Cahier technique no. 114

Transcription

1 Collecion Technique... Cahier echnique no. 114 Residual curren devices in LV J. Schonek Building a ew Elecric World

2 «Cahiers Techniques» is a collecion of documens inended for engineers and echnicians, people in he indusry who are looking for more in-deph informaion in order o complemen ha given in produc caalogues. Furhermore, hese «Cahiers Techniques» are ofen considered as helpful «ools» for raining courses. They provide knowledge on new echnical and echnological developmens in he elecroechnical field and elecronics. They also provide beer undersanding of various phenomena observed in elecrical insallaions, sysems and equipmens. Each «Cahier Technique» provides an in-deph sudy of a precise subjec in he fields of elecrical neworks, proecion devices, monioring and conrol and indusrial auomaion sysems. This consanly updaed collecion can be downloaded from: hp:// Please conac your Schneider Elecric represenaive if you wan eiher a "Cahier Technique" or he lis of available iles. The "Cahiers Techniques" collecion is par of he Schneider Elecric s "Collecion echnique". Foreword The auhor disclaims all responsibiliy subsequen o incorrec use of informaion or diagrams reproduced in his documen, and canno be held responsible for any errors or oversighs, or for he consequences of using informaion and diagrams conained in his documen. Reproducion of all or par of a "Cahier Technique" is auhorised wih he compulsory menion: "Exraced from Schneider Elecric "Cahier Technique" no...." (please specify).

3 no. 114 Residual curren devices in LV Jacques Schonek A graduae of he ESEEIHT engineering school wih a docorae in engineering from he Universiy of Toulouse, J. Schonek was involved in he design of Telemecanique variable-speed drives from 1980 o He hen wen on o manage he harmonic-filering aciviy. He is currenly working as an exper in Elecrical Disribuion Applicaions in he Archiecures and Sysems group of Schneider Elecric. ECT 114 firs issue, february 2006

4 Lexicon Common mode disurbance Any coninuous or ransien elecromagneic phenomenon occurring beween a live par of a power sysem and earh. May be a ransien overvolage, a coninuous volage, an overcurren or an elecrosaic discharge. Differenial mode disurbance Any phenomenon beween differen live pars of a power sysem, e.g. an overvolage. Direc conac Conac of a person wih he live pars of elecrical devices (normally energised pars and conducors). Earh-leakage curren Curren ha flows from he live pars o earh, in he absence of an insulaion faul. Elecrisaion Applicaion of volage beween wo pars of he body of a living being. Elecrocuion Elecrisaion resuling in deah. Exposed conducive par (ECP) Conducive par likely o be ouched and which, alhough normally insulaed from live pars, may be energised up o a dangerous volage level due o an insulaion faul. Faul curren Curren resuling from an insulaion faul. Indirec conac Conac of a person wih accidenally energised exposed conducive pars (ECP), usually due o an insulaion faul. Insulaion Arrangemen prevening ransmission of volage (and curren flow) beween a normally energised par and an exposed conducive par (ECP) or earh. Insulaion faul Break in insulaion causing an earh-faul curren or a shor-circui via he proecive conducor. Inenional leakage curren Curren ha flows o earh via he inenionally insalled componens (resisors or capaciors), in he absence of an insulaion faul. Live conducors Se of conducors for elecrical power ransmission, including he neural, wih he excepion of he conducor for which he proecive conducor () funcion akes prioriy over he neural funcion. aural leakage curren Curren ha flows o earh via he insulaion, in he absence of an insulaion faul. eural sysem See "Sysem earhing arrangemen". Proecive conducors ( or ) Conducors which, according o specificaions, connec he exposed conducive pars (ECP) of elecrical equipmen and cerain oher conducive pars o he earh elecrode. Raed residual operaing curren I n Value of he residual operaing curren assigned by he device manufacurer a which he device mus operae under he specified condiions. According o consrucion sandards, a 20 C, low volage residual curren devices mus operae a residual currens beween I n/2 and I n Residual curren Algebraic sum of he insananeous values of he currens flowing hrough all live conducors in a circui a a poin of he elecrical insallaion. Residual curren device (RCD) Device whose decisive quaniy is he residual curren. I is normally associaed wih or incorporaed in a breaking device. Residual operaing curren Value of he residual curren causing a residual curren device o operae. Sysem earhing arrangemen (SEA) Also referred o as he neural sysem, earhing sysem or earhing arrangemen. Sandard IEC sipulaes hree main ypes of earhing arrangemens ha define he possible connecions of he source neural o earh and of he exposed conducive pars (ECP) o earh or he neural. The elecrical proecion devices are hen defined for each one. Touch volage limi (U L ) Volage U L below which here is no risk of elecrocuion. Venricular fibrillaion A malfuncioning of he hear corresponding o loss of synchronism of he aciviy of is walls (diasole and sysole). The flow of AC curren hrough he body may be responsible for his due o he periodic exciaion ha i generaes. The ulimae consequence is soppage of blood flow. Cahier Technique Schneider Elecric no. 114 / p.2

5 Residual curren devices in LV Today, residual curren devices (RCD) are recognised as he mos effecive means of proecing life and propery agains elecrical hazards in lowvolage sysems. Their selecion and opimum use require sound knowledge of he principles and rules governing elecrical insallaions and in paricular sysem earhing arrangemens as well as exising echnologies and heir performance levels. All hese aspecs are deal wih in his "Cahier Technique", wih in addiion numerous answers provided by Schneider Elecric echnical and mainenance deparmens o frequenly asked quesions. Conens 1 Inroducion p. 4 2 The risks of elecrical currens 2.1 Elecrisaion of persons p Fire hazards p Damage o equipmen p. 7 3 Proecion agains he risks 3.1 Insallaion rules p. 8 of elecrical currens 3.2 Deecion of insulaion fauls p. 9 4 RCD operaing principle and descripion 4.1 Operaing principle p Applicaions p Main characerisics p Technology p Consrains due o he curren sensor p Special applicaions p Conclusion p. 22 Appendix 1: Calculaion of ouch volages p. 23 Appendix 2: Types of converers and faul-curren waveforms p. 25 Appendix 3: Leakage currens for differen sysem earhing arrangemens p. 28 Appendix 4: RCD hresholds and power sysem volages p. 30 Bibliography p. 31 Cahier Technique Schneider Elecric no. 114 / p.3

