DIRECT CURRENT MACHINE DYNAMO – is a rotating r otating machine for converting mechanical energy into electrical energy Intro!"ce voltage # E $ %&'( ) N* N* + %,-a* . /-012olts 3eneral Classification4 5I6Motor 5II63enerator I – DC Motor – a contin"o"s energy conversion !evise "se! to convert electric energy to mechanical energy 3eneral ty)es of 7elf E.cite! Motors4 / 7eries 8o"n! DC Motor – a motor 8here is 8in!ing calle! series fiel! 8in!ing is connecte! n series 8ith the armat"re 7)ee! Characteristics4 2aria9le s)ee! Tor:"e Characteristics4 high starting tor:"e Uses4 elevator; crane; conveyor; hoist gear !rive or =r"n a8ay>
NOTA NOTATION4 2T E 9 2 9c 2s Ii Ia R s R 9c R a R 'i 's 'o
0terminal voltage 09ac? emf or co"nter emf 09r"sh contract voltage !ro) 0series fiel! 8in!ing voltage !ro) 0line c"rrent or in)"t c"rrent 0armat"re c"rrent 0series fiel! 8in!ing resistance 09r"sh contact resistance 0armat"re resistance 0e:" 0e:"iv ival alen entt resi resist stan ance ce !"e !"e to the the )o8 )o8er er !ev !evel elo) o)me ment nt in in the the arma armat" t"re re 0)o8er in)"t 0)o8er !evelo)ment in the armat"re 0)o8er in)"t 0"sef"l )o8er
@ 7h"nt o"n! o"n! DC Motor – a self0motor s elf0motor 8here its fiel! 8in!ing calle! sh"nt fiel! is connecte! across the armat"re 7)ee! Characteristics4 nearly constant or a!B"sta9le s)ee! Tor:"e Characteristics4 me!i"m starting tor:"e Uses4 fan; )"m); grin!er; 9lo8er; etc or r"n a8ay>
Com)o"n! o"n! o"n! DC Motor – 8here its 8in!ing has series an! sh"nt fiel! 8in!ings; either connecte! long+ short sh"nt 7)ee! Characteristics4 varia9le or a!B"ste! s)ee!s Tor:"e Characteristics4 high starting tor:"e Uses4 milling machine; )"nching machine; elevator; crane etc
9 7hort 7h"nt Com)o"n! Com)o"n! Motor %varia9le s)ee!*
II 0 DC 3enerator 0 an energy conversion !evice "se! to convert mechanical energy to electrical energy 3eneral Ty)es Ty)es of 7elf E.cite! DC 3enerators / 7eries o"n! o"n! DC 3enerators – li?e the series 8o"n! DC motor; its fiel! 8in!ing is connecte! in series 8ith the armat"re It is "se! for constant c"rrent a))lication li?e in series street lighting
Com)o"n! o"n! o"n! DC Motor – 8here its 8in!ing has series an! sh"nt fiel! 8in!ings; either connecte! long+ short sh"nt 7)ee! Characteristics4 varia9le or a!B"ste! s)ee!s Tor:"e Characteristics4 high starting tor:"e Uses4 milling machine; )"nching machine; elevator; crane etc
9 7hort 7h"nt Com)o"n! Com)o"n! Motor %varia9le s)ee!*
II 0 DC 3enerator 0 an energy conversion !evice "se! to convert mechanical energy to electrical energy 3eneral Ty)es Ty)es of 7elf E.cite! DC 3enerators / 7eries o"n! o"n! DC 3enerators – li?e the series 8o"n! DC motor; its fiel! 8in!ing is connecte! in series 8ith the armat"re It is "se! for constant c"rrent a))lication li?e in series street lighting
EMED 'r"sh
@ 7h"nt o"n! o"n! DC 3enerator – li?e the sh"nt 8o"n! DC motor its fiel! 8in!ing also calle! sh"nt fiel! 8in!ing is connecte! across the armat"re It is "se! for constant voltage a))lication li?e in electric 8el!ing
7e)erately E.cite! 7h"nt 3enerator – its 8in!ing also calle! sh"nt fiel! 8in!ing is connecte! to an o"tsi!e so"rce %a 9attery or another DC generator* It is "se! for la9oratory e.)eriment )"r)ose 8here voltages are li?ely to 9e varie!
F Com)o"n! o"n! o"n! DC 3enerator – li?e com)o"n! 8o"n! DC motor It has series fiel! 8in!ings an! sh"nt fiel! 8in!ings also either connecte! long sh"nt or short sh"nt Ty)es of com)o"n! 3en Accor!ing to fiel! 8in!ings connection#
Ty)es of Com)o"n! 3enerator Accor!ing to !irection of fl".4 a* C"m"lative Com)o"n! 3enerator – the series fiel! en!ing the sh"nt fiel! for s"))lying )o8er an! lighting loa!s / Un!er Com)o"n!e! – the f"ll loa! terminal voltage is less than the no loa! voltage It is "se! 8hen the loa! is near from the generator @ Glat Com)o"n! 0 the f"ll loa! terminal voltage is the same as the no loa! voltage; it is "se! 8hen the loa! is at me!i"m !istance from the generator Over Com)o"n!e! – the f"ll loa! terminal voltage is greater than the no loa! voltage; it is "se! 8hen the loa! is far from the generator 9* Differential Com)o"n! 3enerator – the !irection of fl". of the series fiel! 8in!ing o))oses the !irection of fl". of the sh"nt 8in!ing It is "se! for electric 8el!ing 'rime Movers / Hy!ra"lic t"r9ines @ 7team T"r9ine Internal Com9"stion Engine
Parallel Operation of DC Generators: Con!itions to 9e met for i!eal o)eration of DC generators in )arallel are4 %/* The no0loa! voltages of 9oth generators sho"l! 9e a!B"ste! to the same val"e %other8ise; c"rrent 8ill circ"late thro"gh the t8o machines that 8ill ca"se a!!itional losses* %@* The e.ternal characteristics c"rve of the t8o generators sho"l! 9e i!entical %other8ise; the generator 8ill not share the loa! )ro)erly* %* The )olarity of the voltages of the t8o generators m"st 9e =o))osing> in the series circ"it of the t8o machines %other8ise; large c"rrent 8ill circ"late in the armat"re 8in!ings of the generators 8hich 8ill !amage the 8in!ings* %F* Gor the case of com)o"n! generators in )arallel there m"st 9e an =E:"alier> connection to ma?e the o)eration sta9le %other8ise; there 8ill 9e =motoriation> ie one of the generator 8ill acts as a motor* DC MACHINE REVIEW PROBLEMS / The fiel! )oles are ma!e of iron; either soli! or laminations an! s"))ort coils of 8ires calle! A fiel! 8in!ings inter)oles C the armat"re D the comm"tator @ hat is the material commonly "se! for 9r"shes on DC motors A car9on 9rass C co))er D al"min"m 'igtails are "se! on car9on 9r"shes to A com)ensate for 8ear C s"))ly the )ro)er )ress"re hol! the 9r"sh in the hol!er D ma?e a goo! electrical connection F Comm"tators are generally fo"n! on A 7ynchrono"s Motors DC Motor C rectifier D transformer J Dirt on the motor comm"tator may )ro!"ce A isolation e.cessive C lo8er tor:"e D )o8er loss , In a DC motor; 8hich of the follo8ing !oes not ca"se s)ar?ing at the comm"tator A froen armat"re C "se of gra)hite 8ith goo! contact )ress"re no loa! on the armat"re D high 9r"sh contact resistance K In DC series motor; ho8 is the fiel! 8in!ing connecte! in the relation 8ith the armat"re 8in!ingL ' A)r -FA long sh"nt 'arallel C series D )arallel – series
1 In com)o"n! 8o"n! !c motor; 8hat is the connection of the fiel! 8in!ing in relation to the armat"re 8in!ingLA sh"nt short C 7eries D )arallel – series Com)aring the sh"nt fiel! 8in!ing 8ith the series fiel! 8in!ing of a com)o"n! !c motor; it 8o"l! 9e correcte! to say that the sh"nt fiel! 8in!ing has A more t"rns 9"t lo8er resistance C more t"rn an! a higher resistance fe8er t"rn 9"t a higher resistance D fe8er t"rns an! a lo8er resistance /- It is a DC motor that ten!s to over – s)ee! 8hen the fiel! o)ene! 8hile r"nning A sh"nt motor series motor C s)lit )hase motor D over – com)o"n!e! motor // In !c series motor that has the line lea!s reverse!; t"rns in the !irection; A same o))osite C 8rong D reverse /@ ith reference to the armat"re 8in!ings; la) 8in!ings are often calle! 8in!ing A ring series C m"lti)le or )arallel D casca!e / The )"r)ose of having a rheostat in the fiel! circ"it of a DC sh"nt motor is A re!"ce s)ar?ing the 9r"shes C control the s)ee! of the motor minimie the starting c"rrent D limit the fiel! c"rrent to a safe val"e /F A motor 8hose s)ee! increases as the loa! increases is a A DC sh"nt DC 7eries C Differential com)o"n! D C"mm"lative com)o"n!
