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Current transformer requirements for protection 1

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TRANSMISSION & DISTRIBUTION
Protection & Control
Course PC3, Dubai
Application of Protective Relaying to
Distribution and ...
CURRENT TRANSFORMER FUNCTION-------,
1, Reduce power system current
to lower value for measurement
2, Insulate secondary c...
CURRENT TRANSFORMER FUNCTION-------.
Two Basic Groups of C.T.
1, Measurement C.Ts
- Limits well defined
2, Protection C.Ts...
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Current transformer requirements for protection 1

  1. 1. TRANSMISSION & DISTRIBUTION Protection & Control Course PC3, Dubai Application of Protective Relaying to Distribution and Sub-Transmission Systems 25th - 29th March 2000 Current Transformer Requirements for Protection ,... AlSTOM T&D Protection & Control ltd St leonards Works Stafford ST17 4lX England Tel: +44 (0)1785 223251 p&c002 Fax: +44 (0)1785 212232 (Lecture) Presented by A. Varghese AlSTOM T&D Protection & Control ltd Registered Office: St leonards Works Stafford Registered in England No. 959256 •
  2. 2. CURRENT TRANSFORMER FUNCTION-------, 1, Reduce power system current to lower value for measurement 2, Insulate secondary circuits from the primary. 3, Permit the use of standard current ratings for secondary equipment REMEMBER : The Relay Performance DEPENDS on the C.T which drives it ~ -
  3. 3. CURRENT TRANSFORMER FUNCTION-------. Two Basic Groups of C.T. 1, Measurement C.Ts - Limits well defined 2, Protection C.Ts - Operation over wide range of currents Note . They have DIFFERENT characteristics -
  4. 4. INSTRUMENT TRANSFORMER STANDARDS lEe lEe 185:1987 CTs lEe 44-6:1992 CTs lEe 186:1987 . VTs EUROPEAN BS 7625 BS 7626 ·BS 7628 BRITISH BS 3938:1973 VTs CTs CT+Vf CTs BS 3941:1975 VTs AMERICAN ANSI C51.13.1978 CTs and'VTs CANADIAN CSA CAN3-C13-M83 " AUSTRALIAN AS 1675-1986 CTs •
  5. 5. CURRENT TRANSFORMER CONSTRUCTION-----, BAR PRIMARY Primary Secondary WOUND PRIMARY -
  6. 6. ) Insulation to stop flash-over front HV prinlary to core & secondary circuit. 'Feeder' or 'Bus-bar' forming I turn of primary circuit. IOOOA? Generator, or systenl - - I voltage source. ..........~ ) Lruninated 'strip' wound steel toroidal core. ) 1000 turns sec. 1 Insulation covered wire, giving inter-turn insulation & secondary to core insulation. Typical protection bar-primary current transformer.
  7. 7. $', S2 '--~-~ r-r.~(:. c.urrenC" drre,c.t:ions· PI '> P2 S r --:;:. S '2. POLARITY pr s. Pl FLIC~ TEST FWb ~~c:k 0" QPpl;e4.l",~" J REV kick 0" "e.~ov~J o~ AVO T ve ,(l.o..t/.... t6 S,
  8. 8. • - BASIC THEORY------------, - R 1 Primary Turn oN Secondary Turns For an ideal transformer :- PRIMARY AMPERE TURNS = SECONDARY AMPERE TURNS
  9. 9. BASIC THEORY-----------.. For Is to flow through R there must be some potential - Es = the E.M.F. Es is produced by an alternating flux in the core. EsC>< d0 dt -
  10. 10. BASIC THEORY ---.."-----------, E.M.F-----..---- SeCcond°try urren Resultant Flux ffi ffi.............,.' ,------~~--8 •
  11. 11. BASIc.. 'HEollV Ip Np >' 0060 Es Zg . = Es ('~IO+;"~ sec~. w,~,~: +Cs·,s+CI"ce). - lo/P : ~~ za _- ~ I tJ., C;s - S~CT
  12. 12. • FL,)X" lEQ",tE"b -To P/lo!)ucE Es rp . 6. A- 'AI~ & • .~ ~e ~.s I=I"u" ci"fSI~ • A - c.+OSS -sad'lOP.l CI-MQ of eoJ.e.- £s : 4·44 NS fAg 'io"k. L WD/....'- Es ~ 4-44 fls f
  13. 13. RELATIONSHIP BETWEEN UNITS 1 Wb 1 gauss 1 kilogauss 1 Wb/m2 = 108 1ines = 1 Iine/cm2 = 103 Iines/cm2 = 108Iines/m2 = 104Iines/cm2 = 10 kilogauss = 1 Tesla -. -
  14. 14. BASIC FORMULAE----------, Maximum Secondary Winding Voltage: Ek = 4.44 x B A f N Volts ....1 Where :- Ek = Secondary Induced Volts ( Knee-point Voltage ) B = Flux Density ( Tesla ) A = Core Cross-sectional Area ( Square Metres ) f = System Frequency ( Hertz ) N = Number of Turns •
  15. 15. BASIC FORMULAE·----------.. Circuit Voltage Required: Es = Is ( ZB + ZCT+ ZL) Volts ....2 . Where :- Is = Secondary Current of C.T. ( Amperes ) ZB = Connected External Burden ( Ohms ) ZCT= C.T Winding Impedance ( Ohms ) ZL = Lead Loop Resistance ( Ohms ) Require Ek > Es - '"" .
  16. 16. W1"H e.'J£Nt.'( t:)S12.SttEl) ~,~O~~ '"TE. LeAl<Ac:e. ReAa~ 5 ~ LOCIJ ~b l~UM.L.'f t:NoRe.b .. TWUS ~~T....n... Rc.T
  17. 17. BASIC FORMULAE~·- - - - - - - - - , Example Calculation: C.T. Ratio = 2000/5 A Rs= 0.31 Ohms IMaxPrimary = 40 kA Max Flux Density = 1.6 T Core C.S.A = 20 cm2 Find maximum secondary burden permissible if no saturation is to occur. Solution: N = 2000/5 = 400 Turns Is max= 40,000/400 = 100 Amps From equation 1 the knee point voltage is ( 4.44 xl.6 x 20 x 50 x 400 ) Vk = 10 4 = 284 Volts ~ Therefore Maximum Burden = 284/100 = 2.84 Ohms. • Hence Maximum CONNECTED burden . 2.84 - 0.31 = 2.53 Ohms
  18. 18. ~ .> '-' w ~ v".;,J o > ~ 'Z -l- -) ~ Iet I I l+so%Iek • ExCI~.tlG C.ull£NT (1&) kNu- Po.",.. ~OLTA~£ ])£F'WlriON •
  19. 19. MAGNETISATION CHARACTERISTIC--------, Typical Magnetisation Characteristic. ~Knee Point :NIMF- ampere-turns per metre.
