7SG14 Duois- Trnsformer Protection Document Relese History This document is issue 2010/02. The list of revisions up to nd including this issue is: Pre relese 2010/02 Document reformt due to rernd R1 Revision History dded. 18/10/2006 odel tle modified to show ltest model rnge nd removes older models Softwre Revision History The copyright nd other intellectul property rights in this document, nd in ny model or rticle produced from it (nd including ny registered or unregistered design rights) re the property of Siemens Protection Devices Limited. No prt of this document shll e reproduced or modified or stored in nother form, in ny dt retrievl system, without the permission of Siemens Protection Devices Limited, nor shll ny model or rticle e reproduced from this document unless Siemens Protection Devices Limited consent. While the informtion nd guidnce given in this document is elieved to e correct, no liility shll e ccepted for ny loss or dmge cused y ny error or omission, whether such error or omission is the result of negligence or ny other cuse. ny nd ll such liility is disclimed. 2010 Siemens Protection Devices Limited
ontents 1 INTRODUTION... 4 2 HRDWRE DESRIPTION... 4 2.1 Generl... 4 2.2 nlogue Inputs... 5 2. Sttus Inputs... 5 2.4 Output Relys... 5 2.5 Fsci LEDS... 5 2.6 Self onitoring... 5 2.7 Protection Helthy/Defective... 6 ORDERING INFORTION... 7.1 tlogue Reference ode... 7.2 Stndrd Softwre odels... 7. Hrdwre Specifiction... 9 4 PROTETION FUNTIONS... 9 4.1 ised Differentil (87T)... 9 4.1.1 Principle Of Opertion... 10 4.1.2 Sequence Of Opertion... 10 4.1. hrcteristic... 10 4.1.4 T Input onfigurtions... 11 4.2 Differentil High Set (87HS)... 11 4. Trip ircuit Supervision... 11 4.4 ircuit reker Fil... 11 5 OPTIONL PROTETION FUNTIONS... 11 5.1 Restricted Erth Fult (64REF)... 11 5.2 DTL Overcurrent (50 DTL)... 12 5. IDTL Overcurrent (51 IDTL)... 12 5.4 Volts per Hertz (NSI 24T)... 12 5.5 Therml Overlod (NSI 49)... 12 5.6 Overvoltge (NSI 59)... 12 5.7 Undervoltge (NSI 27)... 1 5.8 Negtive Phse Sequence (NPS) Over current (NSI 46)... 1 6 OTHER FETURES... 1 6.1 etering... 1 6.2 Dt Storge... 1 6.2.1 Generl... 1 6.2.2 Time Synchronistion... 1 6.2. IRIG- Time Synchronistion... 1 6.2.4 IE 60870-5-10 Time Synchronistion... 1 6.2.5 Rel Time lock Time Synchronistion... 1 6.2.6 Wveform Records.... 14 6.2.7 Event Records... 14 6.2.8 Fult Recording... 14 6. ommunictions... 14 6.4 Settings Groups... 15 7 USER INTERFE... 15 7.1 Liquid rystl Disply... 15 7.2 ck light ontrol... 15 7. LED Indictions... 15 7.4 Keypd... 15 7.5 Rely Identifier... 16 7.6 Settings ode... 16 7.6.1 Settings djustment... 16 7.6.2 Settings nd Displys... 16 7.7 Instruments ode... 18 7.7.1 Hidden Instruments... 18 7.8 Fult Dt ode... 18 8 DIGRS... 19 2010 Siemens Protection Devices Limited hpter 1 Pge 2 of 25
FIGURES Figure 1 - Duois- in E8 cse with front pnel open... 19 Figure 2 - Duois- Rer View... 19 Figure - Duois- urrent Differentil lgorithm... 20 Figure 4 - Duois- Interposing T rrngements... 21 Figure 5 - Duois- enu Structure... 22 Figure 6 - Duois- ised Differentil hrcteristics... 2 Figure 7 - Duois- sic Trnsformer onfigurtions... 24 Figure 8 - Yd11 onnection Digrm... 25 Figure 9 - Yd11 + Erthing Trnsformer... 25 2010 Siemens Protection Devices Limited hpter 1 Pge of 25
1 Introduction The use of current lnce ised differentil relys for the protection of power system trnsformers is wellestlished prctice. The Duois--2xx is numeric, current lnce differentil rely for this nd similr pplictions. The rely hs rnge of dditionl fetures with vrints to suit rnge of differing protection nd control prctices. The most sic rely the 200 is lmost identicl to the existing odulr 1 Duois- rely except it is now ville with rnge of sttus input nd output rely configurtions s well s hving versions tht cn tke ising inputs from up to 5 sets of three phse current trnsformers. This rely includes hrmonic restrined ised differentil (87T), unrestrined highest differentil (87HS) protection s well s Restricted Erth Fult (64REF) protection to suit the UK nd overses mrkets. The other sic rely is the 205 which incorportes urrent Differentil (87T/87HS) protection nd 2 stge DTL Overcurrent for phse nd erth fults for the Str side of the power trnsformer nd single stge DTL Overcurrent for phse fults on the Delt side of the trnsformer which is typicl Estern Europen nd sin requirement where restricted erth fult is not widely used. Options include ircuit reker Fil Protection, Over Fluxing Volts per Hertz protection, Therml Overlod, IDTL Phse nd Erth, over nd under voltge, four stge under frequency, neutrl voltge displcement nd Residul erth fult. The fully numericl design hs een exploited to provide unit whose settings, chrcteristics, nd input/output configurtions re softwre controlled which will llow the rely to e used for wide vriety of pplictions. With conventionl trnsformer differentil relys, in order to otin correct input currents for vrious trnsformer configurtions, it is often necessry to specify dditionl interposing current trnsformers for rtio lnce, phse ngle correction nd zero sequence (or third hrmonic) current removl. With Duois--2xx protection these dditionl interposing trnsformers re not required s current trnsformer str/delt rtio, phse ngle correction nd zero sequence current removl re determined y the rely's internl settings nd lgorithm. urrent mplitude correction is lso ccommodted using Interposing T multiplier settings. The rnge of mplitude correction hs een incresed from 0.5 to 1.5, nd is now 0.25 to.00 x, which llows the ppliction where nonidel current trnsformer rtios re lredy instlled or hve een specified. To prevent the rely operting incorrectly due to mgnetising inrush n lgorithm is used to recognise even hrmonics which inhiit the rely when the even hrmonic content of ny operting signl is ove set level. The Duois- differentil protection hs proven stility for onerous system conditions including no lod with severe system overvoltge. The rely, y wy of its design, hs n inherent immunity for conditions where fifth hrmonic my e present nd will remin stle provided tht suitle settings re employed. Fst differentil opertion is mintined for internl fults. 