beee 2 marks

7/24/2019 Beee 2 Marks

1/25

BASIC ELECTRICAL AND ELECTRONICSENGINEERING

2 MARKS1. What is meant by cha!e"Charge is an electrical property of the atomic particles which matterconsists. The charge of an electron is so small. Charge in motionrepresentscurrent. The unit of charge is coulomb.2. What is meant by C#ent"The ow of free electrons in a conductor is called current. Unit is ampere(A).I = !t$. What is meant by %&'ta!e"The poterntial di"erence between two points is called as #oltage. Unit is$olts ($).$=%! & %=wor' done in oules = charge in coulombs(. State Ohm)s La*.The potential di"erence across any two ends of a conductor is directlyproportional to the current owing between the two ends pro#ided thetemperature of the conductor remains constant.+. State Kich&,)s %&'ta!e La**$+ states that the algebraic sum of #oltages in a closed path is ,ero.-. tate Kich&,)s c#ent La*.

*C+ states that the algebraic sum of currents in a node is ,ero./. Gi-e n&tes &n N&a' Ana'ysis.

*C+ is used.

0o1 of e2uations = n34& n=no1 of nodes/. Gi-e n&tes &n Mesh Ana'ysis.

*$+ is used

5ere mesh currents are found.0. Gi-e sh&t n&tes &n esist&.It is a property of a substance6 which opposes the ow of electrons. It isdenoted by 7 and its unit is 8hm (_)

1. Distin!#ish bet*een a Banch an a n&e & a cic#it.A pair of networ' which connects the #arious points of the networ' iscalled branchA point at which two or more elements are oined together is called node.11. Distin!#ish bet*een a mesh an a '&&3 & a cic#it.A mesh is a loop that does not contain other loops. All meshes are loop&but all loops are not meshes.A loop is any closed path of branches12. Wite &*n the &m#'a & a sta c&nnecte net*&4 isc&n-ete int& ae'ta net*&4"

7A=( 74 79)!( 74 :79: 76)7;=( 74 76)!( 74 :79: 76)


2/25

7C=( 79 76)!( 74 :79: 76)1$. Wite &*n the &m#'a & a e'ta c&nnecte net*&4 isc&n-ete int& asta net*&4"74=( 7A7;:7;7C:7C7A)!7C

79=( 7A7;:7;7C:7C7A)!7;76=( 7A7;:7;7C:7C7A)!7A1(. De5ne 'ine c#ents an 3hase c#ents"

The currents owing in the lines are called as line currents

The currents owing through phase are called phase currents1+. De5ne 'ine -&'ta!e an 3hase -&'ta!e"The #oltage across one phase and neutral is called line #oltage the#oltage between two lines is called phase #oltage16. Gi-e the 3hase -a'#e 7 Line -a'#e & a sta c&nnecte system.$+= 6$ph

18. Gi-e the 3hase -a'#e an 'ine -a'#e & a e'ta c&nnectesystem.I+= 6Iph1/. What is the 3&*e e9#ati&n & a sta c&nnecte system"


3/25

The two maor types of control system are open loop and closed loop2/. .De5ne &3en '&&3 c&nt&' system.The control system in which the output 2uantity has no e"ect upon theinput 2uantity are called open loop control system. This means that theoutput is

not feedbac' to the input for correction.20. .De5ne c'&se '&&3 c&nt&' system.The control system in which the output has an e"ect upon the input2uantity so as to maintain the desired output #alue are called closed loopcontrolsystem$. Menti&n the e&s in M&-in! i&n inst#ments.

5ysteresis error

Temperature error

tray magnetic eld error

>re2uency error ?ddy current error

$1. Menti&n any t*& 3eca#ti&ns t& be ta4en *hi'e #sin! anAmmete.

It should ne#er be connected across any source.

The polarity must be obser#ed correctly.