6 1 Inroducion Compared o oher energy sources, elecriciy has many advanages, bu also many risks. I is used on a daily basis by he general public and many accidens sill occur, resuling in burns, fires and elecrocuion. Sric insallaion rules have been se up by inernaional (IEC, CEELEC) and naional (e.g. FPA in he USA and UTE in France,) organisaions. Dependable proecive devices have been designed by carefully analysing he risks and consequences of equipmen failures or incorrec use. Among hese devices, RCDs (residual curren devices) are recognised by inernaional sandardisaion organisaions as an effecive means o proec life and propery. This documen will presen he subjec in hree seps: c a descripion of he risks relaed o elecrical currens, c an overview of he proecion echniques employed o limi hose risks, c an in-deph presenaion of how RCDs operae. 2 The risks of elecrical currens 2.1 Elecrisaion of persons A person subjeced o an elecrical volage is elecrised. Depending on he level of elecrisaion, he person may be subjeced o differen pahophysiological effecs: c disagreeable sensaion, c involunary muscular conracion, c burns, c cardiac arres (elecrocuion). These effecs depend on various facors, including he physiological characerisics of he person, he environmen (e.g. we or dry condiions) and he characerisics of he curren flowing hrough he body. A person may be subjeced o an elecrical shock in wo manners: c direc conac, e.g. he person ouches an energised, bare conducor, c indirec conac, e.g. he person ouches a meal par of an elecrical machine or device wih an insulaion faul. The dangerous aspec is he curren (magniude and duraion) flowing hrough he human body and paricularly near he hear. a) Direc conac Phases Uc b) Indirec conac 3 Id Uc Fig. 1 : Direc and indirec conac. Cahier Technique Schneider Elecric no. 114 / p.4

7 Figure 2 sums up he work of he Inernaional Elecroechnical Commission on he subjec (sandard IEC , Ed.4, 2005, Effecs of curren on human beings and livesock - Par 1. General aspecs). I indicaes he consequences of AC curren flowing hrough he human body, from he lef hand o he fee, depending on he curren and is duraion. I is especially imporan o consider zones AC-3 and AC-4 where here is real danger. c Zone AC-3 (beween curves B and C 1 ) Usually no organic damage, bu here is a likelihood of muscular conracions and difficuly in breahing, wih reversible disurbances in he formaion and conducion of impulses in he hear. c Zone AC-4 (locaed o he righ of curve C 1 ) In addiion o he effecs noed for zone AC-3, he probabiliy of venricular fibrillaion: v increases up o abou 5% beween curves C 1 and C 2, v increases up o abou 50% beween curves C 2 and C 3, v exceeds 50% beyond curve C 3. The probabiliy of dangerous pahophysiological effecs such as cardiac arres, breahing arres and severe burns increases wih curren and ime. oe ha a 150 ma curren may flow in a person in conac wih a 230 V volage, under unfavourable condiions. Given he curren levels considered dangerous, a maximum permissible value of 30 ma is considered safe. For LV sysems, he dominan componen in body impedance is he skin resisance, which Duraion of curren flow I (ms) A B C 1 C 2 C AC-4.1 AC-4.2 AC AC-1 AC-2 AC-3 AC Threshold = 30 ma Body curren I s (ma) AC-1 : Percepion AC-2 : Involunary muscular conracions AC-3 : Difficuly in breahing AC-4 : Serious pahophysiological effecs AC-4.1 : probabiliy of venricular fibrillaion increasing up o abou 5 % AC-4.2 : probabiliy of venricular fibrillaion up o abou 50 % AC-4.3 : probabiliy of venricular fibrillaion above 50 % Fig. 2 : Time/curren zones of effecs of AC currens (15 Hz o 100 Hz) on persons. Cahier Technique Schneider Elecric no. 114 / p.5

8 depends essenially on he environmen (dry, humid or we condiions). IEC has defined he "convenional ouch volage limi", noed U L, as he maximum ouch volage ha can be mainained indefiniely under he specified environmen condiions. The value used is 50 V AC rms. This value is consisen wih an average impedance value of 1700 Ω and a maximum curren of 30 ma. Effecs as a funcion of volage and frequency IEC provides curves showing he variaion in body impedance depending on he volage and he frequency. Figure 3 shows ha body impedance decreases wih frequency. However, noe ha IEC (Effecs of curren on human beings and livesock - Special aspecs), dealing wih he effecs of AC curren a frequencies above 100 Hz, indicaes ha he hreshold curren for venricular fibrillaion a 1000 Hz is approximaely 14 imes greaer han a 50/60 Hz curren Toal body impedance V CA V V 50 V 100 V 225 V V Frequency (Hz) Fig. 3 : Toal body impedance Z T as a funcion of he frequency and he ouch volage. 2.2 Fire hazards A sudy carried ou in he 1980s and 1990s in Germany by an insurance company on fires on indusrial and commercial premises revealed ha elecriciy was he cause of over 40 % of he fires. The cause of many elecrical fires is a major shor-duraion emperaure rise or elecric arc due o an insulaion faul. The risk increases wih he level of he faul curren. I also depends on he level of fire or explosion hazard specific o he room (sorage of flammable maerials, presence of volaile hydrocarbons, ec.). Many elecrical fires are caused by a combinaion of facors: c an old insallaion, c wear of insulaion, c accumulaion of dus and humidiy. Cahier Technique Schneider Elecric no. 114 / p.6

9 The progressive increase in racking currens on he surface of pollued and damp insulaion resuls in small discharges ha cause carbon deposis. This phenomenon is relaed o surface condensaion and drying cycles and herefore evolves very slowly. If he racking curren exceeds 300 ma, an avalanche phenomenon occurs ha can inflame he carbon deposis which, in urn, may inflame he insulaion and devices. A 300 ma leakage curren represens a real fire hazard. The leakage curren flows from he source o he ECPs, bu does no reurn o he source via he reurn conducor. Bare flamme 37% Lighning 1% Explosion 1% Elecriciy 41% Acciden 7% Cigaree 6% Oher 7% Fig. 4 : Origin of fires in buildings. Leakage curren Carbonised insulaion and dus Small discharges Fig. 5 : Process resuling in a fire. 2.3 Damage o equipmen Cerain elecrical equipmen may be damaged or desroyed by high currens. This is he case for moors during prolonged operaion above raed load and cables if oo many devices are conneced. The overcurren provokes excessive emperaure rise in conducors and may lead o insulaion breakdown and he flow of an earh faul curren. The laer may remain a a low level, difficul o deec, or rapidly degenerae ino a shor-circui and provoke major damage. Cahier Technique Schneider Elecric no. 114 / p.7