/J The armat"re of a motor has of F-- active con!"ctors; the fl". !ensity in the fiel! 9eing ;--ga"ss The a.ial length of the armat"re is @-@ cm The c"rrent is - am)eres Determine the total force e.erte! in the armat"reA K/J N ,FJ1 N C --K N D F@ N /, A motor has a name)late rating of /J h) an! //,- r)m 7olve for the rate! tor:"e A J, l90ft ,1 l90ft C /@@ l90ft D l90ft /K hat is the 9ac? emf of a /- h) sh"nt motor o)erating at //- volts terminals if - am)ere flo8 tho"gh a --J0ohm armat"re resistanceL A /-KJ 2 /-,J 2 C /-JJ 2 D /-1J 2 /1 A /@- 2olt sh"nt motor has an armat"re resistance of --1 ohm an! fiel! resistance of ,- ohms hat is the )o8er !evelo)e! 8hen it !ra8s ,K am)eres c"rrent A /- h) K1 h) C 1K1 h) D JJ h) / A certain sh"nt motor has an armat"re resistance of --K ohm It !ra8s J- am)eres at a terminal voltage of /@- volts Ass"me other miscellaneo"s losses of @ Determine the efficiency of the motor A K/ 1 C J/ D ,J @- In a 9rea? test of as sh"nt motor; ammeter an! voltmeter meas"ring the in)"t rea! F Am) an! @@- – volts The s)ee! of the motor is fo"n! to 9e /- r)m an! the 9alance of a @ – ft 9ra?e arm rea!s @K@ l9 The tare 8eight of the arm is fo"n! to 9e @ l9 Determine the o"t)"t of the motor A , h) 11 h) C 1, h) D ,J h) @/ A !c sh"nt motor !evelo)s /J h) at /@- volts The armat"re resistance is --,/ ohm hat is the c"rrentL J1/ Am)eres /1J Am)eres C ,/J Am)eres D 1/J Am)eres @@ A DC sh"nt motor !ra8s as armat"re c"rrent of 1/, A P a fiel! c"rrent of @A at /@-2 the armat"re effective resistance is --, hat is overall efficientL A J / C F D @ A sh"nt generator 8hen r"nning light as a motor at /--- r)m ta?es /@ Am) from //J02olts mains The fiel! c"rrent is K Am); an! the armat"re resistance is -- ohm Determine stray – )o8er loss of the machine at this )artic"lar val"e of fl". an! s)ee! A JKF@J JK,@J C JKJ@J D JKK@J @F hich statement a9o"t hysteresis loss in !c generator is GA7EL A it varies almost as s:"are of the fl". !ensity it !o"9les if armat"re r)m is !o"9le! C it is in!e)en!ent of lamination D it can 9e minimie! 9y laminating the armat"re @J The e!!y c"rrent loss in a motor is ,-- 8atts 8hen the total fl". is @;---;--- ma.8ells )er )ole an! the s)ee! is 1-- r)m Determine the loss 8hen the fl". is increase! @;J--;--- ma.8ells an! the s)ee! is increase! to /;@-- r)m A @;/- 8atts F@-/ 8atts C /@-- 8atts D /1-- 8atts @, The hysteresis an! e!!y c"rrent losses in a !c machines r"nning at /-- r)m are @J- atts an! /-- atts res)ectively If the fl". remains constant; 8hat is the total iron loss -- r)mL A -, 8atts /J- 8atts C FFF 8atts D J- 8atts @K To start a KJ h); @@- volt; DC motor yo" sho"l! have A an across the line starter C a =start0r"n s8itch> s8itch s"ita9le start 9o. D a com)ensator @1 DC motor starters are "se! for the follo8ing f"nctions EQCE'T one hich one is thisL A Control the s)ee! of the motor imit the starting c"rrent of the motor C 7tart large DC motor D 'revent large voltage !ro) !"ring starting @ The armat"re of a @- volts sh"nt motor has a resistance of -1@ ohm an! ta?es @1@ Am)ere 8hen o)erating at f"ll loa! Calc"late the starting resistance re:"ire! to limit the starting tor:"e to
/J- of the rate! tor:"e %Ass"me a 0volt 9r"sh !ro)*A K Ohm FJJ Ohm C K@ Ohm D F,@ Ohm - A @- 2olts; /J h) !c sh"nt motor has friction an! iron loss of @-- the armat"re resistance is- ohm an! the sh"nt fiel! resistance is //J ohms Calc"late the o"t)"t horse)o8er to achieve ma.im"m efficiencyA /J / C /@K D /KJ / A small !c series motors is )l"gge! to an ac so"rce hat 8ill li?ely to ha))enL A Motor 8in!ing overheats fast C Motor rotor rotates very slo8ly Motor rotor is stac?e! D Motor r"ns @ hich of the follo8ing motor 8ill over s)ee! 8hen it carries only a light loa!L A com)o"n! !c motor sh"nt !c motor C series !c motor D synchrono"s motor A !c series motor !evelo)s /1- l9s0ft of tor:"e 8hen the c"rrent is - Am) The loa! increases so that the motor c"rrent rises to J- Am) The tor:"e no8 is A J-- l9s0ft -- l9s0ft C ,F1 l9s0ft D /-1 l9s0ft F If a self e.cite! !c generator after 9eing installe!; fails to 9"il! ") on its first trial r"n; the first thing to !o is toA increase the fiel! resistance C reverse fiel! connections chec? armat"re ins"lation resistance D increase of the s)ee! of )rime mover J If the armat"re of an 1 – )ole machine 8ere 8o"n! 8ith a sim)le. 8ave 8in!ing; ho8 many )arallel )aths 8o"l! there 9eLA /, 1 C @ D F , In a F )ole; JF slot !c armat"re; calc"late the coil )itchA /1 C /F D / K Inter)ole 8in!ing in the motors are "se! )rimary A to com)ensate for fiel! lea?age C as a means of varying the s)ee! to re!"ce the armat"re reaction D to increase the efficiency 1 Gor 9oth la) an! 8ave 8in!ings; there are many comm"tator 9ars as the n"m9er of A )oles slots C armat"re con!"ctors D 8in!ing elements The comm"tator )itch of the !")le. la) 0 8in!ing in a !c generator is A / C @ D F F- A fo"r )ole !c generator 8ith !o"9le layer la) 8in!ing /@- slots an! F slots )er )ole A , /@C F1D @FF/ The !ifference 9et8een the 9ac? )itch is @ the front )itch is @/ If 8in!ing is la) retrogressive; 8hat is the 9ac? )itchL A @/J @ C @/ D/ F@ A @J--0?8; ,--0volt; /,0)ole generator has a la) – 8o"n! armat"re 8ith @,- con!"ctors If the )ole face ,J of the entire circ"mference; calc"late the n"m9er of )ole face con!"ctor in each )ole of a com)ensating 8in!ingA J C F D , F The )"lley of the ol! 3en – set has a !iameter of @- inches The 9elt e.erts )"ll of J l9s on the )"lley The 3en0set r"ns at -- r)m hat is the a))ro.imate ?8 rating of the 3en0set A KJ @JC @-DJ FF A F )ole !c generator 8ith !")le. la) 8in!ing has F1 slots an! F element )er slot The fl". )er )ole is @J . /-, ma.8ells an! it r"ns at /;J-- r)m hat is the o"t)"t voltageL A ,- 2 ,- 2 C @@J 2 D /@- 2 FJ A @0)ole !c generator 8ith la) 8o"n! armat"re is t"rne! at /1-- r)m There are /-- con!"ctors 9et8een the 9r"shes The average fl". !ensity in the air ga) 9et8een )ole faces an! the armat"re is /@T The )ole have an area of -- s: m 8hat is the no loa! terminal voltageL A @/, 2 2 C F@ 2 D /-1 2 F, The armat"re of sh"nt generator has --J0ohm effective resistance Each 9r"sh has an effective resistance of --/ ohm The terminal voltage is /-- volts 8hile the c"rrent is F/- am)eres hat is the efficiencyL A /,K- 8atts @--- 8atts C @/1- 8atts D /J/1 8atts
FK A DC generator has a no0loa! o"t)"t voltage rating of /@-0volt Its armat"re circ"it resistance is -J an! its fiel! coils are se)arate! energie! If a loa! of @ ?8 at //J volts is connecte! across the o"t)"t; neglecting the effect of armat"re reaction an! the line !ro)s; 8hat )o8er 8ill 9e a9sor9e! 9y the loa!sL A /,K- 8atts @--- 8atts C @/1- 8atts D /J/1 8atts F1 A J-0?8; J--0volt short sh"nt generator has an armat"re resistance; series fiel! resistance an! sh"nt fiel! resistances are --J ohm; --, ohm an! @J ohms res)ectively 7tray )o8er loss is /--8atts an! stray loa! loss is / Calc"late the horse)o8er re:"irement at this loa! A ,J KJ C J- D K@ F A @J-0?8; @- – 2olt short sh"nt generator is !elivering 1-- am)ere at @- volts The sh"nt fiel! c"rrent is /@ am) The armat"re resistance is ---K ohm The stray )o8er at this loa! is J;J-- 8atts an! stray loa! loss of / The generator is connecte! long sh"nt Determine the efficiency at this loa! A @ J C 1 D J- T8o sh"nt generators A P o)erates in )arallel in their loa! characteristics may 9e ta?en as straight line The voltage of generator A falls from @F- 2olts at no0loa! to @@- 2olts at @-- Am) 8hile that falls from @FJ 2olts to - 2olts at /J- Am) Determine the common terminal voltage 8hen the loa! is ,K ?A @@ 2olts @@ 2olts C @F/ 2olts D /J 2olts DC MACHINES SUPPLEMENAR! PROBLEMS / To re!"ce ra!io interference from ho"sehol! motor; the motor are sometimes )rovi!e! 8ith a* con!enser across the 9r"shes c* resistance 9* com)lete enclos"re of the motor !* gro"n!e! motor frame @ An electric motor !evelo)s @- H' at a s)ee! of ,-- r)m hat is the tor:"e in N0mL a* @F- 9* @/- c* @- !* @, a @F- volt !c motor on the 9ra?e test too? J@ Am) 8hen r"nning at /J-- r)m The s)ring 9alance at the en! of the K, cm 9ra?e arm rea!s J N 8hat is the efficiency of the motor loa!L a* -1J 9* -- c* -J !* -1, F A !c sh"nt motor !evelo)s /J h) at /@- volts The armat"re efficiency is J hat is the co"nter emfLa* //F volts 9* //1 volts c* /@@ volts !* //K volts J A !c sh"nt motor !ra8s an armat"re c"rrent of 1/, am)eres at /@- volts hat is the h) o"t)"t of the motor if the armat"re effective resistance is --, ohmLa* /J1 9* KJ c* @@ !* /J , Regar!ing e!!y c"rrent loss in !c sh"nt generator 8hich statement is GA7EL a* it varies as s:"are of the s)ee! 9* it varies as s:"are of the fl". !ensity c* it varies as the s:"are of lamination thic?ness !* it is al8ays constant K If a motor frame is fo"n! e.cessively hot; 8hich of the follo8ing is the EA7T li?ely ca"se a* very high am9ient tem)erat"re c* ina!e:"ate internal ventilation 9* fa"lty starter !* e.cessive loa!ing 1 A FF- 2olt sh"nt motor has an armat"re resistance of -1 ohm an! fiel! resistance of @-- ohms hat is the armat"re )o8er !evelo)e! 8hen giving an o"t)"t of KF, ? at 1J efficiency a* KJ, ? 9* KF,? c* 1F, ? !* K@ ? A !c motor ta?es an armat"re c"rrent of /-J Am) at F1- volts 8hen r"nning at K@-r)m The resistance of the armat"re circ"it is -@ Ohms an! the fiel! resistance is , Ohms hat is the tor:"e !evelo)e! in the armat"reL a* ,,1N0m 9* ,/-N0m c* KJ@N0m !* , N0m /- A @--2 sh"nt motor r"nning at K@- r)m ta?es an armat"re c"rrent of J-A; Its effective resistance is -F- ohm hen a resistance of /, ohm is )lace! in series 8ith the armat"re; hat is the ne8 s)ee!L Ass"me that loa! tor:"e is constant a* K@- r)m 9* ,-- r)m c* KJ- r)m !* ,1- r)m
