Electromagnetic Relays

Attracted Armature Type • Induction Disc Type • Induction Cup Type • Moving Coil Type Electromagnetic Relays

Hinged Attracted Armature Type relay

Shaded Pole Induction Disc Relay • Robust & reliable Construction • Fluxes displaced in space & time • Eddy currents in disc • Disc rotation α driving toque • Brake magnet to avoid over run • Used for over current protection • Used for slow speed relays • Reset/pick up ratio > 95%

Wattmetric type Induction Disc Relay • Two electromagnets • Upper and lower produce two different flux • Energised by two different sources • If energised by same source then R and X would be made different to get phased difference between fluxes

Induction Cup Relay

Induction Cup Relay • Stationary core inside rotating cup • Spindle carries arm - closes relay contacts • Spring for resetting torque • No brake magnet • Principle of Induction motor

Induction Cup Relay • Rotor is hollow cylinder (inverted cup) • Two pairs of coils produce rotating field • Cup has less inertia than disc • Interaction of rotating flux with current • Less magnetic leakage • Torque per VA is 3 times than disc type • Operating time 0.01 s • High torque/inertia ratio • Suitable for higher speeds of operation • Used for distance & directional relays • Stationary core inside rotating cup • Spindle carries arm - closes relay contacts • Spring for resetting torque • No brake magnet • Principle of Induction motor

Moving Coil Relay

Torque Production in Induction Relay

Force Produced in Induction Relay

Electromagnetic Relays