10 3 Proecion agains he risks of elecrical currens 3.1 Insallaion rules The inernaional reference sandard is IEC 60364, Elecrical insallaions in buildings, and in paricular par 4-41, Proecion for safey - Proecion agains elecric shock. I lays down insallaion rules such ha dangerous live pars are no accessible and accessible conducive pars are no dangerous under normal and faul condiions. The sandard has been adoped by many counries, as is or wih local adapaions. In France for example, low-volage elecrical insallaions mus comply wih sandard F C General rules Insallaions mus be designed o provide general proecion agains direc conacs during normal operaion and addiional proecion agains indirec conacs in he even of a faul. c General proecion is implemened by isolaing he live pars, using barriers and enclosures. Proecion in he even of fauls is implemened by one or more of he following means: v auomaic disconnecion of he supply, v double or reinforced insulaion, v elecrical separaion (use of an isolaing ransformer), v use of very low volage. Auomaic disconnecion of supply is he mos common soluion. I enails cerain requiremens: v earhing of ECPs and equipoenial bonding, v specificaion of a maximum disconnecion ime for a faul (e.g. 0.4 seconds for 230 V). A proecive device mus auomaically isolae a circui or device from is supply so ha, following a faul beween a live par and an ECP of a circui or device, a ouch volage greaer han he convenional limi canno be presen for a ime sufficien o creae a danger for a person in conac wih simulaneously accessible conducive pars. c Addiional proecion is required in case he proecion agains direc conacs fails. In paricular, IEC requires insallaion of a device for proecion agains direc conacs for AC circuis supplying general-usage socke-oules up o 20 A locaed oudoors and for socke-oules up o 32 A used o supply porable equipmen inended for oudoor use. The operaing hreshold of he device mus be 30 ma. Sysem earhing arrangemens (SEA) Sandard IEC defines hree main sysem earhing arrangemens (SEA, see Fig. 6), used in differen manners depending on he counry. See Cahiers Techniques publicaions no. 172 and 173. They differ according o wheher or no he neural poin of he volage source is earhed and he manner in which he ECPs are earhed. SEA selecion depends on insallaion characerisics and on operaing condiions and requiremens (environmen, monioring devices, coninuiy of service). c TT sysem In he TT sysem: v he source neural is conneced o an earh elecrode separae from ha of he ECPs, v all ECPs mus be conneced o a single earhing sysem dedicaed o he insallaion. c T sysem This principle of he T sysem is o ransform all insulaion fauls ino a phase-o-neural shorcircui. In his sysem: v he LV neural poin of each source is direcly earhed, v all ECPs in he insallaion are earhed, i.e. conneced o he neural by he (wih separae neural in T-S sysems) or he (combined wih he neural conducor in T-C sysems) proecive conducor. c IT sysem In he IT sysem, he ransformer neural is: v isolaed from earh (isolaed neural), v or conneced o earh via a high impedance (impedan neural), v all insallaion ECPs are earhed. Cahier Technique Schneider Elecric no. 114 / p.8

11 Direcy earhed neural (TT) ECPs conneced o neural (T-C) R B R A R B Isolaed neural (IT) ECPs conneced o neural (T-S) IMD R B R B IMD: Insulaion Monioring Device Fig. 6 : The hree main SEAs are he TT, IT and T sysems defined by IEC The T sysem may be T-C (neural and combined) or T-S (separae neural and ). 3.2 Deecion of insulaion fauls An insulaion faul may be he consequence of insulaion deerioraion: c beween wo live conducors, c beween a conducor and he ECPs or he proecive conducor, c on a single live conducor, making he conducor accessible o ouch. An insulaion faul beween live conducors becomes a shor-circui. In all oher cases, a faul (in common mode) causes curren o flow o earh. This curren, which does no flow back via he live conducors, is called he earh-faul curren. I is he algebraic sum of he insananeous values of he currens flowing in he live conducors, hence he name "residual curren". Remark: If he currens are sinusoidal, Fresnel vecor represenaion may be used and i is possible o speak of he "vecor sum" of he currens. However his represenaion is no relevan in he presence of harmonic currens and he erm "algebraic sum" is herefore more generally applicable. This curren may be due o an insulaion faul beween a live conducor and he ECPs (risk of indirec conac) or o a failure of he measures used o insulae or isolae live pars (risk of direc conac). These siuaions are shown in figure 7 nex page. The insulaion-faul curren beween a phase and earh (common mode) depends on he ype of faul and on he SEA. The curren may creae a dangerous ouch volage, requiring disconnecion of he fauly circui. See Appendix 1 for a summary of calculaions on faul currens and ouch volages depending on he SEA. In he T sysem, he faul curren is equivalen o a shor-circui. The curren is high and he circui can be disconneced by an overcurren proecive device. In he TT sysem, however, he curren is oo low o be deeced and cleared by sandard overcurren proecive devices (circui breaker hermal or magneic proecion, fuses). Cahier Technique Schneider Elecric no. 114 / p.9

12 Similarly, in all cases of direc conac, he faul curren is low and canno be deeced and cleared by sandard overcurren proecive devices. This is also he case for leakage currens ha consiue fire hazards. Under hese condiions, he faul curren mus be deeced and cleared by a special device, i.e. a residual-curren device (RCD), discussed in he nex secion. a) Indirec conac b) Direc conac Id Id Ud R B R A R B R A Fig. 7 : Faul curren = residual curren. Cahier Technique Schneider Elecric no. 114 / p.10

