DC Machines Presentation

7/23/2019 DC Machines Presentation

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DC MACHINES

Engr. Jonathan C. PacaldoREE



References:

1.Electrical Machines, By: Siskind2.Electricity 4, By: Jef el!ik".#C C$rrent Machinery, By:loefer%erchner%Brenne&an

4.Electric Machines and 'rans(or&er, By)nderson%Macneill

Grading System:

*$i++es 2-a/oratory%Co$rse0ork 2-Class Particiation 1-

Midter& Ea& 23-



Introduction

)ltho$gh a (ar greater ercentage o( the electrical&achines in ser5ice are a.c. &achines, the d.c.&achines are o( considera/le ind$strial i&ortance.

'he principal advantage o( the d.c. &achine,

artic$larly the d.c. &otor, is that it provides ane control of speed. S$ch an ad5antage is notclai&ed /y any a.c. &otor. 6o0e5er, d.c. generatorsare not as co&&on as they $sed to /e, /eca$sedirect c$rrent, 0hen re7$ired, is &ainly o/tained

(ro& an a.c. s$ly /y the $se o( recti8ers.9e5ertheless, an $nderstanding o( d.c. generator isi&ortant /eca$se it reresents a logicalintrod$ction to the /eha5io$r o( d.c. &otors. ndeed

&any d.c. &otors in ind$stry act$ally oerate as d.c.generators (or a /rie( eriod. n this chater, 0e



•Most o( the electrical &achine in ser5ice are

)C tye.•#C &achine are o( considera/le ind$striali&ortance.•#C &achine &ainly $sed as #C &otors and

the #C generators are rarely $sed.•#C &otors ro5ides a 8ne control o( the seed0hich

can not /e attained /y )C &otors.•#C &otors can de5eloed rated tor7$e at allseeds

(ro& standstill to rated seed.

•#e5eloed tor7$e at standstill is &any ti&esreater



DC Mac!ines Applications

• 'he d.c. &achine can oerate as either a&otor or a generator, at resent its $se asa generator is li&ited /eca$se o( the

0idesread $se o( ac o0er.•arge d.c. &otors are $sed in &achine tools,rinting resses, (ans, $&s, cranes, aer&ill, traction, tetile &ills and so (orth.

•S&all d.c. &achines ;(ractional horseo0errating< are $sed ri&arily as controlde5ice=s$ch as tachogenerators (or seedsensing and ser5o&otors (or osition andtracking.



Advantages and Disadvantages ofDC Motors



Magnetism

Magnetism is a class o( hysicalheno&enon that incl$des (orces eerted/y &agnets on other &agnets. t has itsorigin in electric c$rrents and the($nda&ental &agnetic &o&ents o(ele&entary articles. 'hese gi5e rise toa &agnetic 8eld that acts on other c$rrents

and &o&ents. )ll &aterials are in?$enced toso&e etent /y a &agnetic 8eld. 'hestrongest efect is on er&anent &agnets,0hich ha5e ersistent &agnetic &o&ents

ca$sed /y (erro&agnetis&.



Magnetic "ield



Magnetic"ield



Ohm's law states that the current through a conductor

between two points is directly proportional to the potential

difference across the two points. Introducing the constant

of proportionality, the resistance, one arrives at the usual

mathematical equation that describes this relationship:

where I is the current through the conductor in units

of amperes, V is the potential difference

measuredacross

the conductor in units of volts, andR

isthe resistance of the conductor in units of ohms. More

specifically, Ohm's law states that the R in this relation is

constant, independent of the current.



Series and Parallel Circuits

With simple series circuits, all components are connected

end-to-end to form only one path for electrons to flowthrough the circuit:



Series Circuits:

•Voltage drops add to equal total voltage•!ll components share the same "equal# current•$esistances add to equal total resistance



With simple parallel circuits, all components areconnected %etween the same two sets of electricallycommon points, creating multiple paths for electrons

to flow from one end of the %attery to the other:



Parallel Circuits:

•!ll components share the same "equal# voltage

•&ranch currents add to equal total current•$esistances diminish to equal total resistance



Generator #rinciple:

)n electric generator is a &achine that con5erts&echanical energy into electrical energy. )nelectric generator is /ased on the rincile that0hene5er ?$ is c$t /y a cond$ctor, an e.&.(. is

ind$ced 0hich 0ill ca$se a c$rrent to ?o0 i( thecond$ctor circ$it is closed. 'he direction o(ind$ced e.&.(. ;and hence c$rrent< is gi5en /yle&ing@s right hand r$le. 'here(ore, theessential co&onents o( a generator are:

;a< a &agnetic 8eld;/< cond$ctor or a gro$ o( cond$ctors;c< &otion o( cond$ctor 0.r.t. &agnetic 8eld.



