List any two types of relays and contactors with their function used in AC locomotive.

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Types of relays and their function in AC locomotive: 1) Buchholz Relay: To protect traction transformer from incipient faults. 2) Earth fault or Ground fault Relay: To protect the system against all kinds of faults related to ground. 3) Notching Relay: To protect DC motor power circuit. 4) No-volt Relay: Ensures that too much current is not applied to DC motor which has lost the speed while the current is off. 5) Overload Relay: This relay detects excessive current in the circuit. 6) Wheel-Spin Relay: Protects motor from rise in current due to over-speeding of another motor. 7) Electromagnetic Relay: For sequencing of operations of machines and equipment. 8) Current Limiting Relay: Sense current values during the starting of motors and maintain them at limiting values during automatic acceleration of motors.

Types of Contactors and their function in AC locomotive: Each contactor makes or breaks the power circuit. i) Electromagnetic Contactor – when operating coil is energized attracts a soft iron armature which in turn operates moving power contact. When coil is de energized moving contact drops ii) Electro-pneumatic Contactor – moving power contact operates to close the circuit when compressed air acts on a piston in cylinder. Releasing air pressure spring forces the piston to open the contact. iii) Cam and Roller operated Contactor – moving contact is carried at one end of hinged arm and roller is carried at other end. Roller is engaged with cam on shaft. Cam shaft can be moved by air engine or vane motor. 


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