>irst use the highest range and then decrease the #oltage range until

the su@cient deection is obtained.69. Gi-e s&me a33'icati&ns & DC m&t&.Sh#nt ; dri#ing constant speed& lathes& centrifugal pumps& machine tools&

blowers and fans& reciprocating pumpsSeies ; electric locomoti#es& rapid transit systems& trolley cars& cranesandhoists& con#eyorsC&m3n ; ele#ators& air compressors& rolling mills& hea#y planners$$. De5ne s'i3. = 0s 0r0s%here& 0s = synchronous speed in rpm.0r = rotor speed in rpm = lip

$(. De5ne synch&ns s3ee.It is gi#en by 0s = 49Bf ! p rpm.%here 0s = synchronous speed& p = no. of stator poles& f = supplyfre2uency in5,$+. Why a sin!'e 3hase in#cti&n m&t& &es n&t se' stat"%hen a single phase supply is fed to the single phase induction motor. Itsstator winding produces a u which only alternates along one space ais.It isnot a synchronously re#ol#ing eld& as in the case of a 9 or 6phase stator

winding&fed from 9 or 6 phase supply.


4/25

$6. Is In#cti&n m&t& #ns *ith synch&ns s3ee & n&t.Induction motor ne#er runs with synchronous speed. It will stop if it triesto achie#e synchronous speed.$8. De5ne orm factor= 7D #alue

A#erage $alueCrest(pea') factor=Daimum $alue7D #alue$/. . Which ty3e & inst#ment is ca''e as #ni-esa' inst#ment"The mo#ing iron instrument are 'nown as uni#ersal instruments& becausethese instruments can be used for AC and EC.$0. What ae the a33'icati&ns & MI inst#ments"i) Used as multirange ammeters and #oltmeters.ii) Used as in epensi#e indicators such as charging and dischargingcurrent indicators in automobiles.iii)?tensi#ely used in industries for measurement of AC #oltage andcurrent where errors of the order of FG to 4BG are accepetable.(. What is meant by ey c#ent am3in!"%hen the conductor mo#es in a magnetic eld an emf is induced in it andif a closed path is pro#ided &a current ows 'nown as eddy current. Thiscurrentintersect with the magnetic eld to produce an electromagnetic tor2ue &whichopposes the deecting tor2ue.(1. .=&* is e'ectica' 3&*e meas#e"i) Using $oltmeter3ammeter method for EC circuits.

ii)Using %att meters for AC circuits.(2. .What & y mean by c&m3ensati&n c&i' in a *attmete";y connecting a compensating coil in series with a pHressure coil &Theerror caused by the pressure coil owing in the current coil can beneutrali,ed.($. What ae the thee ty3es & 3&*e #se in a a.c cic#it"

i) 7eal power or acti#e power


5/25

The power consumed by a pure reactance (+ or c ) in a a.c circuit is

called reacti#e power. The unit is $A7. =?Isin.(8. What is the basic 3inci3'e & a c !eneat&";asic principle of a dc generator is >aradayJs law of electromagneticinduction.That is whene#er a conductor is mo#ed in amagnetic eld

dynamicallyinduced emf is produced in that conductor.(/. .What is the 3#3&se & inte3&'es in m&en .c machine"In modern d.c machines commutating poles or interpoles are pro#ided toimpro#e commutation.(0. What is the #se & c&mm#tat& an b#sh in a .c machine"The commutator con#erts the alternating emf into unidirectional or directemf.The brushes are mainly used to collect current from the commutator.+. What is a .c seies m&t&"

In a d.c series motor&the eld winding is connected in series with thearmature.The eld winding should ha#e less number of turns of thic' wire.+1. Why a seies m&t& cann&t be state *itht any '&a"eries motor cannot be started without any load because under no loadcondition the starting tor2ue is less and motor rotates at dangerous speedand maybe damaged.+2. What is meant by tans&me"The transformeris a static piece of apparatus by means of which electricalenergy is transformed from one circuit to another with desired change in#oltage

and current & without any change in the fre2uency.It wor's on the principleofmutual induction.+$. What ae the i,eent ty3es & sin!'e 3hase m&t&"i)ingle phase induction motorii)ingle phase synchronous motor.iii)ingle phase series motor+(. What ae the t*& ty3es & &t&s & an in#cti&n m&t&"i) 2uirrel cage rotorii)lip ring or wound rotor

