Protection of Electrical Instruments

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Minimum Protection for EHV Lines :

  1. Overcurrent & Earth Fault Relay.
  2. Distance Protection Relay.

Minimum Protection for Transformer :

  1. Overcurrent & Earth Fault Relay at Primary & Secondary Side.
  2. Restricted Earth fault .
  3. Differential protection.
  4. Gas pressure Relay, WT, OT Relay.
  5. Over Voltage protection .

Minimum Protection for HV Feeders :

  1. Overcurrent & Earth Fault Relay.
  2. Translay relay.

  • Minimum Safety Working Clearance of 2.6 mts to be

maintained inbetween bare conductors & live parts in 11kV lines .

  • Different Transmission line Voltages & there Distances.


Transmission line voltages
Transmission line Distances
11 KV(10- 30 km )
33 KV( 30 - 50 Km)
66 KV( 50 - 100 Km)
132 KV( 100 - 200 Km)
220KV( 200 - 300 Km)
400 KV( 200 - 300 Km)


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