// The sim)lest form of a motor controller is a* !r"m s8itch 9* relay c* magnet s8itch !* toggle s8itch /@ Ra)i! sto))ing of an electric motor 9y momentarily reversing its connections to the s"))ly is a* Bogging 9* )l"gging c* inching !* se:"ence o)eration / In a JH'; @-2; /J-- r)m sh"nt motor; the resistance of the armat"re incl"!ing 9r"shes is -/KJ ohm an! that of the sh"nt fiel! 8in!ing is ,/- ohms The stray )o8er losses 8hen the motor !elivers rate! loa! at rate! voltage is -J The efficiency at rate! loa! is nearest to a* 1 9* 1 c* -!* 1J /F A @-H); //-2 DC sh"nt motor has an efficiency of 11 an e.citing c"rrent of FA an! an armat"re resistance of --F ohms hat starting resistance is re:"ire! for f"ll loa! tor:"e a* -1 ohm 9* -F ohm c* -J ohm !* -, ohm /J A /-H); @-2; /-- r)m series motor; having rate! efficiency of 1JJ; armat"re resistance incl"!ing 9r"shes of -@1 ohms an! a fiel! resistance of -/J ohms hat val"e of starting resistance so that the starting tor:"e is e:"al to /J- of the rate! loa! tor:"eL a* FJ ohms 9* FJ@ ohms c* JF ohms !* F,K ohms /, A ,-H); @-2 sh"nt motor has a sh"nt fiel! resistance of 1 ohms an! an armat"re resistance of --F ohms If the resistance in the starter is -,, ohm an! the 9r"sh !ro) is 2 hat is the in)"t c"rrent to the motor at the instant it is starte!L a* @FA 9* @1A c* -A !* FFA /K A series motor is never starte! 8itho"t some mechanical loa! on it 9eca"se it 8ill a* !ra8 too m"ch c"rrent 9* )ro!"ce! vicio"s s)ar?ing of 9r"shes c* !evelo) e.cessive s)ee! an! !amage! itself !* o)en f"se or tri) off circ"it 9rea?er /1 A /--2 !c series motor r"n at F-- r)m 8hen ta?ing a c"rrent of JJAm)ere Armat"re resistance is -- ohm; fiel! resistance is - ohm If the loa! tor:"e remains the same; hat is the in)"t c"rrent 8hen the fiel! is sh"nte! 9y a resistor of --@ ohmL a* ,@A 9* 1KA c* K,A !* 1@A / A !c generator may loose its resi!"al magnetism 9eca"se of a* varying loa!s 9* vi9rations c* over0e.citation !* heating of @- In la) 8in!ing; front )itch is /K an! 9ac? )itch is / hat is the average )itchL a* /1 9* /1J c* / !* /K @/ A fo"r )ole !c generator 8ith la) 8in!ing has F1 slots an! F elements )er slot Ho8 many coils !oes it haveL a* F1 9* 1F c* /@ !* , @@ If the armat"re of an eight )ole !c machine 8ere 8o"n! 8ith sim)le. 8ave 8in!ing; Ho8 many )arallel )ath 8o"l! there 9eL a* /, )ath 9* @ )ath c* 1 )ath !* F )ath @ One of those liste! is not a ty)e of !c generator 8in!ing a* !r"m 9* gramme0ring c* )rogressive !*la) @F In a F)ole; J slots !c armat"re; Calc"late the coil s)anL a* 1 slots 9* K slots c* /- slots !* slots @J In a /- )ole; la) 8o"n! !c armat"re; the n"m9er of active armat"re con!"ctor )er )ole is J- The n"m9er of com)ensating con!"ctor )er )ole re:"ire! is a* J 9* J-- c* J- !* /@, A F)ole; /@ slot la) 8o"n! !c armat"re has t8o coil si!e )er slot Ass"ming single t"rn coil; Calc"late the 9ac? )itch for )rogressive an! retrogressive 8in!ing a* J P 9* P J c* KPJ !* ,PF @K A F)ole !c generator 8ith sim)le. la) 8in!ing has F1 slots an! fo"r element )er slot The fl". )er )ole is @J . /-, ma.8ells an! r"ns at /J-- r)m hat is the o"t)"t voltageL a* ,-2 9* F1-2 c* @@J2 !* /@-2 @1 A @-S8; @@-2 sh"nt generator has an armat"re resistance of --K ohm an! a sh"nt resistance of @-- ohms Determine the )o8er !evelo)e! in the armat"re 8hen it !elivers its rate! o"t)"tL a* @KS8 9* @-1S8 c* /@S8 !* @JKS8 @ A @112 sh"nt generator has constant losses of @11- The armat"re circ"it resistance is -@ohm If the generator is !elivering a )o8er at ma.im"m efficiency; then its armat"re c"rrent is a* /-A 9* /@-A c* /-A !* ,FA
- A F--S8; ,--2 !c sh"nt generator has an armat"re resistance of -- ohm The fiel! resistance is F1 ohms The stray )o8er loss for this machine at rate! voltage an! s)ee! is K@-- atts; hat is the ma.im"m efficiencyL a* F 9* , c* J !* 1J / A sh"nt generator !elivers /JA of terminal voltage of @J-2 The armat"re resistance an! sh"nt fiel! resistances are --@ ohms an! J- ohms res)ectively The iron an! friction losses e:"al to J- The over all efficiency is a* F 9* 1 c* J !* J @ A FF-2 long sh"nt com)o"n! generator has a f"ll loa! c"rrent of @--A Its armat"re resistance; series fiel! resistance an! sh"nt fiel! resistances are --@ ohm; --F ohm an! /-- ohm res)ectively The stray loa! losses are @--- hat is the f"ll loa! efficiency of the generatorL a* K 9* J c* 1 !* A J-S8; F,-2 sh"nt generator has a voltage reg"lation of 1K; Calc"late the loa! terminal voltage a* FKJ 9* J-- c* J-J !* FF The sim)lest 8ay to shift loa! from a !c sh"nt generator r"nning in )arallel 8ith another is to a* a!B"st their fiel! rheostat 9* a!B"st s)ee!s of their )rime movers c* insert resistance in their armat"re circ"it !* "se e:"alier connections J T8o sh"nt generators A an! ; 8ith ratings of @J- an! F--S8 res)ectively having e:"al no loa! voltage of @,-2 an! f"ll loa! voltage of @F-2 Calc"late the terminal voltage 8hen the total o"t)"t is JKJS8 a* @FJK2 9* @1F2 c* @F@,2 !* @F,2 POL!PHASE POWERLINE S!SEM SERVICES RME Revie8 @1 Carig 7"r; T"g"egarao City
3eneral Information Electrical Engineering / Is an electric energy transfer meas"re! in co"lom9 a electric charge 9* ca)acitance c* In!"ctance !* force @ The ratio of the amo"nt of electricity transferre! from one of its )late to the other; to the )otential !ifference )ro!"ce! 9et8een the )lates a electric charge 9* ca)acitance c* In!"ctance !* force Is a )hysical element 8hich e.hi9it the )ro)erty of ca)acitance a a* resistor 9* in!"ctor c* ca)acitor !* charge F is !efine! as 8or? )er "nit )ositive charge moving 9et8een t8o )oints in the fiel! a a* electric c"rrent 9* electric )otential c* electric charge !* electrons J is !efine! as 8or? )er "nit time a* energy 9* )o8er c* voltage !* c"rrent , is the a9ility of !oing 8or? or rate of !oing 8or? a* energy 9* )o8er c* voltage !* c"rrent K The o))osition to the flo8 of c"rrent to a circ"it a a* resistance 9* ca)acitance c* in!"ctance !* electric charge 1 is the )ro)erty of an electric circ"it 8hich ca"ses the circ"it to o))ose any change of c"rrent in the circ"it a* resistance 9* ca)acitance c* in!"ctance !* electric charge The "nit of resistivity is a* ohm )er meter 9* ohm –meter c* mho0meter !* mho )er meter /- The "nit of con!"ctivity is a* ohm )er meter 9* ohm –meter c* mho0meter !* mho )er meter // are materials 8ith con!"ctivities interme!iate 9et8een those of con!"ctors an! ins"lators a a* semicon!"ctors 9* s")ercon!"ctors c* ins"lators !* in!"ctors /@ are materials 8ith lo8 con!"ctivity a))ro.imately /-0/- to /- 0/, mho )er meter a a* semicon!"ctors 9* s")ercon!"ctors c* ins"lators !* in!"ctors / materials having resistivity a))roaches ero a a* semicon!"ctors 9* s")ercon!"ctors c* ins"lators !* in!"ctors /F materials 8ith large val"es of con!"ctivity a))ro.imately in the or!er of /-./- , mho )er meter a* semicon!"ctors 9* s")ercon!"ctors c* ins"lators !* in!"ctors
/J The con!"ction of electricity in the materials is 9y means of in!ivi!"al atomic scale s)ecies calle! a* electrical con!"ction 9* charge carriers c* con!"ctor !* ins"lator /, A heater "ses electric energy at the rate of /-- in @ho"rs 8hen s"))lie! 9y a constant voltage so"rce of /@-2; The energy cons"me! 9y the heater is a a* K@-S 9* -@--S8h c* -@F-S8h !* /@F-S8h /K A /@2 9attery is "se! to s"))ly a /@- loa! in /-ho"rs Ho8 m"ch electric charge! store! in the 9attery a* ,-?Co"lom9 9* /@Co"lom9 c* /--Ah !* -Co"lom9 /1 T8o )oints in an electric fiel! have a )otential !ifference of J2 If an electric charge of JCo"lom9 is moving from )oint to )oint; Ho8 m"ch 8or? is )ro!"ce! !"ring transition a /o"le 9* Jo"le c* @Jo"le !* KJo"le / A co))er con!"ctor Jm long having a cross0section of @mm in !iameter; has a )otential !ifference of /@2 across its terminal The resistivity of co))er at @- -C is /K@ . /- 01ohm – meter The resistance of the 8ire is a* @KF . /- 0ohms 9* -@KFohms c* @KF . /- 0ohms !* @KFohms @- In item /; the c"rrent flo8ing thro"gh the circ"it is a @/@Am) 9* @,JAm) c* J1KAm) !* nota @/ An electric heater; @@-2 ta?es @Am)ere of c"rrent The energy cons"me! 9y the heater in /hr is a* FFS8h 9* FFS8h c* -FFS8h !* 11S8h @@ The ca)acitors having a ca)acitance of /Gara! are connecte! in )arallel The e:"ivalent ca)acitance is a* /Gara! 9* @Gara! c* Gara! !* /+Gara! @ If the ca)acitor in item @@ are connecte! in series; the e:"ivalent ca)acitance is a /Gara! 9* @Gara! c* Gara! !* /+@Gara! @F A coil has an in!"ctance of JHenry If the c"rrent changes from /-Am)ere to @-Am)ere in /secon!; the average voltage is a* J-2 9* /J-2 c* /--2 !* J2 @J A light 9"l9 o)erates 8ith a line voltage of //-2 The filament resistance is @--Ohms 8ith /mm !iameter an! /m long The con!"ctivity of the material is a*@J . /- , mho )er meter 9* J . /- , mho )er meter c* /- . /- ,mho )er meter !* nota AC MACHINES "ALERNAOR# REVIEW LECURE Alternators – An electrical converting mechanical energy to ac electrical energy
3eneral Ty)es of Alternators A* 7ynchrono"s generator – a generator synchrono"s 9eca"se it is !riven at constant s)ee! %synchrono"s s)ee!* an! it is "se! in almost all ty)e of a))lications * In!"ction generator – it is an in!"ction 8hich r"n as a generator 8ith a s)ee! a9ove synchrono"s s)ee! Ts )f is "s"ally lea!ing an! connecte! in )arallel 8ith a synchrono"s generator in or!er to s"))ly )o8er for lighting loa!s C* In!"ction alternator – it generates voltage at higher fre:"ency %J-- H to /-;---H* it is "se! to s"))ly )o8er to in!"ction f"rnace in or!er to s"))ly )o8er to in!"ction f"rnace in or!er to heat an! melt the metal T8o ty)es of alternator4 / Revolving Armat"re Ty)e @ Revolving Giel! Ty)e a 7tator – 7tationary armat"re 9 Rotor – Rotating fiel! )oles A!vantages of 7tationary Armat"re / O"t)"t c"rrent is !elivere! to the loa! 8itho"t )assing it thro"gh 9r"sh contracts @ Easier to ins"late stationary armat"re 8in!ing for high ac voltage
