Overpassings of electric overhead lines upon Ropeways: short-circuit effects due to electric conductor falling or lowering

The great extension of the electric transmission network entails a great number of intersections of overhead lines with other works e.g. streets, railway lines, ropeways, canals and rivers. In Italy, the law rules for installation of overhead lines regard also such cases (termed as "crossings") and compel (depending upon the rated voltage) a sum of installation criteria, electrical clearances, calculations of mechanical checks (for the conductors, the insulator strings and the towers) in order to achieve a suitable reliability in relation to detailed environmental situations particularly conservative. This paper, with relation to the "overpassings" of some electric overhead lines upon ropeways, reports the computations of the current magnitudes of a possible short circuit due to the accidental falling or lowering of an electric conductor upon a wire rope and with the experimental procedures performed in order to both re-create the short circuit occurrences and verify the subsequent damages on wire rope. This study has been promoted and financed by the Autonomous Province of Trento and the Autonomous Region of Valle d'Aosta, and entrusted to the University of Padova (Department of Electrical Engineering) which has developed it through the following phases: 1. Hypotheses of possible occurrences; 2. Calculation of magnitudes and durations of possible short circuit currents; 3. Evaluation of fundamental and meaningful parameters to adopt in the electrical tests; 4. Coordination of electrical tests (tests with strong currents injected into different types of wire ropes, carried out by SVEPPI Laboratory) and of the damage checks by means of sight inspections and tensile tests on the wire ropes (carried out by LA.T.I.F Technological Laboratory). Even if the hypothesised occurrences have a very low probability (considering the conservative requirements of abovementioned Rules for the installation of overhead lines), the study results play a meaningful role since they put in evidence unsuspected phenomena with effects that are undetectable by sight inspections but very detrimental on the safety of ropeways.