Westinghouse . ElectricalPartManuals

1 Westinghouse DB 41-100A Page 1 Type CO Overcurrent Relays Non-dir ecti onal, Sin gle Ph ase, Adjust ab le Time Delay Application Westin gh ouse CO relays , a compl ete coor din ated lin e, as s ur e accurate an d reli abl e pri mary or back up protect ion against ph ase or gr ound faults . Th ey provi de th e back bone of an y protect iv e relayin g system, fr om gen er ator to load . For select iv e coordin ati on betw een relays , seven dif fer ent ti me curve ch ar acteristi cs ar e av ail ab le. All ar e desi gned to op er ate faster at hi gher faul t cur rents . Each typ e has a wi de range of cur rent tap settings an d ti me di al positi ons. Properly ap pl ied , CO relays will provide maxi mum servi ce continuity by tripping th e fewest possible ci r cuit break ers requir ed to dis conn ect a faul ted sect ion.

2 For fast (% cy cl e) cl earin g of heav y faul ts . CO rel ay s can be eq uipp ed with ad just ab le inst ant an eous ov er cur rent un it s. Wh er e col d load pick up presents a problem due to heav y in rush cur rents to devi ces such as refri ger ators , water heat ers , et c. , typ e CO relays can be eq ui pp ed with high dropout inst ant an eous trip un its (ITH) which will provi de inst ant an eous trip pro tect ion for th e protect iv e lin e wh en initi al load cur rent is dropp ed to 90% of th e ITH un it settin g. Wh en ac cur rent is necess ary in th e control trip ci rcui t, th e in di catin g con tact or switch (ICS ) de un it is repl aced by th e typ e ACS in di catin g con tact or sw i tch sealed-in un it.

3 Th e ACS un it is simil ar in cons tr uction to th e liT un it , an d has an ad just a bl e range of .25 to .9 amperes ac. Both non-torq ue an d torq ue controll ed de sign s ar e av ailabl e. Advantages Low burden, high th er mal cap acity , neg ligi bl e temperature er ror. Accur ate pi ckup, continuous "b etw een tap " ad just ment . Simp lifi ed sett ings, eas e of accessibil it y , lower main ten an ce cos t. Sp ace savin g Fl ex it est un iv ers al cas es . for semi-fl ush or projection moun tin g. Device Number: 51 February. 1967 Supersedes DB 41-100A dated September, 1961 E, D, C/2013/DB www . ElectricalPartManuals . com DB 41-100A Page 2 Westinghouse Selector Guide Relay Type C0-2 Time Curve Sh ort Comparative Operating Time<D 7 Sec.

4 C0-4 Long (s t ep ) 25 Sec. C0-5 C0-6 C0-7 C0-8 C0-9 Long 25 Sec. Definite 2 Sec. Moder ately 8 Sec. In v ers e Inv ers e Very In vers e Sec. Sec. C0-11 Ex tremely 0. 8 Sec. Inv ers e Basic Application Diff er enti al protection of bus or gen er ators wh er e rest raint windin gs ar e not required. Str aigh t ov er cur rent protecti on wh ere sh ort op er ating time is necess ary for system st ab il ity. Desi gned primarily to provi de ef f ect iv e rel ay coor dinati on wi th th e select iv e trip ch ar acterist ics of Westin ghouse DB breakers . St ep-time op er ating ch ar acteristi c coordin ates with select iv e trip curve of DB break er an d as soci at ed fuses. Motor protect ion. Lon g ti me settin g (150% of full load ) prevents tripp ing due to motor st arting cur rents , an d al lows motor to car ry moder ate ov er loads for safe per iods.

5 Inv ers e ch ar acteris tic pro vi des fast er tripp ing at high er ov erl oads. For us e wh er e generatin g cap acity an d faul t cur rents vary ov er a wi de range. Relay has fix ed op er at in g ti me (p er ti me di al sett i ng) from ap p roxi mat el y 10 to 20 ti mes tap cur rent , th us providin g defini te select iv e op er ati on for sequen ti al tripping. Ov er current ph ase an d/or gr ound faul t detecti on on trans missi on or feed er lines wh er e moder ate ch an ges in generatin g cap acity occur, or on paral lel lin es wh er e on e lin e may be call ed on to car ry both loads . Rel ay ap proach es definite ti me ch ar acteristics at high currents , al lowing wide ch an ges in faul t cur rent magni tud e with li ttle ch an ge in op er atin g ti me.

