First Finnish DC test network implemented in Pernaja

Marking a first in Finland, Ensto and Porvoon Sähköverkko have during this summer tested the utilization of direct current (DC) low-voltage distribution in the public electricity grid. Since 2006, Ensto has participated in a research project at the Lappeenranta University of Technology, where the applicability of low-voltage DC electricity distribution and the utilization of power electronics in power distribution have been assessed. In addition to participating in this project, Ensto has conducted its own research into the various applications of DC electricity.

Porvoon Sähköverkko Oy, which has previously participated in the testing and development of other Ensto technology, has also participated in the construction of this new test network.
In the initial test network we have, for instance, tested heaters at a summerhouse, vacuumed the kitchen and brewed some coffee.


The idea of the university project is to assess how power electronics could be used to improve the energy efficiency and the quality of electricity distribution. This project will continue until the end of 2009. - In order to obtain tangible experiences, we wanted to expand beyond theoretical research and introduce a practical aspect already during the initial stages. Now we have opened Finland’s first test network in Pernaja, in a traditional Finnish summerhouse environment, says Mikael Nordman, Product Development director at Ensto Utility Networks. - We proposed the building of this pilot installation to our partner, Porvoon Sähköverkko Oy, also because a part of their distribution network is located in the archipelago. Archipelagos are considered to be a very potential application area for this DC distribution technology. Porvoon Sähköverkko Oy CEO Magnus Nylander was immediately excited about testing this new application, and now the project has proceeded to the testing phase, Nordman says.

Low-voltage DC power distribution improves reliability and cost-efficiency

Generation and transmission of electricity is based on the alternating current (AC) technology. Using power electronics and DC electricity in the modern society’s low-voltage networks represents something new. Using DC electricity requires converting the AC electricity that is generated at the power plant into DC for distribution in the low-voltage grid. Yet, before the consumer can use this electricity, it must be reconverted into AC electricity close to the consumer. - From the energy company’s perspective, electricity that is transmitted by means of DC technology ensures a stable voltage level. This is particularly beneficial in archipelagos and in long lines in the countryside, says CEO Magnus Nylander of Porvoon Sähköverkko Oy. – There are many more advantages related to DC networks as well. The electrical network can be constructed using smaller cross sections of the cables, yet achieving the same electricity distribution capacity and reliability. This means significant savings in all construction costs, especially in underground cables. Moreover, the network can be divided into smaller segments in order to ensure a high distribution quality. As each DC network forms an independent protection area, only a small part of the network will be affected by outages, Nylander continues.

Positive test results

During the project, the pilot installation has been tested in laboratory conditions as well as in the field, as part of the public distribution grid. - We have even been able to brew us some coffee, says Nordman, with a twinkle in his eye. - However, electrical safety and the reliability requirements for devices pose great challenges to this new distribution technology, and extensive further research and development are still needed. The load type variations also pose a significant challenge to the power electronics connected to the network. For instance, the loads of the frequency converters that are used widely in industry motors are known, but the loads generated by household appliances are next to impossible to predict.

Future applications for, e.g. sparsely populated areas

It has been found that it is possible to use DC electricity and power electronics for electricity distribution, but it will take years before any solutions that are based on the DC distribution technology are adopted on a wider scale. This new technology will still have to be tested a great deal, and strong evidence found testifying to its functionality before the electrical distribution sector will be ready to accept it. The solving of the electrical safety issues and partial updating of national standards will also consume a great deal of time. - DC technology does, however, open up new possibilities for constructing inexpensive low-voltage networks, and we in the product development team believe that, in a few years, DC technology will be used in the countryside and archipelagos where the transmitted power is low and the distances long, summarises Mikael Nordman.
Magnus Nylander, CEO of Porvoon Sähköverkko Oy, and Mikael Nordman, product development director at Ensto Utility Networks, are satisfied with the test results of Finland’s first DC network that operates in the low-voltage public grid.

DC in brief