Overhead power line crossings over ropeways short-circuit effects due to movement of the electric conductor

The considerable extension of Italy’s electricity supply network creates a great number of intersections between overhead power lines and other features such as roads, railway lines, ropeways, canals and rivers. In Italy, the law rules on the installation of overhead lines1 also deal with such cases (termed “crossings”) and, depending upon the rated voltage, define a number of mandatory installation criteria, electrical clearances, mechanical checks and calculations (for the conductors, insulator strings and towers) in order to achieve adequate reliability relative to specific environmental (and especially conservative) situations. With reference to some overhead power line crossings over ropeways, this report presents calculations of current magnitudes in potential short circuits resulting from the accidental fall or lowering of an electric conductor on a wire rope and the experimental procedures followed in order to recreate some short circuit occurrences and verify the subsequent damage to wire rope. This study has been promoted and financed by the Autonomous Province of Trent and the Autonomous Region of Valle d’Aosta, and performed by the University of Padua (Department of Electrical Engineering), which has developed it through the following phases: 1. Hypotheses of possible occurrences 2. Computation of magnitudes and durations of possible short circuit currents 3. Evaluation of fundamental and meaningful parameters to be employed in electrical tests 4. Coordination of electrical tests (tests with strong currents injected into different types of wire ropes carried out by SVEPPI2 Laboratory) and checks for damage in the form of visual inspection and tensile tests on the wire ropes (performed by LA.T.I.F3 Technological Laboratory). Even if the hypothesized occurrences have a very low probability (considering the conservative requirements of the abovementioned Rules for the installation of overhead lines), the results of the study are meaningful since they draw attention to unsuspected phenomena with effects that are undetectable by visual inspection but highly detrimental to ropeway safety.