13 4 RCD operaing principle and descripion 4.1 Operaing principle The operaing principle of an RCD is shown in figure 8. A sensor comprising a oroid ha surrounds he conducors deecs he algebraic sum of he curren in he live conducors (phases and neural). The oroid winding deecs variaions in he flux induced by he residual curren. In he absence of an insulaion faul, he algebraic sum of he currens in he conducors is equal o zero and he oroid does no deec any flux. If an insulaion faul occurs, he sum is no longer equal o zero and he faul curren in he oroid generaes a curren in he winding. This curren is recified, filered and amplified. If he resuling signal is greaer han a se hreshold, a ime delay is iniiaed (i may be equal o zero for an insananeous response). If he faul is sill presen a he end of he ime delay, an opening order is issued for a conrol device. Use of an RCD is no possible in he T-C sysem because he neural and proecive conducors are no separae and he RCD canno disinguish beween he residual and neural currens. Σ I 0 Fig. 8 : Operaing principle of an RCD. Acuaor Time delay Threshold Waveform processing 4.2 Applicaions Addiional proecion agains direc conacs An RCD can deec low leakage currens ha could flow hrough he body of a person. I hus provides addiional proecion if he normal proecion means fail, e.g. old or damaged insulaion, human error, ec. This can also be referred o as ulimae proecion because i can inerrup he curren even if he oher devices have failed. Use of a 30 ma RCD on all circuis supplying socke-oules up o 20 A is now mandaory, as per IEC , Elecrical insallaions in buildings, Proecion for safey - Proecion agains elecric shock. oe ha an RCD does no limi he insananeous curren flowing hrough he body, bu does limi he ime he curren flows. oe also ha for a direc conac wih a 230 V phase conducor, he flowing curren would be approximaely 150 ma. RCDs wih 10 or 30 ma sensiiviies le he same curren hrough. The wo sensiiviies provide equivalen proecion. However, he 30 ma hreshold provides a cos-effecive compromise beween safey and coninuiy of service. Downsream of an RCD, i is possible o supply a number of loads or circuis as long as he leakage curren does no rip he RCD. For a given leakage curren, a reducion in he hreshold makes i necessary o increase he number of proecive devices. Proecion agains indirec conacs An RCD is he only soluion o proec agains indirec conacs on a TT sysem because he dangerous faul curren is oo low o be deeced by overcurren proecive devices. I is also a simple soluion for he T-S and IT sysems. For example, when he supply cable is very long, he low faul curren makes i difficul o se he overcurren proecive devices. And when he lengh of he cable is unknown, calculaion of he faul curren is impossible and use of an RCD is he only possible soluion. Under hese condiions, he RCD operaing hreshold mus be se o somewhere beween a few amperes and a several ens of amperes. Cahier Technique Schneider Elecric no. 114 / p.11

14 Proecion agains fire hazards IEC (Elecrical insallaions in buildings, Proecion for safey - Proecion agains hermal effecs) also recognises RCD effeciveness in proecing agains fire hazards by requiring heir use wih a maximum operaing hreshold of 500 ma. This hreshold should be reduced o 300 ma in he near fuure, as already recommended by cerain naional sandards such as F C in France. 4.3 Main characerisics An RCD mus be seleced aking ino accoun he ype of load supplied. This applies in paricular o semiconducor-based devices for which faul currens are no always sinusoidal. Examples of semiconducor converers are provided in Appendix 3, wih he waveforms of he faul currens and he corresponding ype of RCD. Type AC, A, B Sandard IEC (General requiremens for residual curren operaed proecive devices) defines hree ypes of RCD depending on he characerisics of he faul curren. c Type AC RCD for which ripping is ensured for residual sinusoidal alernaing currens. c Type A RCD for which ripping is ensured: v for residual sinusoidal alernaing currens, v for residual pulsaing direc currens, v for residual pulsaing direc currens superimposed by a smooh direc curren of A, wih or wihou phase-angle conrol, independen of he polariy. c Type B RCD for which ripping is ensured: v as for ype A, v for residual sinusoidal currens up o 1000 Hz, v for residual sinusoidal currens superposed by a pure direc curren, v for pulsaing direc currens superposed by a pure direc curren, - for residual currens which may resul from recifying circuis, i.e.: - hree pulse sar connecion or six pulse bridge connecion, - wo pulse bridge connecion line-o-line. wih or wihou phase-angle monioring, independenly of he polariy. Cerain elecronic devices can generae faul currens no described above. Examples are provided in Appendix 2. The IEC has begun sudies o cover hese special cases as well. Sensiiviy RCD sensiiviy is expressed as he raed residual operaing curren, noed I n. Preferred values have been defined by he IEC, hus making i possible o divide RCDs ino hree groups according o heir I n value. c High sensiiviy (HS): ma, c Medium sensiiviy (MS): A, c Low sensiiviy (LS): A. RCDs for residenial or similar applicaions are always high or medium sensiiviy. I is clear ha High Sensiiviy (HS) is mos ofen used for direc-conac proecion, whereas MS and in paricular he 300 and 500 ma raings are indispensable for fire proecion. The oher sensiiviies (MS and LS) are used for oher needs such as proecion agains indirec conacs (mandaory in he TT sysem) or proecion of machines. Break ime As indicaed in secion 1, he effecs of elecrical currens depend on heir magniude and duraion. RCD break imes are specified in he produc sandards: c IEC 61008, Residual curren operaed circuibreakers wihou inegral overcurren proecion for household and similar uses (RCCBs). Cahier Technique Schneider Elecric no. 114 / p.12