  20. 20. FUJX. bEJ.JS-rf (B, -reSLA (wbf",") I ~ QEE rc»iT- 1-+ I / 0-8 I' I J o V t MA..,-e2.&Ai... : c:.R.osS, I ~ ~ ~/ ,,- ~ --o 0-02 o~ 0-«. 0-01 0-1 O·f~ MAGIE~FoA:e. (H) ~1lE-~R.NSItNI. (~~~S~!M~ A/m) •
  21. 21. ( SECDNI)Al.y i.M. t:.) Es = 4·44 N f A 8 = l<v 8 w~:- ~ • 4-44 N f A Ie = H.L - Ki,. • H--N IAJ"'.... :- k' - l../ttJ. - L· M€AN MAG-J E1'lc PATH H 2' AM P . .,.."tl.N$ / I"£~ l:.e ~ AMef>S - • t"lcl ~~
  22. 22. ~.UL-r,t'L~ p;y Kv "T"o 08rAv-J VOLl'S 8 ~~ _1 I J ~ --/ V I I ~ V ...... H f'f..,'-1i PL.'-I rt1 l<.t To oITAIN AM.PS I<~ ,c. B = Vo(..~ (e.) <.t x. H : AMPS UNtTS : t<:~ : ~ :. 4-4r4 NfA ~ Kt: .f!. H L -= N r: •
  23. 23. 1- WbI"" r-;-~li~""I"""",r--r-_-:-_!"'1-'r-"_-rt_-r'.-'.. ,-._T""'.-r-_"""T.I--'_r.ir-"J~!-"""t!_-rj -,_."-_-.!_'~'-::~--i '8'lJ:tJtt~t1-ril-r~It_jrt~tf~r·~tl~t"j:~:t1" I I I I i I I I ! • iii!~ I :0- r ... I! I·'i' I' I ~r- I !. ,- -I- I : I I I ' ~~l'lj ! '111:;li:~I!"'!'i"lil I I I' I' !! t--;·- ';'-1' ! - r _1 ,-.! _., -~" ,.,l_t-t-'t·· i--li-+~--t 1-6 I I I ! . I I ! . : , 1 I I . , I !!i 0 i! il l:l.i./'fii!i!I:!1 : III!- ! I I i i i ; I. : Yo I I 1 ! ! i I I ! i '! I ii I I; I I ! I ! LLJ 1 : ! ; : 1! I : ; , , ! I L-i i I I 1 I i ~ , i J V ~ i t : i! i I ; ~ CH. ; ~ 1-401 !. : I O.g L I I I I !Ii. : ! I I ' I 'k!::::1: I i i , ; i ! i 1 i , I I !. I : I , ! ! Y 'i I i ~ i ! I ! ! '" i i i I V I ! . I I .~ . I ; ; i ! i ' i I I ! t:l i I '--1-1..·1-: ! -~;-~-I-t I : ' I- , I o I.: ~ I I i ! ! : I iLl. ,; I . ' i ' i i i ' , ' 0-8 > ! i i IiI: I i Vi 1 ' i ; I 1 J I ! I : i I I I ~ ;.I! I !j i ! I iL.! ! i I I 'l : 1 I! I ~ : ' I I I , JI i ! I _ I ; i j 1 I I , ! l I ; ~ '-0 ' ~ : 1ft! ! ·V: , ; I I I ! 1 I I I , i 0-7 u ; !,lll.Y.::~j 1 !:Il,~ .! l~! "" ; ! -r-t-.~. 'i'- ~.- j' , - , - ':'-!-f-; I' I I' U) 'I-.J.:, I t ' i ; l ! ~ I i ! i ! - I l i I .en ; I _ 'J ! III i i 1-i I; I! 1 I ! J I i , I : i.J. l . : ; : t I' I I I : I I I 0.6 , I ! I~ I i i I l i i! I I! i I! I i I ~ ! r:i. 0·" '% < !: i I I I! ; I I Iii i l ! i! ! I I I I o : ~ 1 I I ~~'"~€ ~ffi! i i i I i 0.S ~ Ili/ll/ I I ! ! ii I o 0"6 ' I ~.S~t~ -'it l l' 1 I l' It- ! f(,.-.,.r.) a2 I I I iii I 1Io... ~ ~ I. I I ! I> I J I .~T'~ -uo~-+__~~~-+~~~ :IC i.11 I " W I 1 I I I l I! I; MAGNEilSING COMPOMENT I I I ; ~ 0-4 I I r I SERIAL HUM~! ~ I!I I i CONTRACT NUM&EP.Q.. 5 i J I I TYPE ~ 1ft I I RATIO % 0'2 I tI I I TURN RATIO II I I I ! SECONDARY RESISTANCE AMP OHMAT7SC ! ; i1 I I I IA I I i I I J 1: I I o V I I , J l I I I i I I 1 I 1 : In o u o 0'02 0'04 0'06 0'08 0'1 0-11 A.T/MM. MUlTlPlY BY Ki TO OBTAIN R.MS. TOTAL EXCITING CURRENT IN AMPS SO H2. IDRA·~::t Ir- f. A- ~'r-~-I-=-----~-------~I~iVI'''. l~f~OYED I -- -.
