What is the difference between circular relay and shuttle relay?
the difference is that in a shuttle relay, you run back and for(e.g. you run 100m to the next person and they run back to where you started, where the next person is waiting e.t.c.). A circular relay is around a track e.g. a 400m track you each run 100m going round the track. hope this has helped.
A contactor, as far as being used to start a motor or the like, is in essence, a relay. A coil is energized and the normally open contacts from the contactor close (normally 3 contacts for an AC motor) and the motor starts. Do I understand your question? Or are you trying to decifer the difference between the coil of a relay and the contacts of a relay?
A reverse power relay is a directional overcurrent relay. Directional relays are relays that sense power flow in one direction, and include (directional) overcurrent relays, reverse power, and impedance based relays. So a reverse power relay is a directional relay, but a directional relay is not necessarily a reverse power relay.