METODOLOGÍA ESTADÍSTICA

The selected grids for the analysis cover networks from the 150 kV till 0.4 kV voltage level. The assets included in these networks are HV/MV transformers, 10 kV trans- mission and distribution cables and MV/LV transformers. The number of assets under consideration in this research can be found in Table 6.1. These numbers cor- respond with 48 MV networks that serve in total 920,000 residential customers. The current share of the residential load in the total peak load of these networks is 21%. In order to identify the impacts of future residential demands for various scenarios on the MV networks, the loadings of these four types of assets are estimated with load-flow calculations.

The values of voltages and currents of networks in normal steady-state operation are calculated using daily profiles of the residential loads as input with a hourly

Table 6.1: Overview of network data of 48 MV networks that are analysed.

Asset type Number of assets

HV/MV transformers 122

MV transmission cables (10 kV) 2,664 km MV distribution cables (10 kV) 14,002 km

6.2. Method 95 Scenario Smart grid strategy Profiles of residential loads Maximum loadings / Peak losses Duration of variable energy losses Maximum allowable loadings Required capacities of network assets NPV of energy loss costs Type and number

of reinforcements Fixed energy losses Characteristics of installed assets NPV of cash flow of reinforcements Variable energy losses Total impacts

Figure 6.1: Block diagram presenting the relationship and consequences of various scenarios and smart grid strategies and their impacts on the distribution network.

resolution. For this research, the load-flow calculations are performed with the com- mercial package Vision [5], which uses the Newton-Raphson method to solve the load-flow equations. It is assumed that the HV side of the HV/MV transformer functions as a slack node. Loads are modelled as constant impedances to have bet- ter convergence of the load-flow algorithm (see Appendix E for more information on modelling of the aggregated residential loads for the load-flow calculations). The Vi- sion network files are fine-tuned with recent measurements of cable and transformer loadings and coincidence factors based on these measurements. The coincidence factors are connected to each node of the MV distribution cable with a load to com- pensate for the fact that maximum power at the beginning of the MV distribution cables is not equal to the sum of the individual peak powers of the connected loads. Also, fictitious loads are applied to compensate for the difference in peak load at the HV/MV substation and the peak loads at the MV transmission and MV distribu- tion cables connected to this substation. In future scenarios, the coincidence of peak demands of individual households may change due to for example a simultaneous demand for heat pumps on a cold day. This is taken into account in the way the

Input

- Network topology and parameters, e.g. nominal capacities of assets - Postal codes of transformer substations - Number of houses supplied by transformer

Input

Historical load data: measured yearly maximum power at

(transformer) loads and coincidence factors

Output

Maximum loading of network assets

Input

- Net load profiles of 10 typical residential areas (the load at MV/LV transformers) - Additional load due to the growth of the number of households (connected to the nodes to which the MV/LV

transfomers are connected)

Load-flow calculations of MV networks

Scenario

Scenario A, B or C

Smart grid strategy

- No smart grid - Minimising network load - Minimising electricity supply costs

Figure 6.2: Block diagram presenting the procedure to calculate the maximum loading of network assets for various scenarios and smart grid strategies.

aggregated load profiles at the MV/LV substations are modelled. The diversity of the loads directly connected to the MV cables has not been altered for the load flows with future residential loads.

For the three future scenarios load-flow calculations are performed to calculate the maximum loading of the network assets in 2040 by altering the existing resi- dential loads in the networks to future conditions. This procedure is presented by the block diagram in Figure 6.2. The loads at the transformer substations that supply residential areas are modified by connecting the aggregated daily profiles of the future residential loads that were modelled in Chapter 5. More precisely, the used profiles for the load-flow calculations are the profiles of the day in the year with the highest peak. The transformer substations in these networks supply on average 72 households. For the scenarios a distinction has been made between al- ready existing and newly developed areas. The residential areas were classified by five degrees of population density, resulting in ten typical residential areas (see Sec- tion 3.5). With the postal code of the transformer substation the population density of the residential area that the transformer supplies is known; this can be used to connect the corresponding net load profile to this transformer. The distribution between already existing and newly developed areas in the various future scenarios is presented in Table 6.2. In all scenarios 0.3% of the existing areas are demolished and rebuilt per year (this corresponds to current figures [1]). As a consequence, in 2040 9% of the current MV/LV substations are supplying newly developed areas. Therefore, load profiles of newly developed areas are randomly connected to 9% of the MV/LV transformers. Also, completely new areas are arising due to the growth in the number of households (see Table 6.2); this will lead to the installation of new MV/LV transformers. The impact of the additional load due to these new areas on the required capacities of the MV distribution and transmission cables and the

6.2. Method 97

Table 6.2: Number of households in the three scenarios. Existing/newly developed Number of households

areas (%) (million)

Current numbers 100/0 7.4

Scenario A 91/9 7.4

Scenario B 66/34 10.0

Scenario C 77/23 8.6

HV/MV transformers is included in the analysis; the installation of new MV/LV transformers is out of scope of this thesis and not included.