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I2>-Protection Module – Unbalanced Load Protection [ANSI 46] Legend: t = Tripping delay t -cool = Cooling time constant Theta(t) = Momentanous heat (thermal) energy Theta 0 = Heat (thermal) energy before the cooling down has started If the heat amount is not reduced when the permitted unbalanced load current is overshoot again, the remaining heat amount will cause an earlier tripping. Typical NPSI-Relay Operating Curves 100001 . 104 1 . 10 3 t ( I2% , 0.5 , 200) t ( I2% , 0.5 , 100) 100 Time (s) t ( I2% , 0.5 , 50) t ( I2% , 0.5 , 20) t ( I2% , 0.5 , 10) t ( I2% , 0.5 , 5) t ( I2% , 0.5 , 1) 10 1 0.1 0.1 1 10 1 I2% (Curren t I2/I2s (%)) 10 K=200 K=100 K=50 K=20 K=10 K=5 K=1 MRA4 02.08 UK Page 261