  24. 24. Ze. 5 SL.oPE: OF MA<:i. CHA~AG.-re:Q.STtc.. v
  25. 25. C.T EQUIVALENT ·CIRCUIT---------, Ip ! p. Is I~ +N I 5. I I N Ze Es Ip = Primary rating of C.T. N = C.T. ratio. ZCi Zb = Burden of relays in ohms (r+jx) ZCT = C.T. secondary winding impedance in ohms (r+jx) Ze = Secondary "excitation impedance In ohms (r+jx) Ie = Secondary excitation current. Is = Secondary current. Es - Secondary excitation voltage. Vt = Secondary terminal voltage across the C.T. terminals ,I I I I Vt Zb I I ~ I , --." -
  26. 26. PHASOR DIAGRAM -----------, Es-.------~~=======-~ Ep Ic Ep= Primary Voltage. Es= Secondary Voltage. m= Flux. Ic = Iron losses (hysteresis & eddy currents) 1m = Magnetising current. Ie - Excitation current. Ip Primary current. Is Secondary current. •
  27. 27. tooA too/f 100ft looll 100R 100/1 • loH.... 100tM E= tool 100 otW4 E=? - ·10000"",
  28. 28. CURRENT TRANSFORMER SATURATION------, FLUX DENSITY / PRIMARY CURRENT / FLUX DENSITY ).----,. "" SECONDARY CURRENT FLUX DENSITY ASSUMED MAGNETISATION CURVE. AMPERE-TURNS ----+++---~ PER CORE LENGTH TIME MEAN MAGNETIC PATH.
  29. 29. CURRENT TRANSFORMER FUNCTION Two Basic Groups of CT : 1. Measurement CTs - Lim'its well defined 2. Protection CTs - Operation over wide range of currents NOTE: They have DIFFERENT characteristics • -
  30. 30. Mc-..SuR Na- C:. $ .. - REQlQ£ Coo'b AU!lIAC.:y UP -ro A-ffJtoX tz0 4 IlATEb OJ~T - Rl:$u,ae. lJ:)W SA"tlJaAT'ON LeJ£L To ~1'EC-T ,f&STiN~S HJS USE N1C.lC&l- ,-.oN ALLI:Jf ~ '-'l11f LOW £)(c:.(T,~<; <:.ua«eNT NIb QIee. PaIN' AT L.£)-.J ~ ~rrf PQ..OTECTtot-( I, (:..".IS - It~ ~T ~ I~fo~ ~ ABoU£ - _UtIlE. Act:.1JItAcr -.lP To MIW~ TMES RA-=b c:SJ_~T. iUS use C4DrfN oQ~TAEb Sit_teeN. STES- f&21'H H~H SA'TUQA'Tlot-l FLUX betlS'f. 8 Pi<oTECoTtON C..' • H •
  31. 31. WAYS OF IMPROVING CT PERFORMANCE Es - 4.44 BANs f- i) Increase B ii) Increase Ns iii) Increase A iv) Reduce burden on CT Ie = H.L/Ns i) Use mumetal, when measurement etc is required ii) Reduce L iii) Wound primary; allows increase Ns • --
  32. 32. INSTRUMENT TRANSFORMER STANDARDS IEC IEC 185:1987 CTs IEC 44-6:1992 CTs IEC 186:1987 VTs EUROPEAN BS 7625 BS 7626 BS 7628 BRITISH BS 3938:1973 VTs CTs CT+VT CTs BS 3941:1975 VTs AMERICAN ANSI C51.13.1978 CTs and VTs CANADIAN CSA CAN3-CI3-M83 " AUSTRALIAN AS 1675-1986 CTs -.
  33. 33. CURRENT TRANSFORMER RATINGS Rated Burden Value of Burden upon which accuracy claims are based Usually expressed in VA Preferred values :- 2.5, 5, 7.5, 10, 15, 30 VA Continuous Rated Current Usually rated primary current Short Time Rated Current Usually specified for 0.5, 1, 2 or 3 secs No harmful effects Usually specified with the secondary shorted Rated Secondary Current Commonly 1, 2 or 5 Amps Rated Dynamic Current Ratio of:- (IPEAK = Maximum current C.T. can withstand without suffering any damage) AP03916 • --
  34. 34. '-HOICE. OF- ~A" 10 C.L..E~L'f I Tl-E PRtf'I~ f<A..,.,,-1<: ~ ~ NO~MAL c:.URR£NT IN HE c:.1Q.c:.UT ~ TH~t-Pr'- (c::.C»l-rl~UOU~) PA.,J~ 5 NoT 10 BE excee:os.~ secolJ~PrQ.'"J AATINc:. s usuPrU...'l Oil S ~ (o-S ANb 2. R-f-tp AQ.E ALso USe~) [~S~ ~(1<1N<:.. 1l.5Ol'E: Lal~M: 15 - IA1-P ~ IF L~<:6J2. ~MAi.'i flA'~~ I'rite:. Q~ulQ.e.b ( e. ;5. ~Q. t..AilCE <:£~S<K'["oRS)~ CAN tlSE 2.0 Pd-P S~ To<:e:n-cSjt '-l C"tH It-tteRpos~ c..'. e..c;. 5000/'2..0 2.0/' •
  35. 35. LINE CT INTERPOSING CT Np BURDEN PRESENTED TO LINE CT = ZCT + ZB x Np2 NS2. • B
  36. 36. CURRENT TRANSFORMER ERRORS -----.. Ip Is It lZe Es Zb I
  37. 37. CURRENT TRANSFORMER ERRORS -------, Current Error Definition. ERROR IN MAGNITUDE OF THE SECONDARY CURRENT, EXPRESSED AS A PERCENTAGE. GIVEN BY :- CURRENT ERROR % - kn = Rated Transformation Ratio Ip= Actual Primary Current Is = Actual Secondary Current Current Error is :- +VE : When secondary current is HIGHER than the rated nominal value. - -VE When secondary current IS LOWER than the rated nominal value. •
  38. 38. CURRENT TRANSFORlvfER ERRORS ------, Phase Error Definition. THE DISPLACEMENT IN PHASE BETWEEN THE PRIMARY .AND SECONDARY CURRENT VECTORS, THE DIRECTION OF THE VECTORS BEING CHOSEN SO THE ANGLE IS ZERO FOR A PERFECT TRANSFORMER. Phase Error is·:- +VE : When secondary current vector LEADS the primary current vector. -VE : When secondary current vector LAGS the 'primary current vector. •
  39. 39. • METElUNG CURRENT TRANSFORMERS. (6s 3 q 38) . TABLE 1 - LIMITS OF ERROR FOR ACCURACY CLASSES 0.1 TO 1 ± ~ Ratio Error : Pha.e Displacement at percentaqe of CLASS at percentaqe of rated current shown below. rated current shown KINUTES CENTIRADIANS 10 - 20 20 -100 100-120 10 - 20 20 -100 100-120 10 - 20 20 -100 100-120 NOT INC NOT INC NOT INC NOT INC NOT INC NOT INC NOT INC 20 100 20 100 20 100 0.1 0.25 0.20 0.10· 10 8 5 0.30 0.24 0.15 0.2 0.50 0.35 0.20 20 15 10 0.60 0.45 0.30 0.5 1.00 0.75 0.50 60 60 30 1.80 1.35 0.90 1.0 2.00 1.50 1.00 120 90 60 3.60 2.70 1.80 TABLE 2 - LIMITS OF ERROR FOR ACCURACY CLASSES J AND 5 +/- % Ratio Error CLASS at percentage of rated current shown below. 50 120 J J J 5 5 5
  40. 40. ACCURACY LIMIT FACTOR - A.L.F. (or SATURATION FACTOR) Ratio of:- IpRIMARY : IRATED up to which the C.T. rated accuracy is maintained. e.g. 200/ 1A A.L.F. = 5 will maintain its accuracy for IpRIMARY < 5 x 200 = 1000 Amps AP03917 -.
