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CONDITION MONITORING
CONTINUOUS MONITORING PROTECTS ALPINE TRANSFORMER
discharges after the transformer had been installed. Under normal circumstances they might have considered returning the transformer to the factory, but given the complexity and cost of doing so, a Vaisala OPT100 Optimus DGA instrument was fitted to monitor the transformer continuously. “Our initial tests showed that the transformer was working well,” explains BKW primary engineer Lukas Eggimann. “However, the detection of discharges, no matter how small, represented a potential risk, so the online DGA monitor was fitted to ensure that alerts would be issued if any abnormalities developed within the transformer.”
T
he installation of a heavy transformer at an alpine location presented the Swiss company BKW with a number of unusual transport issues. Having overcome these challenges, BKW engineers detected small, but rapidly declining
ALPINE TRANSFORMER CHALLENGES In response to increasing demand, and to increase the security and resilience of the power supply in the Gstaad region of Switzerland, an additional 75 MVA transformer 220 kV / 50 kV was required. However, the installation site was located high in the Alps with challenging access issues. For example, it would be necessary to climb steep roads and to cross bridges that are not designed for such heavy loads. Two attached trailers were necessary to carry the transformer, along with a self-propelled vehicle, resulting in a total payload of 123 tonnes, which exceeded the capacity of some bridges. For example, it was not possible to avoid a narrow bridge with a 32-tonne limit, so substantial reinforcement had to be implemented prior to the transformer’s arrival.
ENSURING TRANSFORMER RELIABILITY Following installation, BKW’s transformers are thoroughly inspected by the company’s in- house diagnostic team, as well as the
Technical Commission for High Voltage Issues (FKH). Partial discharges were detected during these assessments, although a strongly decreasing trend was observed over 4 to 5 hours. “There are a number of potential causes of these discharges,” Eggimann explains. “For example, tiny fragments of metal could be present as a result of welding activity during manufacture of the compartment, or the discharges might be caused by other factors such as voids, bubbles or moisture. Whatever the reason, the concern is that they might later develop into serious problems resulting in transformer failure.” The transformer had tested perfectly in the
factory, the discharges were reducing rapidly during onsite measurement, and the costs and complexity of returning the transformer to the factory were prohibitive, so, in order to avoid any potential risk, the Vaisala DGA monitor was installed.
WHY MONITOR CONTINUOUSLY? The traditional method for checking the performance status of transformers is to manually collect oil samples once per year
12 AUTUMN 2024 | INDUSTRIAL COMPLIANCE
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