Securing the largest single unit transformer repair

On the last day of September 2008, ABB in the UK were contacted by ScottishPower (SP) with the question of how large a transformer the repair factory in Drammen, Norway could take and handle. Shortly after answering this question, an invitation to tender was issued by the customer. It turned out to be about a 690/880 MVA and 17/285 kV generator transformer (GSU) at the large Longannet Power Plant (PP), west of Edinburgh. The unit had failed in service, with clear indications of winding damage in LV phase C and there was no spare unit available. Power generation at the PP was therefore substantially cut back and set to incur huge losses of revenue for an extended period of time.

The failed unit was the first out of four identical units manufactured by Bruce Peebles in Edinburgh (later renamed and eventually closed) in 1968 and had been in regular operation for about 40 years, running at high or full load.

Transformer entering the Drammen workshop.

Little documentation on the unit was readily available - not much more than an outline drawing and rating plate photos. A site inspection was deemed imperative in order to gauge the challenge. A team from ABB Transformer Service in Stone and Drammen was quickly set up and went to site. Internal inspections through top hatches as well as an external survey were carried out. It turned out that the unit, being of a bell-type design, had a very special internal transport supporting structure at the top, which is critical to understand in order to safely transport the unit. Moreover, the core was of a 3-leg design, extremely unusual for this size transformer, requiring special lifting arrangements in the factory for this very high active part.

Some critical data
Shipping height:	5.5 meters
Shipping weight:	274 tonnes
Core net height:	5.1 meters

By analyzing photos and other data gathered at site, as well as previous experiences with similar designs, the Drammen Production Manager, Erik Aronsen, was able to conclude that by applying specially designed adapters, the huge unit could be lifted and handled in the Drammen workshop, including in and out of the top-loading vapour-phase oven, although with limited space. ABB Drammen was ready to take on the repair challenge!

Transport
The next challenge was to establish ways and means to transport the unit, with its combined shipping weight and height, from site to the Drammen workshop. At the time of original installation, all four units had been ferried across the Firth of Forth (estuary) on a specially designed vessel, both the Bruce Peebles factory and the Longannet PP being on the waterfront. To find solutions to the transport challenge, the ABB Stone team brought in two UK firms who came up with four different options on how and where to get the unit on to a vessel and then transport it all the way to Drammen. The option to be chosen would depend on which alternative was going to be deemed the most suitable to carry out after further detailed studies and a site survey. ABB was ready to proceed!

After further scrutinizing the sparse data available, ABB Drammen was able to decide on the required materials, man-hours and other requirements to be used in preparing a firm quotation for fault investigation and various repair options. A joint bid was submitted by ABB to SP in early November.

After several rounds of talks, evaluations and negotiations, SP decided eventually in mid

January 2009 to have the unit shipped to Drammen for further investigations, leaving a possible repair to be decided on later. Three weeks later the unit was lifted from the Longannet river embankment on to a barge in an impressive operation using a land-based crane, all arranged by ABB Stone. The operation had to be carried out during a short time frame around peak tide to be able to bring the loaded barge out of the very shallow waters. It was then taken to the nearest port and transhipped to the special ro-ro ship Elektron for the voyage to Drammen.

Arrival by special ro-ro ship to ABB Drammen.

Arrival to Drammen
Upon dismantling the unit in the ABB Drammen workshop, the failure was quickly located which helped in the understanding of the investigations being carried out by SP.

The unusual size and design of the transformer might have been the showstopper, as ABB now would have to replace this huge and abnormal 3-leg core, with SP eagerly awaiting the assessment and proposals. Time was starting to run out. ABB, Drammen had to find out quickly if ABB had ever built such a core before, and then if they could build a replacement core.

“Our mood was frankly dipping a bit, due to the major extra costs this would add to a repair”, says Per Meyer, business development manager at ABB Drammen. “But, on the positive side, it was quickly found out that one core of this type and size had been built by ABB in Europe, in Ludvika, for a nuclear power plant four years ago”. Kurt Gramm, from ABB Ludvika within hours was able to provide detailed design drawings and data for that core to the Drammen team. And within a week, Svein Løvlien, senior design engineer at ABB Drammen, had, after an intensive effort, designed and specified the rather complex replacement core.

For cutting and building the core, an approved outside company had already accepted to do it. So again, ABB could do it, but would SP have it? “It became clear to us that the only real reason for SP to buy the repair would be a significantly shorter delivery time compared to getting a new unit”, Meyer adds. “It was increasingly a matter of risk exposure at the Longannet PP. We therefore had to speed up all our internal ABB processes and approvals and focus on our planning for the repair.” Required risk reviews (technical and commercial) were arranged, supported and executed successfully in record time, and a revised repair offer, now including a new core, was given in mid-April under the condition of ABB receiving a purchase order within less than three weeks in order to maintain the promised delivery time.

Additional discussions followed. Due to the increased value of the project, an evaluation and approval process in Iberdrola, the Spanish owner of SP was required. This was deemed to take until the end of June. The ABB problem with this was that, in order to achieve the shortest possible and crucially important delivery period, ABB would have to order materials before the summer vacation. A deadline had been set by the sub-suppliers of July 1, at the very latest. The decision was therefore taken by ABB Drammen to go ahead and complete design calculations and be prepared to order final winding and core materials by or before that date.

Towards the end of June it emerged that Iberdrola apparently had received an offer for a new replacement unit with a very competitive price and a delivery time getting close to the ABB repair time. It appeared Iberdrola might be favouring buying a new unit instead of the repair, but it was still unclear what the outcome would be.

The ABB Spanish account manager for Iberdrola, Alfredo Parres, was therefore commissioned by the ABB Transformer Service management to use a pre-arranged meeting with Iberdrola management late on June 30 to explain the ABB case directly and clear up any misconceptions. This was expertly done, and the next day SP placed the written purchase order with ABB. The team in Drammen managed at the last minute to place the vital orders with the sub-suppliers. Just in time! Delivery ex works will be in March 2010.

Meyer concludes: “This journey, from the last day of September 2008 to the first day of July 2009, has proved to be a prime example of dedication, proactiveness, determination and excellent team efforts by all involved. Much deserved credit is due to the impressive efforts of the ABB UK and Norwegian teams, not least the technical team in Drammen, and all those involved in making themselves readily available to support the team effort in order to bring it to this very successful outcome”.

Well done to everyone involved for making this the largest single transformer repair for ABB.