Zmutt: renewal of the Medium Voltage (MV) Substations

The station 10kV supplies 5 pumps bringing water from the Zermatt valley to the Grande Dixence dam. The 2 other stations 20 kV are used for powering the Internal Services of the plant and the coupling station.

The old MV cells, built and installed between 1961 and 1964, required a complete renewal.

HYDRO Exploitation, applying its own methodology, carried out all the necessary studies according to the SIA-defined phases, prepared the specifications for the procurement of the equipment and, finally, monitored the assembling of the installations and completed the commissioning process.

The specifications required the replacement of the 10kV MV equipment with six air-insulated "source" cells (2500A, 40 kA, 17.5 kV) and the replacement of the 20kV cells at the coupling station and the power plant with four plus three latest-generation armoured SF6 cells (630A, 16kA, 24kV) for a working life of at least 40 years.

The project also included the replacement of two 630kVA dry transformers for the supply of Internal Services.

The following work was carried out:

• Preparation of detailed diagrams.
• Production monitoring and in-plant testing.
• Dismantling of old installations.
• Repair of the premises.
• Installation of all the equipment and wiring of the new installations
• Installation of a 2500A Duresca link.
• Cold and hot commissioning of the installations.
• Preparation of a final file including the test protocols, diagrams, and instructions for use of the installation and description of the maintenance work to be performed.
• Training of operating staff.

Thanks to rigorous management of the project and works by the various companies and departments of HYDRO Exploitation involved, everything was completed smoothly and on time.