220 kV line Ronsdorf – Letmathe - 220-kV-Leitung Ronsdorf–Letmathe
The 220 kV line Ronsdorf-Letmathe was a 33 km long, double circuit three phase - High voltage - free line , which in 1922 by RWE was built as the first high-voltage line this voltage level in Europe. Its construction was carried out both as a test setup for the as yet untested operation with higher voltages and as the first section of a planned network. The knowledge gained through the operation flowed into the construction of the north-south line , which in turn developed into the backbone of the German high-voltage network.
Until 2007 the line was still in operation with the original masts from the 1920s. In the course of the elimination of the 220 kV level in the Ronsdorf substation and the construction of a new 380 kV switchgear in the nearby Linde substation, the line became dispensable and apart from a short section between Hagen-Oege and the substation in Iserlohn - Genna, it was dismantled without replacement .
Since the end of the First World War , the Rheinisch-Westfälische Elektrizitätswerk has developed from a local power plant operator in the Cologne area to a supraregional energy supplier with the expansion of the golden mine . An overhead line network operated with 110 kV connected the power plants with major consumers, such as the Erftwerk in Grevenbroich and the industrial centers in the Bergisches Land .
At the beginning of the 1920s, when the pipeline network was already over 500 km long, there were plans for a network with the hydropower plants in the southern Black Forest , Switzerland and Vorarlberg under the leadership of the then technical director Arthur Koepchen. A technical problem, however, was the task of transporting the electricity over a distance of around 700 km economically and without major transmission losses. The line to be created for this should therefore be operated with twice the voltage of 110 kV, which was then considered technically possible. It was calculated that with a voltage of 220 kV and a circuit length of 400 km with a transmission power of up to 110 MVA, the maximum transmission loss was 10%.  
Koepchen's vision of a 220 kV network was reinforced by the fact that in 1921 the Southern California Edison Company (SCE) put an overhead line into operation in the USA that was operated at 150 kV and could be converted to 220 kV.  It was part of a hydropower project that connected energy from the Big Creek Hydroelectric Plant to a substation near Los Angeles 270 miles away .
The functioning of this project convinced Koepchen of the technical feasibility of higher voltages. Although 220 kV has not yet been used anywhere in Europe, he took the risk and planned to set up a first test track in the RWE network area.
In the same year, RWE acquired the Braunschweigischen Kohlen-Bergwerke (BKB) based in Helmstedt . This was followed by further plans to expand the network: in addition to the line to the south, a second line to the east to the central German lignite area, in which BKB had shares, was to be built and thus enable energy to be exchanged with the Rhenish coal-fired power plants.
Construction and operation
Based on this idea of creating a connection to the BKB area, the test line was built from 1922 to 1923 on a 33 km long route from southwest to northeast in the Bergisches Land and Sauerland .  If the project turns out to be successful, the line should be extended to the west and east and establish a direct connection from the Cologne area to the Braunschweig region.
The first problems arose with the commissioning: Corona discharges on the insulators increased the formation of sparks, which quickly gave the overhead line the nickname Fireworks Line.  This problem was solved by RWE, in cooperation with AEG , Siemens-Schuckertwerke and Felten & Guilleaume, developing a hollow copper cable with a diameter of 42 mm.  Alternatively - if a full rope had been used - the masts would have had to be reinforced, which in turn would have had an impact on the material consumption and thus the construction and operating costs.
After the line ran successfully in test operation, Koepchen and Ernst Henke , Director and Legal Director of RWE, visited the SCE facilities in California . The result was that the state of the art in the USA at that time was the same as in Germany.  Then the plants of the Pacific Gas and Electric Company were visited, which also obtained their electricity via a line several hundred kilometers long from a hydroelectric power station.
The operation of the Ronsdorf – Genna pipeline and the two equally successful hydropower joint projects in California finally convinced RWE of the feasibility of joint operation between Rhenish coal and alpine hydroelectric power. After W. Lahmeyer & Co. took over the majority of shares in Elektrizitäts-AG in 1923 and thus came into the possession of numerous southern German energy providers, the project actually started a year later, in 1924.
The experience gained through the 220 kV test line was in turn incorporated into the construction of the network system known as the north-south line . Instead of 220 kV, however - as the first high-voltage line worldwide - it was dimensioned for an even higher voltage of 380 kV. 
Substation on the Ronsdorf – Letmathe line, North Rhine-Westphalia
The line began at the Genna substation in Iserlohn - Letmathe , which has a direct connection to the Koepchenwerk pumped storage power station and led to the old Wuppertal-Ronsdorf substation , an important electrical power distribution hub in the Bergisches Land with a connection to the lignite power stations in the Rhenish lignite district .
It ran from the Genna substation along the Lenne near Iserlohn-Letmathe, crossed the Nahmertal near Hagen - Hohenlimburg , the federal motorway 45 , near Hagen-Dahl the Volme led south past Breckerfeld -Zurstraße, crossed the Ennepetal near Peddenöde, led north to Ennepetal - Past Rüggeberg , crossed the Heilenbecker Bachtal at Wellenbecke, and east of Beyenburg the Wupper at the level of the Beyenburger reservoir. The end of the line was the old Ronsdorf substation.
The masts of the line were fir tree masts and differed somewhat in their shape from the masts later used for 220 kV lines of the RWE, as they were erected with less material consumption, have wider trusses and have a square mast tip.
The old 220 kV switchgear in the Ronsdorf substation was dismantled in 2007 and replaced by a 380 kV system built a few years earlier in the nearby Linde substation , which is connected to the 380 kV line Opladen - Dauersberg . The 220 kV transformer was also removed from the Genna substation, so that the system now only has the high voltage level of 220 kV.
In the course of this conversion and due to the old age of the line masts, the line was then completely dismantled along a large part of its length between Wuppertal-Ronsdorf and Oege (point Ochsenkopf ).
The last remaining section on original masts between the point Ochsenkopf and Genna is to be renewed in the next few years due to the age, whereby the new mast construction will be designed for a voltage of 110 kV. This new, approx. 1.3 km long line will then be given the new construction site number 1385. However, not all of the masts have to be renewed, the last mast before the introduction to the Genna substation (see picture), the southern end mast, dates from 1993 from 2007. 
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- 110-kV high-voltage overhead line Genna - point Ochsenkopf, construction control number (sheet) 1385, replacement of masts no. 2-7 . Landscape conservation plan, November 2013 / May 2014