  41. 41. BS 3938 1 CLASSES :- 5P 10P 'X', , DESIGNATION (CLASSES 5P, 10P) (RATED VA) (CLASS) (ALF) AP03548 -MULTI·PLE OF RATED CURRENT (IN) UP TO WHICH DECLARED ACCURACY WILL BE MAINTAINED WITH RATED BURDEN CONNECTED. ---5P OR 10P. I..--VALUE OF BURDEN IN VA ON WHICH ACCURACY CLAIMS ARE BASED. (PREFERRED VALUES:- 2.5, 5, 7.5, 10, 15, 30 VA) Zs =RATED BURDEN IN OHMS •
  42. 42. • PROTECTION CURRENT TRANSFORMERS. TABLE J - LIMITS OF ERROR FOR ACCURACY CLASS SP AND lOP ACCURACY current Error Phase Displacement at Composite Error CLASS at rated primary rated primary current (%) at rated current (%) accuracy limit MINUTES CENTIRADIANS primary current SP ± 1 ± 60 ± 1.8 5 lOP ± J 10
  43. 43. CURRENT TRANSFORMER BURDEN Relay burdens are usually quoted in VA (volt - amperes) A burden of 12.5VA at SA would have an ohmic value of :- 12.5/52 = 0.50 If a relay has a 1VA burden at its 20% setting, then the burden at nominal current (1A) will be:- 1~x 1/0.22 = 25VA Conversion from VA and ALF into volts:- If Ret is known. generally. vK ., ALF(~~+ Rcr x IN ) Example:- 400/1 ct, rated at 15VA 10 P 20 with a Ret of 1.50 Vk ~ 20 (15/1 + 1.5 x 1) = 330v If Ret is not known, then Vout = 15 / 1 x 20 - 300v -
  44. 44. WHAT t)oES C.'T.. Cl.A5SII=CA,'ON T£'-L us ? RA"t"e.~ guCt)EN = 2A'£b VA {ftA"'te.b c:.utUlE)r)2. = 5 :. 5 C,",MS -)Z, MAX c.ud&l (WITH 51. A-c.cu~PCf) =to -, : (Q AI-PS loA Vo/p S OHMS VCIP =50 Vat...S '1o" = lRATe.~ VA) )( (A.LF. x. AA'"tEb c:u••etrT) (O"t'Eb c.ulAetrr'f ALSO, eoMSI~' VA' IIIIl -a.e.LGAb VA -150. 10 = 'Sao VA. 01 VA =(1lA1'9"A) "R-I-I=: X •.'-~.(~~) (M1"CL cu~ lltUS, Cel: CIW bEU"ER a ~ VA) ~ (A.L.F.f vA. (1140 RA,1EO ~JRDEt-:l) •
  45. 45. CURRENT TRANSFORMER DESIGNATION-----, Consider 5VA 5P10 (with lA secondary) equivalent circuit - with rated burden :- •I I I RCT lOA •I I I Emax Vo/p 5 Ohms ( Rated Burden ) I I I I I I '--_ _~,_ _ _.....;':.._J Vo/p= 50 Volts Emax= 50 + 10 Re.T Now consider same C.T with a 2 Ohm burden RCT I max Emu I 1 I , ReT = 1 Ohm ReT = 2 Ohm ReT = 5 Ohm vo/ p I I I , Imax = Emax 2 Ohms 50 + lOR C.T Imax Re.T+ 2 IMAX = 20 Amps IMAX = 17.5 Amps IMAX = 14.2 Amps •
  46. 46. • 20 5~A SP 10 Bu@e.N (t~MP) 5 10 - -... - - -.- -
  47. 47. • CURRENT TRANSFORMER DESIGNATION------, Class "x' Specified in terms of :- ( i) RATED PRIMARY CURRENT ( ii ) TURNS RATIO (Max. Error =O·25~) ( iii ) KNEE POINT VOLTAGE ( iv ) MAG CURRENT ( AT SPlCIFiED VOLTAGE ) ( V ) SECONDARY RESISTANCE (At 75°C)
  48. 48. CHOICE OF CURRENT TRANSFORMER-------, ( 1 ) Instantaneous Overcurrent Relays. - Class P Specification - A.L.F = 5 Usually sufficient - For High settings ( 5 -15 times C.T Rating ) A.L.F = Relay Setting -. ( . . ) IDNIT Overcurrent Relays.11 - Generally Class 10P - Class 5P where grading is critical Note : A.L.F x V.A < 150 ( iii ) Differential Protection. - Class X Specification - Protection relies on balanced C.T output.
