The start of a completely new power transmission technology.
| The world's first HVDC Light test transmission was a 3 MW ±10 kV link between Hällsjön and Grängesberg in central Sweden. It uses a 10 km long, temporarily de-commissioned AC line owned by VB Elnät, a subsidiary of Vattenfall AB. Trial operation in the field started in March 1997. |
The transmission normally serves either as a feeder into the Grängesberg AC grid or into an islanded part of that grid. In the latter case, the DC system feeds into a passive load with no other source of power. The HVDC Light transmission then alone controls the voltage level and frequency.
The 3 MW Hellsjön transmission
During the first years a number of tests have been performed to verify the HVDC Light concept, and between the tests, the stations have been in operation on a 24-hour schedule either in transmission mode or in SVC mode to gather experience. Hellsjön is also a test bench for new components and equipment.
| Main data |  |
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| Commissioning year: | 1997 |
| Power rating: | 3 MW |
| No. of poles: | 1 |
| AC voltage: | 10 kV (both ends) |
| DC voltage: | ±10 kV |
| Length of DC overhead line: | 10 km |
| Main reason for choosing HVDC Light: | Test transmission |
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