This paper presents a novel approach to the modeling of high voltage underground cables. Its main contribution is that it considers induced effects. Indeed, it incorporates the estimate of induced voltages and currents in cable sheaths in steady state due to the nearby cables and sheaths, for different types of sheaths connections and for various single-phase short-circuit configurations and three-phase short-circuits. Furthermore, it allows multiple circuits to be coupled automatically in a simple way. An intuitive and friendly simulation tool has been implemented that allows the automatic generation of multiple coupling circuits and to calculate all these induced effects caused by the connection of the sheaths and the distance between cables. It has been validated by comparing it with the expected theoretical data and to other simulators with satisfactory results.

Introduction

Objections to the construction of overhead power lines (OHL) are becoming increasingly common. This is influenced by several factors, such as their visual impact, strong social opposition, the difficulty of carrying out the relevant expropriation of land within the time and cost constraints imposed by the project, etc. This is happening not only in urban environments where space restrictions make clear that overhead technology is impossible, but also occurs increasingly in rural areas. Besides, high voltage cables have an insulation layer, so electroshock and short circuit risks of high voltage underground cable lines are lower than overhead lines. For all these reasons, in recent years we have seen an improvement in the technology of the manufacture and installation of underground insulated high voltage cables [1]. However, this solution has also drawbacks; the cost of an underground cable of the same length and power transmission capacity than an overhead one can be up to 5.6 times higher for the level of 400 kV, although for 150 kV is comparable in price. In addition, underground cables can cause environmental problems by obstructing runoff and the effect on the underground animal habitats. Moreover, from a technical point of view, electrical calculations for high-voltage (HV) underground cables are very complex and have a number of electrical characteristics that make them very different from those for overhead transmission lines [2–۴]. Although a great deal of research work on PD based cable insulation monitoring, diagnostics and localization has been published in recent years on medium voltage (MV) cables, few of them are found on cross-bonded HV cable systems [5,6]. Besides, the sheaths of these insulated cables are bad conductors and generate magnetic fields that originate induced voltages. Then, depending on the type of connection to ground of the sheaths, currents are generated which in turn also induce voltages in nearby sheaths. Indeed, the sheath current generated on metallic sheath can cause electroshock for human, cable fault and reducing of cable performance. These effects must be considered as they influence both line transport capacity and the design of the protections. Therefore, if the sheath current of high voltage underground cable line is determined before this underground cable is installed in the project phase, the required precautions can be determined according to this estimated value. That is why modeling and simulation are so useful tools. But the modeling of these circuits is not easy, indeed many factors influence the voltages and currents and thus, formulation of the sheath current is difficult and complex [7].