T&D World Magazine

ABB Onsite Transformer Repair Returns Irish Station to Production

ABB’s on-site transformer repair service, that effectively takes the factory to the customer, has helped Edenderry Power Station in Ireland to achieve a fast-track return to normal production, and preserve the reliability of its output to the country’s grid, by restoring its failing GSU (generator step-up unit) transformer to full working order.

The project, which was the first on-site repair carried out by ABB’s UK power service team, was completed in just three weeks from start to finish, enabling Edenderry Power to avoid the major disruption and costly loss in production that would have resulted from sending the unit away for factory repair. Furthermore, the total cost of the exercise came to around one tenth of the cost of a brand new transformer that, based on current lead times, would probably take two years from order to delivery.

Edenderry Power Limited was Ireland’s first large scale Independent Power Producer and was recently acquired by the Bord Na Mona. It operates a state-of-the-art 120 MW peat-fired condensing power plant at Edenderry, 40 miles west of Dublin, that supplies around three percent of Ireland’s national requirement. The power station connects to the grid via a single GSU that steps its terminal voltage up to the 110 kV required for transmission.

In March 2007, Edenderry Power noticed a problem with gassing of the transformer, indicating that a fault had developed, and decided to operate a reduced output, with a consequent reduction in energy efficiency. ABB’s UK power service team was called in and, after analyzing daily gas samples and carrying out additional electrical tests, diagnosed an internal fault on the low voltage connections and was even able to locate its position.

Using the information from the diagnostic survey, ABB was able to reassure Edenderry Power and its insurers that, for the short-term, it was safe for the transformer to remain in service. However, it did need to be repaired before it could be turned to full load again, but with each day of reduced generation likely to cost the customer a significant amount of revenue, sending it away for factory repair was out of the question. Clearly, this was the ideal candidate for on-site repair, as Liam Warren of ABB’s UK power service operation explains:

“Internationally, ABB has a great deal of experience in carrying out on site transformer repairs. Until recently, the service was targeted at customers in remote parts of the world, such as Brazil, where the location and transport infrastructure make taking the transformer back to the factory both difficult and exceptionally expensive. But now we have seen a substantial shift in the drivers for this service. So now it is not really a question of geography as one of pure economics, dictated by the cost to the customer of having a transformer unavailable for service.

“In the case of Edenderry Power, the budget for the on-site repair was around £250K, which makes it extremely cost-effective compared to a new replacement transformer that might cost £3 million. But as ABB and most of our competitors are quoting factory lead-times of around two years, buying new was not an option anyway. If we had taken the transformer back to the nearest repair factory, in Norway, there would have been some additional transport costs. The main concern though was the cost of lost production, as allowing for travel time and the factory work, the power station would be off line for at least six weeks, and possibly longer. By taking the factory to the site, ABB was able to reduce the power station’s down time to just two weeks.”

In July 2007, ABB’s on-site repair team, comprising two transformer engineers and a transformer fitter, swung into action. Their first task was to decommission the transformer. Then a local heavy lifting specialist was called in to help move the transformer to a spare building at the power station that was converted into a temporary, fully equipped, workshop, complete with clean room.

Working round the clock, the ABB team de-tanked the transformer, repaired it, reassembled it and tested it on the spot. A key element in the repair process was ABB’s capability to carry out high voltage tests and to commission the transformer ready to return to service. The work was carried out to exactly the same high standards that would be expected of a factory repair, with every phase conducted strictly to ISO 9001 and ISO 14001 procedures.

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