Armat"re 8in!ing can 9e easily 9race! to )revent !eformation 8hich can 9e )ro!"ce 9y mechanical stress F Easily ins"late! sli) rings 8hich transfers lo8 voltages; lo8 )o8er !c fiel! circ"it T8o ty)es of rotor "se!4 a 7alient )ole constr"ct – "se! for lo8 s)ee! alternator; large !iameter than a.ial length; having more )oles %from , to F- )oles* 9 7mooth cylin!rical constr"ction – "se! for high s)ee! alternator; !iameter is less than a.ial length; having less n"m9er of )oles %@ or F )ole* 'rime movers for Alternator A* Gor large AC generator * Gor 7mall generator / 7team t"r9ine / Use internal com9"stion engine @ 3as t"r9ine Hy!ra"lic t"r9ine F Internal com9"stion engine Gre:"ency of 3eneral Emf f $ %'Ns + /@- * H # here4 ' $ n"m9er of file! )oles Ns $ synchrono"s s)ee!; r)m 3eneral Emf E:"ation %)er )hase* E $ FFF )S )S ! . /-01 volts %rms* %if ) is in lines or ma.8ells* or E $ FFF ) NfS )S ! volts %rms* %if ) is in 8e9er* or E $ @@@ ) &f NfS )S ! volts %rms* %if ) is in 8e9er* or E $ & E S )S ! volts %rms* Notatons4 E $ generate! emf )er )hase# E $ rms voltage )er con!"ctor ) $ fl". )er )ole in 8e9er or Ma.8ell N $ n"m9er of t"rns )er )hase & $ n"m9er of con!"ctors )er )hase f $ fre:"ency in H S ) $ )itch factor or coil s)an factor S ! $ !istri9"tion or 9rea!th factor 'itch Gactor or Coil 7)an Gactor; S ) S ) $ %2ector s"m of in!"ce! emf )er coil* + %Arithmetic s"m of in!"ce! emf )er coil* S ) $ cos%-+@* $ sin %-+@* - $ /1-- 0 8here4 O $ %Coil )itch + 7lot )itch* . /1- - $ %GrC' + G"C'* . /1- Distri9"tion or rea!th Gactor; S ! S ! $ %2ector s"m of coil emf + Arithmetic s"m of coil emf* $ %emf 8ith !istri9"te! 8in!ing + emf 8ith concentrate! 8in!ing* S ! $ sin%n-+@* + n sin % -+@* # here4 - $ /1- - + slots+)ole - $ !istance in electrical !egree 9et8een coil si!es - $ re:"ire! !istance n electrical !egree to ma?e it f"ll )itch coil - $ !istance in electrical !egree 9et8een a!Bacent slots n $ n"m9er of slots )er )ole )er )hase Gor instance4
Notations4 R c $ effective armat"re %stator* resistance )er )hase Qs $ synchrono"s reactance )er )hase $ Q ar Q &s $ synchrono"s im)e!ance )er )hase Q $ lea?age reactance )er )hase Qar $ reactance !"e to armat"re reaction E $ generate! or no0loa! voltage )er )hase E $ generate! no0loa! line0to0line voltage 2 $ ine0to0line terminal voltage I $ ine c"rrent I $ Ia $ armat"re c"rrent or )hase c"rrent 2f $ e.citer voltage R f $ fiel! resistance If $ fiel! c"rrent Alternator 2oltage Reg"lation4 2R $ 5%2 N – 2G* + 2G6 . /-- $ 5%E 0 2* + 26 . /-- Alternator on loa!; the variation of terminal voltage is !"e to the follo8ing reasons4 / 2oltage !ro) !"e to armat"re resistance @ 2oltage !ro) !"e to armat"re lea?age reactance 2oltage !ro) !"e armat"re reaction %maBor reason* 2ector !iagram4 a if lagging
9 if lea!ing
Ia
c if "nity
E E
IaQs
E 2
IaRa
IaRe Ia
IaQs
2
IaQs IaRe
2 Ia
in com)le. form E $ 2 Ia %&s* In magnit"!e E $ %2cos IaR e*@ %2sin IaQs*@ here4 is lagVg )f 0 for lea!ing )f an! $ - for infinity
Test for Alternators a DC Resistance Test – 8hile Alternator is at rest; an! !c fiel! is o)en; meas"re the !c resistance 9et8een the terminals The average of three sets of resistance is calle! R f 9 O)en circ"it Test or No loa! Test – the alternator is !riven at synchrono"s s)ee!; the fiel! c"rrent %e.citation* is a!B"ste! from a lo8 val"e ") to that s"fficient for voltage res)onsi9ility 9eyon! the rate! voltage c 7hort Circ"it Test – the alternator is !riven at synchrono"s s)ee! %rate! fre:"ency*; the fiel! c"rrent %e.citation* is a!B"ste! to give /J- to @-- of rate! c"rrent to flo8
&s $ %Eoc + Isc* – 5%2 + * + Isc6#l
Gor 8ye0connecte! stator Re $ /J R !c# R !c $ W R t
Gor !elta0connecte! 7tator 8in!ings &s $ %Eoc* + %Isc + * $ 2 + %I sc + *# Re $ /J R !c# R !c $ +@ R t here4 R t $ ohmic resistance 9et8een terminals %meas"re! 9y ohmmeter* R !c $ ohmic resistance )er )hase R e $ effective resistance )er )hase 2 $ voltmeter rea!ing or o)en circ"it voltage 9et8een lines Eoc $ o)en circ"it voltage )er )hase Isc $ short circ"it line c"rrent Alternator Efficiency4 $ %'o"t + 'in* . /-- $ 5' o"t + %'o"t 'loss*6 . /-- $ 5%' in – 'loss* + 'in6 . /-- Alternation osses / Rotatoin losses a Griction an! 8in!age loss 9 r"sh friction c 2entilation loss ! Core loss @ Electrical losses a Giel! circ"it co))er loss 9 Armat"re 8in!ing co))er loss c r"sh contact loss 7tray loa! loss
F E.citer loss 'arallel O)eration of Alternators# The re:"irement of connecting t8o alternators in )arallel or connecting in alternator to the 9"s are4 / The t8o effective val"es of voltage are e:"al at the terminals 9eing connecte! @ The t8o fre:"ency are same T8o voltage are e.actly o))osite in )hase %in the local circ"it of the t8o machine* F The )hase se:"ence of the voltages %for )oly)hase machine* are the same J The t8o voltages have the same 8ave form The o)eration of )ro)erly connecte! synchrono"s generator n )arallel 8ith a system is calle! =synchroniing> If any of the a9ove is re:"irements are not met; there 8ill 9e cross0c"rrent 9et8een the alternator 8in!ing thro"gh the common 9"s09ars; 8ith this cross c"rrent; the generator can not 9e synchronie Ma.im"m 'o8er O"t)"t for Alternator4 'ma. $ E2 8atts + Q s If R e is neglecte! 'ma. $ %2+ & s* %E – 2cos * if R e is consi!ere! Ima. $ 5%E@ 2@*6 + Qs E @ @ 'f $ E + 5 %E 2 *6
IQs
$ -here# E $ emf generate! )er )hase 2 $ terminal voltage )er )hase Qs $ synchrono"s reactance )er )hase &s $ synchrono"s im)e!ance )er )hase
I
2
7ynchroniing 'o8er %' 7YN* OG Alternator4 eca"se of some !ist"r9ance on the system; the )o8er angle changes 9y %as sho8n 2o $ 2o*; 8hich ca"se the machine to !evelo) the a!!itional )o8er; there9y ?ee)ing in synchronism This a!!itional )o8er is ?no8n as the =synchronie )o8er> Consi!er the vector !iagram 8ith lagging )f loa!#
Grom the vector !iagram Ia $ %E- + a 0 2 + --* + %&s + * $ /+&s 5 Eo + 0 0 2 + 0 6 Ia $ /+&s 5 Eo cos% 0 * 0 2 cos 6 B+&s 5 Eo sin% 0 * 2 sin 6 Using '! $ %Rectang"lar* of 2oIa < after sim)lifying4 '! $ 2+&s 5Eo cos 0 2 cos % 0 *6 hen 9ecomes # '! $ Eo+&s 5 Eo cos 0 2 cos % *6 An! since 'syn $ '! – '! 'syn $ Eo2+&s 5sin sin % * @ cos % * sin@ +@6 8atts+ 'syn $ Eo2+&s 5cos sin 6 8atts+ ATERNATOR RE2IE 'ROEM / In large ca)acity generator; the moving )art is a*9r"shes 9*armat"re c*)oles !*frame @ hich of the follo8ing is NOT the integral )art of synchrono"s generator systemL a*e.citation system 9*!istri9"tion system c*)rotection system !*)rime mover An e.citer of a generator is a a*sh"nt motor 9*sh"nt generator c*series motor !*series generator F It )lays an im)ortant role in over0s)ee! )rotection of a generator a*governor 9*Differential )rotection c*over c"rrent !elay !*alarm J 7alient )ole ty)e alternators are generally "se! on a* lo8 voltage alternators 9* high s)ee! )rime movers c* hy!rogen coole! )rime mover !* lo8+me!i"m s)ee! )rime mover , The rotor )referre! for alternators a))lie! to hy!ra"lic t"r9ines are a*salient )ole ty)e 9*any of the a9ove c*cylin!rical rotor ty)e !*soli! rotor ty)e K Three )hase alternators are invaria9ly star0connecte! 9eca"se a* higher terminal voltage is o9tain 9* small con!"ctors can 9e "se! c* less t"rn of 8ire is re:"ire! !* magnetic losses are minim"m
1 Increasing the s)ee! of alternator; 8hat 8ill ha))enL a*!ecrease M 9*increase fre:"ency c*increase M2AR !*!ecrease M2AR T"r9o alternators "s"ally have a* F )oles 9* @ )oles c* 1 )oles !* /@ )oles /- hat is the fre:"ency of the generate! emf of a /- )ole alternator !riven at K@- r)mL a* J- h 9* JJ h c* ,- h !* ,@J h // In aircrafts; alternators have o)erating fre:"ency of a*J-H 9*,-H c*F--H !*1--H /@ The n"m9er of cycles generate! in an 10)ole alternator in one revol"tion is a* F 9* @ c* , !* 1 / Determine the n"m9er of electrical !egrees ma!e )er revol"tion for s)ecial0)"r)ose 1 )ole alternatora* @1;1-9* K;@-c* /F;F-!* /;,-/F D"e to 8hich of the follo8ing reasons concentrate! 8in!ing are not "se! in alternators a* increase the voltage harmonics 9* increase co))er iron ratio c* !ecrease the In!"ce emf+)hase !* increase armat"re reactance /J Harmonic com)onent of generate! emf 8ill 9e more in a*short )itch coil 9*f"ll )itch coil c*long )itch coil !*none of these /, The 8in!ing of of a 0)hase; ,0)ole; ,- cycle alternator has 1+ )itch 8hat is the coil s)anL a* -- elect 9* /@-- elect c* /,-- elect !* @-- elect /K Gor a 0)hase 8in!ing 8ith J slots )er )ole )er )hase an! 8ith coil s)an of /@ slot )itch; the val"e of )itch factor is a*-1J/ 9*-1 c*-J/ !*/-J /1 If the alternator 8in!ing has a fractional )itch of J+,; 8hat is the )itch factor %S )*L a*-,, 9*-JK c*-J/ !*-K@ / Determine the 9rea!th or 9elt factor for a 0)hase 8in!ing in 8hich there are J slots )er )ole )er )hase a*-,, 9*-JK c*-J !*-J@ @- A /FF0slots stator has a 8hole0coile!; /@ )ole; 0)hase 8in!ing hat is the n"m9er of coils )er )haseL a* F1 9* /@ c* @F !* , @/ A )art of an alternator 8in!ing consist five coils in series; each coil having an emf of /volts in!"ce in it The coils are )lace! in s"ccessive slots an! 9et8een each slot an! the ne.t; there is an electrical !is)lacement of /@o Determine the emf of the five coils in series a* F1,F 2olts 9* J- 2olts c* F1 2olts !* FK1 2olts @@ Calc"late! generate! emf )er )hase af a /- )ole; 0)hase; ,- H alternator 8ith J slot )er )ole )er )hase an! F con!"ctors )er slots in t8o layers The 8in!ing is short 9y slots P the fl". )er )ole is -/@ e9er a* @-12olts 9* /---2olts c* K@-2olts !* @--2olts @ The harmonic 8hich 8o"l! 9e totally eliminate! from the alternator emf "sing a fractional )itch of ,+K is a*r! 9*Jth c*Kth !*th @F An alternator on o)en circ"it generates ,- 2olts at ,- H 8hen the fiel! c"rrent is , Am) Neglecting sat"ration; !etermine the generate! emf at a fre:"ency of - H an! a fiel! c"rrent of - Am) a* @F-2olts 9* --2olts c* /,-2olts !* /J-2olts @J A - M2A; /1 ?2olt; ; Y0connecte! alternator 8ill have a )er )hase nominal im)e!ance of a* KJ ohms 9* @ ohms c* ,F ohms !* /J ohms @, To get the armat"re resistance of a /-- M; /1 ?v an! - )o8er factor generator; t8o terminals are connecte! to !c so"rce The meas"re! c"rrent an! voltage are 1K, am)eres an! , volts res)ectively hat is the !c resistance )er )haseL @K A generator is rate! /-- M; /1 ?2 an! - factor The effective res istance to ohmic resistance is /J The ohmic resistance is o9taine! 9y t8o terminals to a , volts !c so"rce If the c"rrent F1 Am)eres; 8hat is the )ercent resistance )er )haseL a* /J 9* , c* FJ !* ,
