Sufficient capacity of the network

Capacity of distribution network depends on multiple issues when evaluating the whole power transfer capability. It can be measured by considering the average physical

distri-bution network capacity which includes the installed lines, wires and cables and capaci-ty of the installed HV/MV transformers. An important factor is also efficient use of the network, which can be achieved by advanced monitoring and control systems. “RES-DG hosting capacity” describes the network’s ability to connect distributed generation units to the network. It is important that the hosting capacity is at an adequate level in future and it can be increased by making investments in a way that the capacity of the network increases. By optimizing the use of the installed assets, the recovery can be maximized. At the moment, it is almost impossible to reach highly optimized use of the assets, because there are huge amount of DG production planned in both countries which has to be taken into account. This means that there is no sense to try to optimize the use of the network completely at the moment, without taking into account the long term planning of the network asset management. By introducing flexible interconnec-tion policy for DG in the future, the level of optimizainterconnec-tion could be increased remarka-bly. On the other hand this could lead to a situation, where the production by RES-DG would need to be limited which is not desirable.

Vattenfall’s network in Finland has enough physical grid capacity and in normal op-erating situation, the capacity of the network is good, even during the highest demand in cold winter days. Some problems may occur with high demand, during reimbursement situations, when a feeder under maintenance is replaced temporarily with another feeder or when a primary substation is under maintenance. In general, also the transformer capacity is really high. In addition, during the recent years, VFV has built a number of

“light” primary substations to the network, which has increased the transformer capacity and the network capacity in overall remarkably. In normal situation, none of the trans-formers are being used even near the upper limit of the capacity at the primary substa-tions. It can be said, that when comparing the whole transformer capacity in the network with the highest demand, an average transformer load is under 50 % of total capacity.

In Sweden the situation is quite similar compared with Finland. The capacity of lines and cables of VFS is high enough to satisfy the future needs and increasing de-mand. Transformer capacity in general is good, nevertheless in some parts of the net-work, the transformers and lines need to be changed or have already been changed be-cause of increased loading (demand) which is a part of normal development of the net-work. (Nilsson, 2011) Many of these cases are also related to power quality issues, ra-ther than capacity issues. In general these situations are related to MV/LV transformers in an urban environment. (Lehtonen, 2011) It must also be remembered, that in VFS’s operating area, there are twice as many customers compared with VFV. Sweden has remarkable amount of planned wind power production compared with Finland. It is clear, that these plans and their implementation places huge demands for the network and in order to handle the produced power, the network will face a need for reinforce-ments. This affects mostly the higher voltage level distribution.

However, there are some areas in the network, both in Finland and in Sweden, where the physical capacity will have to be increased in the future. This is mostly a con-sequence of increased demand in those areas and large scale plans for distributed

gener-ation, especially concerning wind power projects, which are planned to be connected to the network. It can be said, that in normal operating situation a congestion risk is at the moment relatively low, both in Finland and in Sweden.

“RES-DG hosting capacity” in Vattenfall’s networks in Finland and in Sweden is at good level. When discussing about low voltage (small-scale) devices, in most parts of the network the impact of the devices is not seen as a threat from capacity perspective.

Rather the increasing complexity of protection and other factors play a more significant role. When talking about larger-scale production units and plants at higher voltage lev-els, the impact is more significant. In these cases, the network often needs reinforce-ments according to the planned amount of generation capacity in a specific area. Many parts of the network are also strong enough to interconnect remarkable amount of gen-eration, without doing any reinforcements. This is a consequence of strategic long-term planning of the network. (Nilsson, 2011) There is Figure 6.8 below about the results for Finland.

Figure 6.8, Results for Vattenfall’s distribution business in Finland based on the au-thor’s analysis and knowledge.

In comparison with Finland, VFS has the same total development, but there can be found some differences concerning the results. For example the “hosting capacity” can be seen slightly higher in Sweden when considering the network structure including transformers and lines. On the other hand when considering just transformer capacity, the study shows that in Finland the average transformer load is relative lower. It must be also remembered that the sizes of the networks are entirely different. Below, there is a Figure 6.9 about the results for network capacity within Vattenfall Sweden.

Figure 6.9, Results for Vattenfall’s distribution business in Sweden based on the au-thor’s analysis and knowledge.