How does electric traction work?
In OHE, or overhead electrification systems, the supply of electricity is through an overhead system of suspended cables known as the catenary. A contact wire or contact cable actually carries the electricity; it is suspended from or attached to other cables above it which ensure that the contact cable is at a uniform height and in the right position. In the following the term catenary is loosely used even when talking about the contact wire. The loco uses a pantograph, a metal structure which can be raised or lowered, to make contact with the overhead contact cable and draw electricity from it to power its motors. (Usually it goes first through a transformer and not directly to the motors.) The pantograph has one or two blades, shoes or collector pans that actually slide against the contact wire. The DC pantographs generally have two shoes, while the AC pantographs have one shoe, owing to the higher current carried by the DC pantograph. The WCAM series of dual-voltage locos have one D
