Protective system for AC traction:
Function Of Each Relay: For transformer -
• Inverse time over current relay– as back up protection on primary (HV side) over current protection of transformer and other equipment.
• Overload thermal relay – protection against sustained overloads on t/f
• Earth fault relay – earth fault protection of transformer
• Buchholz relay – Protection from incipient earth or inter winding faults inside the transformer
For catenary -
• MHO relay – wrong coupling protection
• MHO relay – over current protection at farthest point.
• over current relay - over current protection against faults near substation
• Under voltage relay – protection against faults far away from substation