@1 To get the armat"re resistance of a !elta connecte! J-- ?8; @-0v; 1J )o8er factor generator; t8o terminals are connecte! to a ,02olt DC The meas"re! c"rrent is -A hat is the armat"re resistanceL a* -,K 9* -/ c* --, !* -- @ 7ynchrono"s im)e!ance test is ta?en on a 0)hase generator Un!er short circ"it con!ition; the c"rrents in the three lines are @,@A; @KA; an! @KFA hat c"rrent sho"l! 9e "se! for the testL a* @,A 9* @JKA c* @F,A !* @JFA - A generator rate! /--M; /1 ?2olt an! - )o8er factor has an effective ac resistance of -F, ohm 9et8een terminals The fiel! c"rrent of /- Am) )ro!"ces an o)en circ"it emf of /;1-- volt 9et8een terminals The same fiel! c"rrent re:"ire! to )ro!"ce rate! f"ll0 loa!e! c"rrent at short0circ"it hat is the synchrono"s reactance )er )haseL a* /K@ ohms 9* @K ohms c* /K ohms !* @, ohms / If the e.citation of /- A in a single )hase alternator gives a c"rrent of /J- A on short circ"it an! terminal voltage of --2 on o)en circ"it; 8hat the internal !ro) 8ith a loa! c"rrent of ,-AL a* ,-2 9* /1-2 c* @F-2 !* ,-2 @ If the loa! on an isolate! alternator increase! 8itho"t increasing the )o8er in)"t to the )rime mover The alternator a*8ill shot !o8n 9*voltage increases c*s)ee! ") !*fiel! c"rrent 8ill increase A /-- M; /;1-- volts - )o8er factor synchrono"s generator has an ohmic resistance of -/ ohm an! synchrono"s reactance of -F@ ohm is o)erating at rate! con!ition Gin! the angle 9et8een the voltages a* JJ !eg 9* KFJ !eg c* ,K@ !eg !* @J !eg F A 0)hase /--M; @@ ?2; 8ye connecte! alternator s"))lies f"ll loa! 1J )o8er factor lagging Its resistance is -/ ohm an! synchrono"s reactance is -K ohm )er )hase 8hat is the voltage reg"lationL a* @FJF 9* //1 c* @@ !* /@J J A /J-- ?2A; @;-- 2olt; 0)hase; 10)ole; ,- H alternator has an ohmic resistance 9et8een terminals of --1 ohm The ratio of effective to ohmic resistance is /J The fiel! ta?es K- Am) at /@- 2olts from e.citer e:"i)ment The friction an! the 8in!age loss is /J ?; iron losses are J ? an! stray loa! loss is /J? hat s the efficiency at rate! loa! an! 1- )f laggingL a* F 9* 1K c* @ !* J , hat is the sol"tion to re!"ce rotor friction to a large generatorL a* "se 7G, gas in the rotor cham9er 9* "se l"9ricant oil n the rotor cham9er c* "se hy!rogen gas in the rotor cham9er !* a))ly an vac""m in the rotor cham9er K The !ar? an! 9right lam) metho! is "se for a* transfer of loa! 9*synchroniing c*9alancing of loa! !*)hase se:"ence 1 O"t of the follo8ing con!itions; the one 8hich !oes not have to 9e met 9y alternators 8or?ing in )arallel is a* the machine m"st have e:"al rating 9* terminal voltage of each machine m"st 9e the same c* the machines m"st have the same )hase rotation !* the machine m"st o)erate at the same fre:"ency A generator is 9eing synchronie! to a large system The act"al system voltage an! fre:"ency are /K ?2 an! ,- H res)ectively The generator voltage an! fre:"ency are /, an! ,- H res)ectively hen the generator is s 8itch to the system Choose 8hich one ha))ens a* 3enerator !elivers M2AR 9* 3enerator ta?es in M2AR c* 3enerator !elivers M !* 3enerator ta?e in M
F- A generator is 9eing synchronie! to a large system The act"al system voltage an! fre:"ency are /1 ?2 an! ,- H res)ectively The generator voltage an! fre:"ency are /1 ?2 an! ,-/ H res)ectively 8hen the generator is s8itche! to the system Choose 8hich one ha))ens a* 3enerator !elivers 9oth M an! M2AR 9* 3enerator ta?es in M2AR c* 3enerator !elivers M !* 3enerator ta?es M F/ The !istri9"tion of loa! 9et8een t8o alternator o)erating in )arallel can 9e change 9y changing a*)hase se:"ence 9*fiel! e.citation of alternator c*!riving tor:"e of )rime mover !* all of these F@ hen t8o alternators are o)erate! in )arallel an! the fiel! c"rrent of one of the generator is increase!; it 8ill a* ta?e a large share of the loa! 9* s)ee! ") c* ca"ses a flo8 of reactive 2AR 9et8een t8o machines !* ta?e a smaller share of the loa! F The !riving )o8er from the )rime mover !riving an alternator is lost 9"t the alternator remain connecte! to the s"))ly %ie its )o8er circ"it 9rea?er faile! to tri)* an! its e.citation is on The alternator 8ill a* 9ehaves as an in!"ction motor 9* sto) P get 9"rnt c* 9ehaves as synchrono"s motor 9"t 8ill rotate n reverse or o))osite !irection !* 9ehaves as synchrono"s motor an! rotate at the same !irection FF Dam)er or =Amortisse"r> 8in!ing are "se! in alternation to a*achieve synchronism 9* )revent h"nting c* re!"ce 8in!age losses !*start ") FJ hich of the follo8ing relay come into o)eration in the event of fail"re of )rime0mover connecte! to the generatorL a* "chhol relay 9* Reverse )o8er relay c* Differential relay !* Distance relay F, The )o8er factor of an alternator is KJ The o)erator is or!ere! to increase the )o8er factor to 1- hat shall he !oL a* increase the voltage 9* increase the e.citation c* o)erate the governor !* !ecrease the e.citation FK T8o /J-- ?2A AC generators r"nning in )arallel s"))lies the total loa! of @;@J- ? at -- )f lagging One machine is loa!e! to /--- ? at -1J )f lagging hat is the ? P )f of the other machineL a* /KJ- P -1 lagging 9* FK- P -, lea!ing c* /J P -F lagging !* /@J- P -K1 lea!ing F1 T8o alternators are !riven 9y sh"nt motors The sh"nt motors have s)ee! loa!0!ro) characteristic of an! F res)ectively The alternators are in )arallel an! each carrying J? there is no a"tomatic s)ee!0loa! control An a!!itional J- ? is s8itch on hat are the res"lting loa!s of the alternators ass"ming that the s)ee!0loa! control of each is not a!B"ste!L a* K1JK? P K/F? 9* 1@J/? P ,KF? c* K1? P KJ? !* 1-/?8 P ,,? F A ; Y0connecte!; /---?2A; ,,?2olt t"r9o0alternator has a synchrono"s reactance of 1K ohms )er )hase 9"t negligi9le resistance 8hen it is s"))lying f"ll loa! at 1- )o8er factor lagging to a large )o8er system; the emf is F// volts )er )hase if the e.citation s re!"ce 9y J hat is the ne8 val"e of armat"re c"rrentL a*1KJAm) 9*@KJAm) c*KK@Am) !*KJJAm) J- A ; Y0connecte!; /---?2A; ,,?2 alternator has a reactance of 1K ohms )er )hase 9"t negligi9le resistance hen it is s"))lying )o8er to a large )o8er system; the emf s F// volt )er )hase If steam s"))ly is gra!"ally increase 8itho"t changing the e.citation hat is the ma.im"m loa! c"rrent an! ma.im"m )o8er that the generator can s"))ly 9efore gong o"t of synchronismL a* 1KJA P ,;,-- ? 9* ,,/A P J;,-- ? c* 1KJ A P /--- ? !* ,,/ A P 1-- ? AC Machines 7"))lementary 'ro9lems / In case of t"r9o alternators the rotor is "s"ally ma!e of a* cast iron 9* laminate! stainless steel c* forge! steel !* manganese steel
@ hat ?in! of rotor s most s"ita9le for t"r9o0alternators 8hich are !esigne! to r"n at high s)ee! a* salient )ole 9* non0salient )ole ty)e c* either A or !* none of these In an alternator one of the a!vantages of !istri9"ting the 8in!ing is to a*im)rove the voltage 8aveform 9*none of the a9ove c* re!"ce nose !* save on co))er F A , )ole; three )hase AC generator has K@ slots; the coil s)an is /@ 8hat is the )itch factorL a* /-9* - c* -1J !* -,, J The 8in!ing of a 0)hase; ,0)ole; ,- cycle alternator has five0si.ths )itch hat is the chor!ing angleL a* -- 9* /1-- c* /J-- !* -, Determine the 9elt factor for a 0)hase 8in!ing in 8hich there are /1 slots )er )ole a* -,, 9* -,K c* -J1 !* -J, K A 0; ,- h; /-0)ole alternator has /@- slots an! F t"rns in every coil The coil )itch is short 9y @ slots The 8in!ing !istri9"tion factor of the alternation is a* -@J 9* -,K c* -1K !* -JK 1 A F )ole; /J-- r)m alternator 8ill generate emf at a* @- H 9* ,- H c* J- H !* F- H Calc"late the voltage generate! 9et8een lines of a 8ye0connecte! ,- H; alternator 8ith the follo8ing !ata4 slots $ /FF; )oles $ 1; t"rns )er coil $ ,; fl". )er )ole $ /1 . /- , lines; coil s)an $ slots / – /, an! 8in!ing 9eing 8hole coile! a* /@K,2olts 9* ,J2olts c* @;@--2olts !*/;/--2olts /- A /-- M2A; /1 ?2olt; ; Y0connecte! alternator 8ill have a )er )hase nominal im)e!ance of a* KJ ohms 9* @ ohms c* / ohms !* J ohms // A generator is rate! /--M; /1?2 an! - )o8er factor The effective resistance is /J The ohmic resistance is o9tain 9y connecting t8o terminals t8o a !c so"rce The c"rrent P voltage are 1K, Am)eres an! , volts res)ectively hat is the )ercent re sistanceL a* 9* @ c* F@ !* / /@ A 8ye0connecte! alternator 8as teste! for its effective resistance The ratio of the effective resistance to ohmic resistance 8as )revio"sly !etermine! to 9e /J A /@0v 9attery 8as connecte! across t8o terminals an! the ammeter rea! /@- am)eres hat is the )er )hase effective resistance of the alternatorL a*-/J ohm 9*-//K ohm c*--,1J ohm !*--,/K ohm / A generator s rate! /-- M at @@ ?2; an! - )o8er factor The effective ac resistance to ohmic resistance is /J The ohmic resistance is o9taine! 9y connecting t8o terminals to a !c so"rce The c"rrent P voltage are 1K, Am)eres an! , 2olts res)ectively hat is the resistance )er )haseL a*--J/ ohm 9*-F@ ohm c*--,1J ohm !*--,/K ohm /F A generator is rate! /-- M at @@ ?2; an! - )o8er factor The effective ac resistance to ohmic resistance is /J The ohmic resistance is o9tain 9e connecting t8o terminals to a /@ volts !c so"rce If the c"rrent is /@- Am)eres; 8hat is the )ercent effective resistance )er )haseL a* /J 9* , c* FJ !* , /J A generator is rate! /-- M; /1 ?2; an! - )o8er factor The effective resistance to ohmic resistance ratio is /J The ohmic resistance is o9tain 9y connecting t8o terminals of the 8ye connecte! 8in!ings to a DC so"rce of , volts The c"rrent !ra8n is 1K, am)eres hat is the )ercent effective resistance a* 9* F@ c* / !* @ /, A !c resistance test is con!"cte! on 0)hase; @--?2A; @F- volts; !elta connecte! generator hen the t8o terminals are connecte! from , volts !c so"rce; the ammeter inserte! in the line rea!s /J- Am)eres The effective resistance to ohmic resistance is /@J hat is the )ercent resistance )er )haseL a* KJ 9* 1K c* @, !* F, /K If; in a 0)hase alternator; fiel! c"rrent of J- A; )ro!"ces a f"ll loa! c"rrent of @-- A on short circ"it an! /K- 2 on o)en circ"it; then its synchrono"s im)e!ance is
