Underground MV power cable joints: A nonlinear thermal circuit model and its experimental validation

Thermal Effects of Ground Faults on MV Joints and Cables

“…Ci represents the thermal capacity of the volume, whereas Gi is a current generator reproducing the heat source due to Joule losses inside the volume, which depend on the temperature T according to (2). Dielectric losses are negligible, as already demonstrated by the authors in [13]. The thermal problem inside the joint and the cable has been solved in polar coordinates: considering the i-th cylindrical elementary volume, the resistive bipoles R ri and R ai take into account the thermal resistance along radial and axial directions, respectively.…”

“…C i represents the thermal capacity of the volume, whereas G i is a current generator reproducing the heat source due to Joule losses inside the volume, which depend on the temperature T according to (2). Dielectric losses are negligible, as already demonstrated by the authors in [13].…”

“…Among them, double ground faults, commonly named cross-country faults (CCFs), have been considered, since the related fault currents are high and quite comparable to line-to-line fault currents. In [13], the authors presented a 2D model only considering cable lines and joints, whereas in [14], a full 3D model also including ground was developed, taking into account thermal exchanges between the ground surface and the external environment. In this Section, the authors firstly recall the model described in [14], and then present the method to evaluate the influence of CR inside the joint during thermal transients caused by CCFs.…”

“…The equivalent electrical network is solved by a home-made software developed by the authors in the Scilab environment [13,14]. The system of differential equations is solved in a transient state through the backward Euler algorithm: according to the formulation in [29], since each capacitance may be replaced by a voltage-controlled current source with a resistance in parallel, the equivalent network becomes purely resistive and is solved by nodal analysis.…”

“…In order to investigate this issue, this paper focused on MV joints' thermal behavior during severe ground faults, which are able to cause very large current values to flow through the cable screens. Based on the circuit model already developed in [13] and further improved and validated in [14] in order to simulate real cable operations and laying conditions, a full 3D model of the cable-joint system is presented. Differently to [14], the electric CR inside the joint is taken into account.…”