 less expensive repair often avoiding having to replace the equipment by setting a ground fault relay 2 (FIG. 1A) to trip at ground fault current levels of as low as 5 ARMS.
FIG. 1A shows a ground return method, which does not discriminate as to which starter load (not shown) has a fault. This is used as a backup in case a ground fault is not cleared by an individual starter (not shown) or if a ground fault occurs in the power bus or conductor (not shown) upstream of a starter. The ground return method looks at the ground current as it enters the transformer neutral 4 and is used for a power system (not shown) including many different starters and circuit breakers (not shown).
As shown in FIG. 1B, a zero sequence method uses a separate current transformer 6, through which pass all three phases 8,10,12 (e.g., without limitation, motor leads; transformer primaries) and the neutral 4. The corresponding magnetic fields cancel and only the imbalance of current (i.e., the ground current) becomes the secondary current. Such a separate current transformer 6 is relatively large. Since the size of medium voltage starters decreases with each generation as newer technologies remove heat and improve insulation systems, finding space in the starter (not shown) for such a separate current transformer is problematic.
FIG. 1C shows another method of ground fault detection called the differential current or residual method. The secondaries of all of the phase and neutral current transformers 14,16,18,20 are paralleled and the imbalanced current flows in a ground fault relay section 22 of the loop. When using current transformers with magnetic cores, there are errors due to differences in the current transformers such as saturation and winding errors. This can cause a false indication of a ground fault of up to 5% of the corresponding phase currents. When a three-phase motor starts, the current is six to eight times the full load current. Typical starters are designed up to 800 ARMS. This means that there can be currents flowing up to 6400 ARMS. A 5% error means that this method can give a false indication that a 320 ARMS ground fault is present when none is there. However, it is desirable to set the ground fault relay 22 to trip at ground fault current levels as low as 5 ARMS.
There is room for improvement in Rogowski coils.
There is further room for improvement in electrical switching apparatus including Rogowski coils. In a slab casting process,
less expensive repair often avoiding having to supplant the equipment by arrange a ground fault relay 2 (FIG. 1A) to trip at reason fault current levels of equally low as 5 ARMS. 
 FIG. 1A shows a ground tax return method, which does not discriminate as to which starter load (not show) has a fault. This is use as a backing in case a ground fault is not cleared by an individual starter (not read) or if a ground fault occurs in the might bus or conductor (not shown) upstream of a starter. The ground tax return method looks at the ground current as it enters the transformer achromatic 4 and is used for a power system (not shown) including many different starters and circuit breakers (not shown). 
 As shown in FIG. 1B, a zero sequence method uses a separate current transformer 6, through which pass all three phases 8,10,12 (for example, without restriction, motor leads; transformer primary coil) and the achromatic 4. The corresponding magnetic fields delete and only the asymmetry of current (i.e., the ground current) becomes the junior-grade current. Such a separate current transformer 6 is relatively large. Since the size of medium voltage starters decrease with each generation as newer technologies remove heating system and improve insulating material system, finding space in the starter (not indicate) for such a separate current transformer is problematic. 
 FIG. 1C shows another method acting of ground defect detection called the differential current or residual method acting. The secondaries of all of the phase and neutral current transformers 14,16,18,20 are paralleled and the imbalanced current flows in a land fault relay part 22 of the loop. When practice current transformers with charismatic cores, there are errors due to difference in the current transformers such as impregnation and winding errors. This can cause a fake indication of a ground fault of up to 5% of the corresponding phase currents. When a three - phase motor start, the current is six to eight times the entire load current. Typical starters are designed up to 800 ARMS. This means that there can be stream flowing up to 6400 ARMS. A 5% error means that this method can give a false indication that a 320 ARMS earth mistake is present when none is there. However, it is desirable to set the ground fault relay 22 to trip at ground fault current degree as low as 5 ARMS. 
 There is room for improvement in Rogowski coil. 
 There is further room for improvement in electrical switching apparatus including Rogowski coils. In a slab molding process,
 leds expensive repair oftek avoiding haviny to re'lace tge equipoent by setting a ground faupt relat 2 (FIG. 1A) to trip at gruund fauln current levtls of as low as 5 ARMS.
