Answer / ashish

its a type of overcurrent - earth fault relay --
IDMT -- inverse definite min. time , having diff types--
normal inverse / long inverse / short inverse type

the relay are of 3 types
1) electro mechanical (whose opeartion way is described by
others)
2) static and latest are 3) numericals --no moving part.

the simple way to explain its principle is that
THE RELAY OPERATIONAL TIME IS INVERSELY PROPORTIONAL TO
THE FAULT CURRENT. IN NORMAL INV IDMT FOR A 2.0 TIMES
CURRENT WITH TMS (TIME MULTIPLIER SETTING) of 1.0 THE RELAY
OPERATInG TIME IS 10 SEC,.. WHEREAS FOR THIS SAME SETTINGS
IF CURRENT IS DOUBLED THE TIME REQUIRED IS ALMOST 5 SEC..

but after 20 amp(in 1 A relay) the time reqd is same.

Answer / ajay k mathew

Inverse Definite Minimum Time relay.aluminium or copper disc rotate b/w electromagnet and damping magnet.fluxes induce eddy currents and interact to produce torque.disc rotate to a point where it operates a pair of contact and remove fault

Answer / santhosh.9289

the current in the main winding produces magnectic field that displaced to closing winding,auminium disc produces eddy current that disc make rotate.as the current disc of rotation is high minimum time of operation

actually i can't understand what is 3dB ? and it's really not clear to me.please any one let it me be cleared.

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