2 Hrdwre Description 2.1 Generl The structure of the rely is sed upon the odulr II hrdwre nd softwre pltform illustrted in Figure 1 & 2 where the required crds plug in from the front fter opening the front fsci. odules re interconnected y mens of rion cle. The rely is ville in stndrd Epsilon cse sizes E8, E12 nd E16 depending upon the options required. The odulr II design provides commonlity etween products nd spre prts cross rnge of protection nd control relys including Duois, Ohmeg, Delt, Tu nd Iot. Typicl cse sizes re: NLOGUE INPUTS STTUS INPUTS OUTPUT RELYS SE 8 5 E8 8 19 21 E12 8 27 29 E16 8 19 21 E12 12 11 1 E12 12 27 29 E16 16 19 21 E16 20 11 1 E16 Ech nlogue module hs four inputs; the first three re for mesuring the T secondry line currents from ech of the three phses, nd. The fourth input is lso normlly current input for restricted erth fult or conventionl erth fult pplictions. However it is possile to specify voltge input chnnel for Volts/Hertz, under/over voltge pplictions. n nlogue module with 4 sets of voltge inputs is lso ville for specil pplictions. The most sic 2 winding relys cn e fitted into n E8 cse nd consist of the following modules: 2010 Siemens Protection Devices Limited hpter 1 Pge 4 of 25
1) Two nlogue Input modules (4 x I per module) 2) One ontroller PU module ) One Power Supply nd sic I/O module 4) One Front Fsci In the lrger cse sizes dditionl Sttus Input (up to mximum of 27) nd Output Relys (up to mximum of 29) my e specified. dditionlly nlogue modules with three current input nd one voltge input circuit my e specified for exmple if over fluxing (V/f) protection is required. This my e in plce of n existing module (which would then lose n erth fult input) or my e n dditionl module s long s the chosen cse style cn ccommodte it. 2.2 nlogue Inputs Up to 5 nlogue modules my e used in the lrgest cse style E16. Ech module consists of up to 4 chnnels of current nd/or voltge depending upon the rely model. In order to ensure high ccurcy true RS mesurements nd ccurte phse nd slip frequency clcultions, the voltge signls re smpled t minimum of 8 smples per cycle for oth 50Hz nd 60Hz system frequencies. This smpling rte lso provides high ccurcy nd wveform storge records 2. Sttus Inputs The rely cn ccommodte from to 27 sttus inputs in totl in increments of 8. The user cn progrm the rely to use ny sttus input for ny function. timer is ssocited with ech input nd pickup nd drop-off time setting my e pplied to ech input. Ech input my e mpped to ny front Fsci LED nd/or to ny Output Rely contct. This llows the Rely to ct s the focl point for lrms for the trnsformer zone nd typiclly is used to provide locl indiction of uchholz Gs, Winding Temperture lrm etc without hving to use dditionl externl flgging elements. The pplictions Guide provides detils of the connections. 2.4 Output Relys The rely cn ccommodte from 5 to 29 output relys in totl in increments of 8, ll of which re cple of hndling circuit reker tripping duty. ll relys re fully user configurle nd cn e progrmmed to operte from ny or ll of the control functions. The three relys on the Power Supply/sic I/O module hve /O contcts. dditionl modules re ville with either 8 N/ contcts or 4 N/ nd 4 N/O contcts In their norml mode of opertion output relys remin energised for minimum of 100msec nd mximum dependent on the energising condition durtion. If required, however, outputs cn e progrmmed to operte s ltching relys. These ltched outputs cn e reset y either pressing the TEST/RESET utton, or y sending n pproprite communictions commnd. The opertion of the contcts cn e simply checked y using the Protection Helthy setting on the Output Rely enu to energise ech rely in turn. Do not forget to reset this setting ck to its correct vlue which mtches the scheme wiring. The output relys cn e used to operte the trip coils of the circuit reker directly if the circuit reker uxiliry contcts re used to rek the trip coil current nd the contct rting of the rely output contcts is not exceeded for 'mke nd crry' currents. With filed reker condition the current 'rek' my e trnsferred to the rely output contcts nd where this level is ove the rek rting of the contcts n uxiliry tripping rely with hevy-duty contcts should e utilised. 2.5 Fsci LEDS In the E8 cse there re 16 user progrmmle LED flg indictors. In the E12 or E16 cse style there re 2 LED flg indictors. y opening the front pnel it is possile to insert strip into slip in pocket, which provides legend informtion out the mening of ech LED. The legend my e specified when ordering the rely or lterntively the user cn crete customized legend. The user cn customise which LED is used for which purpose s well s eing le to progrm ech LED s eing ltching or self resetting. 2.6 Self onitoring The rely incorportes numer of self-monitoring fetures. Ech of these fetures cn initite controlled reset recovery sequence, which cn e used to generte n lrm output. In ddition, the Protection Helthy LED will give visul indiction. wtchdog timer continuously monitors the microprocessor. If the softwre fils to service the wtchdog timer the wtchdog will time out nd cuse reset. The Output Rely modules re locked in hrdwre if the wtchdog timer expires. 2010 Siemens Protection Devices Limited hpter 1 Pge 5 of 25
The memory loctions tht control the Output Relys re surrounded y gurd res to intercept unintentionl ccess. dditionlly the Output Rely modules incorporte n opertionl timeout feture which prevents output contcts from eing held energised if the microprocessor fils to service them. The voltge rils re lso continuously supervised nd the microprocessor is reset if ny of the rils flls outside of their working rnges. ny filure is detected in sufficient time so tht the micro cn e shut down in sfe nd controlled mnner. The progrm memory is supervised y R check which runs continuously to verify its contents. The dt memory is supervised y vlidtion checksums nd oundry mrkers to ensure tht sensitive dt is not overwritten or corrupted. 2.7 Protection Helthy/Defective The normlly closed contcts of rely 1 re used to signl protection defective, whilst the normlly open contcts re used to signl protection helthy. When the D supply is not pplied to the rely or prolem is detected with the opertion of the rely then this rely is de-energised nd the normlly closed contcts mke to provide n externl lrm. When the rely hs D supply nd it hs successfully pssed its self-checking procedure then the Protection Helthy contcts re mde nd the Protection Defective contcts re opened. 2010 Siemens Protection Devices Limited hpter 1 Pge 6 of 25
