Emax Low voltage air circuit-breakers - ABB Download Center

Operation and protection functionsProtection functionsThe PR121 trip unit offers thefollowing protection functions:• overload (L)• selective short-circuit (S)• instantaneous short-circuit (I)• earth fault (G).Overload (L)The inverse long time-delaytrip overload protection L istype l 2 t = k; 25 current thresholdsand 8 curves are available.Each curve is identifiedby the trip time in relation to thecurrent l = 3 x l1 (l1 = setthreshold).Selective short-circuit (S)The selective short-circuit protectionS can be set with twodifferent types of curves witha trip time independent of thecurrent (t = k) or with a constantspecific let-through energy(t = k/l 2 ).15 current thresholds and 8curves are available, allowinga fine setting. Each curve isidentified as follows:– for curves t = k by the triptime for l > I2– for curves t = k/l 2 by the triptime for l = 10xln (ln = ratedcurrent of the circuitbreaker).The function can be excludedby setting the DIP switches tothe combination labelled“OFF”.Adjustable instantaneousshort-circuit (l)The protection I offers 15 tripthresholds and can be excluded(dip switches in “OFF”position).Earth fault (G)The earth fault protection G(which can be excluded) offers7 current thresholds and4 curves. Each curve is identifiedby the time t4 in relationto current I4. As per S protectionthe trip time can be chosenindependent of the current(t = k) or with a constantspecific let-through energy(t = k/l 2 ).Note: the current values abovewhich G is disabled are indicatedin the installation manual.4ttt =kI 2t =kI 2t = kt = kI1SDC200116F0001I1SDC200117F0001ABB SACE 4/3