Customer: Kraftwerke Oberhasli AG (KWO)
Location: Switzerland

Application: Converter and Distribution Transformers
Rating: 50MVA

Date: 2012

Kraftwerke Oberhasli AG (KWO) is one of the leading hydropower companies in Switzerland. At the time of writing KWO have nine power plants, with 26 turbines and a total capacity of 1,125MW. These are spread over eight reservoirs on the Grimsel and Sustenpass. In total they produce around 7% of the electricity coming from Swiss hydroelectric power plants.

For a specific project KWO needed four 50MVA converter transformers along with a number of auxiliary distribution transformers for an underground installation. In the past these transformers had always been filled with mineral oil, which necessitated the installation of a complicated fire suppression system.

In 2010 the Midel team from M&I Materials met with a wide variety of interested parties to discuss the benefits of using MIDEL 7131 in place of mineral oil for the converter transformers. The attendees at the meeting included personnel from KWO, the Utility BKW and the Swiss Institute for the Promotion of Safety and Security (SWISSI). The fire safety of Midel impressed all those present so much that they decided to evaluate in depth whether the fire suppression could be removed if MIDEL 7131 was used in place of mineral oil.

The transformers for this project were already on order, so there was a need to change the fluid from mineral oil to MIDEL 7131. The M&I team worked in conjunction with KWO and the transformer manufacturer ABB to ensure that MIDEL 7131 was a possibility for this particular application. In the meantime a comprehensive risk assessment was carried out by SWISSI, to demonstrate that MIDEL 7131 was of equal safety to the mineral oil and a fire suppression system combination. The conclusion of this study was that MIDEL 7131 was viable and in some cases superior to using mineral oil with suppression.

Following the successful outcome of the interaction with ABB and the SWISSI report, KWO received and installed the MIDEL 7131 filled transformers, without any fire extinguishing system. This allowed them to save substantial costs in terms of capital installation, but also removed the ongoing expense of maintenance of the extinguishing system.

Based on this project a joint paper was written between M&I Materials and KWO and was presented at a recent Cigre Paris session, demonstrating that M&I work in conjunction with their customers at every step of the way for a successful outcome.