09-05-2017, 04:18 PM
From wikipedia ... don't know whether this is the rationale for the double wire on our LRT:
Quote:Depot areas tend to have only a single wire and are known as "simple equipment" or "trolley wire". When overhead line systems were first conceived, good current collection was possible only at low speeds, using a single wire. To enable higher speeds, two additional types of equipment were developed:
Stitched equipment - uses an additional wire at each support structure, terminated on either side of the messenger/catenary wire.
Compound equipment - uses a second support wire, known as the "auxiliary", between the messenger/catenary wire and the contact wire. Droppers support the auxiliary from the messenger wire, and additional droppers support the contact wire from the auxiliary. The auxiliary wire can be of a more conductive but less wear-resistant metal, increasing the efficiency of power transmission.
Dropper wires traditionally provide physical support of the contact wire without joining the catenary and contact wires electrically. Contemporary systems use current-carrying droppers, which eliminate the need for separate wires.