Time-Overcurrent - GE Grid Solutions

1 GE Multilin115 IACIACTime-OvercurrentTime- overcurrent protection of ACcircuits and and Benefits 6 inverse time/current operating curves Target seal-in units available Instantaneous units available Drawout caseApplications Feeder, AC machines & transformers Applications where operating time is inverseto operating currentProtection and Control Ground and f time O/C and U/C Overload motor protection Instantaneous overcurrent (optional) listing of IAC Models, onpages 310 through 314 is organ-ized by time/ currentcharacteristics into find a known model number:1. See WHERE TO FIND IACMODELS on this page to deter-mine correct table and Turn to that table for sequentiallisting of find a model number for aknown application: 1.

2 See APPLICATION, to determinetime/current characteristicsand/or specific See WHERE TO FIND IACMODELS to determine correcttable and Use the rating and commentcolumns of that table to deter-mine Model Number withdesired relays are used in the protec-tion of industrial and utilitypower systems against eitherphase or ground are single phase (althoughsome models contain more thanone unit), non-directional, currentsensitive, ac devices . The basicoperating mechanism (the timeunit) produces one of severalavailable operating characteris-tics. The operating time isinversely related to operatingcurrent which permits close coor-dination with other protectivedevices. It consists of a magneticcore operating coil, an inductiondisc, damping magnet, and amechanical target.

3 The IAC relaymay also include one or morehinged armature instantaneousovercurrent units, with IAC relay is mounted in adrawout case, permitting frontaccess to the relay for testing andmaintenance. Testing can beaccomplished, without removingthe relay, by using XLA relays are used for protectionof feeders, transmission lines,alternating current machines,transformers, and for numerousother applications where a relayis required whose operating timeis inversely related to Inverse Time/CurrentCharacteristicsSix inverse time/current operat-ing characteristics are availablefor the time unit of the IAC (seeFigure 1). Fig. 1. Typical operating characteristics of 60Hz IAC relays. The No.

4 5 time-dial setting isshown for each curve, and the range of timeadjustment from to 10 time-dial settingsis shown for the extremely inverse, theinverse short time, and the inverse long three standard time charac-teristics are as follows:INVERSE TIME relays (see Table 1)are generally applied where theshort-circuit current magnitude isdependent largely upon thesystem generating capacity at thetime of the INVERSE TIME relays (seeTable 2) are best applied onsystems where the magnitude ofthe short circuit current flowingthrough any given relay isdependent mainly upon the rela-tive location of the fault withrespect to the relay and onlyslightly or not at all upon thesystem generating INVERSE TIME relays (see Table 3)

5 Are intendedfor applications, such as on utilitydistribution feeders, where suffi-cient time delay must beprovided to allow a re-energizedcircuit to pick up without unnec-essary tripping during the inrushperiod, and at the same timecoordinate properly with powerfuses and fuse of These DesignsTime/Current Characteristics60 Hz50 HzIAC 51, 52, 60 Inverse TimeTable 1 Table 8 IAC 53, 54, 80 Very Inverse TimeTable 2 Table 9 IAC 77, 78, 90 Extremely Inverse TimeTable 3 Table 10 IAC 55, 56, 68, 85, 95 Inverse, Short TimeTable 4 Table 11 IAC 57 Inverse, Medium TimeTable 5 Table 12 IAC 66 Inverse, Long TimeTable 6 Table 13 IAC 59 Inverse, Over- and UndercurrentTable 7 Table 14 Where to find IAC modelsThree additional time characteris-tics are available as follows:INVERSE SHORT TIME relays (seeTable 4) are used on equipmentwhere tripping must be relativelyfast but should not approach theoperating time of an instanta-neous unit.

6 Protection of powerrectifiers is an example of suchan MEDIUM TIME relays(see Table 5) are used as genera-tor or transformer neutral relaysor as backup protection for feederground faults. Also, the inversemedium time relay may be usedwhere a slower relay is requiredto obtain LONG TIME relays (seeTable 6) are designed for applica-tions requiring long time major area of usefulness is inthe protection of motors againstoverloads under conditionswhere the customary thermaldevices are not UnitInstantaneous units are used toprovide tripping with no inten-tional time delay for currentsexceeding a predeterminedvalue. Typically, if the fault currentmagnitude under maximumgenerating conditions triples as afault is moved toward the relaylocation from the far end of theline, then an instantaneous unit dropout instantaneous unitsare available and are usedtogether with other devices toobtain time-delay tripping.

7 Oneapplication is motor protection,where the high dropout unitsupervises the time unit for trip-ping during starting and overloadconditions. For special feederapplications, the high dropoutunit can supervise the time unitto prevent the overtravel fromcausing undesired tripping and topermit shorter ApplicationsMOTOR PROTECTION RELAYS provide overcurrent protectionfor starting, overload, and faultconditions. The IAC66K relay hasan inverse long time characteris-tic (as described above), whichapproximates the motor thermallimit, and two instantaneousovercurrent units. The first instan-taneous unit is set above themaximum motor starting currentand protects for fault conditionsonly. The second, a special highdropout unit, is customarily usedfor supervising the time overcur-rent unit to permit tripping forstall and heavy overload condi-tions.

8 Operation of only the timeunit indicates a light or moderateoverload condition and can beused as an alarm. The IAC66 Mrelay is similar except that thehigh dropout instantaneous unitis used in conjunction with a time delay telephone relaywhich blocks operating duringinitial inrush conditions, allowingthe unit to be set more CENTER PROTECTIONTheIAC66T relay, which has a statictimer unit used with a highdropout instantaneous unit, isdesigned to protect medium volt-age circuits supplying lowvoltage load centers. This relaycoordinates width the short timeand long time overcurrent tripcharacteristics of 600 V air AND UNDERCURRENTRELAYS(see Table 7) are usedwhere an indication of the varia-tion of a current betweenmaximum and minimum limits isrequired.

9 These relays do nothave a time dial. The time charac-teristics are determined by thecontact CONTROLLED RELAYS have wound shading coilsconnected to terminal of the time-overcurrentunit thus depends on the closingof an external contact acrossthose terminals. The overcurrentrelay can be supervised by someexternal device, such as a direc-tional units are avail-able in several ranges to meetcurrent pickup settings of to 16 A. Sensitivity is deter-mined by discrete tap-plugsettings, and a time dial providesa continuously adjustable timedelay over the entire range. IACmodel numbers which end in 8__A , such as IAC51B801A,provide an extended range ofsettings with a ratio of maximumsetting to minimum setting of 8 other IAC relays have a ratioof 4:1.

10 The available tap settingsare listed below for the commontime overcurrent units:AVAILABLE SETTINGSTime overcurrent units with 8:1range of settings: A unit: , , , , 1, , , 2, , 3, and 4 A taps A unit: , 2, , 3, 4, 5, 6, 7,8, 10, and 12 A taps 2-16 A unit: 2, , 3, 4, 5, 6, 7, 8,10, 12 and 16 A tapsOther common IAC time overcur-rent units: A: , , , 1, , 2 A A: , , , , , A A: , , , , , ,and A A: , 2, , 3, 4, 5, and 6 A A: , , , , 4, 5 A A: , , , , , ,and A A: 4, , 5, , 6, , 8 A A: 4, 5, 6, 7, 8, 10 and 12 A * A: 4, 5, 6, 8 10, 12 and 16A*Some 4-16 A units alsohave 7 A OvercurrentInstantaneous overcurrent unitsare available in several ranges tomeet current settings between 160 A.