inverse time relay is one in which the operating time is approximately inversely proportional to the magnitude of the actuating quantity. Fig. 10.a show the time current characteristics of an inverse current relay. At values of current less than pickup, the relay never operates. At higher values, the time of operation of the relay decreases steadily with the increase of current. The inverse-time delay can be achieved by associating mechanical accessories with relays.

In an induction relay, the inverse-time delay can be achieved by positioning a permanent magnet in such a way that relay disc cuts the flux between the poles of the magnet. When the disc moves, the current set up in it produce a drag on the disc, which slows its motion.
In other types of relays, the inverse time delay can be introduced by oil dashpot or a time limit fuse. Fig.10 shows an inverse time solenoid relay using oil dashpot. The piston in the oil dashpot attached to the moving plunger slows its upward motion. At a current value just equal to the pickup, the plunger moves slowly providing maximum time delay.
The inverse-time characteristics can also be obtained by connecting a time-limit fuse in parallel with the trip coil terminals as shown in Fig. 10 c. The shunt path formed by time-limit fuse is of negligible impedance as compared with the relatively high impedance of the trip coil. Therefore, so long as the fuse remains intact, it will divert practically the whole secondary current of the CT from the trip Coil. When the secondary current exceeds the current carrying capacity of the fuse will blow and the whole current will pass through the trip coil, thus opening the circuit breaker. The time lag between the incidence of excess current and the tripping of the breaker is governed by the characteristics of the fuse. Careful selection of fuse can give the desired inverse-time characteristics.