Abstract
The decentralized feed-ins from distributed energy resources (DER) represent a significant change in the manner in which the power grid is used. If this leads to high loads on electrical equipment, its aging can be accelerated. This applies in particular with regard to the thermal aging of older generations of power cables, namely paper insulated lead covered (PILC) cables. This type of power cable can still be found frequently in medium voltage (MV) networks. If aging of these cables is significantly accelerated in the presence of DER, distribution system operators (DSO) could face unplanned premature cable failures and a high replacement demand and costs. Therefore, this paper investigates the thermal aging of PILC cables in a MV distribution network benchmark for different load scenarios, using standardized load profiles and representative expansion scenarios for wind power and photovoltaics plants in particularly affected network areas in Germany. A main objective of this paper is to present a methodology for estimating the thermal degradation of PILC cables. An approach is used to draw simplified conclusions from the loading of cables to their conductor or insulation temperature. For this purpose, mainly Joule losses are considered. In addition, thermal time constants are used for the heating and cooling processes. Based on the insulation temperature, thermal aging is determined using the Arrhenius law or the Montsinger rule. However, it is important to note that there is an urgent need for research on reference data in this area. For this reason, the results of the lifetime estimation presented in this paper should only be considered as an approximation if the selected reference data from the literature for the aging model are actually applicable. The lifetime assessment is performed for a highly utilized line segment of the network benchmark. Accordingly, extreme values are examined. Different operational control strategies of DSO to limit cable utilization are investigated. The results show that the expansion of DER can lead to a short but high cable utilization, although the average utilization does not increase or increases only slightly. This can lead to significantly lower cable lifetimes. The possible influence of these temporarily high loads is shown by comparing the resulting cable lifetime with previous situations without DER. It is also shown that DSO could already reduce excessive aging of PILC cables by preventing overloads in a few hours of a year. In addition to these specific results, general findings on the network load due to the influence of DER are obtained, which are of interest for congestion management.
Highlights
In order to limit climate change, a transition of the energy system to generation technologies without direct emissions of greenhouse gases is a basic prerequisite
This paper describes the thermal aging of paper insulated lead covered (PILC) cables
High utilization or overloads in radially operated distribution networks occur especially in substations and the adjacent line segments, such as line segment 2 in the network benchmark. The utilization of this line segment is determined by means of a load flow analysis for three different load scenarios, namely without distributed energy resources (DER), wind power- and PVdominated
Summary
In order to limit climate change, a transition of the energy system to generation technologies without direct emissions of greenhouse gases is a basic prerequisite. Key technologies in this respect are wind power and photovoltaic (PV) plants. These distributed energy resources (DER) are characterized by fluctuating power generation due to their dependence on the natural availability of solar radiation and wind. These plants are primarily connected to the distribution grid due to their power size. The expansion of DER leads to a change in the utilization of the power grid—especially of the distribution network
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