  49. 49. • 1, 0 'fEI'2.CURRE~ : R.. 2, EAR:T+J: - - Rr R,. R.. -
  50. 50. OV£Rc..UI2RENT -RELA'f VIe. CHECK. AsSUME V"UAES: If~..- 722..6 A. c :T .. ,OCX) Is A 7.5VA tOP20 Rcr" O.Zt;,.JL Rr - O.~../Z.. (MCGG) RL - O.1~ ..tL ~ To SEE IF Vie. IS L.AR6e ENou(O.H: R~I'lED VO&.l"AGE :& Vs = I~ (Rc:r + Rr • R~ ) • 722.fiJ ,..5 ( O.2.G + 0.02. + 0.13) .CXX> = 36. f,!, )( O. 4~ - 15.54 V'OI,Zs. CUIZRENT Vie. APPRO'k11MTES 1t) :- Vk. ~ VA )C ALF + Rcr Jt I".. ALF I" .. ?:P w 20 + 0 .~ K.5)t 20 ~ .EG VOL."1'S. 15 Vk. > Vs -r.HE~~E C:T {k. 15 ..De.~u~. •
  51. 51. ~ore F=OR.. E-AJCr+l FAUL7 APPUCATlON!S ReGlUIRIi ~ &E ... E 10 ~ 10" 'lELA~ SETTING. OfecK 1C see. IF V" IS l..AR.Ge. ENOU;'-H: Tar~ lND CONWECTEO = 2Rl + Ra ... ZRr - a If O. 1!S + 0 .2tD + 2. v. O. 02. ::.EG .~!.. ~ A 0." -r'lPICAL e~ F"AUL-T seiliNG .:; 3:)-z..'I~ = '..51.. ~E~£FoRe C.T cAN- ____-----______----______-'-A__ - -
  52. 52. CHOICE OF CURRENT TRANSFORMER------. CONSTANT V.A. VARIABLE OPERATING CURRENT RELAYS. Consider a constant V.A relay as a secondary burden ( Neglect C.T. secondary impedance & lead burden ) Let Is = C.T. secondary current. ZR = relay impedance at setting. I R = relay current setting. VR = voltage which has to be applied to the relay when set at I to cause operation. I M = magnetising current of C.T. corresponding to V Y = magnetising admittance of C.T. VA = Volt - Amperes required operate the relay. •
  53. 53. CHOICE OF CURRENT TRANSFORMER-------, 1M = VRY = VA . Y IR Also 1s = IR + IM = IR + VA . Y ................ 1 IR Differentiating with respect to 1R dIs = 1 - VA . Y dI R IR2 Now, for a minimum value of I R 1 - VA Y = 0 J2R IR2= VA Y Substituting IR in equation 1 Is(min) = .JVA . yO + VA Y - 2 .JVA -v':::;V=A=Y;:;o Also 1M = lR =.JVA . yO Y Since Is(min) = 2 .JVA Y and IR = .JVA yO and 1M = 1 = VR· Y = ZR . Y 1R VR/ZR :. ZRY = 1 Minimum primary current for relay operation as setting is varied occurs when the shunt mag impedance and relay impedance are matched. This coincides with the min VA output to the relay. - -
  54. 54. • CHOICE OF CURRENT TRANSFORMER--------. Ampere-Turns IT IT IT IT Operating Current I 1/2 1/3 1/4 Turns on Relay T 2T 3T 4T Reactance of relay X 4X 9X 16X prop to turns sq Operating Voltage IX 2IX 3IX 4IX VA r2 x r2 X r2 X r2 X Is=Ip/N •• ,I Vr I, a: :> 4rX d (I.) 3IX c 0.0 Excitation~ ..,.J 0 2IX Characteristic. :> ~ ::1 0... ..,.J IX :::l 0 abc d magnetisng current -1m
  55. 55. CHOICE OF CURRENT TRANSFORMER-------, .,J ~ cu s.. s.. ::t U Jp/N ________________~•• JP/N -Is --------I~~ ----I.~ J. ~~----------~~ Is~----~e~====~------~p [. (b) Es z..-. :::z -+ >..,.E! s.. ---«3 S II s.. 0.. a.. - Relay Operating Current IR Le. Optimum relay performance is obtained at an intermediate tap setting and not at the minimum current setting. •
  56. 56. • HIGH IMPEDANCE DFFERE NT1AL PROTN.
  57. 57. UNSATURATED CT VS RL •·· J=o~ SlAalLl"Y ;. R« SAT'u~ATED CT HoJJ LIHE.At ~ES~ ("E'11fDs.&.) RL..'1 Rs-r : S-rA6lLISltJG- fESISTAAJC€ Whe" tae,,,,,Hd .~ c:.-r -- ({EQUliEMENTS ALtowA£LE MAGt-J£l1SIIJ(f CtJtfE:tJ( ;.. Ie ': Is -IR n Is ::. RE~U"!ED E:F=FEc-r''JE SEi'T.NG I R :II RELAY S(TT.NG cJ~Ite:NI I •
  58. 58. SECoNDA(ly MUSi" NEVE(/. 6£ I-El=T ole. w,.,.t- ~t<'MA(l.y ENE/l.Ci-1SEJ:) !~ ~-f 1"4!.f+ ole w;.." ~ Wf~ in, ttfftrc+,·"e. V ~ HIG-H sec.y Fo~ ~'~'" :rm~o.lW:& E~ ~..~ ~~~ Z, c:a" be t.J~ ,;~ fo4- Qt .;,~ ~..2*. :!.I4NC %8. "'Q)t1~1W C+eS+ 10l+1li.,e "f~ 2 Ji ·J(~-ftc).Vtc: ~~ec. V~t4 ~ P~-l~ ~."".s. _~cA~ ~~,e • • QSS"""'I", J:,..~ Cclt ~ow ~~ c.o+e s~+.~- V~ :. I<ICe. fb:'r VoK.,e. Z-f. Vp ..,. 3kV ) ~ Q ME'~U_ NON#I...NEAi. e:sas't'~ +o,~; r ~ Io+'~-e..