15 c IEC 61009, Residual curren operaed circuibreakers wih inegral overcurren proecion for household and similar uses (RCBOs). c IEC , Low-volage swichgear and conrolgear, Annex B, Circui-breakers incorporaing residual curren proecion. c IEC , Low-volage swichgear and conrolgear, Annex M, Modular residual curren devices - MRCD (wihou inegral currenbreaking device). The sandardised break imes are indicaed in he able of figure 9 and in he curves in figure 10 for G and S ype devices. c G (general use) for insananeous RCDs (i.e. wihou a ime delay) c S (selecive) for RCDs wih a shor ime delay (used in France, for example, for serviceconnecion circui breakers) (s) Fig. 10 : Maximum break-ime curves for S (selecive) and for G (general use) RCDs. S G Type In I n Sandard values of break ime (s) and non-acuaing ime (s) a a residual curren (I ) equal o: 5 A, 10 A A A I n 2 I n 5 I n 20 A, 50 A 100 A, 200 A 500 A General Any value Any value Maximum break imes S u 25 > Maximum break imes Minimum nonacuaing imes Fig. 9 : Sandardised values of maximum break imes and non-acuaing imes as per IEC Technology RCD classificaion depending on supply mode: "Wihou auxiliary source" or "Funcionally independen of line volage". In his ype of device, he ripping energy is supplied by he faul curren. This highly dependable supply mode is recommended for residenial or similar applicaions where he user is no aware of he dangers of elecriciy. Many counries, paricularly in Europe, recognise he effeciveness of hese devices for residenial and similar uses (sandards E and 61009). "Wihou auxiliary source" or "funcionally dependen on line volage". In his ype of device, ripping requires an auxiliary source of energy ha is independen of he faul curren. The source is generally he proeced circui. When he circui is energised, he RCD is supplied. If here is no volage, he RCD canno operae, bu here is no danger. Cahier Technique Schneider Elecric no. 114 / p.13

16 These devices are designed o operae in spie of volage drops as long as he ouch volage can exceed 50 V (ouch volage limi). This condiion is me if a device coninues o operae when supplied by only wo phases wih a volage drop o 85 V beween phases. This is he case for Vigi modules, he RCDs used wih Merlin Gerin Compac circui breakers. Anoher disincion for RCDs is wheher or no heir operaion is fail-safe. Two ypes of devices are considered fail-safe: c hose where ripping depends only on he faul curren, i.e. all devices wihou an auxiliary source are fail-safe, c hose, more rarely used, ha auomaically rip when condiions can no longer guaranee ripping in he presence of a faul curren (e.g. during a volage drop o 25 V). Remarks: IEC indicaes ha for devices wih auxiliary sources ha are no fail-safe, "Their use is permied if hey are insalled in insallaions operaed by experienced and qualified people". Sandard F C , sipulaes ha hey may no be used in household insallaions or similar applicaions. RCDs wihou auxiliary sources, for which operaion does no depend on he supply condiions of he proeced circui, offer high performance and are paricularly well suied o high-sensiiviy applicaions in residenial insallaions or for final circuis ha mus be rese by unqualified persons, for he reasons lised below: c Final disribuion circuis are operaed and occasionally insalled by unqualified persons (wihou knowledge concerning he insallaion or awareness of he risks involved). c Final circuis are generally single-phase (Ph/) circuis and occasionally wo-phase (Ph/Ph). c This echnique coninues o provide proecion, even if he neural or a phase are disconneced upsream of he RCD. c The devices operae even if he volage drops o 0 V. c For addiional proecion agains direc conacs, a high-sensiiviy RCD is recognised as Ia Ir Fig. 11 : The faul curren, via he oroid, supplies energy o an elecromagne whose moving par is held by a permanen magne. When he operaing hreshold is reached, he elecromagne counerbalances he aracion of he permanen magne and he moving par, drawn by a spring, opens he magneic circui and mechanically acuaes circui-breaker opening. A Fig. 12 : Examples of RCDs "wihou auxiliary source" and "wih auxiliary source". Cahier Technique Schneider Elecric no. 114 / p.14

17 an efficien means if he fails (does no exis, is no conneced or breaks). This echnique offers a furher advanage if he earh resisance rises significanly above 500 ohms (old insallaions, dry periods, corrosion on he earh elecrode, ec.) in ha cerain RCDs wih auxiliary sources, conneced beween a phase and he, do no operae correcly under he above condiions. c This echnique is paricularly robus given ha no elecronic componens are coninuously conneced o he disribuion sysem. The resul is excellen insensiiviy o overvolages and componen ageing. (Elecronic componens, if presen, are conneced o he secondary of he zero-sequence curren sensor and herefore play a role only if a faul occurs and under very low volage condiions.) c This robusness is well suied o insallaions ha are no moniored, generally he case for residenial applicaions. Operaing es An RCD is a safey device. Whaever he echnology used, i mus always be equipped wih a es sysem. Alhough RCDs wihou auxiliary sources are he mos reliable, implemenaion of fail-safe sysems on RCDs wih auxiliary sources offers an enhanced degree of safey ha does no, however, replace he periodical es. c Why es RCDs periodically? In pracice, a perfecly fail-safe sysem, paricularly concerning inernal fauls, does no exis. For his reason, in France, RCDs using auxiliary sources are reserved for indusrial and large commercial insallaions and RCDs wihou auxiliary sources for domesic and similar insallaions, which is consisen wih heir inheren possibiliies described above. In all cases, periodical esing is recommended o deec inernal fauls. c Principle For a es, a curren is generaed ha flows in only one of he live conducors surrounded by he oroid, as shown in figure 13. The resisor is sized o le hrough enough curren o rip he RCD, aking ino accoun any leakage currens likely o reduce he es curren. The maximum permissible value is 2.5 imes I n (for an adjusable device, I n is he lowes possible seing). The above principle is very common because i is he means o check he enire sysem, i.e. oroid, relay and breaking device. I is used on earh-leakage proecion socke-oules and on residual-curren circui breakers wih and wihou inegral overcurren proecion. Wih respec o residual-curren relays wih separae oroids, he same principle is someimes used. Cerain relays, for example Merlin Gerin Vigirex relays, are equipped wih a buil-in es funcion and also coninuously monior he coninuiy of he deecion circui (oroid/relay link and oroid winding). Tes R Ies Fig. 13 : Simplified diagram of he circui for periodical ess. 4.5 Consrains relaed o he curren sensor The sensor is a oroidal ransformer. I surrounds all he live conducors and is herefore excied by he magneic field corresponding o he algebraic sum of he currens flowing in he phases and neural. The curren induced in he oroid and he elecrical signal a he erminals of he secondary winding are herefore proporional o he residual curren. This ype of sensor can deec residual currens from a few milliamperes up o several ens of amperes. Cable wih a The basic operaing principle of an RCD requires ha he sensor surround only he live conducors. The proecive conducor mus herefore be separaed from he oher conducors, as shown in figure 14 nex page. Large conducors Large recangular sensors are available o measure he residual curren of large conducors (see Fig. 15 nex page). Currens should no be summed by using more han one oroid. Cahier Technique Schneider Elecric no. 114 / p.15

