Eaton Cutler-Hammer Digitrip RMS 510 Instructions Manual

Also see for Cutler-Hammer Digitrip RMS 510: Instructional Leaflet Instructions Instruction leaflet

AD 33-855-4Page 76The SHORT DELAY TRIP TIME curve in Figure14-1 shows the time to trip response of the TripUnit to FAULT currents. There are actually eightdifferent SHORT DELAY TRIP TIME curves avail-able on the Trip Unit (selected by the Short Time -switch setting), three of which follow a constant lztslope for best coordination with downstreamdevices, five of which are FLAT (fixed trip time)'The lowest level of FAULT current to bring on thisresponse is selected by the Short Delay Pickupsetting on the TriP Unit.The SHORT DELAY TRIP TIME curves available onthe Trip Unit (selected by the Short Time switchsetting), can also be modified by a feature of theDigitrip RMS system called ZONE SELECTIVEINTERLOCKING.The INSTANTANEOUS TRIP TIME curve in Figure14-1 shows the time to trip response of the TripUnit to FAULT currents. This curve is FLAT, provid-inq the most rapid trip time possible (with noinientional delay) to be able to clear the fault asfast as possible and minimize the damage to thesvstem. The lowest level of FAULT current to bringon thi" respon"" is selected by the lnstantaneousPickup setting on the TriP Unit.ln most applications, main Breakers will have LongDelay and Short Delay functions, but will omit thelnstantaneous function to allow a downstreamfeeder Breaker to clear the fault without trippingthe main Breaker, thereby enhancing systemstability.ln many applications, feeder Breakers will haveLong Delay, Short Delay, and lnstantaneous func-tioni to allow a downstream device to clear thefault without tripping the feeder or the mainBreaker, thereby maximizing system stability.ln some applications, feeder Breakers will haveLong Delay and lnstantaneous functions, but omitthe Shod Delay function. This is fine for coordina-tion with upstream main Breakers, but the feederwould not normally allow a downstream device toclear the fault without tripping the feede[ therebycompromising the system stability.ln some applications, feeder Breakers will haveLong Delay and Short Delay functions, but will omitthe lnstantaneous function to allow proper opera-tion of an unusual load or coordination with down-stream devices.LONG DELAY TRIP TII\4E\ \t2tFLAT SHOBT DELAYTBIP TIMEINSTANTANEOUS TRIP TIIV]EJ>l=l-.-->CURRENTOPERATINGCONDITIONSFig. 14-1 Time-Cunent CurvesEtT.il Ftfective 9/01

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