Ordering informtion.1 tlogue Reference ode The rely is ordered y reference to code. n exmple of ctlogue reference code for model used to protect trnsformers in the UK is DU-201-E 50. This code cn e roken down into four prts. DU The rely is Duois 200 series rely uilt on odulr 2 hrdwre. (DU2 ws odulr 1) 201 This numer specifies the rely functions included. The 201 for exmple is two winding differentil rely with ised differentil, differentil highset nd restricted erth fult for oth windings. E These two letters specifies the hrdwre included on rely model. The first letter E specifies the power supply nd sttus (digitl) input rting. The second letter specifies the rrngement of output contcts nd sttus inputs. For this DU-201-E the rely hs 48/110V dc power supply, 19 off - 110V rted sttus inputs nd 21 off - output contcts ( /O nd 18 N/O). 50 The rted frequency of the power system must lso specified, in this cse 50Hz for the UK. The following two tles provide the informtion with which to specify Duois 200 rely model.2 Stndrd Softwre odels The current stndrd models re given in the tle elow:- 2010 Siemens Protection Devices Limited hpter 1 Pge 7 of 25
T REF DU- 201-** DU- 204-** DU- 207-** DU- 209-** DU- 220-** DU- 221-** DU- 22-** DU- 01-** DU- 04-** DU- 06-** DU- 07-** DU- 20-** DU- 21-** DU- 2-** DU- 401-** DU- 404-** DU- 405-** DU- 501-** DU- 505-** S/W O DEL 200-202 - 207-212 - 210-211 - 20-200 -W 202 -W 206 -W 207 -W 210 -W 211 -W 20 -W 200-4W 202-4W 204-4W 200-5W 204-5W T/ VT INPU TS I N SE SI ZE DI FF 87 + 87 H S 8 / 0 E8 2 W 8 / 0 E8 2 W 8 / 0 E8 2 W 8 / 0 E8 2 W 7 / 1 E8 2 W 7 / 1 E8 2 W 8 / 0 E1 2 2 W 12 / E1 0 2 W 12 / E1 0 2 W 11 / E1 1 2 W 12 / E1 0 2 W 11 / E1 1 2 W 11 / E1 1 2 W 12 / E1 4 0 2 W 16 / E1 4 0 2 W 16 / E1 4 0 2 W 16 / E1 4 0 6 W 20 / 0 20 / 0 E1 6 E1 6 5 W 5 W RE F 87 RE F P O IDTL/ DTL + INSTL/ DTL 51/50 1W / / / 1W / / W DERIV ED 1 EF 50N/ 51N / / ESUR ED EF 50G/51 G 1W / 1W / NP S O 46 2 ST GES FIL 50 F 2 ST GES UNDER/ OVER VOLTG E 27/59 4 STGES UNDER/ OVER FREQUE NY 81 4 STGES OVERF LUX IDTL /DTL 24 1/2 STGE S THER L OVER LOD 49 1W 1 1 1/2 1 1 1 1/2 1 1W W / W W W 1W 1W 1 1 1 1 W / W W / W W / W W W / W W 4W / 4W W W / W +sum W W W / W +sum W / W W W 1 1 1 1 W 1 1 1 1 W 4W / 4W W / W +Su m W / W +Su m 0 / 1W 2 stges 0 / 2 stges W 4W 1 1 Notes: 1. The derived EF is clculted using the phse T inputs. 2. nw indictes the numer of windings tht re covered.. The over current nd erth fults my e summed from two or more sets of T s to relise virtul T position to ssist with grding. This is indicted with +Sum on the rely model. 4. The relys my e supplied with comintions of fetures. 5. 207-[DU-207] supersedes 205-[DU-202] 6. 20-[DU-22] supersedes 201-[DU-20] 2010 Siemens Protection Devices Limited hpter 1 Pge 8 of 25
. Hrdwre Specifiction The two remining letters (E - in our exmple) specify the hrdwre nd rting. The first letter is chosen from the following list: 1 ST LETTER POWER SUPPLY STTUS INPUT RTING RTING 0V dc 0 0V dc 48 48/110V dc 0 D 48/110V dc 48 E 48/110V dc 110 F 220V dc 110 G 220V dc 220 H 110V c 110 I 110V c 48 J 110V c 220 K 110V c 0 The sttus inputs re generlly fed from dc supply, ut c voltge my lso e used suject to confirmtion. The pek voltge nd pickup/drop off dely must e considered when using the inputs from n c supply. The second letter is chosen from the following tle: 2 ND LETTER TYPE ND NUER OF OUTPUT ONTTS NUER OF STTUS (DIGITL) INPUTS /O + 2 NO /O + 10 NO 11 /O + 18 NO 19 D /O + 26 NO 27 E /O + 2 NO 11 F /O + 26 NO 11 G /O + 22 NO + 4 N 27 H /O + 10 NO 27 I /O + 4 NO + 4 N 19 J /O + 6 NO + 4N 19 K /O + 10 NO 19 L /O + 4 NO 5 /O + 42 NO 4 N /O + 46 NO+ 4NO 51 O /O + 6 NO + 20 NO 27 Sttus inputs re typiclly used for flg indiction of externl protection e.g. ucholz, trip circuit supervision nd inputs to scheme logic. The scheme logic tht my e user defined is clled Reylogic. The rely stndrd logic uses Reylogi, nd this my e dded to or edited if the user wishes. The mix of dditionl I/O modules my e different from tht ove. new letter designtion my e llocted if required. 4 Protection Functions 4.1 ised Differentil (87T) Figure shows the overll lock digrm of the 87T current differentil lgorithm. The currents entering nd leving the trnsformer re mesured, tking into ccount the Power Trnsformer vector grouping nd trnsformtion rtio. Softwre interposing current trnsformers cn e pplied to ech set of current inputs to correct for ny mgnitude nd vector mismtch nd to remove zero sequence components where necessry. They re then summed to form n operte signl which is pplied to three prt ised differentil chrcteristic on phse-y-phse sis. Figure gives rief overview of the 87T current differentil functionlity. Three phse currents from up to 5 sets of current trnsformers re scled in mgnitude nd vector group y up to 5 sets of interposing current trnsformers. The operte nd restrint quntities re clculted nd fed to the ised differentil module, differentil high set nd mgnetising inrush detection modules. 2010 Siemens Protection Devices Limited hpter 1 Pge 9 of 25