Magnetic"ield

Magnetic #oles

Rotation



RIGH$ HAND R%&E



Generated'oltage



9

Magnetic"lu(

Conductor



Construction of a DC Generator



"IE&D S)S$EM

'he ($nction o( the 8eld syste& is torod$ce $ni(or& &agnetic 8eld 0ithin0hich the ar&at$re rotates. t consists o( an$&/er o( salient oles ;o( co$rse, e5en

n$&/er< /olted to the inside o( circ$lar(ra&e ;generally called yoke<. 'he yoke is$s$ally &ade o( solid cast steel 0hereasthe ole ieces are co&osed o( stackedla&inations. ield coils are &o$nted onthe oles and carry the d.c. ecitingc$rrent. 'he 8eld coils are connected in

s$ch a 0ay that ad!acent oles ha5e



"rame



Armature Core *Rotor+



Armature Core

'he ar&at$re core is keyed to the &achine

sha(t and rotates /et0een the 8eld oles. tconsists o( slotted so(t=iron la&inations;a/o$t .4 to .A && thick< that are stackedto (or& a cylindrical core. 'he la&inations areindi5id$ally coated 0ith a thin ins$lating 8l&so that they do not co&e in electrical contact0ith each other. 'he $rose o( la&inating

the core is to red$ce the eddy c$rrent loss. 'he la&inations are slotted to acco&&odateand ro5ide &echanical sec$rity to thear&at$re 0inding and to gi5e shorter air ga

(or the ?$ to cross /et0een the ole (ace



Armature ,indings

'he slots o( the ar&at$re core hold ins$lated

cond$ctors that are connected in a s$ita/le&anner. 'his is kno0n as ar&at$re 0inding.

'his is the 0inding in 0hich 0orking e.&.(.is ind$ced. 'he ar&at$re cond$ctors are

connected in series=arallelD the cond$ctors/eing connected in series so as to increasethe 5oltage and in arallel aths so as to

increase the c$rrent. 'he ar&at$re 0indingo( a d.c. &achine is a closed=circ$it 0indingDthe cond$ctors /eing connected in asy&&etrical &anner (or&ing a closed loo or

series o( closed loos.



Commutator



Commutator

) co&&$tator is a &echanical recti8er0hich con5erts the alternating 5oltagegenerated in the ar&at$re 0inding intodirect 5oltage across the /r$shes. 'he

co&&$tator is &ade o( coerseg&ents ins$lated (ro& each other /y&ica sheets and &o$nted on the sha(t

o( the &achine. 'he ar&at$recond$ctors are soldered to theco&&$tator seg&ents in a s$ita/le&anner to gi5e rise to the ar&at$re



-rus!es

'he $rose o( /r$shes is to ens$reelectrical connections /et0een the rotatingco&&$tator and stationary eternal load

circ$it. 'he /r$shes are &ade o( car/on andrest on the co&&$tator. 'he /r$sh ress$reis ad!$sted /y &eans o( ad!$sta/le srings.( the /r$sh ress$re is 5ery large, the

(riction rod$ces heating o( the co&&$tatorand the /r$shes. n the other hand, i( it istoo 0eak, the i&er(ect contact 0ith theco&&$tator &ay rod$ce sarking.



C t ti i D C G t



Commutation in a D.C Generator

ommutation is the positioning of the !generator brushes so that the commutator

segments change brushes at the same time

the armature current changes direction. Moresimply stated, commutation is the mechanical

conversion from " to ! at the brushes of a

! machine.

Commutator Action

http://2.bp.blogspot.com/_v2T5FtcWTMk/RhOGmMskosI/AAAAAAAABAk/xZsk70Osn2M/s1600-h/commu2.GIF



Commutator Action

#he commutator converts the " voltage generated

in the rotating loop into a ! voltage. It also serves

as a means of connecting the brushes to the rotating

loop. #he purpose of the brushes is to connect thegenerated voltage to an e$ternal circuit. In order to

do this, each brush must ma%e contact with one of

the ends of the loop. &ince the loop or armature

rotates, a direct connection is impractical. Instead,the brushes are connected to the ends of the loop

through the commutator.

DC Machines Presentation

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