Lifetime Assessment of PILC Cables with Regard to Thermal Aging Based on a Medium Voltage Distribution Network Benchmark and Representative Load Scenarios in the Course of the Expansion of Distributed Energy Resources

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.

Steam Storage Rankine Cycle for Unutilized Applications in Distributed High-Temperature Waste Heat Recovery

“…Both suffer from peak loads. Due to an increase in renewable energies and weather-dependent fluctuations in the provision of power, distribution networks are increasingly reaching their limits, which leads to faster aging of the existing cables [29]. Since grid extension is associated with high costs, operators are trying to avoid overloads by means of intelligent controls and extensive planning.…”

State-Space Load Flow Calculation of an Energy System with Sector-Coupling Technologies

“…Both cable types must be considered in regard to their thermal aging behaviors. On the one hand, a PILC relies on the same insulation material as oil-immersed transformers, and [60] suggests that the parameters listed in [58] may be transferable; although, unfortunately, experimental proof is not provided. As a result of this uncertainty in [60], relying instead on determined data.…”

“…where Θ max is the highest permissible conductor temperature, P d the current power dissipation, P d,rated power dissipation at rated load, I c the current conductor current and I rated the cable's highest rated power. Further details and in-depth analysis concerning the approximation of ∆Θ c are given in [60,68].…”

Thermal aging management for electricity distribution networks: FEM-based qualification of underground power cables

“…For asset managers of power cable systems around the world, the main challenge is how to manage effectively the vast electricity distribution networks consisted of a large number of expensive underground cable lines, many of which are approaching the end of, or have passed, their designed lifespans [8]. The researchers and scientists have so far analyzed load diagrams [9,10], thermal IEC-based (analytical) models [9,10], and thermal FEM-based (numerical) models [11][12][13] of various power cables for the purposes of associated thermal aging management. The most frequently analyzed power cables are those with cross-linked polyethylene (XLPE) insulation, which have the expected total service lifespan of 40 years and which are not considered to be replaced or relocated during their designed lifespans [9,12,14,15].…”

“…Hence, it is necessary to estimate the condition of underground cable lines based on limited available data such as cable specifications and service (environmental and operating) conditions. In addition, it is known that hot spots can accelerate thermal aging of cable insulation [18], as well as that the Arrhenius model is widely used to quantify the effects of temperature and time on the aging process [1,2,6,7,9,10,14,16]. There are a large number of publications dedicated to the thermal aging management of power cables and the application of the Arrhenius model.…”