Figure 6 shows the ised differentil chrcteristics. The first horizontl prt of the chrcteristic (initil setting) tkes into ccount oth T nd rely input circuitmesuring errors for norml lod levels. The second sloping prt increses the rely setting s the loding on the trnsformer increses to tke into ccount of the tp chnger percentge rnge under emergency overlod nd low level through fult conditions. The third curved prt further increses the setting to stilise the rely when.t. sturtion occurs for hevy through fult. To void ml-opertion on energistion ecuse of mgnetising inrush/sympthetic inrush condition, the even hrmonics re used to inhiit opertion nd setting llows for the cross locking of other phses to e selectle etween OFF, locking or Restrining. The locking type of inrush (ROSS locking) ws developed nd used in the first odulr 1 Duois. The Reyrolle 21 to 421 relys used restrining method (SU). With the Duois 200 relys it is possile to select either of these methods. PHSE ROSS SU EH PHSE IS INHIITED SEPRTELY FRO ITS EVEN HRONI ONTENT ny phse detects mgnetising inrush condition ll three phses re locked from operting the mgnetising inrush current from ech phse is summted nd compred to ech operte current individully 4.1.1 Principle Of Opertion On conventionl Str/Delt power system trnsformer the protection current trnsformers re connected in Delt on the primry side nd Str on the secondry side. Under norml lod nd through fult conditions, the currents fed to the primry side of the rely nd the currents fed to the secondry side re lnced in mgnitude nd phse. If fult occurs in the power trnsformer, the currents on the primry side nd the currents on the secondry side re not lnced nd the rely is designed to operte when the difference current etween primry nd secondry exceeds proportion of the verge through current. For trnsformer differentil protection it is necessry to correct the phse reltionship nd mgnitude of the.t. secondry currents resulting from the rrngement of the primry nd secondry power trnsformer windings. Previously this ws ccomplished using complicted comintion of interposing.t. s nd str / delt connections of the current trnsformer circuits. Duois- elimintes this for ll pplictions. Figure 4 shows the equivlent interposing current trnsformer connections otined from the internl vector group compenstion settings. Input nd output currents re shown in cpitl nd smll letters respectively. On the right hnd side is the function used to derive the correct phse reltionship, t ech side re the current vectors to illustrte the chnge in the phse reltionship etween the input nd corrected vectors. The interposing current trnsformers hve n overll 1:1 rtio; those with Yd trnsformers use 1:0.577 to chieve the overll 1:1 rtio. Vector group compenstion cn e pplied, independently, to oth primry nd secondry currents. In ddition, progrmmle rtio correction.t. s re provided with current mplitude multiplier djustle from 0.25 to.0 in 0.01 steps. For exmple if the secondry line current ws 0.5mps t the trnsformer rting multiplier setting of 2.0 would e pplied to relise rely current of 1.0mps. The multiplier of.0 my e used to dvntge if the zone length is long s the urden on the T cn e reduced. It is only for pplictions outside these rnges of djustment tht externl interposing T s will e required. 4.1.2 Sequence Of Opertion n nlogue to digitl converter smples ech current wveform simultneously t set intervls nd t ech intervl the lgorithm looks ck t the lst full cycle worth of dt to check for possile fult condition. Figure illustrtes the operting sequence on three-phse sis for the protection lgorithm. The line current smples re comined if necessry to correct for phse nd mgnitude differences nd to remove zero sequence components i.e. the functions normlly chieved using externl interposing current trnsformers. Simulting the ction of the selected trnsformer connection does this. The Yd IT onnection setting will lso remove third hrmonics from the mesurement of differentil current. (Figure 4) The vector sum nd the sclr sum re used to clculte the differentil operte nd restrint currents. The even hrmonics re detected using Wedmore filter nd compred to percentge of the operte currents on per phse sis nd if this level is exceeded used to prevent the rely from operting under mgnetising inrush conditions. 4.1. hrcteristic The numericl technique provides n extremely flexile operte/is chrcteristic with vrile slopes. In generl terms, the rely will operte when the vlue of 2010 Siemens Protection Devices Limited hpter 1 Pge 10 of 25
r I r I 1 2 + r... + (Vector summtion on phse-y-phse sis) I n 7SG14 Duois--200 Description of Opertion differentil current is greter thn pre-set minimum pickup vlue nd greter thn pre-set proportion of I + I +... I 1 2 n 2 (Sclr summtion on phse-y-phse sis over 2) s illustrted in Figure 5. ll settings on the chrcteristic re under softwre control nd the chrcteristic hs een mde flexile to cover the wide rnge of ppliction encountered in trnsformer protection. 4.1.4 T Input onfigurtions The Duois- comes in Versions for 2 or winding trnsformers with up to 5 sets of current trnsformers. The rely is lso used to provide differentil protection to other circuit types such s rectors, usr zones, motors, genertors nd overll genertor unit protection. Figure 7 shows the some typicl configurtions tht my e used. In ddition, other configurtions re ville on request. The T nd rely connections must e mde in the correct mnner with regrd to current flow. 4.2 Differentil High Set (87HS) This function is sometimes mistkenly thought of s highest over current function. It is not, s it is n unrestrined differentil function nd is fundmentl to the overll rely design to provide fst tripping for high level internl fults. It is included in the rely for two min resons. The first reson is the differentil high set function provides fst trip time for hevy internl fults where trnsient T sturtion my slow down the ised differentil. The second is it is very fst operting, typiclly under one cycle nd therefore limits fult dmge for solid short circuits. The differentil high set protection opertes when the RS vlue of the differentil signl I1 I2 is greter thn pre-set vlue which cn e vried. Note it is lwys recommended to use this prt of the rely. The setting used for this function is included in the clcultion for the rely T requirements. The differentil high set is n integrl prt of the protection designed to give fst coverge t high internl fult currents with sturted current trnsformers. It is lwys recommended to use this feture of the rely. The high set should e set s low s possile ut not less thn the mximum phse through fult current nd not less thn the hlf the lrgest pek of mgnetising inrush current. typicl setting for power trnsformer would e in the 7 x In. 4. Trip ircuit Supervision Sttus inputs on the Duois--200 rely cn e used to supervise trip circuits while the ssocited circuit rekers () re either open or closed. Since the sttus inputs cn e progrmmed to operte output contcts nd LED s, lrms cn e lso generted for ech trip circuit independently. To use the function specify which sttus inputs re Trip ct Fil inputs in the STTUS INPUT menu nd progrm the sme sttus inputs to e Inverted Inputs in the sme menu nd pply time delys (normlly 400ms dely on pickup) s required for this function. See the pplictions Guide for more detils on the trip circuit supervision scheme. 