Development of Planning and Operation Guidelines for Strategic Grid Planning of Urban Low-Voltage Grids with a New Supply Task

Abstract

In contrast to rural distribution grids, which are mostly “feed-in oriented” in terms of electrical power, urban distribution grids are “load oriented”, as the number of customer connections and density of loads in urban areas is significantly higher than in rural areas. Taking into account the progressive electrification of the transport and heating sector, it is necessary to assess the required grid optimization or expansion measures from a conventional, as well as an innovative point of view. This is necessary in order to be able to contain the enormous investment volumes needed for transforming the energy system and aligning the infrastructures to their future requirements in time. Therefore, this article first explains the methodological approach of allocating scenarios of the development of electric mobility and heat pumps to analyzed grids. The article continues with describing which power values need to be applied and which conventional and innovative planning measures are available for avoiding voltage band violations and equipment overloads within the framework of strategic grid planning. Subsequently, the results of grid planning studies are outlined and evaluated with an assessment model that evaluates capital as well as operational costs. On this basis, planning and operation guidelines for urban low-voltage grids are derived. The main result is that low-voltage grids can accommodate charging infrastructure for electric mobility, as well as heat pumps to a certain degree. In addition, it is concluded that conventional planning measures are not completely avoidable, but can be partially avoided or deferred through dynamic load management.

Systematic Evaluation of Possible Maximum Loads Caused by Electric Vehicle Charging and Heat Pumps and Their Effects on Common Structures of German Low-Voltage Grids

“…It is advisable to avoid loading cables and transformers beyond 50%, as these levels are regularly reached (e.g., every working day); this minimizes losses and provides a certain amount of redundancy. However, since the grid calculations in this study were conducted using the maximum simultaneous power (Section 2.3) that only happens rarely (e.g., once a year), loss considerations are less relevant and redundancy limitations can be tolerated for these exceptional cases; thus, it is acceptable for the lines and transformers to have the maximum short-term thermal overloadings of 100% and 120%, respectively [25,26].…”

Maximum Tolerated Number of Simultaneous BEV Charging Events in a Typical Low-Voltage Grid for Urban Residential Area

“…When evaluating the robustness of the LV grid, a particular focus should be given to the network bottlenecks [26]:…”

“…The maximum short-term overloads for the transformer and lines were assumed to be 120% and 100%, respectively, based on empirical values of aging processes and typical planning and operating principles for urban distribution networks [26]. The voltage deviation at the LV level was restricted to ±5% of the nominal voltage to ensure that the voltage band was maintained, even in the worst-case scenario, i.e., when a local substation uses a transformer with a fixed voltage ratio.…”