When energy prices started to rise in 2022, the cost of electrical losses at Kuopion Sähköverkko Oy in Finland increased dramatically. The demand on the network is on the increase, and there are plans to build a new substation to help alleviate this situation. The substation will affect the network's switching configuration. In addition, finding a configuration that will work in contingency situations has proved to be a tedious task. How can we reduce electrical losses and facilitate contingency planning? Can the benefits of the new substation be assessed already at the planning stage? In Kuopio, a bold approach was taken to find solutions to these challenges with a tool that optimizes the switching state of the medium-voltage network.
An electricity utility Kuopion Sähköverkko Oy is responsible for supplying electricity to around 64,000 customers in its network area that covers about 1,600 km of electricity network. There are seven substations and 643 transformer stations. Network Manager Atte Iivanainen says that they currently have a network management team of seven people. The team is responsible for general and long-term planning, project planning, construction, documentation, information systems and pricing. When the workload is heavy, new assisting tools can help.
New substation, laborious process and dramatic increase in costs
Kuopio is a municipality with a high migration rate, and the Savilahti area in particular is a developing district. There is both residential and industrial development in the area, and more large electricity consumers are expected in the next 5–10 years. It is estimated that the electricity demand in the Savilahti area will increase by around 23 MW.
Jukka Taipale, Development Engineer, explains that they carried out a substation contingency plan in 2022.
– A network topology, or normal switching state, was defined for the network, and the network is to be run against this topology. In practice, the topology was defined according to the network automation and the junctions in the network. We looked at how to improve the availability of the network and how to deal with outages with minimum disruption.
However, the network topology will change, as a new substation is planned to facilitate the situation in Savilahti. This will affect the dynamics of the existing electricity network. Once completed, the new substation would reduce the dependence of the Savilahti area on the existing substation, provide new connections to other substations, and reduce the load on the important Levänen substation in 20 kV contingency.
It is precisely the contingency situations that have been the most burdensome for the network operations team. When a substation is taken out of service for maintenance or renovation work, electricity has to be transferred via another substation. The number of possible switching states is huge, and going through them manually involves a lot of repetitive work.
Another case is the dramatic increase in the cost of electrical losses. In 2022, energy prices started to rise, which led to a 176% increase in the utility's costs compared to the previous year.
– Naturally, we were interested to see if something could be done about the situation, and Trimble had a solution that we decided to try, says Jukka, explaining the background to the switch optimization project.
Kuopion Sähköverkko uses Trimble's Network Information System, into which the network optimization tool can be integrated. This makes it possible to optimize the medium and low voltage networks from many different angles using the network model, both in normal operation and in contingency. For example, the aim can be to reduce losses and minimize the load grade on lines and transformers, as was done in Kuopio when the medium voltage network was balanced and the contingency planning was facilitated.
In Kuopio, the aim was also to see whether the benefits of the new substation could be assessed by optimizing the switching states of the medium voltage network already at the planning stage of the project. Optimization was tested by first balancing the network to reduce electrical losses under normal operating conditions and in the current topology. The next step was to try to reduce electrical losses in the topology changed by the new substation. Finally, contingency planning for the 20 kV network was carried out.
The loss analysis was carried out in three different scenarios: first the 10 kV network, then the 20 kV network and finally the 20 kV network in the topology with the new substation.
The task of the utility was firstly to define the objective of the optimization and secondly to define the technical boundary conditions of the optimization, i.e. the values within which the optimization should remain. The voltage drop limit was set at 5 %, the load grade for the main transformer at 75 % and the load grade for the lines at 100 %. No limit was set for the interruption costs and the annual outage duration, but the behavior of these parameters in the optimization was examined. In addition, the calculation voltage was set for 10 and 20.5 kilovolt networks. The price of electrical loss was set at €100 per megawatt-hour.
The result was a proposal for a new switching state and a report on the improvements achieved. In this optimization experiment, the values were calculated and did not reflect the actual situation.
– For 10 kV, both interruption costs and annual outage time were reduced. Most importantly, the peak dissipation power was reduced by more than 100 kW. And the voltage drop was improved with this new optimized switching state, says Jukka Taipale.
Before the experiment, transformers were considered to be the biggest cause of losses, as the network is mainly under relatively low load.
– Of course there are losses from the network, but they were thought to be quite small compared to the transformers. However, the calculated result showed that the losses were split 53–47% between the network and the transformers. The peak power loss using time was a good three thousand hours and the potential savings would be around €33,000 per year with these proposed switching states. This is a considerable sum, Jukka explains.
The next step was to work on the 20 kilovolt network, which is considerably longer in Kuopio than the 10 kilovolt network.
– The losses with the optimized 20 kilovolt network dropped dramatically – by more than 300 kilowatts. The voltage drop was also improved, as was the maximum load grade of the lines. The peak power loss using time was almost 2,900 hours and the potential savings over €99,000 per year. A very high potential in terms of savings in electrical losses, and that's where the euros start coming in annually. So we are very optimistic about using this tool, Jukka continues.
How about the new substation, would it bring more savings? In Kuopio, another loss analysis was carried out on the 20 kilovolt network, where the new substation was digitized. So one new main transformer and a few kilometers of medium voltage network were added to the network. The situation was compared to the optimized network.
– It turned out as we expected. The new substation would do little to reduce losses. In other words, the construction of a new substation cannot be justified in financial terms, says Jukka.
– At least not in terms of saving on electrical losses, Atte Iivanainen adds.
The next step was to look at contingency in the 20 kilovolt network. When one of the main transformers is out of service, the switching state has to be changed. Finding a viable alternative can take a great deal of time and involves a lot of manual, repetitive work. An optimization tool can help to make contingency planning more efficient. The user selects the main transformer to be replaced, and the process of optimization runs through a large number of different switching states to find the best alternative.
Kuopion Sähköverkko chose the scenario where the Savilahti substation’s 40 MVA main transformer was to be replaced.
– The results describe the current situation of our network. So not the optimized network. And only the neighboring substations were included in the analysis, says Jukka.
Finding the optimized switching state in contingency took a couple of hours and the results show that the maximum transformer load factor dropped by ten percentage points, the maximum line load factor dropped somewhat, and the maximum voltage drop was also brought down.
– The process for contingency analysis of the 20 kilovolt network is significantly improved. The network operations team will not have to scratch their heads so much with the new connections and the new main transformer, Jukka says, explaining the results of contingency planning.
Did the experiment meet the expectations of Kuopion Sähköverkko?
Jukka Taipale says that the results of the switching state optimization were surprising, especially the considerable potential savings that can be achieved by improving the current switching state.
– The calculated value is that you can save about €130,000 per year in electrical losses in the medium-voltage network alone by optimizing the switching states, Jukka continues.
– And compared to 2021, which was a more normal year in terms of electrical loss costs, the saving is 14%.
– So we're talking about big sums, he says, adding that it's worth looking more at power than at the cost of electrical losses, which of course scales according to the current price of electricity.
The analysis also showed that the planned substation will not have a significant impact on losses. This result was expected, but what was surprising was the even distribution of losses between the transformers and the network.
– Important information was sought and obtained to support decision-making, says Atte Iivanainen.
He continues that further analyses will be carried out in Kuopio, involving different substations and main transformers. The future and the construction of the new substation are being considered from many angles, as the project will take at least five years.
– This is an attempt to anticipate the Energy Transition. Valuable information was obtained and the situation will continue to be examined. We are very satisfied and we will certainly make changes to the network's switching states on the basis of this experiment. We care about money, he says.