4.4 ircuit reker Fil The ircuit reker Fil element my e triggered from n internl protection function or n externl protection function. It my lso e locked y sttus input. When trip occurs the ReTrip Timer nd cktrip Timers re strted for ech phse. When either timer expires, if the current check element in tht phse is lso operted then ReTrip or cktrip output will e issued. n dditionl locking element ensures tht the element hs fst reset. This monitors the RS current level nd genertes locking signl if switch off condition is detected. 5 Optionl Protection Functions 5.1 Restricted Erth Fult (64REF) It is usul in mny prts of the world to supplement differentil protection with restricted erth fult protection. This is ecuse of the very sensitive fult detection nd high speed of opertion tht cn e chieved. Restricted Erth 2010 Siemens Protection Devices Limited hpter 1 Pge 11 of 25
Fult is inherently more sensitive thn phse differentil s the element receives fult current mesurement from the neutrl T, wheres the differentil elements do not. REF is unffected y trnsformer mgnetising inrush conditions. ny fults either involve erth or quickly develop to include erth nd so its use is very eneficil. Figure 8 nd Figure 9 shows typicl connections to the restricted erth fult elements on the HV nd LV side of the rely. s cn e seen from the digrms REF my e fitted to oth the STR (WYE) nd DELT sides of the trnsformer. If the DELT side of the trnsformer includes n in-zone erthing trnsformer then the REF element is positioned in the prllel connection of the line nd neutrl.t. s. This ensures opertion only for the winding where the erth fults exist. oth elements re connected to individul erth fult trnsformers nd hve wide rnge of current settings. Externl series resistors re required s shown which effectively converts the elements into voltge operted devices. The stility of the system depends upon the voltge setting eing greter thn the mximum voltge which cn pper cross the REF elements under through fult condition. Ech REF element cn e individully deselected if not required. See the pplictions guide section for further detils on the ppliction of REF. 5.2 DTL Overcurrent (50 DTL) s n option DTL Overcurrent functions cn e dded to ech set of inputs nd there my e up to 2 stges with seprte pickup nd time delys per phse nd erth fult. In ddition it is possile to locte elements on the summtion point of sets of inputs to provide true winding protection even when the T s re idelly positioned. 5. IDTL Overcurrent (51 IDTL) s n option IDTL Overcurrent functions using IE or NSI pick-up curves with definite time or decying dropoff cn e dded to ech set of inputs. There my e up to 2 stges with seprte pickup nd time delys per phse nd erth fult. In ddition it is possile to locte elements on the summtion point of sets of inputs to provide true winding protection even when the T s re idelly positioned. 5.4 Volts per Hertz (NSI 24T) The volts per hertz function (V/f) protects the power trnsformers ginst overheting due to sustined over voltge or under frequency system conditions tht cuse excessive flux in the trnsformer core. n inverse time chrcteristic is used to mtch the therml withstnd cpility of the trnsformer, if this is known. Plin dul Definite Time Lg (DTL) elements re used to modify the chrcteristic for exmple to tke into ccount of genertor rc withstnd cpilities or when the trnsformer cpility curve is unknown. 5.5 Therml Overlod (NSI 49) This feture provides therml overlod protection for cles nd trnsformers within the rely zone. Therml protection is used to sfegurd ginst system normlities rther thn fults (normlly hevy lods, etc). The temperture of the protected equipment is not mesured directly. Insted, therml overlod conditions re detected y clculting the verge of the currents flowing in the phse conductors. This verge vlue is fed to the therml lgorithms. Should the verge current rise ove defined level (the Overlod Setting I/O) for defined time (the operting time t), the system will e tripped to prevent dmge. Time to trip t(mins) τ ln I 2 I (I ) = 2 2 θ dditionlly, lrms will e given if: The verge current exceeds the Therml Overlod level (Therml Overlod lrm). If left t this level the current would result in therml overlod trip. The therml stte of the system exceeds specified percentge of the protected equipment s therml cpcity (pcity lrm). The step rise in the therml stte of the system is greter thn specified percentge of the equipment s therml cpcity (Lod Increse lrm). The therml overlod feture cn e pplied to either winding s desired. It is usul to llocte the therml function to the source side winding. 5.6 Overvoltge (NSI 59) odels tht include voltge input provide definite time overvoltge function tht my e used to protect the power trnsformers ginst over voltges. Severl stges my e specified if required. 2010 Siemens Protection Devices Limited hpter 1 Pge 12 of 25
5.7 Undervoltge (NSI 27) odels tht include voltge input provide definite time under voltge function. The under voltge element my e gurded y n under voltge locking element to prevent n under voltge output when the trnsformer is deenergised. 5.8 Negtive Phse Sequence (NPS) Over current (NSI 46) odels tht include NPS over current function hve oth lrm DTL nd trip DTL/IDTL stges with seprte pickup settings. 6 Other Fetures 6.1 etering The Duois- metering feture provides rel-time dt ville from the rely fsci in the Instruments ode or vi the communictions interfce. The following displys re ville: RS Line urrents for,, for ech set of three phse current inputs RS Rely urrent for,, for ech set of currents fter interposing T corrections nd multipliers re pplied. RS Operte urrents,, for the differentil chrcteristic. RS Restrin urrent,, for the differentil chrcteristic. RS gnetising Inrush (Even Hrmonic) urrents,, for the differentil chrcteristic. RS Erth Fult or Restricted Erth Fult urrent if this function is present. Digitl input sttus Output rely sttus Time nd Dte Other rel time mesurements re included when optionl protection functions re specified. 