Swissgrid is planning and implementing several projects of great strategic importance for the Swiss transmission grid in the canton of the Grisons. They include upgrading the Bonaduz substation. The installation of a transformer will increase the operational flexibility of the substation and consequently improve security of supply in the canton of the Grisons and in Switzerland as a whole. The groundbreaking ceremony marks the start of the construction work, which is expected to last until the end of 2025.
The canton of the Grisons is the second largest producer of electricity from hydropower after the canton of Valais. This means that the Grisons transmission grid plays a key role in Swissgrid’s strategic grid – not only for transporting energy to the consumer centres in Central Switzerland and for exchanging electricity with Austria and Italy, but also for ensuring interregional and regional security of supply within the canton itself.
Swissgrid is planning and implementing a series of expansion and modernisation projects in view of the strategic importance of the Grisons transmission grid. In particular, they include the expansion of the line between Pradella and La Punt to two power systems at 380 kilovolts (kV), which was completed in November 2022, as well as the modernisation of the Pradella – Sils i.D. (Albula line) and the Sedrun – Tavanasa line in Surselva and the replacement of the line between Marmorera and Tinizong. Other important projects for strengthening security of supply in the Grisons involve the modernisation of the two substations in Tavanasa and Bonaduz.
New transformer for the Bonaduz substation
The Bonaduz substation was built in the 1960s. It consists of one 380-kV and one 220-kV switchgear, which need to be modernised and upgraded. In addition, the Bonaduz substation still does not have a transformer to connect the two voltage levels. Transformers are the heart of substations. They are used to increase or reduce the voltage, and connect the 380-kV grid to the 220-kV grid. Swissgrid has decided to equip the Bonaduz substation with a powerful modern 400 megavolt-ampere (MVA) transformer in the same way as the Tavanasa substation. This will enable Swissgrid to increase the operational flexibility of the Bonaduz substation and to strengthen security of supply in the Grisons transmission grid.
Construction phase of around two-and-a-half years
The groundbreaking ceremony on Friday, 16 June 2023 marks the start of work to modernise the Bonaduz substation and to install the new Siemens transformer. The 220-kV switchgear will be fitted with a second busbar. Both switchgear will be supplemented with a transformer bay and a coupling bay. Their protection and control technology will be modernised and housed in a new building. According to the current schedule, work on the Bonaduz substation will last until the end of 2025. Swissgrid anticipates total costs of around CHF 56 million.
Greater protection for substations and measures for the environment
Swissgrid’s transmission grid comprises 125 substations housing 147 switchgear and 26 transformers. Swissgrid is gradually increasing physical protection in its substations. It uses various measures to prevent unauthorised access, vandalism and theft of material. As part of this undertaking, Swissgrid is replacing the existing fencing at the Bonaduz substation with new fencing that encloses the installations and prevents intruders from climbing over or crawling under it.
Swissgrid attaches great importance to the welfare of small animals such as weasels, amphibians and reptiles. For this reason, near-natural small structures such as cairns are being set up at the Bonaduz substation to serve as hiding places and homes for the animals.