THE MAIN TRANSMISSION CONNECTIONS FROM HELSINKI ENERGY'S (HE's) POWER PLANTS are connected to the national grid via two 110-kV transmission lines that were erected on the eastern and western boundaries of the city in the 1950s. Electricity consumption has increased twelve fold in the last 50 years and, in the event of a western power plant shutdown, the transmission capacity of the western line is inadequate to maintain the security of supply to Finland's capital city, Helsinki. This 110-kV transmission line between the power plant and the nearest substation is 3.5 km (2.2 miles) in length being routed over a sea gulf in front of a respected habitation area, near water recreation centers, an open-air historical museum and in front of the residence of the President of Finland. The panoramic view from the city overlooking this inner sea gulf and small uninhabited islands is an attractive vista enjoyed and appreciated by Helsinki's citizens.

In Europe, many transmission projects have been met with opposition, particularly overhead lines, which have been criticized for their perceived risk from electric and magnetic fields (EMF), for being visually detrimental to the landscape and for decreasing property values. These issues have delayed the approval of overhead line projects, and in many countries, costly underground cable solutions have been adopted. The public and media no longer view overhead lines as signposts of technological progress, even though the benefits of electrification are taken as a matter of course. Many of the opposing arguments are understandable, and the industry has not always been very reciprocal with its neighbors and their feelings.

At HE, communication with all stakeholders is one of the core values of the company's environmental strategy. Since the late 1980s, we have practiced EMF risk communication through open dialogue with concerned individuals or groups. Good design also has been our aim in constructing facilities in cooperation with city planners and different political boards. This is a necessary obligation, as the company is owned by the city. Therefore, in view of the increasing attention being given to transmission line projects, and due to the sensitive location of the 110-kV circuit that needed to be upgraded, HE sought its neighbors' and public participation and cooperation in this project.

The design phase of the project to renew the western 110-kV transmission line started in late 1999. The planning and permit processes were complete by the end of 2002. Construction of the foundations began in March 2003, the towers were erected that summer, and the new 110-kV line was first energized in November 2003.

ENERGY USAGE IN HELSINKI

Helsinki's population of 550,000 people, living on latitude 60°N on the shore of the Baltic Sea, enjoy four distinct seasons with temperature extremes that vary from 25°C (77°F) in summer to -25°C (-13°F) in winter. These climatic conditions result in huge energy demands, and the security of supply of the extra-high-voltage/high-voltage systems is therefore a crucial system design factor. Since the 1950s, the city has had a centralized district heating system, the power and heat being produced in a very efficient combined heat and power (CHP) process supplied mainly by HE's three power plants. Two coal-fired CHP plants are located near the center of the city, and the third, a gas-fired CHP plant, is on the city boundary. The main pipelines of this district heating system that connect the power plants to the heat distribution network are installed in large tunnels some 50 m (160 ft) below ground level in granite bedrock.

The capital is connected to the national grid by two 400-kV/110-kV substations, one in the east and one in the north, and a 110-kV double-circuit overhead transmission system (Fig. 1). The interconnecting cable system is partially installed in the same tunnels used for the district heating system, and the medium-voltage and low-voltage distribution networks in the central districts of Helsinki are mainly underground.

The electricity market in Finland has been liberalized since 1995, so customers have the freedom to choose their suppliers for both electrical energy and heat. In 2005, HE's net sales were 7600 GWh electricity and 7100 GWh heat, with 93% of buildings and houses being connected to the city's district heating system. As an electricity company, HE also supplies customers outside the capital and nearly 50% of the power purchased is sold elsewhere in Finland. Fingrid, the nation's sole operator is responsible for the transmission system outside Helsinki.

110-KV TRANSMISSION LINE TOWER DESIGN

The existing 50-year-old lattice towers had to be replaced, as they were not designed to support the increased weight of a 110-kV line having larger twin cross-section conductors. At the initial planning phase, HE was very aware of the landscape values of the proposed transmission line route and anticipated opposition on aesthetic grounds, expecting the main question posed by neighbors and local associations would be: “Why not underground the new line?” Based on economics, building similar lattice towers for the upgraded transmission line would have been preferable, but HE was keen on adopting a new approach, a decision that was in accord with the city planners who support high-class design.

