In the municipality of Trysil, near the Swedish border, Norwegian distribution network operator Eidsiva Nett has experienced a reduction in the number of residential customers. However, at the same time, it has seen a significant increase in the number of vacation homes and activity centers. These changes have resulted in a large fluctuating power demand during weekends and reduced energy consumption during the remainder of the week.
The distribution network supplies customers in large rural areas through long radial 22-kV overhead lines, many of which have small cross-section conductors, thus creating voltage-quality problems. The increasing expectations of its customers prompted Eidsiva Nett to seek a cost-effective alternative solution to resolve these voltage fluctuations.
The utility's demographic changes have increased the peak load on the network but reduced the total energy consumption and, consequently, revenues. As the area grows even more popular as a leisure destination, Eidsiva Nett may have an opportunity in the future to reinforce its distribution network. In the meantime, the utility had to solve the problem of voltage fluctuations on an overhead distribution line that extends some 52 km (32 miles) at minimum cost.
The problem of voltage fluctuations is familiar, and in spite of constantly investing in the distribution network, it is difficult to foresee and make provisions for unexpected changes in power consumption, even though the overall demand for energy continues to increase. The problem is made worse as utility investment decisions are based on asset life spans of 40 to 50 years. Therefore, it is prudent sometimes to seek quick-fix solutions that will not delay larger projects or investments targeted to supply customers with a high-quality and reliable source of electrical energy.
Initially, the utility considered the possibility of installing series- or parallel-connected capacitors, but design studies confirmed this would not produce the required voltage increase. Also, the capacitor would need dynamic tapping to prevent potential resonance problems. As the recorded load variations were relatively frequent, Eidsiva Nett decided not to install a transformer with an on-load tap changer because of the burden and wear imposed on the tap changer. Therefore, for this remote overhead line, the utility decided to adopt an install-and-forget solution.
Eidsiva Nett discussed the need for a new solution with Magtech A.S., a Norwegian technology company that designed and produced a voltage regulator for use on the low-voltage (230-V) network in 2004. The research and development project to produce a 22-kV voltage regulator was supported by a consortium comprising the Research Council of Norway, Magtech, Norsk Trafo Service and the distribution network operators Skagerak Nett A.S., Haugaland Kraft and Eidsiva Nett. The goal was to demonstrate a solution that could continuously correct voltage fluctuations within a few seconds. In the future, this characteristic probably will be necessary to follow frequent and fast voltage swells caused by distributed generations or sags caused by e-mobility applications such as electric vehicle charging.
Additionally, another feature requested by the consortium was to design equipment that offered a minimum of 20 years of maintenance-free operation. The project was known as voltage stabilization for a weak 12-kV to 24-kV network with distributed generation.
The existing 22-kV overhead line to Trysil offered a good opportunity to test the first solution, even though there was no distributed generation connected to the network. This circuit had a need for fast voltage correction, and the solution would prove cost-effective if it could offer stable voltage without the need for future equipment maintenance.
System analysis studies confirmed the optimum position for the voltage regulator was some 30 km (19 miles) from the 66/22-kV source substation. This location would provide for voltage maintenance within statutory limits for the remaining 22 km (14 miles) of the circuit.
The voltage regulator, developed by Magtech, was positioned in the rural community of Ljoerdalen. Although the 22-kV line has been in commission for many years, the existing condition indicated it was not at its end of life and had adequate thermal capacity. As the downstream power demand was 600 kW, a 1-MW voltage regulator was developed to have some spare thermal capacity.
Design and Installation
The Magtech-designed voltage regulator includes auto transformers and controllable inductors employing cross-magnetization technology. The regulator was designed with three single-phase units to provide the improved flexibility required for testing and commissioning. Also, it eases the problem of transportation to the site. With the regulator mounted in a ground-mounted cabin, the consortium decided a communication system should be installed to establish a link to the control center so the behavior and signal status could be monitored. As this voltage regulator was installed for testing on the 22-kV network, three pole-mounted air-break switch disconnectors were installed adjacent to the voltage regulator to give the required flexibility to disconnect, bypass and ground the unit for measurements and maintenance purposes.
