Automatic Weight Tension and Temperature Compensation: The tension in overhead lines in traction systems depends on the temperature. Higher temperatures lead to expansion of conductors and hence sag. It is therefore necessary to minimize the sag to least by giving more tension to the conductors. This adjustment of tension and sag is done automatically to facilitate spark less collection of current from the overhead lines by the current collectors mounted on the top of high speed loco. It works as follows: The tensioning device consists of pulley block or a winch with suitable reduction ratio. This arrangement is made on the two sides of the tensioned catenary and contact wire. With variations in the temperature the tension in the contact wire and catenary are maintained due to the pull of the counter weights of around 400 kg shown in the figure. The tension in the contact wire and catenary is around 1000 kg.