a* 1,, 9* J c* F !* F, /1 The )o8er factor of an alternator s !etermine! 9y its a* loa! 9*s)ee! c*e.citation !*voltage rating / A 0)hase; /--- ?2A; @;-- 2olts alternator is short circ"ite! an! o)en circ"ite! an! is o)erates at rate! c"rrent ith the short circ"it remove! an! the same e.citation; the voltage 9et8een stator terminals is 1,- volts The effective ac resistance 9et8een stator terminals is /@ ohms Determine the )ercent voltage reg"lation at - )o8er factor loagging a* @ 9* /J c* @ !* @,K @- A @J ?2A; @@- 2olt 0)hase alternator !elivers rate! ?2A at -1F )o8er factor The effective ac resistance 9et8een the armat"re 8in!ing terminals is -/1 The fiel! ta?es Am)eres at /JJ 2olts If the friction an! 8in!age loss is F,- 8atts an! the core loss is ,/8atts hat is the h) !elivere! 9y the )rime moverL a* @, 9* /JF c* @1/J !* @ @/ In a large alternator !am)ers a* re!"ce fre:"ency fl"ct"ation 9* re!"ce voltage fl"ct"ation c* increase sta9ility !* none of the a9ove @@ A generator is 9eing synchronie! to a large system The act"al system voltage an! fre:"ency are /K ?2 an! ,- H res)ectively The generator voltage an! fre:"ency are / an! ,- H res)ectively 8hen the generator is s8itch to the system Choose 8hich one ha))ens a* 3enerator !elivers 9oth M an! M2AR 9* 3enerator !elivers M c* 3enerator !elvers M2AR !* 3enerator ta?es n M @ It is never a!visa9le to connect a stationary alternator to live 9"s09ars 9eca"se it a* is li?ely to r"n as synchrono"s motor 9* 8ill get short circ"ite! c* 8ill !ecrease 9"s09ar voltage tho"gh momentarily !* 8ill !ist"r9 generate! emf of the other alternator connecte! in )arallel @F An alternator is o)erating 8ith /-- Am) fiel! c"rrent If the fiel! c"rrent is increase! to /@J Am) 8ith the same electrical loa! on the machines; it 8ill a* 9e less li?ely to go o"t of synchronism 9* 9e more li?ely to go o"t of synchronism c* o)erates at ne8 )o8er factor angle !* overheat @J Dirt acc"m"lation in generator can "se all of the follo8ing e.ce)t a* lo8 )o8er factor 9* flashover c* )oor voltage reg"lator !*overheating @, T8o0 alternators o)erating in )arallel !elivers )o8er at a line )otential of @@-- 2olts to an in!"ctive loa! of /J- ? at 1- )f If the armat"re c"rrents of the t8o alternators 9e e:"al one 9e o)erating at "nity )f Ho8 m"ch )o8er !oes each alternator s"))ly to the loa!L a* //K@ ? for "nity )f P @1 ? 9* //@K ? for "nity )f P 1@ ? c* 9oth KJ ? one at "nity )f !* /-- ? for "nity P J- ? @K T8o0 synchrono"s generators connecte! in )arallel are !riven 9y 8ater8heel 8hose s)ee!0loa! characteristics are as follo8s4 The s)ee! of the first falls "niformly from ,@F r)m at no0loa! to ,-- r)m at f"ll0loa! at /--- ? The s)ee! of the secon! 8ater8heel falls "niformly from ,- r)m to no0loa! to ,-- at /--- ?2 loa!ing The o"t)"t of each generators 8hen the loa! is /@J- ?2A; -1- )f are nearest to a* J-- ? each 9* ,,K ? an! ? c* FFJ ? an! JJJ ? !* K-- ? an! -- ? @1 Hy!rogen is "se! in large alternators mainly to a*re!"ce !istortion of 8ave form 9*strengthen the magnetic fiel! c*cool the machine !*re!"ce the e!!y c"rrent losses
@ T8o i!entical @--- ? alternator o)erates in )arallel The governor of the first machine is s"ch is that the fre:"ency is !ro)s "niformly from J- H at no0loa! to F1 H at f"ll0loa! The corres)on!ing "niform s)ee! !ro) of the secon! machine is J- H to FKJ H hat is the ma.im"m loa! that can 9e !elivere! 8itho"t overloa!ing either machineL a* ,-- ? 9* F--- ? c* ,-- ? !* /K@ ? - A 8ye0connecte! t"r9o alternator having synchrono"s reactance of -J an! negligi9le resistance is connecte! to a large )o8er system having a 9"s 9ar voltage of /1 ?2 s"))lying a loa! of /J--- ?2A at -1 lagging )o8er factor If the steam s"))ly is c"t0off; 8hat c"rrent 8ill the machine carry ass"ming negligi9le lossesL a*@J,JJ A 9*1F@, A c* J@J,@ A !*,@KJJ A
AC MOTOR RE2IE ECTURE I In!"ction Motors An in!"ction motor is one in 8hich the magnetic file! in the rotor is in!"ce 9y c"rrent flo8ing in the stator 8in!ings The rotor has no connection 8hatsoever to the line It !iffers from the synchrono"s motor; the rotor of the in!"ction motor !oes not rotate as fast as the rotating fiel! in the armat"re The armat"re !ifference in s)ee! is calle! the sli) The sli) is "s"ally e.)resse! as a )ercentage of synchrono"s s)ee! 7li) $ %N 7 – NR *+N7 . /-- # N R $ N7 %/0s* 7li) is also the meas"re of the rotor 8in!ing losses; ie 7li) motor $ Rotor Co))er oss+Rotor 'o8er In)"t %RC+R'I* 7li) is also connecte! 8ith rotor efficiency; the higher the sli); the lo8er the efficiency; ie $ NR +N7 . /-- TY'E7 OG 0'HA7E INDUCTION MOTOR74 / 7:"irrel0cage ty)e – the rotor 8in!ing is )ractically self0containe! an! its not connecte! either mechanically or electrically 8ith the o"tsi!e )o8er s"))ly or control circ"it it consist of n"m9er of straight 9ar "niformly !istri9"te! aro"n! the )eri)hery of the rotor an! s?e8e! an! short circ"ite! at the 9oth en!s 9y en! ring to 8hich they are integrally Boine! 7)ee! characteristics4 nearly constant s)ee! Tor:"e characteristics4 starting tor:"e !e)en!s on the resistance of the rotor 8in!ing A))lications4 constant s)ee! service as fans; 9lo8ers; com)ressors; )"m)s; ect @ o"n!0rotor ty)e – this is a 0)hase motor that has another 0)hase 8in!ing instea! of a s:"irrel0cage rotor; the terminals of 8hich are connecte! to sli)0rings r"shes ri!es this sli) rings an! !eliver the c"rrent to an e.ternal 0)hase rheostat or varia9le resistor to vary the characteristic of the motor At start; all the resistance are in the circ"it# as a the motor )ic?s0") s)ee!; the resistance are gra!"ally !ecrease "ntil the finally the sli) rings are short circ"ite! 7)ee! characteristics4 varia9le s)ee! Tor:"e characteristics4 9y inserting vario"s val"e of resistance in the rotor circ"it; a variety of tor:"e val"es %high or lo8* are o9taina9le A))lications4 here high starting 8ith lo8 starting c"rrent or 8here limite! s)ee! control is re:"ire!; as in fans; centrif"gal an! )l"nger )"m)s; com)ressors; conveyors; hoist an! cranes; etc INDUCTION MOTOR GUNDAMENTA GORMUA74 / 7ynchrono"s s)ee! N 7 $ /@- + '
@ F J ,
7li) s)ee! $ N7 0 NR 7li); 7 $ %N7 – NR * + N7 $ /-- Rotor fre:"ency; f R $ 7 %f* Rotor reactance; QR $ 7 %Q @* Rotor stan!still in!"ce voltage; E@ $ a2 # if a is less than /E@ $ 2+ a if a is more than /K Rotor in!"ce voltage )er )hase ER $ 7 %E @* 1 E:"ivalent loa! resistance )eer )hase R loa! $ R @ 5%/07*+76
'OER GORMUAR7 / Rotor 'o8er In)"t; R'I $ I @@ R @+7 @ Rotor Co))er oss; RC $ I @@ R @+7 Rotor 'o8er In)"t; R'D $ I @@ R loa! $ $ I@@R @5%/07*+76
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8atts )er )hase 8atts )er )hase 8atts )er )hase
AD2ANTA3E7 OG 7YNCHRONOU7 MOTOR O2ER INDUCTION MOTOR4 They can 9e o)erate! at lea!ing )o8er factor an! they im)rove the )o8er factor of an in!"strial )lant from the one that is normally lagging to that is close "nity They less costly in certain horse)o8er an! s)ee! range They can 9e constr"cte! 8ith 8i!er air0ga) in!"ction motor; 8hich ma?es them 9eter mechanically They "s"ally o)erate at higher efficiency; es)ecially at lo8 s)ee! "nity )o8er factor range AD2ANTA3E7 OG INDUCTION MOTOR O2ER 7YNCHRONOU7 MOTOR4 They are an! r"gge! hence easier to maintain an! o)erate Their s)ee! can 9e easily a!B"ste! or varie! over a 8i!e range They are chea)er to first cost
METHOD7 EM'OYED TO 7TART 0'HA7E MOTOR74 / Across the line starting – this c"stomarily "se! 8hen the motor m"st o)erate at a high starting tor:"e it is to 9e "se! in connection 8ith a time !elay over0c"rrent relay 8hich 8ill 9ecame o)erative 9efore the 8in!ing can 9e !amage 9y the s"rge c"rrent @ Re!"ce voltage starting – this is "se! I or!er to re!"ce! the staring in r"sh c"rrent 8hich may have !etrimental effects on the line voltage an! may !ist"r9 other a))arat"s A ine resistance starting – it "ses s"ita9le high c"rrent; lo8 ohmic – val"e resistance is remove! in ste)s or all at once ine reactance starting – it "se s"ita9le iron –core reactance in re)lace of the resistance in %a* to accom)lish the res"lt C A"to0transformer starting – is "ses ta))e! a"to – transformers in o)en –!elta connection to re!"ce the motor voltage D ye0!elta starting – it "se! 8hen the motor is !esigne! for !elta o)eration at its rate! voltage The motor )hase 8in!ing are connecte! 9y contractor for a
8ye circ"it starting As a res"lt; each )hase 8ill ta?e the normal line c"rrent !ivi!e! 9y 'art 8in!ing metho! – This metho! is )artic"larly a!o)te! to D"al0voltage motors %those !esigne! to o)erate at t8o voltages* The motor 8in!ing is !ivi!e! into t8o i!entical 8ye0connecte! sections One of 8hich is "se! 8hen is "se! 8hen the motor is starte! an! after its accelerates to a9o"t rate! s)ee!; the t8o section are Boine! in )arallel for normal o)eration Test for In!"ction Motor4 A No –loa! Test4 hen s"))lie! 8ith rate! voltage an! fre:"ency; voltage; c"rrent; an! )o8er in)"t are meas"re! The no0loa! )o8er in)"t re)resent core loss; friction P 8in!age; small stator co))er loss an! rotor co))er loss %8hich is almost negligi9le* 'in $ ' N $ core loss $ friction P 8in!age small c"rloss TO A7IC 'ART7 OG 7YNCHRONOU7 MOTOR4 A Giel! %rotor* str"ct"re – carrying !e0e.cite! 8in!ing Armat"re %stator* str"ct"re – often has 0)hase 8in!ing 8hich is connecte! to an AC so"rce
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TORXUE A77OCIATED ITH 7YCHRONOU7 MOTOR4 7tarting Tor:"e – Tor:"e !evelo)e! 8hen voltage is a))lie! in stator '"ll – in tor:"e – amo"nt of tor:"e or loa! at 8hich the motor 8ill )"ll into ste); 8hen it is starte! as an in!"ction motor %@ to J* 9elo8 synchrono"s s)ee! "ntil it is synchrono"s to the system R"nning Tor:"e – tor:"e !evelo)e! 9y the motor 8hile r"nning '"ll0o"t Tor:"e – ma.im"m tor:"e at 8hich the motor 8ill !evelo) )"lling o"t0of0 ste) or o"t of synchronism; 8ith an increase in tor:"e )ro!"ces 9ac?8ar! shift = >; too m"ch shift of tor:"e angle of the rotor %at a9o"t W !istance 9et8een a!Bacent )ole* 8ill ca"se motor sto)
A''ICATION OG 7YNCHRONOU7 MOTOR74 A* 'o8er factor Correction4 hen synchrono"s motors are em)loye! as a )f correction !evice; it is calle! =synchrono"s con!enser>; this can 9e !one 9y r"nning the synchrono"s motor 8itho"t mechanical loa! 8ith fiel! over0e.cite! * Constant s)ee! loa! !rives4 hen constant s)ee! is re:"ire! s"ch as !rives for centrif"gal )"m); !c generator; 9elt !riven reci)rocating com)ressor; fans; 9lo8ers etc C* 2oltage Reg"lators4 At the en! of a transmission line; the voltage is controlle! METHOD7+'ROCEDURE7 GOR 7TARTIN3 7YNCHRONOU7 MOTOR4 / Girst; main fiel! 8in!ing is short0circ"ite! @ Re!"ce voltages; 8ith the hel) of a"to0transformers; 8ere a))lie! across stator terminals; the motor starts ")
hen it reaches a stea!y %as B"!ge! 9y its so"n!*; a 8ea? e.citation is a))lie! 9y removing the short0circ"it on the main fiel! 8in!ing If e.citation is s"fficient; then the machine 8ill 9e )"lle! into synchronism F G"ll s"))ly voltage is a))lie! across the armat"re %stator* terminals 9y c"tting o"t the a"to0transformers J The motor may 9e o)erate! at any !esire! )o8er factor 9y changing the !c e.citation III – 7IN3E0'HA7E AC MOTOR4 %A* single0)hase In!"ction Motor – it is similar to IM; 9"t it is NOT self0starting %/* 7)lit0)hase motor – it has stator 8in!ings; 8hich is the main an! the a".iliary 8in!ings a 7tan!ar! s)lit0)hase motor – in series 8ith a the a".iliary 8in!ing is a centrif"gal s8itch that 8ill !isconnect this 8in!ing from the so"rce once the motor has reache! KJ to 1- of its synchrono"s s)ee! Uses4 grin!er; 9lo8er; etc
