Time-limited instantaneous overcurrent protection in relay protection

Instantaneous protection helps to protect equipment against phase-to-phase, phase-to-neutral and phase-to-ground short circuits. It trips without additional time delay as soon as the setting current is exceeded. This is the simplest form of overcurrent protection, both in concept and in implementation (relay design). Working Principle: When the current in an overcurrent relay exceeds a critical level, the magnetic effect of the coil activates the moving element. [pdf]