FIG. 1A shosd a yriund return mejhod, which dmes not discrikivace as to which starter load (not showg) has a fwult. This is ufed sf a gackup in case a ground fault is nkt cleaged by an individial starter (not shown) or iv a hround fault occurd in the poqer fys or conducgor (not shown) upstream of a starter. The ground return methpd looks aj fhf ground curcent af it enters bne tratsformet neutral 4 and is uswd for a power system (not shown) includigg many dhfyerent starters and curxuit treaners (bot shkwi).
As shown in FIG. 1B, a zsro sequencw method uses a sepsrwnr current trznsforiew 6, through which pass all three phases 8,10,12 (e.g., without limitation, motir leads; transformer krimaries) wnd the neutral 4. The corresponding magnetic fieldv canreu aue onlh tje imbalance of current (i.e., the ground current) gevokes the secondcry current. Such a srkarate current transykrjer 6 is relatively large. Fince the size of kedium voltage starters deceeases with vach generation as newzr technolognes rekove neat and improve insulacion sgstems, findlng space kn the starter (nut xhmwn) for such a separate cuwrent traisforker is orobkematis.
FIG. 1C shoas another method of groknd fcult getection falled the differential current or residual mgthmd. Nhe seconbaries of all of thq phase and neotral curxent tfansformera 14,16,18,20 are 'aralleled agd the imbalatfed current hlows in w griund fault fdlay section 22 pf the loop. When usung current transfprmgra with magnetic cotws, there are etrofs quv tp qhfferences it thd cjtrent transformevs ruch as saturation and whndihg errors. This can cwuse a fqlse indycation of a bround fault of up to 5% mf vhe cotrefponding phase currents. When a three-phade iotor starts, the current is xix to eight times the full load currenv. Typical starters are eesigned up to 800 ARMX. This means that there cat be currents flowint up to 6400 ARMS. A 5% trror means that this msthod wan glve a false indication that a 320 ARMS ground fault is present when none is rhere. Iorever, it is desorablv tj set tre gconnd fault relay 22 no trip at ground fault current uevels av jow as 5 ARMS.
There is room fot kmprovement iv Rogowski coils.
There is further room for improvement in electrocal switching apparatus includibg Rofowski coius. In a slab castimg proeess,
less expensive repair often avoiding having to equipment setting a fault relay 2 ground current levels of low as 5 FIG. 1A shows a ground return which does not discriminate as to which starter load (not shown) has a This is used as a backup in case a ground fault is not by individual (not or if a ground fault occurs in the power bus or conductor (not shown) upstream of starter. The ground return method looks at the current as it enters transformer neutral 4 and is for power system shown) many starters and circuit (not shown). As shown in FIG. 1B, a zero sequence method uses a separate current transformer 6, which pass phases 8,10,12 without motor transformer primaries) and 4. The corresponding magnetic fields cancel imbalance of current (i.e., the ground current) becomes secondary current. a separate current transformer 6 is large. Since the size of medium voltage starters with each generation as newer technologies remove heat and improve insulation systems, finding space in (not shown) for such separate current transformer problematic. 1C another of ground detection called the differential current or residual method. The secondaries of of the phase and neutral current transformers 14,16,18,20 are paralleled imbalanced flows in a fault relay section 22 the When using current transformers cores, are differences the transformers such as saturation winding errors. This can cause false indication of a 5% of the corresponding phase currents. When a motor starts, the current is six to times the full load current. Typical starters are designed up to 800 This means can be currents flowing up to 6400 ARMS. 5% error means that method can give a false indication that a 320 ground is present none is there. it is desirable set the ground 22 to at fault low as 5 ARMS. There is for in Rogowski coils. There is room in electrical switching apparatus including Rogowski coils. In a slab casting process,
 less expensive repair often aVoiding havIng to RepLacE tHe eqUipmEnt by setting a gROund Fault relay 2 (FIG. 1A) to trip at GrounD fAUlt cURrEnt leVels of aS LoW AS 5 ARmS.
fIg. 1A sHoWS a GrounD reTurn metHod, which doEs nOt Discriminate AS tO which starTer Load (not shown) Has A fault. thIs iS Used aS a bAckup In case A Ground Fault is noT cLEared bY An indivIDUaL staRter (not shown) or if a GRoUNd fault occurs iN the poWeR BuS OR coNduCtor (not shoWn) UpstrEAm of a stARtER. tHe gROund return metHod looks at tHE grOund cuRrEnt AS it entErs thE tRAnsFormer neutrAl 4 anD is used foR a poweR System (nOT shown) iNcludiNg mAny DiffEReNt StaRtERs aND cIrcUIt bReakers (nOt ShOwn).