loc? – Rotor Test4 hen re!"ce! voltage is a))lie!; hol! the rotor firmly so that cannot rotate; voltage c"rrent an! in)"t )o8er are meas"re!; Ammeter rea!ing re)resents the 9lac? rotor in)"t c"rrent %short circ"it c"rrent* The )o8er in)"t re)resent =stator an! rotor co))er an! small core loss> %almost negligi9le* 'in $ 'R $ stator C" loss rotor C" loss small core loss $ total co))er losses small core loss %almost negligi9le* for ; Y – connecte! stator in!"ction motor4 Re $ 'R +I@R # &e $ %2R * + IR then Qe $ %&e@ – R e@* e:"ivalent resistance P reactance Do"9le 7:"irrel Cage In!"ction Motor4 The main !isa!vantages of s:"irrel0cage IM is its )oor 9eca"se of lo8 rotor resistance The starting tor:"e co"l! 9e increase! 9y having cage of high resistance; 9"t the motor 8ill have )oor efficiency "n!er r"nning con!itions %9eca"se there 8ill 9e more co))er losses* This can 9e accom)lishe! 9y intro!"cing t8o rotor cages The o"ter cage has a high0 resistance 9ar lo8 in!"ctance an! 9eing close to the rotor; 8hile s"rface; 8hile the inner0cage is lo80resistance 9ars an! has high in!"ctance an! 9eing nearly s"rro"n!e! 9y ion CA7CADE+CONCATENATED OR TANDEM O'ERATION4 In this metho!; t8o in!"ction motors are "se! an! are or!inary mo"nte! on the same haft so that 9oth r"n the same s)ee! %or else they may 9e geare! together* The stator 8in!ing of motor A %a 8o"n! rotor IM* is connecte! to the main so"rce; an! its rotor 8in!ing is the Boine! to the stator 8in!ing of motor %a s:"irrel IM or 8o"n! rotor IM* II – 7ynchrono"s Motors An AC motor that can r"n only at !efinite constant s)ee! calle! =synchrono"s s)ee!> regar!less of the loa! a))lie! to it 7ome Characteristics Geat"res of 7ynchrono"s Motor are4 / It r"ns either at synchrono"s s)ee! or not all; i;e; 8hile r"nning it maintains a constant s)ee! The only 8ay to change is s)ee! is to vary the s"))ly fre:"ency @ It is inherently self0starting It has to 9e r"n to synchrono"s %or near synchrono"s* s)ee! 9y some means 9efore it can synchronie! to the s"))ly; so in )ractice they are
9"ilt 8ith =!am)er or amortisse"r 8in!ing> this !am)er 9ars on the rotor come into )lay !"ring transient or starting It also )revent h"nting s8inging of the rotor 8ith varying loa!s It is also ca)a9le of 9eing o)erate! over a 8i!e range of factor correction )"r)oses ; in a!!ition to s"))ly tor:"e to !rive mechanical loa!s 9 Ca)acitor – similar to the stan!ar! s)lit )hase motor; only it has a ca)acitor connecte! in series 8ith the a".iliary 8in!ing to ma?e the starting tor:"e higher Uses4 refrigerator; air con!itioning "nit; )"m); etc c Ca)acitor start an! r"n motor – it has t8o ca)acitors; one for starting another for r"nning Uses4 same as ca)acitor start motor 7ha!e! )ole motor – it "ses sha!ing coils instea! of a".iliary 8in!ing Uses4 small fans
9 C"mm"tator Motor – it rotor is the !c armat"re / Universal Motor – it is small series 8o"n! motor 8hich can 9e o)erate! "sing ac or !c so"rce at a))ro.imately same o"t)"t )o8er Uses4 se8ing machine; )orta9le tools; ect @ Re)"lsion – its 9r"shes are short circ"ite! ma?ing the armat"re as a large magnet Uses4 vac""m cleaner; floor )olisher; etc Re)"lsion 7tart0in!"ction r"g motor – similar to the re)"lsion motor; only the c"mm"tator is a"tomatically short circ"ite! once the motor has reache! 1- of its synchrono"s s)ee! F Re)"lsion in!"ction motor – similar to re)"lsion motor only it has s:"irrel cage 8in!ing )lace! on the rotor This motor start as in!"ction motor an! re)"lsion motor at the same time Uses4 refrigerator; com)ressor; gasoline )"m); etc 9* Une.cite! / synchrono"s Motor – it r"ns at a constant s)ee! an! it is self0 starting These are t8o ty)es4 / Rel"ctance Motor – it has a s:"irrel0cage rotor of "nsymmetrical magnetic constr"ction 8hich is achieve! 9y removing some teeth of the symmetrical motor )"nching Uses4 timers; recor!ing instr"ment; )hotogra)hs; etc @ Hysteresis motor – it o)erates on the )resence of a contin"o"sly0 revolving magnetic fl".; "s"ally sha!e!0)ole )rinci)le is em)loye!; the only !ifference it has smooth chrome0steel cylin!rical rotor having high retentivity so that hysteresis loss is high Uses4 !riving0ta)e !ec?; t"rn0ta9les; cloc?; etc
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Metho!s Em)loye! to 7tart 7ingle 'hase Motors4 7)lit0)hase metho! %ca)acitor start is the most )o)"lar* 7ha!e!0)ole metho! Re)"lsion metho! Re)"lsion0in!"ction metho! Metho!s of Reversing the Direction of Rotation4
7tan!ar! 7)lit 'hase Motor Yo" reverse the connection of the Ca)acitor 7tart Motor main or the a".iliary 8in!ing 9"t Ca)acitor R"n Motor not 9oth Ca)acitor 7tart R"n Motor Re)"lsion In!"ction Motor – yo" move the 9r"shes in the rotation of the original rotation; "ntil the !irection of rotation is reverse! Universal Motor – yo" interchange the 9r"shes
AC MOTOR RE2IE 'ROEM7 / The frame of the in!"ction motor is "s"ally ma!e of a*silicon steel 9*9rone c*cast iron !*al"min"m @ The shaft of in!"ction motor is ma!e of a*high s)ee! steel 9*cast iron c*stainless steel !*car9on steel In s:"irrel cage in!"ction motors; the rotors slots are "s"ally given slight s?e8 in or!er to a*re!"ce 8in!age loss 9*re!"ce acc"m"lation of !irt an! !"st c*re!"ce e!!y c"rrent loss !*re!"ce magnetic h"m F 7li) rings are ma!e of a* co))er 9* car9on c* )hos)hor 9rone !* al"min"m J The cra8ling in an in!"ction motor is ca"se! 9y a* high loa!s 9* harmonics !evelo)e! in the motor c* im)ro)er !esign of machine !* lo8 voltage s"))ly , A 0)hase in!"ction motor !elta connecte! is carrying f"ll loa! an! one of its f"se 9lo8s0 o"t; then the motor 8ill a* 8ill contin"e r"nning 9"rning its one )hase 9* 8ill sto) an! carry heavy c"rrent ca"sing )ermanent !amage to its 8in!ing c* 8ill contin"e r"nning 9"rning its t8o )hase !* 8ill contin"e r"nning 8itho"t any harm to 8in!ing K O"t of the follo8ing metho!s of starting a 0)hase in!"ction motor; 8hich one re:"ires si. stator terminalsL a*!irect0on0line 9*a"to0transformer c*rotor rheostat !*star0!elta 1 T8o of the )o8er s"))ly terminals to a 0)hase in!"ction motor got interchange! !"ring reconnection after maintenance hen )"t 9ac? into service; the motor 8ill a* rotae in the !irectional as it 8as 9* rotate in o))osite !irection as it 8as c* fail to rotate !* 9"rn o"t A 0)hase# F )ole; ,- H in!"ction motor has f"ll loa! s)ee! of /KF, r)m hat is the sli) s)ee! of the motorL a* J, r)m 9* F, r)m c* JF r)m !* ,- r)m /- The rotor efficiency of a ,- H; F0)ole in!"ction motor is J hat is the s))e! of the motorL a* /K,- r)m 9* /KJ- r)m c* /K11 r)m !* /K/- r)m // A 0)hase FF- volts; J- H in!"ction motor has F s li) The fre:"ency of the rotor emf 8ll 9e a* @-- H 9* @ H c* J- H !* -@ H /@ hat is the s)ee! of an in!"ction motor of , )oles if the )ercent sli) is @JL a* /F,@ r)m 9* 1KK r)m c* //K- r)m !* /KJJ r)m / An in!"ction motor r"ns at //,F r)m hat is the sli)L a* 9* F c* @ !* J /F An in!"ction motor r"ns at //J- r)m hat is the fre:"ency of the rotorL a* /H 9* / H c* JK H !* @J H /J The name)late s)ee! of a ,- H in!"ction motor is //,F r)m If the s)ee! at no loa! is //11 r)m; 8hat is the )ercent s)ee! reg"lationL a* @-, 9* @KK c* @1, !* F@F
/, A F )ole; ,- H; 0)hase in!"ction motor has a f"ll loa! s)ee! of /KJ- r)m hat is the s)ee! at half loa! in r)mL a* /KK9* /KKJ c* J-!* 1KJ /K An AC s:"irrel cage in!"ction motor has a s)ee! rating of /KJ- r)m If the lea!s 8ere s"ch that they co"l! 9e reconnecte! for conse:"ent 8in!ing; 8hat 8o"l! 9e the res"lting s)ee!L a* J-- r)m 9* 1KJ r)m c*/K1- r)m !* FJ- r)m /1 An in!"ction motor has rotor resistance an! stan!still reactance of -/ ohm an! J ohm )er )hase res)ectively The rotor emf at stan!still is ,- volts )er )hase; for a sli) of J; 8hat is the )o8er !evelo)e!L a* /K h) 9* KJ h) c* /- h) !* /J h) / A @- H'; )hase F-- 2olt; ,- H; F )ole in!"ction motor !elivers f"ll0loa! at J sli) The mechanical rotational losses are F-- atts Calc"late the electromagnetic tor:"e a* J1J N0m 9* 1JJ N0m c* J N0m !* JJ N0m @- A )hase/J- h); ,- H; F,- 2olts; , )ole in!"ction motor has a f"ll loa! tor:"e of ,K l90ft hat is the f"ll loa! sli)L a* /J 9* @1 c* !* F @/ A F0)ole; ,- H; -0)hase in!"ction motor has a 9loc?e! rotor reactance of -F ohm )er )hase an! the rotor resistance is -/ ohm )er )hase At 8hat s)ee! 8ill the motor !evelo) ma.im"m tor:"eL a* /@-- r)m 9* /J-- r)m c* /J- r)m !* /,@- r)m @@ If the ma.im"m tor:"e of an in!"ction motor is @-- ?g0m at sli) of /@ an! the tor:"e at , sli) 8o"l! 9e ?g0m a* /-- 9* /,- c* J- !* F@ If a motor has a sli) of @ at rate! voltage; !etermine the a))ro.imate val"e of the sli) 8hen !evelo)ing the same tor:"e at /- a9ove the rate! voltage a*/1 9*/KJ c*/JJ !*/,J @F A FF-2 0)hase; J- h); /KJ- r)m s:"irrel cage in!"ction motor is connecte! to FF- 2 9"s thro"gh a fee!er 8hich the voltage !ro) of /- of 9"s voltage 8hen the motor is !ra8ing rate! c"rrent The ma.im"m contin"o"s )o8er the motor can safety !eliver to its loa! is nearly e:"al to a* F- h) 9* FJ h) c* F@ h) !* F1 h) @J A s:"irrel cage motor is starte! at J- its rate! voltage hat is the starting tor:"e relative to its rate! voltage starting tor:"e a* J- 9* /-- c* @J !* KJ @, A three )hase @- volts; KK )o8er factor; KJ h) in!"ction motor !ra8s a starting c"rrent J times of f"ll loa! c"rrent hat is the starting c"rrentL a*//@J am)eres 9*,am)eres c* @J- am)eres !* /@ am)eres @K A /- h); JJ- 2olts; ,- H; 1K efficiency an! KJ )o8er factor 0)hase in!"ction motor has starting c"rrent of J times the f"ll loa! c"rrent If the motor is "se! in a FF- 2 at ,- H system hat is the starting c"rrentL a* ,- Am) 9* F/JAm) c* F1 Am) !* J@F Am) @1 Magnetic contractor re:"ire! for 8ye0!elta starting motors a* @ 9* / c* !* F @ Gor 8o"n! rotor motor; 8here is the re!"ce! voltage starting !evice a))lie! a* rotor 9* 'anel 9oar! c* 7tator !* fiel! - In a magnetic contractor; NO an! NC a".iliary contracts are "se! for a* electrical interloc?ing 9* mechanical interloc?ing c* over voltage )rotection !* over c"rrent )rotection / A @J h); @- 2olts; 0)hase motor 8ith 1J )o8er factor has a starting c"rrent of JJ times rate! c"rrent To re!"ce the starting c"rrent; a 8ye0!elta starter is stalle! hat is the ne8 starting c"rrentL a* /J Am) 9* -@ Am) c* /J Am) !* /JJ Am) @ A KJ H); FF- 2olt; 0)hase; /- Am); /K- r)m in!"ction has starting c"rrent of , times the f"ll0loa! c"rrent 8hen starte! at f"ll voltage The motor is e:"i))e! 8ith an a"to0 transformer or starting com)ensator If the a"to0transformer is set ,J ta); the starting line c"rrent is nearest to a* @JF Am) 9* ,- Am) c* @/, Am) !* , Am)