The late Professor Antti Nurmesniemi (1927 - 2003) had a long and celebrated career as an industrial designer. His work has become classic, from coffee pots and furniture to office interiors, and from metro trains to high-voltage transmission towers. In the 1990s, he was responsible for individually designed towers that had been constructed at some visible crossings of the national grid, so HE invited him to design a series of towers for the transmission line over the inner sea gulf. This alternative was likely to be more costly than lattice towers, but HE wanted to have an innovative design that would be seen for the next 50 years.

Professor Nurmesniemi presented an A-shaped tower made of rounded steel elements that satisfied structural demands and, when seen from a distance, also looked graceful. An architect's slogan is: “If you cannot hide a structure, make it visible.” Besides this original design, the color of the towers was to be nontraditional. A blue color was chosen purposely to stand out from colors that appear in nature.

PROJECT ALTERNATIVES

HE studied 110-kV cable schemes that offered the same transfer capacity as an alternative to rebuilding the existing 110-kV transmission line, and considered two cable solutions:

  • Lay the double-circuit cable link with 12 single-core cables on the seabed. However, the inner sea gulf is relatively shallow, about 12 m (39 ft) deep plus mud 10 m (33 ft) thick, and cables laid on the seabed would be vulnerable to damage from boat anchors in this recreational body of water.

  • Construct a cable tunnel 3 km (1.86 miles) deep in the bedrock. HE's existing large underground tunnels serve several purposes as they carry district heating pipelines, fresh water pipes, and 110-kV, 20-kV and ITC cables. On the projected route of the transmission line, none of these additional utility services were required.

Finally, other key factors in selecting the new 110-kV transmission line scheme were:

  • Cost

    The cost of the cable schemes were estimated to be at least three times the cost of the overhead line solution

  • Security of supply

    This was considered to be higher in the case of overhead lines compared to the cable systems due to the ease and speed in which faults can be located and repaired in the event of a mechanical or other failure.

  • New line corridor

    There was an opportunity for HE to use the existing line corridor or opt for a new route that involved moving the line further out to sea, which would release valuable building and recreational land for the city. The latter new line corridor was selected as shown in Fig. 2.

MAGNETIC FIELDS

HE calculated the magnetic field exposure in close proximity to the proposed twin conductor double-circuit 110-kV overhead lines. With a symmetrical phase design (R-S-T versus T-S-R), and maximum circuit loading 1200 A on each circuit, the highest magnetic field under the line would be between 2 µT and 4 µT at ground level. And, at the edge of the right of way, the magnetic field is even much lower, hence exposure levels are well below the European Union's recommendation for permanent public exposure limit of 100 µT. As is customary for all of HE's transmission line projects, magnetic field levels are made available to the media and general public. It should also be noted that in Finland electricity safety regulations do not permit habitation under overhead lines. The reason is electrical safety, not the perceived health effects of exposure to magnetic fields.

110-KV TRANSMISSION LINE CONSTRUCTION

Three companies responded to HE's open invitation to tender for the construction of the double-circuit 110-kV transmission line. The turnkey contract to build the circuits was awarded to the Finnish company Eltel Networks Ltd., which has long-term experience in aesthetic tower projects and whose contract also included the structural design of the architecturally designed A-shaped towers. Basically, the 3.5-km (2.2-mile), 110-kV transmission line contract comprised the erection of nine towers between Salmisaari Power Plant and Meilahti 110-kV/10-kV Substation. The five new landscape towers over the sea are erected at intervals of 500 m (1635 ft); the remaining towers on the 110-kV transmission line are traditional lattice design.

Site foundation works commenced in March 2003. The winter of 2002-2003 was very cold in Helsinki and proved advantageous for construction work. The sea ice reached 90 cm (35 inches) thick and was strong enough to carry the vehicles needed for foundation work. To construct the foundations for the open sea towers, a small island and temporary bridge were built. The foundations for these towers were pile driven into the granite bedrock at 21 m (69 ft) under sea level through the mud layer, and only the tie bars were drilled to the rock and tested. The drilling pole alternative was considered and rejected to avoid disturbing the mud that would have clouded the water and been detrimental to fish. Figures 3, 4 and 5 show the sections of the landscape tower being assembled, and Fig. 6 shows the completed landscape tower.

The land section of the transmission line is routed through a recreation park in close proximity to the residences of Finland's President and Prime Minister, so HE agreed not take down any trees, an undertaking the contractors were able to fulfill. The new lattice towers were erected in the same position as the existing supports; hence, construction of this section was deferred until the existing line was dismantled (Fig. 7).

