Relays Used in Over-current Protection

  • The choice of relay for overcurrent protection depends upon the time / current characteristic and other features desired.

  • The following relays are used.

  1. For instantaneous over-current protection – Attracted armature type, moving iron type, permanent magnet moving coil type, and static type.

  2. For inverse time characteristic – Electromagnetic induction type, permanent magnet moving coil type, static

  3. Directional over-current protection – Double actuating quantity induction relay with directional feature.

  4. Static over-current relays

  5. HRC fuses; dropout fuses, etc are used in low voltage, medium voltage and high voltage distribution systems, generally upto 11 KV.

  6. Thermal relays are used widely for over-current protection.