Overhead Contact Systems for electric transit vehicles utilize catenary or single contact wire suspended from cantilevers, bracket arms or span wires. For single contact wire, inclined pendulum suspension provides optimal performance for pantograph or trolley pole current collectors, though it is under-utilized in the United States. Typical suspension for single contact wire consists of direct suspension hangers or stitch suspension with steady arms where stagger is achieved by pulling off the contact wire with the hanger (direct suspension) or steady arms (stitch suspension). This results in the full weight of the contact wire in the span length being supported by the stitch or line insulator. This rigid point of attachment results in a heavy, stiff suspension leading to current collector bouncing, arcing and premature contact wire wear as the upward movement of the wire is restricted and a hard spot is created. It also results in excessive sag at elevated temperatures and contributes to an increased angle at the support span approach.
Inclined pendulums can be utilized in constant tension systems or variable tensioned systems where they impart a semi-constant tensioning into the line and keep the wire tension relatively stable over a particular temperature range. The expansion/contraction of the contact wire is taken up in the inclination of the pendulums where they rise or fall so that the tension and sag in the contact wire remains relatively consistent. In addition, they provide less resistance to uplift of the current collectors at the suspension point so that rising of the contact wire occurs as the collector approaches and passes under it. The vertical angle of the contact wire approaching the span support is kept to minimum levels and collector performance during hot weather conditions tends to remain trouble free. Further, the energy wave set up in the wire from the moving collector is not grossly reflected at the suspension point as with direct suspension thus allowing the collector to pass through smoothly without bounce or loss of continuous contact.
This paper describes the benefits of inclined pendulums in constant and variable tensioned systems such as creating a semi-constant tensioning effect, preventing current collector bounce and premature contact wire wear at the supports by reducing the uplift resistance on current collectors. It also provides the least visual obtrusiveness of all the suspension systems. In addition, this paper will present the associated costs of the inclined pendulum suspensions.