18 Fig. 14 : Running cables wih a conducor. High-amperage conducors To obain a reliable and linear response from he oroid, he live conducors mus be placed as close as possible o is cenre o ensure ha heir magneic effecs compensae for each oher perfecly in he absence of residual curren. This is because he magneic field of a conducor decreases proporionally wih he disance. In figure 17, phase 3 causes local magneic sauraion a poin A, i.e. is effec is no proporional. The resul is he same if he oroid is posiioned near a bend in he cables (see Fig. 18 ). For high currens, parasiic residual inducion may resul in a signal on he oroid secondary and nuisance ripping. The risk increases when he RCD seing is low wih respec o he phase currens, paricularly when a shor-circui occurs. In difficul cases, (e.g. where Iphase max. / I n is high), here are wo soluions o avoid nuisance ripping: c use a oroid much larger han necessary, e.g. wice he size required for he conducors, Fig. 15 : Recangular sensors for large cables or bars If his difficuly is encounered in a main lowvolage swichboard downsream of he ransformer, a oroid may be insalled a he head of he insallaion, on he earhing conducor of he ransformer LV neural poin (see Fig. 16 ). According o Kirchhoff's curren law, he residual curren deeced a () is idenical o ha a (G) for a faul occurring in he LV sysem. HV / LV G Fig. 17 : Incorrec cenering in he oroid causes local magneic sauraion a poin A ha can resul in nuisance ripping. 3 A RCD RCD oroid oroid Fig. 16 : Toroid supplies he same informaion as oroid G. Fig. 18 : The oroid mus be insalled far enough from bends in cables o avoid nuisance ripping. Cahier Technique Schneider Elecric no. 114 / p.16

19 c fi a meal sleeve inside he oroid. The sleeve mus be made of a magneic maerial (sof seel, magneic shee meal) (see Fig. 19 ). When all hese precauions are aken, i.e.: c cenering of he conducors, c oroid oversizing, c magneic sleeve, he raio Iphase max./i n can be as high as 50,000. An RCD wih a buil-in oroid represens a readyo-use produc for conracors and elecricians. The manufacurer carefully designs he complee soluion and herefore: c perfecly ceners he live conducors and, for low currens, can design and properly disribue a number of primary urns around he oroid, c can "operae" he oroid a higher inducion o maximise he energy measured and hereby reduce sensiiviy o sray inducion caused by high currens. Magneic sleeve Fig. 19 : A magneic sleeve posiioned around he conducors inside he oroid reduces he risk of ripping due o he magneic effecs of high ransien currens. 4.6 Special applicaions Discriminaion The goal of discriminaion and proecion coordinaion is o ensure ha only he fauly par of a circui is de-energised by ripping of he proecive device. c "Verical" discriminaion This ype of discriminaion concerns he operaion of wo proecive devices insalled in series on a circui (see Fig. 20 ). Given he olerances around he RCD hresholds and break imes, boh curren and ime discriminaion are used. v Curren discriminaion because, according o sandards, an RCD mus operae for a faul curren beween I n /2 and I n. In fac, a facor of 3 is required beween he seings of wo RCDs o avoid simulaneous operaion of he wo devices, i.e. I n (upsream) > 3 I n (downsream). v Time discriminaion for cases where he faul curren suddenly exceeds boh raed operaing currens (see Fig. 21 nex page). I is necessary o ake ino accoun he response ime, even minimal, of all mechanisms, o which i may be necessary o add deliberae ime delays. The double condiion o ensure non-ripping of D a for a faul downsream of D b is: I n (D a ) > 3 I n (D b ) and r (D a ) > r (D b ) + c (D b ) or r (D a ) > f (D b ) where: - r = non-acuaing ime - c = disconnecion ime beween he insan he operaing order is given by he measuremen D a D b Fig. 20 : Verical discriminaion. RCD RCD relay o he insan of disconnecion (including he arcing ime), - f = break ime, from deecion of he faul hrough o complee inerrupion of he faul curren; f = r + c. The hreshold deecion circuis of elecronic relays may exhibi a faul memorisaion phenomenon. I is herefore necessary o ake ino accoun a "memory ime", ha can be hough of as a virual increase in he ime ha a curren flows, o ensure ha hey do no operae afer opening of he downsream device. Cahier Technique Schneider Elecric no. 114 / p.17

20 a) r c a) r c b) r c b) r c Discriminaion o discriminaion Ifaul Ifaul Faul deeced Db open Faul deeced Db open Fig. 21 : The ime delay of an upsream RCD (a) mus ake ino accoun he non-acuaing ime r and he disconnecion ime c of he downsream RCD (b). oe: Paricular aenion mus be paid when deermining discriminaion condiions for circui-breakers wih add-on RCDs and residual-curren relays used ogeher (see Fig. 22 ). This is because: - a circui breaker wih an add-on RCD is defined in erms of he non-acuaing ime (r), - a residual-curren relay is defined in erms of he ime beween he insan he faul occurs and ransmission of he opening order, o which i is necessary o add he response ime of he breaking device. I is herefore necessary o calculae he successive f and r imes (a 2 I n, he convenional curren for he non-operaing es of delayed RCDs) for each RCD, from downsream o upsream. c Horizonal discriminaion Someimes referred o as circui selecion, sipulaed in sandard FC15-100, secion , i means ha an RCD is no necessary in a swichboard a he head of he insallaion when all he ougoing circuis are proeced by RCDs. Only he fauly circui is de-energised. RCD RCD Vigicompac Vigirex r = 60 ms r = 200 ms RCD Vigirex RH RCD r = 15 ms Vigicompac c = 30 ms f = 45 ms r = 60 ms f < 140 ms Fig. 22 : Two examples of ime discriminaion beween a Vigicompac circui breaker wih add-on RCD and a Vigirex relay (Merlin Gerin). oe ha hese imes are much shorer han he auhorised acuaing imes in figure 9. Cahier Technique Schneider Elecric no. 114 / p.18