The tubular sections used for the landscape towers were made of Finnish Rautaruukki steel. The engineering workshop TTP Companies Ltd. fabricated the steel work, and welded, galvanized and painted the tower structures. These towers, which are 60 m (196 ft) tall and weigh 50 metric tons (55 tons), were pre-assembled in 6-m and 12-m (19.6-ft and 39.2-ft) sections and transported to the seashore. A special crane truck was stationed on a pontoon platform to lift the sections for the erection of the towers.

Following the harsh winter was an exceptionally warm summer in 2003. Operations involving the delicate lifting and tower assembly were undertaken during a period of calm sunny weather. The experienced Eltel Networks construction team erected the first landscape tower in four days, the first ever of this design done in such a short amount of time. The team was able to assemble each of the four remaining landscape towers in a day.

The twin conductors per phase comprising 305 Al1.39-St1A “Duck” were installed using a normal tension stringing method. Insulator sets are of V-type with glass cap and pin insulators. The existing lattice towers and their foundations were dismantled, with the steel structures intended for recycling.

Throughout the construction period an excellent team spirit developed between all of the partners, and Professor Nurmesniemi was a regular attendee at the project and site construction meetings. The existing 110-kV circuits were de-energized for a period of seven weeks, somewhat less than the 11 weeks specified in the project construction program. The rebuilt 110-kV transmission line was commissioned in November 2003 (Fig. 8). Overall, the 3.4 million euros (US$4.15 million) project was slightly less than the estimated cost even with the additional cost of the five landscape towers. The additional towers, which were regarded as an environmental investment, cost 1.1 million euros (US$1.34 million).

COMMUNICATIONS AND PUBLIC RELATIONS

At the initial planning stages of the transmission line renewal project, HE published the planned route, the cable and overhead line alternatives, and the proposed design of the towers. Meetings were organized with neighbors and local associations, press releases were prepared for the media and all information was available on HE's website with an invitation for comments and suggestions. Even before the final decision of the Board, it appeared that most of the stakeholders, city planners and neighbors had accepted HE's technical and security-of-supply arguments for the overhead line scheme, and the landscape tower design gained popularity in the media.

In January 2003, together with the Fingrid Co., HE organized an exposition of designed landscape towers to honor the 75th anniversary of Professor Nurmesniemi. The exposition was called “Grand Lines.” The previous landscape towers commissioned by Fingrid won the esteemed design award of the Chicago Athenaeum Museum in the Good Design competition in 1999.

SUMMARY

At HE, one of the main aims was the interaction between different stakeholders throughout the whole project. Although most of the events and press releases were planned in advance, HE was flexible on individual demands for further information. In summer 2003, a contest to name the new landscape towers, or the entire line, attracted 1500 proposals. HE invited a jury, comprising a designer, journalist, linguist and the project engineer, who selected “Antti's Steps” as the name of the new line, a reminder of the shape of the towers crossing the inner sea and in honor of Professor Antti Nurmesniemi.

At the beginning of this project, HE had no idea that a technical renewal project of a transmission line, although located in a sensitive landscape, would gain such popularity throughout the various stages of the project. But maybe this resulted from the communicative approach, the possibility for people to express their opinion before final decisions, and from the respect for the landscape values along the route of the line.

A cultural researcher invited to speak about “The Aesthetics of Everyday Life” emphasized that we do not need to consider technology, culture and environment to be separate or competitive factors in a society. By concluding that the visual and aesthetic world of experience in our everyday life is valuable collectively expresses the views of the population that Helsinki Energy serves.

ACKNOWLEDGEMENTS

The author is very grateful to Jari Hakulinen, M.Sc. (Tech.), and Pauli Vanhala, M.Sc. (Tech.), from Helsinki Energy and Kai Nieminen, M.Sc. (Tech.), from Eltel Networks for their technical contributions to this article. The creative persistence of Mauri Vatanen, M.Sc. (Tech.), from Helsinki Energy in initiating the new approach was of great value for the success of the project.

Dr. Martti Hyvönen has had a 25-year career as an occupational health physician, mainly in the electricity industry. Besides dealing with working conditions and worker's health, since the 1980s Hyvönen has been involved with issues like asbestos, air pollution and electromagnetic fields, which are simultaneously environmental and public health issues. In 2001, Hyvönen was named environmental director for Helsinki Energy. In addition, he participates in committee work on environmental and sustainable development issues at national and European levels. martti.hyvonen@helsinginenergia.fi