The Magtech development team responsible for the design and construction of the voltage regulator assisted Eidsiva Nett staff with installing and commissioning the unit, and establishing the remote control communication link with the control center. The world's first tailored-design magnetic voltage regulator (magnetic voltage stabilizer) for a high-voltage network was commissioned at Ljoerdalen in Trysil in December 2009.
The unit was commissioned initially in the bypass mode and then made operational through the air-break switch disconnectors activating the regulation. This automated regulator can be operated locally by pushing a single button or from the control center located in the town of Elverum.
The unit has operated as required, delivering corrected voltage during the decade's coldest winter, so the design principles, based on Magtech's worldwide patented technology, have been proven. As this test version includes additional monitoring equipment, the unit will be simplified when designed for mass production. The positioning of the voltage regulator, with respect to the line length and circuit loading, is regarded as important and critical to ensure the required voltage improvements are realized.
Future Development and Applications
At present, a large number of small hydropower plants in Norway are planned and many already are installed in mountainous areas and along the steep Norwegian coastline, as farmers and landowners take the opportunity to use small rivers and streams to add income to their traditional earnings. This business opportunity is being driven by increased electricity tariffs and the demand for new green power that receives economic support.
Often, the energy produced exceeds, by a significant margin, the energy consumption in the area; this can result in the existing overhead line, originally built for local consumption, having voltages in excess of the statutory maximum. The generation, which is linked to water flow rates, is not constant, so this form of distributed generation can have a significant impact on the network voltage levels.
Investment in distributed generation is the responsibility of the power producer, and the installation of voltage control equipment at the point of interconnection often forms a major component of the total cost of small power plants. Similarly, it is difficult for distribution utilities to decide on the thermal loading of new overhead lines in the absence of information on the timing and capacity of new distributed generation connections. Looking further into the future, the demand for green power will result in distributed generation in the form of photovoltaic and wind power installations.
It is of benefit for distribution utilities to defer to investment decisions on network reinforcement by considering the installation of high-voltage regulators. This practice will help more micro and mini power plants to be profitable, encouraging the growth of all forms of distributed generation based on green energy technologies. Thus, creating a cost-efficient distribution network having minimum interconnection costs will help to establish and increase society's use of green energy, thereby creating a smart grid.
The 22-kV voltage regulator will now be further evaluated and, together with system investigations, provide the basis for future system solutions and products that will contribute to making the grid smarter, controlling the costs incurred by network operators, developers of distributed generation and customers.
Collaborative R&D Consortiums
The research, development and installation of the 22-kV voltage regulator is the result of collaborative efforts by the Research Council of Norway, Magtech, Norsk Trafo Service and the distribution network operators, Skagerak, Haugaland Kraft and Eidsiva Nett. It often proves extremely difficult for manufacturers to secure access to operational grid systems and distribution networks to install and test new equipment in view of the cost of resources and risks to customer supplies.
The development of this new equipment serves to illustrate the benefits of collaborative research and development consortiums. They increasingly are required to meet the challenges electric utilities face as they struggle to improve the quality and reliability of customer supplies at a time when concerns about global warming are increasing the use of distributed generation from renewable energy sources, creating real-time active distribution networks.
The management of distribution networks will become even more complex because of the connection of distributed generation, even though automated management systems, dynamic energy pricing or the switching of customers on or off can be used to balance demand with production.
Inevitably, there will be voltage variations on distribution networks, and several strategies and multiple solutions will be required to solve these problems.
Eidsiva Nett has taken steps to stabilize the voltage on its extended overhead line networks by installing the world's first magnetic voltage regulator for installation on a 22-kV distribution network.
The author wishes to acknowledge the support and technical information provided by the consortium partners, Karl Borgerud and Christian Hartmann at Magtech AS, and the staff from Eidsiva Nett, for their roles in the development and installation of the 22-kV voltage regulator.
Tormod Leistad (firstname.lastname@example.org) joined Eidsiva Energy Co. in 1977. Initially, he was employed on the construction of medium- and low-voltage distribution networks. Since completing his technical studies in 1997, Leistad has been a project engineer for the utility.
Eidsiva Nett www.eidsivaenergi.no
Haugaland Kraft www.haugaland-kraft.no
Magtech AS www.magtech.no
Norsk Trafo Service www.norsktrafoservice.no
Research Council of Norway www.forskningsradet.no