6 Ph ase an d/or gr ound faul t detecti on of subtrans missi on lin es or feed ers . Als o supplied as pri mary protect ion or back -up for ot h er relays . Wi de range in time lever settin gs an d sl ope of curves faci lit ate coordin ati on an d as s ur e selectiv e op er ati on. De gr ee of inv ers eness requir ed is deter min ed by faul t cur rent magnit ud e, op er at in g ti me desi red, an d th e ch ar acteris tics of nearby rel ay s on th e system. Us ed on feed er ci rcuit break ers which must coor din ate with main an d branch lin e section al izin g fuses. Als o us ed wh er e long time delay is required for li ght ov er load, such as wh er e feed er is en er gi zed af ter ex t e nded out age.

7 (!) Values shown are with lfl1 0 time dial setting. and with 10 times tap value current applied. Factors to Consider in Selecting Proper Relay Type Apparatus or Circuit to be Protected: In general, th e ap pl icati on wi ll in di cat e th e us e of a sp ecif ic relay, Sh ort -ti me rel ay s act fast to av oid eq ui pmen t damage. Long ti me rel ay s hold of f tripping on heav y initi al ov erl oads or mor e ex tended moder ate ov er loads . At hi gher fault currents , defin ite-t ime an d moder ately inv ers e rel ay s maint ain const ant op er atin g time, despi te vari ati on in con nected gen er ati on an d fault cur rents. In vers e an d ex t remely inv ers e relays op er ate resp ectiv el y faster on hi gher fault cur rents.

8 Selective Operation, Sequential Trip ping: To maint ain maxi mum continuity of servi ce, as smal l a sect ion as poss ibl e sh ould be remov ed from a system durin g a fault . A common meth od is to set each successiv e relay, progr essing from th e generator, to op er ate 0. 3 secon d soon er (ex cl us ive of cir cuit break er op er at in g ti me) so th at th e relay near est th e fault will op er ate fi rst to remov e th e faul ted sect ion. See fi gur e 1. Relay t /Time ----:_-:::. I Sec. Power Distance (Ohms)__. Circuit Breaker Fig. 1 Coordination With Adjacent Relays: To as s ur e select iv e operati on, relays in all sect ions of th e protect ed line sh ould have simi lar op er atin g curves.

9 Otherwis e, curves may int er cept , resulting in in cor r ect relay op er ati on. See figur e 2. Coordinated Mis-Matched Fig. 2 Relay Tap Range: Magn itud e of faul t current av ail abl e at a gi ven locati on is us ually d et er mined by system st udi es. Tap range selecti on depends on th e faul t cur rent as seen by th e relay , which is deter mi ned by th e current transf or mer rati o an d its op er atin g ch ar acteristi cs un der fault conditi ons . Ac or De Trip Circuit: Wh er e a de cont rol sour ce (24 to 25 0 volts ) is av ai labl e, ci r cuit cl os ing rel ay s ar e us ed . If de is not av ai l ab le, ci r cuit op enin g relays ar e us ed with www . ElectricalPartManuals .

10 Com ac tri ppi ng, us ing the ou tpu t of a cu rre nt transf ormer to ene rgi ze the ci rcui t bre aker tri p coi l. Under normal conditions, the normally closed contacts of the re lay shunt the bre aker trip coil. High Speed Short Circuit Fault Pro tection: Relays equi ppe d wi th instanta ne ous ove rcurre nt li T or IT H units provide instantaneous ove rcurre nt tri ppi ng, in ad di ti on to tri ppi ng wi th ti me delay on mode rate ove rloads. Construction and OperationCD Tw o basi c desi gns are avai lable: Non-torque Controlled This, the mos t wi dely us ed ty pe , is de si gne d so that the re lay contacts clos e when tap valu e is applied. See figu res 9 and 10. Torque Controlled This ty pe has the lag coi l connecti ons of the 'T' indu cti on unit ele ctromagne t brou ght ou t to separate te rmi nals.