Gin! the )ercentage ta) in an a"to0transformer starter to start a s:"irrel cage motor against W of f"ll loa! tor:"e The short circ"it c"rrent on normal voltage is , times the f"ll loa! an! the f"ll loa! sli)is a* K@ 9* 1/J c* 1J/ !*,J FA , )ole; ,- H; 0)hase in!"ction motor o)erates 8ith sli) @ to re:"ires // Am) an! J-- atts 8hen !riving its rate! loa! At no0loa! this re:"ires F Am) an! @- atts; 8hen the rotor is 9loc? FF- atts an! J@ 2olts are re:"ire! to calc"late a c"rrent of /F Am) Calc"late the efficiency of this motor at rate! loa! a*1/J 9*1/J c*1J/ !*11J J A 0)hase motor; /- h); @F- volt; -1J )o8er factor has a loa! of , h) One 8in!ing is s"!!enly c"t; a* the motor 8ill r"n 9"t re!"ce s)ee! 9* the motor 8ill sto) c* the motor 8ill r"n !* the motor 8ill r"n 9"t overheat , A F0)ole in!"ction motor an! , )ole in!"ction motor are connecte! in c"m"lative casca!e The fre:"ency in the circ"it of the ,0)ole is o9serve! to 9e /- H Determine the act"al s)ee! of the concatenate! set; 8hen the s"))ly fre:"ency is ta?en at ,- H a* ,-- r)m 9* K/1 r)m c* J11 r)m !* K-1 r)m K hich of the follo8ing motor has no inherent starting tor:"eL a* s)lit )hase motor 9* synchrono"s motor c* !c series motor !* in!"ction motor 1 hich of the follo8ing metho! is "se! to start a synchrono"s motor a* resistance starter in the armat"re circ"it 9* !am)er 8in!ing c* !am)er 8in!ing in conB"ction 8ill star0!elta starter !* star0!elta starter At 8hat s)ee! 8ill a synchrono"s motor o)erate; if it has /- )oles an! is connecte! to ,H so"rce a* K@- r)m 9* /@- r)m c* /1-- r)m !* ,-- r)m F- A F )ole synchrono"s motor has a s)ee! of /,FJ r)m at certain instant; 8hat is gthe fre:"encyL a* J1@ H 9* JJ H c* JJ H !* JF1 H F/ A /- H); @J- 2; 0)hase star connecte! synchrono"s motor has an effective armat"re resistance of -@J ohm an! synchrono"s im)e!ance of F ohms )er )hase To 8hat voltage m"st motor 9e e.cite! to give f"ll loa! o"t)"t at "nity )o8er factorL Ass"me armat"re efficiency of 11 a* @@ 2 9* @KK 2 c* @J 2 !* @J- 2 F@ A F/, 2olts; 0)hase star0connecte! synchrono"s motor has negligi9le resistance an! synchrono"s reactance of /- ohms Ass"ming rotational loss of J-- 8atts hat is the ma.im"m horse)o8er that the motor can !eliver if the e.citation is hel! constant at F,2oltsLa* /K 9* @ c* / !* @J F A single )hase /- H); @@-0v motor rate! KJ)f; KJ, efficient has a loa! of 1 h) at @/-2 Gin! the line c"rrentL a* ,,K A 9* J A c* F, A !* 11F A FF hich is statement a9o"t s)lit )hase motor is GA7EL a* it has t8o 8in!ings calle! main an! starting 8in!ing 9* the t8o stator 8in!ings are connecte! in series across the s"))ly c* the main 8in!ing has lo8 resistance 9"t high reactance !* the starting 8in!ing has a high resistance 9"t lo8 reactance FJ If starting 8in!ing of a single )hase in!"ction motor is left in the circ"it; it 8ill a* r"n faster 9* !ra8 e.cessive c"rrent P overheat c* r"n slo8er !* s)ar? at light loa! F, If a single )hase motor r"ns hot the )ro9a9le ca"se cannot 9e a* 9lo8n f"ses 9* lo8 voltage c* high voltage !* shorte! stator coils FK If a single )hase in!"ction motor r"ns slo8er than normal; the most li?ely !efect is a* 8orn 9earing 9* short circ"it in the 8in!ing c* o)en0circ"it in the 8in!ing !* none of the a9ove
F1 7elect the motor that 8ill give relatively high starting tor:"e a* sha!e! )ole motor 9* short c* ca)acitor r"n motor !* ca)acitor start motor F A s)lit )hase in!"ction motor is !efective; 9"t if the motor is energie! an! the rotor is rotate! 9y the han!; the motor r"ns hat is 8rong 8ith the motorL a* one 8in!ing is o)en 9* loose connection c* ca)acitor is !efective !* 8in!ing is 9"rn o"t J- hat is the )art of a synchrono"s motor that allo8s it to !evelo) starting tor:"eL a* Cran?ing system 9* )"lley c* Ammortisse"r 8in!ing !* 'ilot starter
AC MACHNE7 %TRAN7GORMER* RE2IE ECTURRE Transformers Is an electrical machine that transfers electrical energy from one circ"it to another 8itho"t changing the fre:"ency; it 8or?s on the )rinci)le of electromagnetic in!"ction; also its 8in!ings are lin?e! 9y a common magnetic circ"it
Classification of transformers / Accor!ing to the core constr"ction4 a Core ty)e – 0core # High 2oltage; high )o8er 9 7hell ty)e – E0ty)e c erry ty)e – Circ"lar ty)e @ Accor!ing to the )"r)ose for 8hich "se!4 a Transmission transformer 9 Distri9"tion transformer c 3enerator transformer ! Testing transformer e Instr"ment transformer / c"rrent %CT* @ )otential %'T* Accor!ing to the metho! of cooling4 a7elf0coole! %AA* 9 Gorce! air coole! %GA* cOil0self0coole! %OA* ! Gorce!0oil coole! 8ith air or 8ater %OA+GA* I!eal Transformer A transformer is consi!ere! i!eal if there is no voltage !ro) across its 8in!ings; if resistance an! lea?age fl". are neglecte!; in 8hich losses are neglecte!; )o8er in)"t is the same as )o8er o"t)"t Transformer 3enerate! 2oltage E:"ation E' $ FFF f m N' in rms 2olts E7 $ FFF f m N' in rms 2olts here4 f $ fre:"ency in H m $ m"t"al fl". in 9 N $ n"m9er t"rn for every 8in!ings $ a constant e:"al to F%///* 8here /// is the form factor of sin"soi!al 8ave Note4 S f $ RM7 val"e + A2E val"e $ %/ + @* ma. val"e + %@ + * ma. val"e $ ///
Transformer osses an! Efficiency $ %O"t)"t + In)"t* . /-- $ 5O"t)"t + %O"t)"t osses*6 . /-- $ 5%In)"t – osses* + In)"t6 . /-- Transformer osses / Core osses0are fi.e! losses res"lt of hysteresis an! e!!y c"rrent losses in the magnetic circ"it %core* of the transformer Hysteresis oss; 'h $ S h f m/, $ S h 2/, + f -, m $ S % E+f * 'h f # 'h $ S h f if m P m is constant @ @ @ E!!y C"rrent oss; ' e $ S ef m $ S e2 # 'e f @# 'e $ S e f @ if m P m is constant Note4 'h P 'e can 9e !etermine 9y o)en circ"it test @ Co))er losses – vary 8ith the loa! an! res"lt of heating of transformer 8in!ings 'c" $ I'@r ' I7@r 7 9ase! from e.tract e:"ivalent circ"it 'c" $ I )@R e) $ Is@R es 9ase! from a))ro.imate e:"ivalent circ"it Note 4 'c" can 9e !etermine! 9y short circ"it test Test on Transformers4 a O)en circ"it test 9 7hort circ"it test Con!itions of Ma.im"m Efficiency4 $ 5'OUT + % 'OUT 'O77E7*6 . /-- $ 5%2Icos * + %2Icos i@R e 'S *6 . /-- to have ma. efficiency4 ta?e !+!I $ 5%2Icos I@R e 'S *%2cos* 0 2Icos%2cos @IRe*6 + %2Icos I@R e 'S *@ !ivi!ing 9y 2cos P sim)lify# I@R e $ 'S 2aria9le loss $ Constant loss All0Day Efficiency4 It is the ratio of the energy !elivere! 8ith in @F hr )erio! to the energy in)"t in the same )erio! of time Gor !istri9"tion transformers 8hose )rimary energie! for @F hr a !ay; th"s the core loss of this transformer m"st 9e !esigne! to 9e lo8 as )ossi9le It is al8ays less than the commercial efficiency all0!ay $ 5%ENER3YOUT'UT+!ay* + %ENER3YOUT'UT+!ay ENER3Y O77+DAY* . /-- at ma. all !ay efficiency4 Energy Co))er oss $ Energy Core oss Transformer 'olarity Con!itions4 / hen the voltmeter rea!ing is greater than the in)"t test voltage the )olarity is A!!itive; 2 $ 2'/ %2'/+a* @ hen the voltmeter rea!ing is less than in)"t test voltage the )olarity is 7"9tractive; 2 $ 2'/ %2'/+a* Note4 y the stan!ar!s all /; @-- ?2A; 1,,- 2olts or less are ADDITI2E A"to Transformer# The a"to transformer is one having a single contin"o"s 8in!ing; )art of 8hich is common to 9oth )rimary an! secon!ary circ"its It can 9e "se! for either ste)0") or ste)0 !o8n a))lication 8ith a relatively small change in voltage 9et8een the in)"t an! o"t)"t voltages; an! sho"l! not "se! 8hen there is a large change in voltage 9eca"se the circ"its are connecte! electrically
'arallel O)eration of Transformers4 Im)ortant con!itions that m"st 9e f"lfillment if t8o or more transformers are to 9e o)erate! s"ccessf"lly in )arallel to !eliver a common loa! / 2oltage ratings of 9oth )rimaries an! secon!aries m"st 9e i!entical; or the transformation are the same %other8ise; c"rrent 8ill circ"late thro"gh the transformer 8in!ings 8hich 8ill contri9"te to the losses of the transformer* @ The transformer m"st 9e )ro)erly connecte! 8ith regar!s to )olarity %other8ise; a large c"rrent 8ill circ"late thro"gh the transformer 8in!ing 8hich co"l! !amage the 8in!ings* a The e:"ivalent im)e!ances sho"l! 9e inversely )ro)ortional to the res)ective ?2A ratings %other8ise; the transformer 8ill not share the loa! in )ro)ortional to their ratings* &e a /+7 # & e/ + &e@ $ 7@ + 7/ 9 The ratio of the e:"ivalent resistance to the e:"ivalent reactance of the all transformer sho"l! 9e the same %other8ise; each transformer 8ill not ta?es its correct fraction of the loa!* Re/+Qe/ $ Re@+Qe@ Also the con!ition for the t8o transformers connecte! in )arallel to o)erate at the same )f Is/ $ 5%a@ – a/*2s/ a@&es@Ioa!6 + %a/&es/ a@&es@* Is@ $ 5%a/&es/Ioa! – %a@ – a/* + %a/&es/ a@&es@* Gor the circ"lating c"rrent %set Ioa! $ -* Ic/ $ %a@ – a/*2s/ + %a/&es/ a@&es@* or Ic@ $ 0%a@ – a/*2s/ + a/&es/ a@&es@ Most Common Transformer Connections4 / Y – Y 8ith connecte! ne"trals has the a!vantage the 8in!ings are s"9Becte! to the line voltage !ivi!e 9y this connection 8itho"t ne"trals are rarely "se! since high "ne:"al voltage may res"lt from an "n9alance loa! @ 0 connection s"ita9le for mo!erate voltage; large c"rrent o)eration 0 Y connection 'rimarily "se! to ste)0") the voltage it is also "se! in ste) – !o8n a))lications 8here a conventional !istri9"tion voltage is re!"ce! to s"))ly t8o voltages for lighting an! )o8er loa!s F Y 0 connection "se for ste))ing !o8n voltages J T %scott* connection "se! to convert to @ or vice – versa , 2 – 2 %o)en !elta* connection a* "se! 8hen the loa! is still small so that to "se of 0 9an? is "n8arrante! 9* Use! if one transformer of the 0 9an? fails K A"totransformer – also calle! as a =com)ensator> "se! for re!"ce! voltage starting; also "se! for ste))ing !o8n or ") the voltages
Instr"ment Transformers4