21 The RCDs placed on he oher circuis (parallel o he fauly one) do no deec he faul curren (see Fig. 23 ). The RCDs may herefore have he same r seing. In pracice, horizonal discriminaion may presen a problem. uisance ripping has been observed, paricularly on IT sysems and wih very long cables (sray capaciance in cables) or capaciive filers (compuers, elecronic sysems, ec.). Tripping may occur on non-fauly circuis, as shown in figure 24. RCD RCD Surge arresers Depending on local uiliy regulaions, RCDs are conneced upsream or downsream of surge arresers. If he RCD is placed upsream, i deecs he curren surge produced by lighning and may rip. A delayed or reinforced-immuniy RCD is recommended. If he RCD is downsream, a sandard RCD may be used. Disurbances caused by leakage currens There are a number of ypes of leakage currens likely o disurb RCD operaion: c leakage currens a power frequency, c ransien leakage currens, c high-frequency leakage currens. These currens may be naural, flowing hrough he capaciance disribued hroughou he cables in he insallaion, or inenional, i.e. he curren flowing hrough componens used inenionally, namely capaciive filers insalled on he supply circuis of elecronic devices (compuers, variable-speed drives, ec.). The purpose of hese filers is o bring he devices ino compliance wih he emission and immuniy sandards made mandaory by European EMC direcives. Fig. 23 : Example of horizonal discriminaion. c Leakage currens a power frequency (50 or 60 Hz) (see Fig. 25 nex page) These currens are generaed by he supply source and flow hrough naural or inenional capaciance. For a single-phase device in a 50 Hz sysem, coninuous leakage currens of approximaely 0.5 o 1.5 ma per device are measured. These leakage currens add up if he devices are conneced o he same phase. If hese devices are conneced o all hree phases, he currens cancel ou when hey are balanced (he algebraic sum is equal o zero). Because of hese leakage currens, he number of devices ha can be conneced downsream of an RCD is limied. See Appendix 3 for a comparison of leakage currens in he differen SEAs (TT/T or IT), which explains why he number of devices ha may be conneced in an IT sysem is lower han in he TT or T sysems. Given ha RCD ripping may ake place saring a 0.5 I n, i is advised, in order o avoid nuisance ripping, o limi he coninuous leakage curren o 0.3 I n for TT and T sysems and o 0.17 I n for an IT sysem. D a (A) long cables D b RCD (B) Cp RCD Fig. 24 : In he even of a faul, D a may open insead of D b. Cahier Technique Schneider Elecric no. 114 / p.19

22 A RCD B RCD currens are no synchronous over all hree phases and heir sum consiues a nonnegligible leakage curren. In order o preven nuisance ripping, RCDs mus be proeced agains hese HF currens (equipped wih low-pass filers). This is he case for indusrial RCDs of he Vigirex range and for he Merlin Gerin S, A si and B ype RCDs. Flow off of curren generaed by lighning Surge arreser Fig. 25 : Depending on local regulaions, in an insallaion conaining a surge arreser, he RCD may be placed a A (S-ype or immunised RCD) or a B (sandard RCD) Use of an RCD wih a narrow operaing range (0.7 I n o I n) reduces his consrain. A narrow operaing range is available from "si" (super-immunised) or Vigirex RCDs from Merlin Gerin. c Transien leakage currens These currens appear when energising a circui wih a capaciive unbalance or during a common-mode overvolage (see Fig. 26 ). For example, measuremens carried ou when saring a worksaion equipped wih a capaciive filer revealed a ransien leakage curren wih following characerisics: v ampliude of he firs peak: 40 A v oscillaion frequency: 11.5 khz v damping ime (66 %): 5 periods RCDs wih a cerain non-acuaing ime avoid nuisance ripping caused by his ype of waveform. Examples are "si" ype RCDs (I n = 30 ma and 300 ma), Vigirex and S-ype RCDs (I n 300 ma). c High-frequency leakage currens High-frequency leakage currens (a few khz up o a few MHz) are caused by he chopping echnique used by variable-speed drives or he elecronic ballass of fluorescen lighing. Cerain conducors are subjeced o high volage gradiens (approx. 1 kv/µs), which generae major curren spikes hrough he sray capaciance of circuis. Leakage currens of a few ens or hundreds of ma can flow (common mode) and be deeced by he RCD, as shown in figure 27 for a variable-speed drive. Unlike he 50 Hz - 60 Hz leakage currens for which he algebraic sum is zero, hese HF Variable-speed drives For combinaions of RCDs and variable-speed drives using frequency conversion, i is necessary o simulaneously ake ino accoun a number of consrains: c leakage currens when energising, c coninuous leakage currens a 50/60 Hz, c coninuous HF leakage currens, c special curren waveforms for fauls a he drive oupu, c curren wih a DC componen for fauls on he DC bus. Fig. 26 : Leakage curren caused by he capaciance disribued hroughou he cables or flowing hrough he inpu capaciors of devices (doed lines). a a Device wih capaciive filer Fig. 27 : RCD disurbance caused by high-frequency leakage currens. M Cahier Technique Schneider Elecric no. 114 / p.20

23 An analysis of hese phenomena and soluions o saisfy he consrains are presened in deail in Cahier Technique publicaion no. 204, LV proecion devices and variable-speed drives. See also Appendix 2, Types of converers and faul-curren waveforms. Uninerrupible Power Supplies (UPS) In insallaion wih backup sources such as UPSs, he proecion sysem mus ake ino accoun he differen possible configuraions. In paricular operaion on AC power or on he baeries, bypass swiches closed or no, ec. In he example in figure 29, he insallaion (TT sysem) includes a UPS. If AC power fails, i is necessary o earh he neural downsream of he UPS (i.e. close conacor K) o ensure correc operaion of he RCDs. However, his earhing operaion is no indispensable o proec persons because: c he insallaion becomes an IT sysem and he firs faul is no dangerous, c he probabiliy of a second insulaion faul occurring during he limied ime of operaion on baery power is very low. Modular version Swichboard version Fig. 28 : RCDs wih HF-curren filering (Vigirex RH99M and RH99P from Merlin Gerin. on-prioriy loads 3L 3L 3L Auomaic 3L 3L 3L bypass swich AC bypass circui Relay o deec volage failure 3L Manual bypass swich (Mainenance) K Prioriy loads Faul supplied by AC power Faul supplied by UPS baery Fig. 29 : When loss of AC power is deeced, conacor K closes o recreae he TT sysem downsream of he UPS. Cahier Technique Schneider Elecric no. 114 / p.21

