The initial expansion phase at the Tierfehd site began in 2009. After 40 years of operation, all the power transmission and auxiliary power supply facilities needed to be completely over- hauled. In addition, the production systems are being expanded with a pumped storage plant with a capacity of 140 MW at Tierfehd. A further pump storage plant with a capacity of 1000 MW (Linthal 2015) is under construction. The infrastructure of the electrical energy systems has been expanded accordingly.
With the completion of the 220 kV and 50 kV switchgears on April 28, 2010, the Glärnisch Ost high-voltage line was connected to the GIS system. At the same time, trial operation was begun for the main components for auxiliary and emergency power. Simultaneously, the existing equipment in the cavern and the operating building were connected to the new station.
In August 2010, dismantling of the existing switchyards began. This meant that construction work on the connecting canal between the two lakes could be continued and completed.
Starting in October 2010, the 9.5 kV and 16 kV systems were first installed in the cavern, and the 16 kV system was then installed in the operating building. On the construction side, the prerequisites for retrofitting the 380 kV switchgear and the network coupling were satisfied.