  59. 59. ME"~oSIL.$ - * NON LI NEAl tlESIS-rANC€ ~ bEPOIf)S o#tJ SI,E ANb St-4APE. vocrNrC Re"~I~ -ro PASS A +h~,l, -neE' blS e. VAilE'S' ~lo~ 00 Fo~ A -rt4,IJ blSc:. '-0 'Sooc:> Fo~ A THiele blSC It exAMPLE SPEe)Flc.A.,..,o ~ bOO A Iss / PIS 17..7..2 600 - t:>sc: I),AMETEl ,.tItS.)("co. 3 - N0f16eL ot:- ~'Sc~ p _ AL.L.. ~IS:S- 'N PAIl.ALl.El... S '~'2."2.. - K ~ O'Z.O 10,40 ~ ,. 0·,>. -
  60. 60. ) -' . ImA V-I Curve of 600AIS11Spec 256 Metros"! 10mA 100mA 1A 10A DC or PEAK CURRENT 100A V-I Curve of 600AIS11 Spec 1088 Metrosi' _ ... _ f-- -,;..,;....... ....,- I' . ···IH!;.!ij':·,[.',..... " ,..... ·r".. I::::........ : . , . .. ~. ---+---+-+-f-+4+H 1--..- -+-.--t-.-t--t-t-H+I I:!;::, '.1 •.. 70V-r---L~,-L.~,~,~,~.~.--~--~,~,-L,~,~"u.+---~~)~,~,~,~,~.~.~~L-~,-,~,~,~,U,,+---~~,-~~,_,~,,u.~. •
  61. 61. METROSIL FOR CAG TYPE RELAYS Introduction The 'Metrosii' non-linear resistor units listed below have been specially designed for use with GEC ALSTHOM T & D Protection & Control type CAG 14 and similar relays and are intended to be connected across the relay circuit (relay and stabilising resistor). Metrosil Units for Relays with a 1 Amp CT The Metrosil units used with 1 Amp CT's have been designed to comply with the following requirements:- 1) At the relay voltage setting, the Metrosil current should be less than 30mA rms. 2) At the maximum secondary internal fault current the Metrosil unit should limit the voltage to 1500V rms if possible. The Metrosil units normally recommended for use with 1Amp CT's are as follows:- Nominal Characteristic Recommended Metrosil Type Relay Voltage Setting C (3 Single Pole Relay Triple Pole Relay Up to 125V rms 450 0.25 600AlS1/S256 600AlS3111SS02 125 - 300V rms 900 0.25 600AlS1/S10SS 600AlS3/1/S1195 Note: Single pole. Metrosil units are normally supplied without mounting brackets unless otherwise specified by the customer. Metrosil Units for Relays with a 5 Amp CT These Metrosil units have been designed to comply with the following requirements:- 100mA rms (the actual maximum currents passed by the units is shown below their type description). At the higher relay voltage settings, it is not possible to limit the fault voltage to 1500V rms hence higher fault voltages have to be tolerated (indicated by', **, ***). 1) At the relay voltage setting, the Metrosil current should be less than 2) At the maximum secondary internal fault current the Metrosil unit should limit the voltage to 1500V rms for 0.25secs. The Metrosil units normally recommended for use with 5 Amp CT's and single pole relays are as follows:- Secondary internal fault RECOMMENDED METROSIL TYPE current Relay Voltage Setting Amps rms Up to 200V rms 250V rms 275V rms 600A/S1/S1213 600AlSlIS1214 600AlSlIS1214 50A C = 5401640 C = 670/S00 C = 670/800 35mA rms 40mA rms 50mA rms 600AlS2/P/S1217 600AlS2/P/S1215 600AlS2/P/S1215 100A C =4701540 C = 570/670 C = 570/670 70mA rms 75mA rms 100mA rms 600A/S3/P/S1219 600AlS3/PIS1220 600AlS3/P/S1221 150A C = 4301500 C = 520/620 C = 570/670 ** 100mA rms 100mA rms 100mA rms 300V rms 600A/S1/S1223 C = 740/870' - 50mA rms 600A/S2/P/S1196 C = 6201740 * 100mA rms 600A/S3/P/S1222 C = 6201740 *.. 100mA rms In some situations single disc assemblies may be acceptable, 2400V peak •• 2200V peak ••• 2600V peak contact GEC ALSTHOM T & D Protection & Control for detailed applications. Notes: 1) The Metrosil units recommended for LIse with 5 Amp CT's can also be applied for use with triple pole relays and consist of three single pole units mounted on the same central stud but electrically insulated from each other. To order these units please specify "Triple pole Metrosil type" followed by the single pole type reference. 2) Metrosil units for higher relay voltage settings and fault currents can be supplied if required. -