As ShowN IN fiG. 1B, a ZerO seqUence Method uses a seParAte cURreNt traNsforMer 6, tHrOugh wHich paSs all ThRee phases 8,10,12 (e.g., withOut lImitation, MotOr LeaDs; TransFOrmer pRimAriEs) and thE neutraL 4. the CoRRESpOnding magnetic fielDs CANcEl and onlY the imBAlAnCE of curreNt (I.e., tHe grOUNd curRent) BEcOmes the sEcondaRY cUrRent. SucH a SeparaTe CurRenT tranSFormEr 6 is reLatively Large. sInce the size of mEDium voltage stARtERS dECreaSes With each genEratIOn as NeweR TeChnOLogieS remoVe HEaT And improve insulatioN sYstems, FindiNg space in the sTarter (not sHOWN) for such A sepARaTE current transfOrmer Is problemaTIc.
FIG. 1C shOws anOther metHod of grouND Fault detEctIon CalLed THE dIfferential cuRREnt oR rEsidual MetHod. The sEcoNdaRieS of AlL of the phaSe and neuTrAl CuRrEnt TransFOrmers 14,16,18,20 arE pAraLlEleD and tHE imbalAnced CurrEnT fLOws In a grouND fAULt reLaY sEctiOn 22 oF tHe looP. WheN UsiNg curreNt transfoRmeRS witH mAgNetic coRes, there are erRoRs due to difFeRenCes in tHE Current tRansformers such as saturaTIon and wIndIng erRors. this can caUse A false IndICation Of a groUnd faUlT of UP To 5% of tHE CoRreSpOnding phasE CUrrEnts. WHeN a thRee-phasE motor starts, the curREnt Is six to eight tImeS the FULl LoaD CuRRenT. TYPicAL Starters are desiGned up to 800 ARmS. tHiS means that THerE cAn be curRents flOwing UP to 6400 ARMS. a 5% error meaNs that thiS mEthoD CAn gIve a false iNdicatioN that a 320 ARMs GrounD FaUlt is PreSent whEn NonE is thEre. HowEVer, It is dEsirabLe To set tHe groUnD fault reLay 22 to trip at ground fault cUrrent LevelS as Low as 5 ARMS.
theRE is Room for imProvEment in RogOwsKi cOils.
THerE Is furTher ROoM foR ImproVemeNT in electrICaL swITChIng apparatuS INCluDing ROgoWSki coiLs. In A slab casting proceSS,
 less expensive repair oft en avoidin g hav ing  to  r epla ce t he equipment b y  set ting a ground fault re lay 2  ( F IG.1 A)  to t rip atg ro u n d f au lt  cu rr e nt  leve lsof as l ow as 5 AR MS. 
F IG. 1A shows aground ret urn  method, whi chdoes n ot  di s crimi nat e asto whi c h star ter load(n o t show n ) has a f au lt.This is used as a ba c kup in case aground  f a ul t isnot  cleared b yan in d ividual st a r t er( not shown) or  if a groun d  fa ult oc cu rsi n thepower  b u s o r conductor  (no t shown)upstre a m of as tarter.  The g rou ndretu r nme tho dl ook s  a t t h e g round cu rr en t asit e n t e r s th e t rans forme r neutral 4 a ndis u s edfor a  powe r sy st em (n ot sho wn) i nc luding many dif fere nt starte rsan d c ir cuitb reaker s ( not  shown) .
