. In order to maintain a constant voltage of 600V during the maximum load, a Siemens buffer battery with capacity of 972 A/h was delivered and installed. After 1920 new and more powerful and modern equipment were delivered and put into operation: 400 kW AEG and 500 kW Siemens mercury rectifier units, 600 kW CHKD rectifier unit. In 1966 the first silicone rectifier – CHKD 1500A (900kW) – was put into operation in Yunac Rectifier Station.

The power of the electric transport in Sofia was supplied by rectifier stations (RS). They were constructed in this order: RS Pavlovo, RS Veslets, RS Yunac, RS Dimitrovska, RS Medical Academy, RS Levski and RS Nadezhda.

From 1970 to 1975 five new silicone rectifier stations were constructed and put into operation, namely: RS Krasna polyana, RS Darvenitsa, RS Perlovets, RS Voenna rampa and RS Vazrazhdane.In 1971 the Vazrazhdane telemanagement system was put into operation with the capability for remote control of 20 RS. In light of the quick development of tram transport, new stations were put into operation after 1975: RS Motopista, RS Lyulin, RS Iskar, RS Druzhba, RS Aliende, RS West park, RS Bakarena fabrika, RS Banishora, RS Hadzhi Dimitar.

 The increase in the installed power from 1901 to 2000 was respectively from 550 kW to 125,950 kW, while the processed electricity went up respectively from 500kW/h to 68,500 kW/h, peaking in 1990 at 85,900 kW/h. The installation of a new system for remote control of rectifier stations (Telegir 805) was started in 2000. The quipment was supplied by the Swiss company Landis-Gir and had the capability to control 40 RS. Currently, the power supply for the electric transport in the city of Sofia is delivered by 24 RS with more than 73 rectifier generators.

Catenary.

Until 1924 current collection was performed by roll sliders, which were later replaced by a new sliding structure. Round 50 mm2 copper wire was used as a conductor. In 1927 it was replaced with profiled wire, with the connection to the non-conductors and the splicing performed using special connectors. These days 100 mm2 wire is used. Porcelain non-conductors were tested and put into experimental operation in 1930.



By 1931 the connection points were at a distance of 35-40 m, however, due to poor current collection, sparking and burning out of the conducting wire, these distances were reduced to 15-20 m.

At the end of 1961 the tram catenary was more than 100 km long and the trolleybus catenary – more than 52 km long. The following 10-15 years were characterized by reconstruction of the existing networks. At the end of 2001 the total length was more than 210 km for the tram and 274 km for the trolleybus networks.


At the end of 2006 the total length was more than 263 km for the tram and 257 km for the trolleybus networks.

In 1930 a successful experiment was carried out for the first time to electrically control the movement of an incoming switch point of tram rails. At the end of 2001 all incoming switches were automated and controlled from the tram driver cabin. For the first time, in June 2000, a remote radio control was introduced in front of the Hemus Hotel – the turnoff to Lozenets. Using the same principle, the first automated trolleybus switch with remote radio control was installed on trolleybus line No 5 – turnoff to District Hospital. 

Cable Grid.

Average voltage cables (10/20 kV)

From 1901 to 1961 the voltage supplied by the regional substations was 7kV. From 1961 to 1967 a gradual transition was made to supply voltage of 10kV. Two power sources were supplied for each rectifier station. Initially the supplying cables were of the oil variety and later, after 1965, began the use of other cables in this order: dry cables with copper wires, cables with aluminium wires and cables with polyethylene insulation. At the end of 2001 there were 57 10/20kV supplying cables of total length of 158,320 m.

Constant current cables – 600V.

Initially, the supply of the tram and trolleybus catenary was conducted by oil cables. As at 1961 the total length of the catenary was more than 105,000 m and that of the air feeding lines – 15,000 m. In 1975 the total length was increased to 450,000 m.

In 1981 a new type of dry cable with copper wire was introduced. A stage by stage replacement of oil cables was started, with almost all of the cables replaced by 1990. Their total length amounted to 525,650 m. 

In 1995 a dry cable with plastic covering and 500 mm2 aluminium wire was produced. It completely replaced the more expensive (more than three times) cable with copper wire. 

As at 2001 the total length of the catenary exceeded 643,800m, with the number of cables being 667.

As at 2006 the total length of the catenary exceeded 740,000 m.


RAILWAY ROAD.

Initially, maintenance of the railway track was performed by a specially created group and a unit manufacturing spare parts in a specialized workshop. Since 1965 the Termitno-strelkovata Workshop and the group of catenary networks and rectifier stations were combined in a branch named Railway Track, Networks and RS. In the end of 1975 the company was entered into the composition of Elektrotransport under the name Railway Track Division. In 1987 it was restructured as Transremontstroy joint-stock company, which was a subsidiary of SKGT Holding EAD. 

When the first trams were put into operation in Sofia, the railway track was 23,377 m long, with the tram lines having a single track with designated places to let oncoming vehicles pass and no u-turn at the end. 

Tracks were of the Feniks type (grooved) and were connected with joint connections. The arcs were made of double Vinyol-type tracks, with the inner rail serving as a counter rail. The constructed lines had a track gauge of 1,000 (1,009) mm.

The first switches were imported by the Belgian company and later from England, Austria, Czech Republic and Germany.

In 1936 the workshop for the manufacture of switches manufactured the first joint switch, a copy of those delivered from the Czech Republic. Since 1936 to the present moment all switches, crossings and other facilities, units and components, required for the tram track are manufactured by the Switch Workshop of the company. Until 1970 the tram track was mainly laid over paved roads. 

After 1970 several technologies were used: concrete tram railway track, tram panels with length of 12.5 m and others. In 1982, together with specialists from Hungary, the construction of a tram track with panels of length of 6 m was started. Using this method a railway track of more than 50 km was built.

In 1983 a new automatic tram switch was developed, which was awarded the golden medal at the technical exhibition in the City of Plovdiv. The first experiments for construction of heaters on the tram switches began.

During 1980-1985 were purchased: unique tie undercutting machine for tram track, rail bending machine Zhismar, chute cleaner, burnishing machines, boost wrenches, track drilling and track cutting machines.

In 1987 began the construction of a tram track with normal track gauge of 1,435 mm.

During 1998-2008 the improvement of the technology for development of tram switches was continued with experiments on a new type of spring tongues. The experiment was conducted along with specialists from the Czech company – Prashka Stroyarna.

The total length of tram track at the end of 2001 was 169,000 m for track gauge of 1 009mm and 39,000 m for normal track gauge of 1,435 mm. The total number of tram switches in operation was 231 and in the depots it was 292. The total length of tram track at the end of 2006 was 169,000 m for track gauge of 1,009 mm and 40,000 m for normal track gauge of 1,435 mm.