Upgrading & uprating

Transforming Forsmark

25 June 2009

The planned power uprate at Sweden’s Forsmark nuclear power plant depends not only on turbine and generator upgrades, but also on improved transmission equipment. By Jorgen Soderberg and Lars Engdahl

Nuclear power currently contributes around 45% of all Sweden’s power needs. Following the closure of the 1200MW Barseback nuclear power plant in 2005 the country’s remaining nuclear facilities are being modernized and re-qualified in order to cover the shortfall in power generation. Vattenfall is investing SEK6 billion (EUR569 million) to upgrade Forsmark’s efficiency, production capacity, ability to meet increased environmental and safety requirements, and for life extension. In total it will be able to increase the output of the three reactors by 410MW.

Forsmark produces around one sixth of all kilowatt-hours of electricity used in Sweden; its current total power output is approximately 3160MW. It is the country’s most recently constructed nuclear power plant, with three BWRs (boiling water reactors) commissioned between 1980 and 1985. Formark is 66% owned by Vattenfall, with the remainder split between Swedish consortium Mallansvensk Kraftgruppe (25.5%) and utility E.ON Karnkraft Sverige (8.5%).

“We have many major challenges to confront, such as our safety culture, and the generation shift among our employees,” Vattenfall said in a statement.

Initially, the Forsmark modernization programme is focusing on unit 3, where a new turbine and main generator is being installed to increase gross output from 1290MW to 1360MW. Siemens has won the contract for the HP turbine (it replaced the LP turbine at Forsmark 3 in 2004). A contract is out for tender for the generator.

Based a history of collaboration that goes back to construction of Forsmark’s original 400kV substation, ABB won the EUR34 million contract for electrical balance of plant equipment that link the generator to Sweden’s power grid. ABB’s Sweden-based centre of competence for nuclear power projects will carry out electrical system studies, design, engineering, installation and commissioning. This includes the supply of three new generator step-up transformers (GSUs), two auxiliary transformers and an excitation transformer.

Logistics is a particular challenge in this project since Forsmark has just one planned shutdown per year. The lack of multiple shutdowns restricts access to carry out the system studies and measurements. Every third year, the plant shuts for a longer period. When this comes around, in 2014, the installation and commissioning of the new equipment will be carried out on a fast-track basis.

Perhaps the single most important element of the Forsmark 3 project is the three new single-phase generator step-up (GSU) transformers, each rated at 560MVA, 415/25kV, that will increase the 25kV output from the generator to the 415kV required for connection to Sweden’s national grid. The GSUs will be manufactured locally at ABB’s Ludvika facility.

The transformer
ABB’s GSU transformer recently supplied to Oskarsham. The Forsmark unit is an exact copy.

The GSUs, which feature forced air/ forced oil cooling, are of the same basic design as the three-phase GSU installed recently by ABB at E.ON’s Oskarshamn 3 nuclear power plant, a project nearing completion (see NEI April 2009, pp22-4). The Oskarshamn project has many similar aspects to Forsmark, since the objective was to facilitate an increase in generation capacity from 1150MW to 1450MW.

In addition to the GSUs, ABB is also supplying two auxiliary transformers. They will provide electrical power for vital services throughout the power plant, such as pumps, ventilation and lighting. ABB is also supplying the excitation transformer that will supply the essential power for the excitation of the generator field coils. All three transformers will be manufactured at ABB’s Vaasa plant in Finland.

The new main generator at Forsmark, rated at 25 kV/1667MVA, will have a similar nominal current to the existing 20.5kV plant. This makes it possible to reuse the existing isolated phase busducts and generator circuit breakers and their subsystems, though ABB will replace all of the IPB insulators.

Isolated phase busducts link the generator to the step-up transformer, provide connections to auxiliary service transformers in the power plant and protect against adverse environmental conditions.

The power produced by the generator is transferred to the step-up transformers via the GCB (generator circuit breaker). A fault current of up to 200kA out in the field is serious enough, but close to a generator it could be catastrophic – the induced magnetic forces could bend solid steel shafts. The Forsmark GCB can interrupt the generator-fed short circuit currents within a maximum of four cycles, instead of several seconds. ABB will overhaul the GCB on site.

The main design considerations throughout the project are to provide an eBOP system for Forsmark capable of handling a gross electrical output of up to 1500MW. New equipment to be installed is based on a design-life of 30 years from commissioning (ie up to 2044). Requalified equipment will be designed for a 10-year life from project completion. The overriding considerations through the design process are to achieve maximum availability, as well as optimum cost efficiency based on an life cycle cost analysis.

Author Info:

Jorgen Soderberg ([email protected]) and Lars Engdahl ([email protected]), ABB

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The transformer The transformer

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