The current collector is the vehicle’s only moving point of contact with the overhead line. In a 3 kV DC system it operates with a contact force of 70–120 N, and in AC systems at 45–105 N, with the contact wire positioned 4.9 to 6.1 m above the top of rail and with stagger of up to 0.4 m on curves. Everything installed at and downstream of the current collector operates under continuous vibration, displacement and impact, at temperatures from −25 to +70 °C, and in icing and frost conditions.
Three phenomena broadly determine equipment selection in this zone. The first is overvoltage: switching surges from the vehicle’s own apparatus and lightning surges from the overhead line - a surge arrester is installed on the roof at each disconnector, and its continuous operating voltage and discharge current are selected according to the line voltage and insulation class. The second is the electric arc created when the contact strip loses contact with the wire - the strip must withstand heating and the resulting energy impulse. The third is safety in the event of contact-strip damage: the ADD system automatically lowers the pantograph when pressure is lost in the strip channel, and information about its state must reach both the driver’s cab and the main circuit breaker.
Equipment used in this zone includes: carbon and metallized contact strips, traction surge arresters, fuse-links and roof disconnectors for HV auxiliary circuits, pantograph-status monitoring components (ADD, PPD, OHD), and relays and connectors carrying these signals to the vehicle control system.