6.2 Dt Storge 6.2.1 Generl Detils of rely opertion re recorded in three forms, nmely Wveform records, Event records nd Fult Dt records. ll records re time nd dte stmped with resolution of one millisecond. 6.2.2 Time Synchronistion Time nd dte cn e set either vi the rely fsci using pproprite commnds in the System onfig menu or vi n IRIG- input or vi the communictions interfce 6.2. IRIG- Time Synchronistion N connector on the rely rer provides n isolted IRIG- GPS time synchronistion port. One IRIG- source my e connected to severl devices in chin using co-x cle nd N T-pieces. The IRIG- input hs 4k-ohm impednce nd expects modulted -6 Volt signl to provide time synchronistion to the nerest millisecond. Some IRIG- sources output voltges ove this level nd my require n externl terminting resistor to e dded to the lst rely in the chin to mtch the output drive requirements of the IRIG- source, typiclly 50 or 75 ohms. 6.2.4 IE 60870-5-10 Time Synchronistion Relys connected individully or in ring or str configurtion cn e directly time synchronised using the IE 60870-5-10 glol time synchronistion. This cn e from dedicted susttion utomtion system or from Reydisp Evolution ommunictions Support Softwre. 6.2.5 Rel Time lock Time Synchronistion In the sence of IRIG- nd IE60870 time synchronistion the rely contins yer 2000 comptile rel time clock circuit which mintins rel time in the sence of D supply (See Note). 2010 Siemens Protection Devices Limited hpter 1 Pge 1 of 25
6.2.6 Wveform Records. The wveform record feture stores nlogue nd digitl informtion for the current inputs, sttus inputs nd output relys nd LED s. Internl wveforms from the operte, restrint nd mgnetising inrush currents for ech phse re lso stored for post fult dignostics. Wveforms my e returned to V TEH Reyrolle P Ltd for nlysis. The wveforms re stored with smpling resolution of t lest 8 smples per cycle depending upon rely model. The wveform recorder hs the ility to store records for the previous five trip opertions of the rely. These re lelled 1-5 with 1 eing the most recent record. This however, cn e ltered using the Record Durtion setting, which offers the following selection: Five records of one second durtion 1 Two records of two seconds durtion One record of five seconds durtion 1 Fewer records my e ville on W, 4W & 5W models ecuse of the incresed memory requirements. The wveform recorder will e triggered utomticlly when ny protection element opertes. It cn lso e triggered y ny of the following mens : Vi the Trigger Storge sttus input signl. Vi the IE870-5-10 communictions interfce. The wveform recorder hs settle pre-fult triggering cpility. 6.2.7 Event Records The event recorder feture llows the time tgging of ny chnge of stte (Event) of the rely. s n event occurs the ctul event condition is logged s record long with time nd dte stmp to resolution of 1 millisecond. There is cpcity for mximum of 500 event records tht cn e stored in the rely nd when the event uffer is full ny new record will over-write the oldest. The following events re logged: hnge of stte of Output Relys. hnge of stte of Sttus Inputs. hnge of stte of ny of the control functions of the rely. Pick-up or opertion of ny of the protection functions. 6.2.8 Fult Recording The led flg configurtion, dte nd time of the lst five fults re recorded for disply vi the Fsci LD. Note : the rel-time clock, wveform records nd event records re ll mintined, in the event of loss of uxiliry d.c. supply voltge, y the ckup storge cpcitor. This cpcitor hs the ility to mintin the chrges on the rel-time clock I nd the SR memory device for typiclly 2- weeks time durtion. This time, however, is influenced y fctors such s temperture nd the ge of the cpcitor nd could e shorter. This overcomes the need for dt storge ck-up internl ttery. 6. ommunictions Two ST type fire optic communiction ports, O1 nd O 2 re provided t the rer of the rely, which give superior E performnce. n isolted RS22 port, O 2 is provided t the front of the rely for locl ccess using P. ommuniction is comptile with the IE870-5-10 FT 1.2 trnsmission nd ppliction stndrds. For communiction with the rely vi P (personl computer) user-friendly softwre pckge, REYDISP EVOLUTION [1], is ville to llow trnsfer of the following: Rely Settings Wveform Records Event Records Fult Dt Records Instrument nd meters ontrol Functions 2010 Siemens Protection Devices Limited hpter 1 Pge 14 of 25
ommunictions opertion is descried in detil in Section 4 of this mnul. For informtion out ll spects of the communictions protocol used in the Duois- rnge of relys see [2]. The use of Reydisp Evolution ssists gretly when commissioning Duois trnsformer protection schemes. 6.4 Settings Groups Depending up on the rely model then up to four lterntive setting groups re provided, mking it possile to edit one group while the rely protection lgorithms operte using nother ctive group. n indiction of which group is eing viewed is given y the Gn chrcter in the top left of the disply. Settings tht do not indicte Gn in the top left corner of the LD re common to ll groups. chnge of group cn e chieved either loclly t the rely fsci or remotely vi communiction interfce commnd. The progrmmle pssword feture enles the user to enter 4 chrcter lphnumeric code to secure ccess to the rely settings. The rely is supplied with the pssword set to NONE, which mens tht the pssword feture is not ctivted. The pssword must e entered twice s security mesure ginst ccident chnges. Once pssword hs een entered then it will e required therefter to chnge settings. It cn, however, e dectivted y using the pssword to gin ccess nd y resetting it ck to NONE. gin this must e entered twice to de-ctivte the security system. s soon s the user ttempts to chnge setting the pssword is requested efore ny setting ltertions re llowed. Once the pssword hs een vlidted, the user is logged on nd ny further chnges cn e mde without re-entering the pssword. If no more chnges re mde within 1 hour then the user will utomticlly e logged off, re-enling the pssword feture. Note tht the pssword vlidtion screen lso displys numericl code. If the pssword is lost or forgotten, this code should e communicted to V TEH Reyrolle P Ltd nd the pssword cn e retrieved. If the code is 1966067850 then 4 spces hve een entered s the pssword. This is cused y ENTER eing pressed three times on the hnge Pssword setting screen. De-ctivte pssword y typing NONE s descried ove nd pressing ENTER, if this ws set un-intentionlly. 