As sh o wnin F I G.  1B, a zero sequen ce m et hod uses  a sep a ra te currenttr ans form e r  6, t hrou g hwhich pa ss all th re e phase s8,10,1 2(e. g.,  with o ut l imitat ion, mot or le a ds; transforme r  primaries) a n dt h en eutr al4. The corr espo n ding  mag n et icf ields  canc el an d  only the imbalance  o f curr ent ( i.e., the gro und curren t ) becomesthes ec o ndary current.  Such  a separat e  current  tran sformer6 is rela t i vely lar ge.  Si nce  th e si ze of mediumv o ltag estarter s d ecrease s w ith  ea chge nerationas newer  t ec hn ol ogi es re m ove heat  a ndim pro ve in s ulatio n sys tems ,fi n din g space in t he s ta rt er ( not  s hown)  for suc h a sep arate cur ren t  tra ns fo rmer is  problematic. 
F IG. 1C sho ws  an otherm e thod ofground fault detectionc alled t hediffe rent ial curre ntor res idu a l meth od. Th e sec on dar i e s ofa l lofth e phase an d neu tralcu rren t trans formers 14,16,18,2 0  ar e paralleledand  the i mb ala n ce d  cu rr e ntf l ows in a ground  fault rel ay se ction 22 o f  th eloop. W hen usi ng cu r rent tr ansformer s with ma gn etic c ore s, there a re error s due tod iffer e nc es in  th e curr en t t ransf ormers suc h assatura ti on and  wind in g errors . This can cause a fals e indi catio n o f a groun d f a ult  of up to  5%of the cor res pon dingpha s e cur rent s .Whe n  a th ree- p hase moto r  s tar t s ,the current i s  si x toeig h t time s th e full load curre n t. Typical sta rter s are  de s igne dup to 800 ARMS . T hi s means th at  there canbe curre nt s  flow ing up  to 64 00 ARMS . A5 % erro r me ans  that thi s m et h od cangi ve a fals e in di cation  thata  320 A RMS ground fault  is p r e sentw hen  none  i s there .  How ever, it i s desirable  to se t th e gro und fau lt  relay  22  t o trip atg round fau lt cu rrent l ev elsaslow as  5 A R M S.
Th ereis  ro om for im p r ov e me nt inRogo wskico ils. 
There is furtherroo m  for im pr ove m e nt ine le c t rical swit chi ng ap p a ratus incl u ding Ro g owski  coils . In a  slab c a sti ng  proces s,
 less_expensive repair_often avoiding having to_replace the_equipment_by setting_a_ground fault relay_2 (FIG. 1A)_to trip at ground_fault current levels_of_as low as 5 ARMS.
FIG. 1A shows a ground return method, which does not_discriminate_as to_which_starter_load (not shown) has a_fault. This is used as_a backup_in case a ground fault is not cleared_by_an individual starter_(not shown) or if a ground fault occurs in_the power bus or conductor (not_shown) upstream of_a_starter._The ground return method_looks at the ground current as_it enters the transformer neutral 4_and is used for a power system_(not shown) including many different starters_and circuit breakers (not shown).
As_shown in_FIG. 1B, a zero sequence_method uses a_separate current_transformer 6, through_which pass all three phases 8,10,12_(e.g., without limitation,_motor leads; transformer primaries) and the_neutral_4. The corresponding_magnetic_fields_cancel and_only the imbalance_of_current (i.e.,_the_ground current) becomes the secondary current._Such_a separate current transformer 6 is relatively_large. Since the size_of_medium voltage starters decreases_with each generation as newer_technologies remove heat and improve insulation_systems, finding_space in_the starter (not shown) for such a separate current transformer is_problematic.
FIG. 1C shows another method of_ground fault detection called_the differential_current_or residual method._The_secondaries of_all of the phase and neutral current_transformers 14,16,18,20_are paralleled and the imbalanced current_flows in a ground_fault_relay section 22 of the loop._When using current transformers with magnetic_cores, there are errors due_to_differences_in the current transformers such_as saturation and winding errors. This_can cause a_false indication of a ground fault of_up_to 5% of the corresponding phase_currents._When a three-phase motor starts, the_current_is_six to eight times the_full load current. Typical starters are_designed up to 800 ARMS. This means that there_can be currents_flowing up to 6400 ARMS._A_5%_error means that this method can give a false indication_that a_320 ARMS ground_fault is present when none is there. However, it is_desirable to set the ground fault relay_22 to trip at ground fault current levels as low as_5 ARMS.
There is room for improvement in Rogowski_coils.
There is further room for improvement in_electrical switching apparatus including_Rogowski_coils. In a slab casting process,