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RELAY SETTINGS Part 2

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We just gone through the Different Relay characteristics,PSM, TMS and all.Its the time to get hand on these. This could be some what different while coming to practical scenario from the theory part, but hold on you could make it nailed! Typical Overcurrent and E/F relay    Just consider the problem with a fault current of  5000A in feeder equiped with a CT of ratio 400/5A for overcurrent along with a relay setting of  125% .We will see the actual relay operating time with all the relay characterics.   here the rated CT secondary is 5A   then the relay pickup would be 125% of 5A=1.25x5=6.25A   the fault current in the relay coil =5000x5/400 =62.5A   so, the Plug setting multiplier is  62.5/6.25=10   from the Standard Inverse characteristics the tripping time is t=TMS x 0.14/(I r 0.02 -1)  where  I r is the PSM   by taking TMS of 1 tripping time will be  t=1 x 0.14/(10 0.02 -1)     ...