7 User Interfce The user interfce is designed to provide user-friendly method of entering settings nd retrieving dt from the rely. The rely fsci includes 20 chrcter y 2 line, cklit, liquid crystl disply (LD), 16 (E8), or 2 (E12) light emitting diodes (LED) nd 5 push uttons. 7.1 Liquid rystl Disply The liquid crystl disply is used to present settings, instrumenttion nd close dt in textul formt on 2 lines y 20-chrcter interfce. 7.2 ck light ontrol To conserve power the disply cklighting is turned off if no push uttons re pressed for 5 minutes. fter n hour the whole disply is de-ctivted. setting within the SYSTE ONFIG ENU llows the timeout to e djusted from 5 minutes up to LWYS ON. 7. LED Indictions The following indictions re provided: Protection Helthy Green LED. This LED is solidly illuminted to indicte tht D volts hve een pplied to the rely nd tht the rely is operting correctly. If the internl rely wtchdog detects protection rely unhelthy condition then this LED will continuously flsh. Progrmmle Red LED. n LED ENU is provided to steer ny output to ny LED. 7.4 Keypd Five pushuttons re used to control the functions of the rely. They re lelled ENTER nd NEL. Note tht the utton is lso lelled TEST/RESET. When the rely front cover is in plce only the nd uttons re ccessile. This llows only red ccess to ll the menu displys. 2010 Siemens Protection Devices Limited hpter 1 Pge 15 of 25
7.5 Rely Identifier The Rely Identifier setting in the SYSTE ONFIG ENU my e used to plce circuit identifier onto the rely fsci e.g. OLDON SGT1. This informtion is lso returned s prt of the System Informtion commnd from Reydisp Evolution ommunictions Support Softwre. 7.6 Settings ode 7.6.1 Settings djustment The push-uttons on the fsci re used to disply the rely settings, disply the operting signls, e.g. currents, on the LD nd to reset the fult records nd flg indiction on the LDs. There re five push-uttons mrked red-up, red-down, enter, cncel, nd right/test/reset only two of which re ccessile when the rely cover is on, nmely red-down nd right/rest/reset. RED DOWN / DEREENT In the Settings Disply this push-utton is used for scrolling down through list of settings or signls. In Settings odifiction mode it is used for selecting the next vlue of (or decresing) the displyed setting or for deselecting it position in prticulr control setting. RED UP /INREENT In Settings Disply or Signl Displys this push-utton is used for scrolling ck up through list of settings or signls. In Settings odifiction mode it is used for selecting the previous vlue of (or incresing) the displyed setting or for selecting it position in prticulr control setting. ENTER This push-utton is used when the cover is removed to select etween two modes of opertion nmely Settings Disply or Settings odifiction. When this push-utton is pressed nd rely setting is eing displyed prt of the disply will flsh to indicte tht the setting eing displyed cn e modified y using the INREENT or DEREENT keys on the fsci. When the required vlue of the setting hs een estlished my e entered into the rely nd cted upon y pressing the ENTER key gin. NEL This push-utton is used when the cover is removed to return the rely disply to its initil sttus. It cn e used to reject ny ltertions to the setting eing modified provided the ENTER key hs not een pressed to ccept the chnges. TEST/RESET This push-utton is used to reset the fult indiction on the LEDs on the fsci It lso cts s lmp test utton ecuse when pressed ll of the LEDs will momentrily light up to indicte their correct opertion. The RED DOWN nd RED UP push-uttons my then e used to scroll through the vrious signls. 7.6.2 Settings nd Displys The disply menu structure is shown in Figure 5. This digrm shows the three min modes of disply, which re the Settings ode, Instruments ode nd the Fult Dt ode. When the rely is first energised the user is presented with the following messge, SETTINGS DEFULTED PRESS ENTER 2010 Siemens Protection Devices Limited hpter 1 Pge 16 of 25
This shows tht the rely hs een set with the stndrd fctory defult settings nd must e loded with the correct settings for the ppliction. If this messge is displyed ENTER must e pressed to cknowledge this initil condition, the disply will then indicte the rely softwre vrint. e.g. DUOIS--200- Pressing the TEST/RESET key on this disply initites n LED test. Pressing RED DOWN t this disply llows ccess to the three disply modes, which re ccessed in turn y pressing the TEST/RESET key. The Settings ode contins 11 setting su-menu s. These hold ll of the progrmmle settings of the rely in seprte logicl groups. The su menus re ccessed y pressing the key. This enters the su menu nd presents list of ll the settings within tht su menu. Pressing RED DOWN scrolls through the settings until fter the lst setting in the group the next su menu is presented. ccess to this group is vi the sme method s efore. If prticulr su menu is not required to e viewed then pressing RED DOWN will skip pst tht prticulr menu nd present the next one in the list. Note tht ll screens cn e viewed even if the pssword is not known. The pssword only protects ginst unuthorised chnges to settings. While viewing n editle screen pressing the ENTER key llows the user to chnge the displyed dt. flshing chrcter(s) will indicte the editle field. Pressing INREENT or DEREENT scrolls through the ville setting vlues or, pressing TEST/RESET moves right through the edit fields. Note tht ll settings cn e incremented or decremented using the INREENT or DEREENT keys nd they ll wrpround so tht to go from setting minimum vlue to the mximum vlue it is quicker to press the DEREENT key, rther thn scroll through every setting. lso, to fcilitte quicker setting chnges n ccelertion feture is ville which if INREENT or DEREENT re depressed nd held, then the rte of scrolling through the setting vlues increses. If ESPE/NEL is pressed during setting chnge opertion the originl setting vlue is restored nd the disply is returned to the norml view mode. If chnges re mde to the setting vlue then pressing ENTER disles the flshing chrcter mode nd displys the new setting vlue. This is immeditely stored in non-voltile memory. The next sections give description of ech setting in the rely. The ctul setting rnges nd defult vlues cn e found in the Rely Settings section of this mnul. 2010 Siemens Protection Devices Limited hpter 1 Pge 17 of 25
