THERMAL ANALYSIS OF POWER LINES: METHODOLOGIES AND APPLICATIONS

The thermal analysis of cables aims at computing the temperature rise inside the cables due to the heat generated inside the conductor during the normal operation of the cable. The temperature limit of the cable is given by the insulation material: if this limit was exceeded the insulation would be damaged. For this reason it is necessary to calculate the cable ampacity that keeps the cable temperature under the insulation limit. The heat generated by the conductor ows radially from inside to outside (the surrounding medium can be air or earth, in case of buried cable) through all the cable layers. The cable ampacity is calculated solving a circuit that represents the thermal behaviour of the cable. The Standards, in particular the Standard IEC 60287, consider many possible congurations. The Standard IEC 60287 allows to choose the cable (it is possible to specify the dimension and the material of each cable layer) and the layout (cables in air or buried). In case of underground cables, the user can decide how the cables are buried (directly in ground or in conduits), the material surrounding the system and the ambient temperature. The Standard IEC 60287 has some lacks: - it does not consider the presence of external heat sources in addition to the power line cables; - it performs only a steady-state analysis; - it is useful only when a tridimensional analysis is not necessary. In the normal practice, in case of buried cables, it is not unusual that there are external heat sources in addition to the power line cables. And the power line is not always supplied by a costant current; it can be supplied by a load curve and there can be a transient. Moreover in some congurations the 2D section changes along the third dimension, therefore a 2D model is very conservative: a 3D analysis is useful. In all these cases where the Standards are not applicable, another method can be applied. The numerical solver used allows to: - consider any heat sources; - study the transient behaviour; - analize a 3D model. The method has been applied to study a particular part of the power line: the junction zone. In the junction zone the magnetic eld is higher and it can be necessary to shield the power line. The shielding method considered is the High Magnetic Coupling Passive Loop technology. If this system is applied a thermal analysis of the junction zone has to be performed because of the presence of a new set of conductors, in addition to the power line cables. In this case the Standard IEC 60287 is not applicable because: - there are heat sources dierent from the power line cables; - a 3D model is necessary to study the eect of the ending connections of HMCPL and the cable joints.