Kemijoki Oy, which was founded in 1954, is one of the most important players in Finland’s renowned carbon neutral electricity system – responsible for balancing half of the country’s grid output – as well as being the leading provider of hydro and regulating power in the colder North and East of the country. Hydropower is emission free and crucially enables weather dependent wind and solar power to also be integrated into the electric system and stored to meet peak demand. Kemijoki’s innovative business model across its 20 power plants brings unique agility: they can adjust the production of safe and secure hydropower by the second, providing proven flexibility for Finland’s increasingly clean grid on an hourly as well as annual level.
The challenge – most northern power plants
Two of Kemijoki’s most northerly plants up in the Arctic Circle – Matarakoski built in 1993 - 1995 and Kelukoski 1999 - 2001, both with a 11 MW output and powering some 10,000 family homes between them – had long been running on their original SF6-based HPA circuit breakers, originally supplied by ABB Stromberg, based in Vaasa.
Despite being technically competent, the aging circuit breakers were due to be replaced and no longer in line with Kemijoki’s strict environmental diversification program or the latest global Dual Logo Standard. Lack of available spare parts was also becoming an issue on breakers that had been in commission for around 30 years.
However, completely overhauling the existing switchgear operation wasn’t financially sustainable and downtime had to be at the absolute minimum because of the key part Kemijoki hydropower plays in the country’s energy security and production.
The ‘retrofit’ solution
ABB provided a type tested and SF6-free alternative without the need to make extensive and expensive switchgear renewals, which really kept costs low and downtime minimal. It was also a comprehensive turn-key solution including design, supply of materials, plus installation and commissioning. Colleagues from the Finnish-based Service division are experts at retrofitting, and they carried out the upgrade.
A customized 12kV version of the market leading MV VD4G vacuum circuit breaker family was specified, which clears potentially harmful short-circuit faults in tens of milliseconds, thereby preventing severe damage and lengthy plant downtime. Resin-insulated vacuum interrupters guarantee higher protection of the core components and it’s a complete asset protection solution that safely masters fault conditions with delayed current zeros and severe transient recovery voltages.
The benefits – saving time, money and resource
Jarkko Virtanen, Vice President, Electrical and Machinery Technology at Kemijoki Oy, said: “Good operational preconditions at the river are a prerequisite for cost-effective hydropower production, so ABB made it very easy for us with a plug and play model that we did to instruction to save valuable time, money and resource.
“Compared to a full overhaul of the complete medium voltage switchgear, we saved almost a month of downtime with the retrofit – taking just hours rather than several weeks – and in an industry where 24/7 power output is expected that’s a lot of vital energy production and lost revenue saved. We also have a much more reliable operational procedure, because it handles the currents much better, and cost effectively extends the life cycle of our generator applications by at least another 20 years.”
Sixten Holm, Business Development Manager for ABB’S Service division in Finland, added: “We have a long-standing and collaborative partnership with Kemijoki Oy and it works because we know and trust each other. They welcomed the input and expertise of our Service division and together we arrived at a solution that brings much higher plant reliability and meets stricter safety standards.
“VD4G represents ABB’s optimum solution for generator applications where the highest possible protection is needed, especially in case of critical short-circuit conditions, while the retrofit’s smaller footprint provides a cost-optimized solution that saves valuable and essential time during site commissioning.”
Now that a successful blueprint has been established, retrofit solutions are being planned for other power plants, while the open switchgear system of Kemijoki’s larger and more heavy-duty power plants are being considered for the latest in DPA pressure breakers – which help to provide continuous, regulated power to critical equipment, irrespective of any disturbances or disruptions occurring on the main power supply.