  62. 62. METROSIL FOR MFAC TYPE RELAYS IN SOME APPLICATIONS OF VOLTAGE OPERATED HIGH IMPEDANCE RELAYS A NON-LINEAR RESISTOR IS REQUIRED TO LIMIT THE CURRENT TRANSFORMER SECONDARY VOLTAGE TO A SAFE LEVEL DURING MAXIMUM INTERNAL FAULT CONDITION. Introduction The GEC ALSTHOM T & D Protection & Control type MFAC High Impedance Differential Relay has three setting ranges 25V to 175V in 25V steps, 25V to 325V in 50V steps and 15V to 185V in 5V steps. Single element or three element 'Metrosil' units are provided for use with single and triple pole relays ,..-espectively. The Metrosil unit chosen 3pends on the setting range used and the required short time rating. Recommended Metrosil Units for MFAC Relay Relay setting range /(fIJt) - +c:>t:"> 25V - 175V 15V - 185V 25V - 325V Continuous Ratings I 'C' Characteristic 450 900 Short Time Ratings Metrosil Assembly Type Standard 600A/S1/S256 Standard 600A/S1/S1088 Special 600A/S2/S comprises two standard C = 450 discs in series Special600A/S2/P/S6198 II.. comprises two special discs in parallel I Nominal C )/C510 450 450 900 Characteristic B ,.,-2S 0.25 0.25 0.25 Photo Courtesy of GEC ALSTHOM T & D Protection & Control 1 phase relay IdCiV~/J//Sh3's 600ArS-l/S256 600AlS1/S256 600AlS1/S1088 Max. Continuous Rating rms 200 V 350 V 3 phase relay 6ooAIS311IS~37.4 600A/S;J/1/SHU2 600A/S3/1/S1195 Unit 'C' Value Short Time Rating 450 22A for 3 seconds 30A for 2 seconds 45A for 1 second 900 17A for 3 seconds 30A for 1.5 seconds 39A for 1 second 900 22A for 3 seconds 30A for 2 seconds 45A for 1 second 900 30A for 3 seconds SOA for 2 seconds 90A for 1 second Where higher ratings are required, special Metrosil units can be provided with more discs in parallel per elementto suit a particular application. •
  63. 63. 'N.J i:c...,. ION TE.S1 N~. No.tMAL. sE'tv,e~ ~- -reST WINO' NCf- ole.· IfIJ-:r6::-r'ON ",A -res" WINDING- ;.. Pt.,NAt.Y w,Jlllt)Ncr ole.· IRc.. T :t:.s = ~~ + I<c:.~ • IT ::'"~ RC.T~= . , "i.e. NeE.b LeSS ~T TO O~£RPtTe (J.Er..AV. •
  64. 64. FAULT CURRENT IN POWER SYSTEM (PRMARY CURRENT IN CT) -i,t/L, '-I = ... v,.. stn (",,1-..-9-¢) - '!.!:J SIn (9-s6).e r, %, 1 " _f.t/I., = + II sin (wt-+-e-cp) - I, s.i le-c;).e. i = YM t ~, •
  65. 65. REPRESENTATON OF CURRENT TRANSFORMER L, ; .'l.' N. '-2- ,. N'&. lc.,- • l..s r+--,--:---c:::::J----aAJ'~... ~ - - -I le ;' M c:r ~«MINAL.S I '-------'-------~I- - - _..' R~ : IfoN LOSS ttESIS'-ANc.E - ~
  66. 66. • • L, R. . LS r--~---.---C==I---...1nmZll~- ~ - - -,.L.e. M I ~_ _---'____________ J A A _~t~, =+ I,. tb s,;" (wt-..e-;) - 1,.~ SIn (~~)e ~ ~ A A -~t~J : .. .J:z. sin(~T+.-4» - .I~ s~ (f:l!J-</J) e. .8'( vSu~JG- L1 IN ALL. FYl~HE'f AwALYSS ) ;"'HE t«'MAIlY CJl<:u1' AH~ IDEAL. c::r. NEe ND, se- eoWSI~ctet> AG-AIN # wI-£fE :.. A. A I-z. :. N. It - 1'1, 1M-- . - . -N1.. Nl. ::,
  67. 67. ,.. A -t.;t/L., l.l. ~ + J:2, S;1'" (w;'+9-<;6) -:1:, sin (~-s6) e 'l t . MQ)('~"'1'f +ta~sle"t oc.cvts w"~,, :- ·ol . t..2. -- -- . (..1- -• • - +Z - 2. ~ " . 1()I'l.. s;n (~T-~) - .I~ S,n (-1. e. " 11( A -I..t/L.Il. s,'", ('->t - ~) • I~.e I2. SIn (~-~) + e. A 1 "" -(MIL, ) -I..'i:/L, -
  68. 68. SIMPLIFIED CoT E~JIJALENT C'RCUIT (l) Most C:r.s fo~ f»'0+ech~I' Q~ c1es5~ w;~ low +eQ<::hlnee . :. Ass,",""e LC,T =0 0 .... AssuMe. La ~ 0 (iii) r , 0 0 Up +0 KNEE POIIJ'T' VOL'TA(i.c Vtc ) c:T'o "'Q~MrlI'Srl~ C~,,~ is o.,~r~Q{e, ,.~~ . - rJc+ So be~OItd VIC ~ ~c..r •
  69. 69. • FLUX REQUIR.ED TO TRANS~o~M l.2. " . l2. =L2. Q.e. + l., d.c. e . J:e QSSu~c:l StfQ" co"'PQMcl ~,~ ~1.. . :.. ..1. CQI' ~ e~SlclCled as . . . l'Z,. - l'2.Q.c..... c..l..d.c.- • S.,.EAbY S-rA1C ~ .. 1( .% ".c:. - - J:~ s,i (~- "i.)- - . 4 _~,i:I', L'%.••c: . - -rtZANS'E"''T' OJdarr - ~e.- - (ZESUL"'S
  70. 70. • . L.'2. e.. - N~ (Vo~- cit -t7., ¢ - f e '* (WD)-•• -N -t:. • • --
  71. 71. .. • l. Q.C • CPQ.C.. ~ I:11.e1.. $'" (....;--{) ~+ N.,. '" t - :r~ ~'l. Lc:.os ('-A.)-t - {)] WN1. 0 = "= - .:t'l. ~'"' cos (""t - ~) A) N'L " "·. ¢Q.c..:' :t:'1. ~1- .U N'1. . ~1-ed.e. :. L cl.c. 1>rJ.c. f A -l.t/,. ~ :[-z.. R1- . e c:l+ N"l.. '" [ e. -IM:It. ]:- - J:l. ~"'-. L I- ~.ftt " - l,tl£.. ] - .:t'Z., R'L. L I [ , - e.- N,.. t.. A rpd.C. oc:.ui$ WHeN t = -0 . A. A. cfJd.c. ~ .l:'2. Ill.. L I- N"2..~' •
  72. 72. -. -- -- -- " It. A 1> -:. ¢QoC 0 + ¢ doc 0 A A ;: :!'1 ~1.. 1- l:"L f"l,. l, wN.... N2,. i, A A - 1:'1. fl'to. [ , + WIl~11 :t:2,.f1. [( + wT,]- --WtJ~ ~ AI - .I-z. 21. L~ X'/R·1- WN1.. A - cfQoc 0 [ + X'JR, 1- A. - "'«oc.o [ + w T.1- ~"'E«" ,.., ;: )..t/~I = Pt,I'tAII.;Y TIME' ~At.rr.
