Inverse Definite Minimum Time, IDMT

In IDMT relay, its operating is inversely proportional to fault current 
and also a characteristic of minimum time after which this 
relay definitely operates.

Example, for a fault current of 25KA - the time delay may be 2s ;
& for a fault current of 30KA - the time delay may be 1.5s.

Thus as the fault current increases the time delay decreases.