Modeling of German Low Voltage Cables with Ground Return Path

Abstract

In this contribution, measurement data of phase, neutral, and ground currents from real low voltage (LV) feeders in Germany is presented and analyzed. The data obtained is used to review and evaluate common modeling approaches for LV systems. An alternative modeling approach for detailed cable and ground modeling, which allows for the consideration of typical German LV earthing conditions and asymmetrical cable design, is proposed. Further, analytical calculation methods for model parameters are described and compared to laboratory measurement results of real LV cables. The models are then evaluated in terms of parameter sensitivity and parameter relevance, focusing on the influence of conventionally performed simplifications, such as neglecting house junction cables, shunt admittances, or temperature dependencies. By comparing measurement data from a real LV feeder to simulation results, the proposed modeling approach is validated.

An Optimal Power Flow Algorithm for the Simulation of Energy Storage Systems in Unbalanced Three-Phase Distribution Grids

“…The neutral conductor is explicitly represented (see Figure 2) as the current and voltage drop on the neutral conductor have to be considered to be able to ensure the compliance with the given grid limits. The diameter of the neutral conductor is smaller than for the other conductors for several cable types [44]. Hence, it is necessary to model the current on the neutral conductor explicitly to be able to take into account the burden of the neutral conductor.…”

“…This is not possible using Kron's reduction. The reason for this modelling approach is that the voltage drop on the neutral conductor can be significant in German low voltage grids under unbalanced conditions if the soil is not or only weakly conductive or the distance between the grounding points is large [44].…”

“…In real low voltage grids, there are inductive and conductive couplings between the different phases as seen in Figure 4. For a correct calculation, especially for unbalanced power flows, these mutual impedances have to be considered [44]. Taking into account the mutual impedances leads to the following impedance matrix z:…”

“…The mutual impedances are not the same as the distances between the different conductors inside the cable are not the same. As can be seen in [44], the assumption of same impedances leads only to minor differences in the results, therefore the mean value of the mutual impedance z M is used for all mutual impedances in this paper.…”

“…As shown in [44], neglecting this conductive path leads to significant deviations. To model the conductive path through earth, an approach presented in [44] is used. It consists of an imaginary point that represents the earth.…”