Bieudron power plant: Diagnostic work on three transformers

Cleuson-Dixence SA commissioned HYDRO to carry out diagnostic measurements on the three 465 MVA and 410/21 kV group transformers of the Bieudron hydroelectric power plant. This work enables ageing processes, insulation defects or mechanical problems to be detected at an early stage and targeted corrective actions taken.

Removing the insulating gas

This presented particular challenges, due to the design of the medium-voltage side and the gas-insulated cable compartments on the high-voltage side. The first step was to open up access to the connections. To do this, the gas was extracted in a controlled manner and the compartments partially dismantled. Once the measurements were completed the compartments were closed, the insulating gas reinjected and the transformers put back into service.

Strategic equipment

Power transformers are among the most critical installations in the energy supply sector. It is vital that they function properly, particularly in hydroelectric power plants, where they act as the bridge between generation and distribution in the grid. HYDRO has the skills, experience and equipment to perform the following diagnostic measurements on power transformers:

• Insulation resistance
• Winding resistance
• Transformer ratio
• Loss factor and capacity of the transformer and its bushings
• FDS (frequency dielectric spectroscopy)
• FRA (frequency response analysis)