Ans: Contactor in power circuit of locomotive is used to connect relevant sections for operation. Connecting or disconnecting the power circuit at different conditions of operation and at different locations.
They are classified by their methods of closing the movable contact – 1) electromagnetic 2) electro -pneumatic 3) cam & roller operated
Application : 1) Electromagnetic – used in the circuits carrying low currents such as taken by auxiliary motors. 2) Electro pneumatic – used to control heavy power currents. 3) Cam & roller operated – used for group switching.