  73. 73. • EXAMPLt Pe.ak I=I~)( l~",d " "¢ ~ st>4.c..[I+XI/~I] " = CPQ.C:, [ I + ~TI] . • • 18·85 A = ('l·gS)( cpa.c. A'~o ;f :r:,,: - 20 )C .:raN ('2.0 )(!....J.ecl ~)- ",. " 'fQ.e. :: 2.0)( rfN A '"... 1> ::. 20)t Iq -Ss )( {JN "~ 400 )( t:PN-
  74. 74. I' n IC. 15 ".... 1% Il to 3 , 7 '- 5 --
  75. 75. o -A I -!.~I -- - / .. / ...rf!-'~~..JJ V '" ... "- /. ,. . "'- TOT AI.. F1-UX ¢ I., I ~// TRANSIC'NT F1-UX. <PJ.C. TIME --------- 't="G. S. &::'L.,.UX'· t.EQvteE'ME: Nt Fa ~ '"T1ZA NS;:'O e,.., I N ~ o~~SE-r PelMAey c.J(2,!crv-r". • -
  76. 76. To~AL Fl.UX "'·6. = 1:1. R"to (-Sl~..st) "'" l:~e...-r,... {e-t;'-l._e-i:/T'J w N7. ,.,J'1. (j'1.-'1i) l' - .r~ 2-a. [ (-0 -1:11; ) • t ]- '"'"T. e. - e - $,,,..., "'" 1tJ'2. - I"I. R~ [ ...,1, (- e -th;) _Sin I4)T]- ""'N~ :r~o N L..oSS 't;No£ib ,.., AS$v~£l) r.."~~JE'A( •
  77. 77. ')( ':) .J ~ ~ CI. 5 G- w o.c ( ...4: ." ,g. -~ ,"" ." ........J ,....... I '..' ~-­ .--"-, ...... ,....-... "f ~,/ ....-",,;'- I I .. I X :3t. .-- X 3lJ. c:=~. - c: c ---.c---------..-/ --- ~t ..."% 0 III ~j v • ~lY ~ --. rD uJ -::t Fv1 -VI W pi - ~,
  78. 78. TiME "-0 SATuRATE -- • • .. • • .t=Ul..l.Y or::':SE:r l. J • I,.~ [. "'"~1i (e.-thi. -e.-tk;)-5,:,out1 1i-ii u.JhClC. .:tl. is +I-e +.M.1. lClI,,~ of pt~, ~-r--.ed P'",~ rieCkl, ~ euHe-.t. •
  79. 79. .. . . ~hCH Vx lS C:r: SQt.....,..+.~ vot-oa~'t. ~,....,ted ~ <:oH.ee:H, ~~.fo+.., ~, u.f ~ +'~-t' t . -- + ~ ~ ...l.-. ft'c:•.,.. SQ "'.... -. Tl~I .~ -. • 5clT......+.~ voHa.,e -h» -ha..s~ C)*$e.TO.'~ Vo~ ..n:, ++ca1S.p... s+.cacl, s-t-ie e••_: •
  80. 80. ;'I-;-~[nl j1~I , I • I I I I ~L 111Tii In,li~'-;l;~::~ -¥ I =,o til ~. l r-I. <4 z I '1--~~-- II I i I ~ I ; I ' "r,j' r-Hi'.: "I rr-mm III 1~-rlln Ii i~r II I: !Un II 1~'fW' I II "Ii ,"i It,dl ill I .'" I ll" II! II! H I!i IJtt Jti I III 1111 I i It! III214$71214571 al4S71 ~ %0 o t:; 'I :! 11 ~I 5 I.. ar ~I ..•.. 10 100 1000 TIME TO SATUP.ATION - ms I ; . ! 1 I ! tlJ %14$71 Z~~S:TI • 100 TIME TO SlQ'Ucu:nar.- InS ~"i.g. (Ec.A'1'ioNSW,P '~-r....srN SA1".atA-nolll ~Ac"!"o~ 1<• .4)10' -r;Ml" ~a $A"r<JbT...., =o~ O.j:C"I~ v,,~~ c,,: ~. 04"'0 -r~ . e.-r.~ _"I"M e~$I$"f',"E ~O>~.
  81. 81. I I, 111111 I I 11111·11 IJl.ill!th~ ! ~ I 1/ III i,I I I IIII I , I I III , . . . , , . :<::: • · . .. , :lUtl ~ , .. , . , .... , , ;~=;=;- f:': , , • t • I , I , . , r ~ 1/ ..""".... · I ,t , I ~ , . . , J I I I I • . """,~. I _: I I .! i :uo -; , , '.l..:-: I I , I , , I j , I .v-.........-:-,~ , t • , I I. i f "'--;--·1iTn I I I I I I III I ~...,:..-1"I~ I t ' . 1.30 zq • • t i I I I I I 1 I I I I 1 I 1I1I ...P"'/."~~ 1 I I I !! I -:-l I I I III " I 111111~..8+t- I I I I I i~ III 100 I I I I I 1'17. , , , .... 'I IJ~j±8t'1 I I I I : I lit . I I j I I I I I'- I . ' I I I . 1 I j I I I I II ~~ I ! , ; i i;;II',{ I . ;,1 ~I"I I , 1 III I I I' , I l.-!--!-'illl I : t ... . .. ~ ~::i. , .,.,-~~. • • • • I I , • I l i t I , ;'/~--L~~ .' : , I I I • I I ..,.... .. , " I I I rrTr-_- I I I ~ , I • •:·...~~~I: ,1-- I t I I I , I I L 1 I I I I I ,~ ~~I~..il I I I I II III I I III t I I I II I ~ I j 1111- I I I I II !II I I I I III ::;..-- I I IIII "&~ I 1, ''{.. : 10" 10" I. I IiI! I I', IIIIIII , II i L lUi 1-11m-lITIT II----jTffW! J ~.5 S '10'. 1.3!J ~ 3 .. 5 G S LO' : J. ~ .s Ii & to· - Tl,!- Fot +~"CQS M ,,C~~ ::r,.. - .. Of. ~ JoJ} of r.-r-u,.,.Js.el'JT. •
  82. 82. B H oIV eo"NIilV"nON Ac.- C:1:S• ~ V)< obi...~c:I ~ C_ ~ QlOld --" ',Pl.' ~leQS ~"_c..c4 += ~ lot 2sll(f'. , losS ~ f CiC:Cw.e., ~.:r,... t.u:~~ l oS$ o-t +~To"~"':' of •
  83. 83. CLASS TP G-~~ CQS5 """,,'~ d-e~,';ed ~-tOfWQ..a! when. ""~S~)";' 0. ~S,.64 ev.~ w~~ e.)(f'0"~1-,Q H~ c:kecl~l';~ d·c:. o~t-. CLASS TPS Lo,"", eQ ~Q~e .f'",)c c.-r. ~~~~ cl1!,;..n"ec! b~ !- tiJ. M AG-NE-r,sA..,.,0 IU (!u/.vE ,,', ~ s£eo'""oNL" ~;~) fl.EMA~ENe.E F=Ac:T'o(t. cLASSes -rP)( ~t> 'r{)y . -r~i I ~ P..fof'AI~ -te.c:rl-e.c:l -+0 MAX. Pet/1asS 1&£ CI.I4Il -rPX L..ow4S+ EMoo'" I.olh.i!t ~t,,~ ~~"o- E~ c....~t;".x ~ -rPx -f-t- ~.+~*'ecl ~, - -

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