Electromagnetic Relays

Electromagnetic Relays

• Attracted Armature Type

• Induction Disc Type

• Induction Cup Type

• Moving Coil Type

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

• Stationary core inside rotating cup

•Spindle carries arm - closes relay contacts

•Spring for resetting torque

•No brake magnet

•Principle of Induction motor

• 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

Moving Coil Relay

Torque Production in Induction Relay

Force Produced in Induction Relay

Electromagnetic Relays

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