It is an inverse definite minumum time relay. In IDMT relay
its operating is inversely proportional to fault current
and also a characteristic of minumum time after which this
relay definately operates.
It is inverse in the sense , the tripping time will decrease as the magnitude of fault current increase.
"for a fault current of 25KA-the time delay may be 2s.
& for a fault current of 30KA the tme delay may be 1.5s.thus as the fault current increases the time delay decreases.
is an inverse definite minimum time relay
there are 2 precautions to be considered when using this these precautions are the time setting and the current tap setting
these are to be considered since the relay is dependent on the inverse of time