When the GSU (generator step-up unit) transformer at the Edenderry Power Station in Ireland began to fail, ABB recommended a different approach to the traditional one of returning the unit to the factory for repair. In this case, the power service team suggested that the factory came to the customer, so avoiding the major disruption and costly loss of production that would have resulted from sending the unit away.
The project, the first on-site repair carried out by ABB’s UK power service team, was completed in just three weeks. Furthermore, the total cost of the exercise was around one tenth of the cost of a brand new transformer which, based on current lead times, would have probably taken two years to make and deliver.
Edenderry Power Limited is Ireland’s first large-scale independent power producer. It operates a state-of-the-art 120MW peat-fired condensing power plant at Edenderry, 40 miles west of Dublin. This supplies around three per cent of Ireland’s national requirement.
The power station connects to the grid via a single GSU that steps its terminal voltage up to the 110kV required for transmission.
DIAGNOSTICS
In May 2007, Edenderry Power noticed a problem with gassing of the transformer, indicating that it could be about to fail, and decided to operate at reduced output, with a consequent reduction in energy efficiency.
ABB’s UK power service team was called in and, after analysing daily gas samples and carrying out diagnostics, found an internal fault on the low voltage connections and was even able to locate its position.
ABB engineers were 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 take full load again.
ON-SITE REPAIR
With each day of lost generation likely to cost the customer over £100k, 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 £250,000, which makes it extremely cost-effective compared with a new replacement transformer that might cost £3 million. But as ABB and most of its 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.”
HOW IT WAS DONE
In July 2007, ABB’s on-site repair team of two transformer engineers and a transformer fitter swung into action. First they decommissioned the transformer, then a local heavy lifting specialist was called in to help move it to a spare building at the power station which was converted into a temporary, fully-equipped, workshop, complete with clean room.
Working around 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 ability to carry out high-voltage tests and 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.