7.7 Instruments ode In Instrument ode metering points cn e displyed to id with commissioning, the following meters re ville ETER xx Line urrents xx Rely urrents Operte urrents Restrin urrents DESRIPTION urrents entering the rer terminls of the rely urrents presented to the urrent Differentil elements fter interposing T vector group nd mgnitude correction urrent Differentil element operte spill currents which should e low vlue unless fult exists within the protected zone or the interposing T vector group or mgnitude correction settings hve een incorrectly set urrent Differentil element through fult restrin currents which re mesure of the loding on the trnsformer g urrents Inrush mesure of the even hrmonics in the operte current Sttus Inputs Output Relys Dte nd Time The stte of the D sttus inputs The stte of the Output Rely contcts Dte & Time Note tht meters re usully displyed s multiples of nominl i.e. x In, 1 mp or 5 mp. 7.7.1 Hidden Instruments t the Instruments ode title screen, pressing ENTER nd DOWN simultneously revels some dditionl metering for clirtion purposes. The reference chnnels s well s D offsets my e displyed long with the RS vlues in rw D counts. The reltionship etween current nd D counts is 1 x In = 600 counts. 7.8 Fult Dt ode In Fult Dt ode, the time nd dte of rely opertions re recorded together with record of the LED flg sttes. 2010 Siemens Protection Devices Limited hpter 1 Pge 18 of 25
8 Digrms Figure 1 - Duois- in E8 cse with front pnel open Figure 2 - Duois- Rer View 2010 Siemens Protection Devices Limited hpter 1 Pge 19 of 25
T1 T1 T1 onnection Yy0,Yd1,...Ydy0 ultiplier 0.25,0.26,...00 INTERPOSING URRENT TRNSFORER OPERTE ND RESTRINT Tn Tn Tn onnection Yy0,Yd1,...Ydy0 ultiplier 0.25,0.26,...00 INTERPOSING URRENT TRNSFORER -eters tht my e displyed on Fsci LD WEDORE FILTER RS RS RS Inrush Inhiit Level OFF,15,16,...25% GNETISING INRUSH DETETOR Initil Setting 10,20,...50 % is Slope 0,10,...70 % is Slope Limit 2,,...20 xin OPERTE ND RESTRINT S SL Differentil High Set OFF, 4,5,...25 xin HIGH SET & 87T TRIP & 87T TRIP & 87T TRIP 87HS TRIP 87HS TRIP 87HS TRIP I Figure - Duois- urrent Differentil lgorithm 2010 Siemens Protection Devices Limited hpter 1 Pge 20 of 25
N Yy0 (0 phse shift) = = c = n = N c N Ydl (-0 phse shift) = - = - c = - c Zero sequence removed Y y2 (-60 phse shift) N n = - = - c = - c Yd (-90 phse shift) N = - = - c = - c Zero sequence removed Y y4 (-120 phse shift) N n = = c = c Yd5 (-150 phse shift) N = - c = - c - = Zero sequence removed Y y6 (180 phse shift) N = - = - c = - n c Yd7 (150 phse shift) N = - = - c = - c Zero sequence removed Y y8 (120 phse shift) N = = c = n c Yd9 (90 phse shift) N = - = - c = - c Zero sequence removed Y y10 (60 phse shift) N n = - = - c = - c Yd11 (0 phse shift) N = - = - c = - c Zero sequence removed H\ORDSHED\DUOINTT Ydy0 (0 phse shift) N n = (2--) = (2--) c = (2--) c Zero sequence removed Figure 4 - Duois- Interposing T rrngements 2010 Siemens Protection Devices Limited hpter 1 Pge 21 of 25
NEL/ESPE RELY IDENTIFIER LED TEST SETTINGS ODE INSTRUENTS ODE FULT DT ODE SYSTE ONFIG ENU TO VIEW HV Line urrents 0.00 0.00 0.00 xin FULT 1 ISED DIFFERENTIL ENU TO VIEW HV Erth urrent 0.000 xin LV Line urrent 0.00 0.00 0.00 xin FULT 5 RESTRITED ERTH FULT ENU TO VIEW STTUS INPUT ENU TO VIEW LV Erth urrent 0.000 xin HV Rely urrents 0.00 0.00 0.00 xin NOTE : THE RROWS IN THE DIGR REPRESENT THE KEY PRESSES REQUIRED TO NVIGTE THE ENU SYSTE. RED UP REYLOGI ONTROL ENU TO VIEW LV Rely urrents 0.00 0.00 0.00 xin ENTER NEL / ESPE TEST/RESET Operte urrents 0.00 0.00 0.00 xin RED DOWN REYLOGI ELEENTS ENU TO VIEW Restrin urrents 0.00 0.00 0.00 xin OUTPUT RELY ENU TO VIEW g Inrush urrents 0.00 0.00 0.00 xin LED ENU TO VIEW Sttus Inputs 1- _ Output Relys 1-5 1 DT STORGE ENU TO VIEW Time & Dte 16/07/2001 11:49:17 OUNITIONS ENU TO VIEW Figure 5 - Duois- enu Structure 2010 Siemens Protection Devices Limited hpter 1 Pge 22 of 25
6 5 4 2 1 0 Single Phse ised Differentil hrcteristics Single Infeed Fult Line FSTEST TRIP REGION FST TRIP REGION TRIP REGION Operte urve STILITY REGION Where = is slope = is slope limit K 2 = 2-2 2 2 is Slope Limit is Slope Tp hnger induced Spill urrent 0 1 2 4 5 6 7 8 9 10 IS RESTRINT SIGNL = ( I1 + I2 +... + In )/2 (sclr sum of currents over 2) OPERTE SIGNL = I1 + I2 +...+ In (vector sum of currents) Initil Setting Figure 6 - Duois- ised Differentil hrcteristics 2010 Siemens Protection Devices Limited hpter 1 Pge 2 of 25
W1 + W2 = Protected Zone W1 + W2 + W = W W1 + W2 + W = W If no through fult cn occur on usr then is lso suitle with Ts prlleled s required. W1 + W2 + W + W4 = 4W If no through fult cn occur on usr then W is lso suitle with Ts prlleled s required. W1 + W2 + W + W4 = 4W If no through fult cn occur on usr then W is lso suitle with Ts prlleled s required. W1 + W2 + W + W4 + W5 = 5W If no through fult cn occur on usr then 4W is lso suitle with Ts prlleled s required. Figure 7 - Duois- sic Trnsformer onfigurtions 2010 Siemens Protection Devices Limited hpter 1 Pge 24 of 25
P1 P2 P2 P1 S1 S2 S2 P2 S2 S1 S1 P1 PROTETED ZONES Duois--200 Trnsformer Protection HV Winding.T's S2 S1 N1 17 18 21 22 25 26 18 22 26 N2 17 21 25 LV Winding.T's S1 S2 Rs HV REF 25 26 LV REF 26 25 Rs N S2 S1 HV NEUTRL T Figure 8 - Yd11 onnection Digrm P1 P2 P2 P1 S1 S2 S2 S1 P2 P1 P2 P1 S2 S1 S2 S1 PROTETED ZONES Duois--200 Trnsformer Protection HV Winding.T's S2 S1 N1 17 18 21 22 25 26 18 22 26 N2 17 21 25 LV Winding.T's S1 S2 Rs HV REF 25 26 LV REF 26 25 Rs N N S2 S1 S1 S2 HV NEUTRL T LV NEUTRL T Figure 9 - Yd11 + Erthing Trnsformer 2010 Siemens Protection Devices Limited hpter 1 Pge 25 of 25