24 5 Conclusion A a ime when elecriciy has come o play an increasingly dominan role in residenial, commercial and indusrial applicaions, i is useful o review and quanify elecrical hazards and provide informaion on residual-curren devices (RCD). As for all devices, hey have heir srong and weak poins. o ye fully perfeced, hey noneheless play an increasingly imporan role in he proecion of life and propery. All indusrialised counries make exensive use of RCDs, wih a variey of sysem earhing arrangemens, in boh indusry and housing. The following are he mos imporan poins o be reained from insallaion sandards and curren pracice. c For he proecion of persons agains direc conacs, an RCD is no only very useful, bu ofen an addiional measure required by sandards, whaever he SEA. I is he ulimae line of defence in he proecion of human life. c For he proecion of persons agains indirec conacs, an RCD is: v compulsory for he TT sysem, v necessary for he IT sysem if here are several earh elecrodes, v recommended for very long circuis on T and IT sysems. c RCDs also provide proecion agains: v fires of elecrical origin. They are he only effecive means o limi fire hazards caused by racking currens, whaever he SEA, v desrucion of machines in he T sysem. Modern RCDs coninue o progress in erms of reliabiliy and immuniy o inerference phenomena ha are no insulaion fauls. The purpose of his documen is o furher knowledge of RCDs and hereby conribue o he safey of life and propery. Cahier Technique Schneider Elecric no. 114 / p.22

25 Appendix 1: calculaion of ouch volages This secion indicaes briefly how ouch volages due o insulaion fauls are calculaed, depending on he SEA. For more informaion, see Cahier Technique publicaion no. 172, Earhing sysems in LV. T sysem A U 0 Id D C B Ud Rd Ud = 0.8 U o 2 U 0.8 U if R = R ph and Rd = 0 Id = o o RAB + Rd+ RCD R ph +R In a 230/400 V sysem, he ouch volage Ud is herefore 92 V. This volage is greaer han he convenional ouch volage limi U L and represens a danger, i.e. he circui mus open. In general, given he level of he faul curren Id, opening can be iniiaed by he overcurrendeecion devices. When he resisance values R ph and R are high or unknown, RCD proecion is required. Fig. 30 : Touch volage for insulaion fauls on a T sysem. Cahier Technique Schneider Elecric no. 114 / p.23

26 TT sysem U 0 Id Ud R b R a U Id o R Ud = U a o Ra + R b Ra + Rb In a 230/400 V sysem, he ouch volage is approximaely 115 V (if R a =R b ). This volage is greaer han he convenional ouch volage limi U L and represens a danger, i.e. he circui mus open. If he earh resisance is approximaely 10 Ω, he faul curren is approximaely 11 A. In general, opening canno be iniiaed by he overcurren-deecion devices. Use of an RCD is herefore mandaory. Fig. 31 : Touch volage for insulaion fauls on a TT sysem. IT sysem Insulaion monioring device (IMD) If U Surge limier If If Cf Cf Cf Cf Ud R b If Ic n Ic 1 Ic 2 R b If Even wih high leakage capaciances of approximaely 1 µf, he leakage curren If for he firs faul is less han 0.1 A. The resul is a harmless ouch volage of approximaely one vol. Disconnecion is no necessary for he firs faul. If a second faul occurs, he siuaion is ha of he T sysem. Fig. 32 : Touch volage for insulaion fauls on an IT sysem. Cahier Technique Schneider Elecric no. 114 / p.24

27 Appendix 2: ypes of converers and faul-curren waveforms Sandard E50178 (Elecronic equipmen for use in power insallaions) indicaes he ypes of RCD o use in combinaion wih differen semiconducor assemblies. I also indicaes he corresponding faul-curren waveforms. Connecion Mains curren in normal operaion Faul curren 1 L Single-way connecion 2 L Single-way connecion wih back - e.m.f. ioad 3 L1 L2 L3 Three-phase sar connecion 4 L Two-pulse bridge connecion 5 L Two-pulse bridge connecion half-conrolled Fig. 33 : Faul currens corresponding o differen semiconducor assemblies (coninuaion p. 26). Cahier Technique Schneider Elecric no. 114 / p.25

28 Connecion Mains curren in normal operaion Faul curren 6 L1 L2 Two-pulse bridge connecion erminal connecion beween phases 7 L1 L2 L3 Six-pulse bridge connecion (Three-phase bridge connecion) 8 L A.C. power conroller phase conrol 9 L A.C. power conroller muli-cycle conrol Fig. 33 (coninuaion of page 25) : Faul currens corresponding o differen semiconducor assemblies. Circuis no. 8 and 9 mus be proeced by ype AC, A or B RCDs. Circuis no. 1, 4 and 5 mus be proeced by ype A or B RCDs. Circuis no. 2, 3, 6 and 7 mus be proeced by ype B RCDs. Examples of loads requiring ype A or B RCDs: c Equipmen wih single-phase diode recifiers (circui no. 4) v Examples include pumps, fans, aircondiioners, lifing and handling equipmen, lifs, packing machines, special machines (exile, machine ools, ec.). Power raings are 0.37 o 2.2 kw for 230 V/50 Hz (for higher raings, he supply is generally hree-phase). An insulaion faul is possible if a braking resisor is conneced o he DC circui (DC bus). An inernal insulaion faul is highly unlikely. v Power supplies for DC circuis Examples include welding equipmen, baery chargers, elecronic devices (PLCs, regulaors, elephone exchanges, ec.), exciaion windings of DC moors, elecromagne coils. The maximum power raing is 3 kw (for higher raings, he supply is generally hree-phase). Remark. Mos of he ime, hese devices have an isolaing ransformer upsream of he recifier. In his case, an insulaion faul beween he DC circui and earh does no cause a faul curren. I is hus possible, for example, o operae wih one baery pole earhed. v Swich-mode power supplies Examples include compuer hardware, sereo and video equipmen, ec. Cahier Technique Schneider Elecric no. 114 / p.26