HVDC > HVDC Development > The early HVDC development - 1
The key challenge in the HVDC technique was the development of reliable and economic valves which could convert high-voltage alternating current into high-voltage direct current and vice versa.
Long distance transmission. The early challenges in Sweden.
Trunk line system in Sweden 1952 with the first 400 kV line and the 220 kV network. | During the 1940s the Swedish State Power Board (now Vattenfall AB) was planning the long transmission system from the new Harsprånget hydroelectric power plant in the far north to the load centres in the southern part of the country. High-voltage direct current (HVDC) was considered for the Harsprånget transmission, but the system and component development work that was being made by ASEA (now ABB) had not yet advanced sufficiently for a practical application of the technique. Therefore it was decided to build a 400 kV AC transmission system. The first part of this system was energized in 1952 and it was then the highest voltage used anywhere in the world.
The key challenge in the HVDC technique was the development of reliable and economic valves which could convert high-voltage alternating current into high-voltage direct current and vice versa. Experiments performed in different parts of the world on mechanical moving contact devices did not prove successful. On |
the other hand, the mercury-arc valve offered one possible line of development. From the end of 1920's, when ASEA embarked on the development and manufacture of static converters and mercury-arc valves for voltages up to about 1000 V, the possibilities of developing valves also for higher voltages were investigated.
This necessitated the study of completely unknown fields, where earlier technical experience could only be applied to a limited degree. For a number of years it was indeed an open question whether there existed any solution at all to the challenges. When the HVDC system finally proved to be a technical reality, there still remained uncertainty as to whether it could compete in practice and be economical. By then the already established power transmission systems had also made significant progress.
While electrical machines, transformers, etc., can be designed with great precision with the aid of mathematically formulated physical laws, the design of the mercury-arc valve must be based to a large degree on empirically acquired knowledge. When trying out higher voltages, one is confronted by specific physical challenges. In a power line or high-voltage apparatus raising the voltage is met by increasing the insulation clearances. In the mercury vapour atmosphere of the mercury-arc valves it does not help at all to increase the spacing between the electrodes.
The story continues....
Dr. Uno Lamm and the mercury-arc valve