6 MARKS1. A $ ( 3&'e + h> in#cti&n m&t& #ns at 1(6 .3.m. 5n its ?& s'i3.S&'#ti&n0 s = 49Bf!p= 49BKFB!L= 4FBBr.p.m.7unning speed of motor

n= 4L-Br.p.m.lip =( 0 s0)! 0 sK4BB


6/25

=(4FBB34L-B) 4BB ! 4FBB= 9.--/G2. E@3'ain the *&4in! 3inci3'e & Tans&me.A Transformer is a de#ice that transfers electrical energy from one circuitto

another by electromagnetic induction (transformer action). The electricalenergy isalways transferred without a change in fre2uency& but may in#ol#echanges inmagnitudes of #oltage and current. ;ecause a transformer wor's on theprinciple ofelectromagnetic induction& it must be used with an input source #oltagethat #aries inamplitude. There are many types of power that t this descriptionM forease of eplanationand understanding& transformer action will be eplained using an ac#oltage as the inputsource.The amount of power used by the load of an electrical circuit is e2ual tothecurrent in the load times the #oltage across the load& or < = ?I. If& foreample& the load inan electrical circuit re2uires an input of 9 amperes at 4B #olts (9B watts)and the source iscapable of deli#ering only 4 ampere at 9B #olts& the circuit could notnormally be used

with this particular source. 5owe#er& if a transformer is connectedbetween the sourceand the load& the #oltage can be decreased (stepped down) to 4B #oltsand the currentincreased (stepped up) to 9 amperes. 0otice in the abo#e case that thepower remains thesame. That is& 9B #olts times 4 ampere e2uals the same power as 4B #oltstimes 9amperes.A Tans&me c&nsists & the &''&*in! 3ats

A 3imay c&i' & *inin!.A sec&nay c&i' & *inin!.A c&e that s#33&ts the c&i's & *inin!s.

The primary winding is connected to a FB hert, ac #oltage source. Themagneticeld (u) builds up (epands) and collapses (contracts) about theprimary winding. Theepanding and contracting magnetic eld around the primary windingcuts the secondarywinding and induces an alternating #oltage into the winding. This #oltagecauses

alternating current to ow through the load. The #oltage may be steppedup or down


7/25

depending on the design of the primary and secondary windings.$. Ca'c#'ate the amnt & esistance R in a cic#it !i-en -a'#es& -&'ta!e E anc#ent I;the amount of resistance (7) o"ered by the lamp

(. ca'c#'ate the amnt & -&'ta!e s#33'ie by a battey !i-en-a'#es &c#ent I an esistance R;the amount of #oltage pro#ided by the battery+. Ca'c#'ate the e'ectic 3&*e in the !i-en cic#it an isc#ss thee,ect &inceasin! the battey -&'ta!e.The formula for determining the power in an electric circuit1 by multiplyingthe#oltage in N#oltsN by the current in NampsN we arri#e at an answer inNwatts.N +etOs applythis to the gi#en circuit.In the abo#e circuit& we 'now we ha#e a battery #oltage of 4P #olts and alamp resistance of 6_. Using 8hmOs +aw to determine current& we get10ow that we 'now the current& we can ta'e that #alue and multiply it bythe #oltage to determine power16. What is meant by DE


8/25

4BB 74374R939LBB = B74R934BB 74 : 9LBB = B(743-B)(743LB) = BThere >ore 74 = -BM 74 = LB%hen 74 = -B M 79 = 4BB -B = LB

%hen 74 = LB M 79 = 4BB 3 LB = -B0. rom A 3Q ;& %e ha#e a potential drop of I74.>rom E 3Q A& %e ha#e a potential drop of $.

um of potential drops = I74:I79:I76


9/25

are connected to a EC power source.The current from the EC powersource ows fromthe positi#e lead& through the brush labeled A4 through one commutatorsection& throughthe armature coil& through the other commutator section& through the

brush labeled A9and bac' to the negati#e lead.This current will generate lines of uaround the armatureand a"ect the lines of u in the air gap. 8n the side of thecoil where thelines of uoppose each other& the magnetic eld will be made wea'er. 8n the side ofthe coil wherethe lines of u are riot opposing each other& the magnetic eld is madestronger.;ecause of the strong eld on one side of the coil and the wea' eld onthe other side&the coil will be pushed into the wea'er eld and& because the armaturecoil is free torotate& it will rotate.The tor2ue a#ailable at the motor shaft (turning e"ort) is determined bythemagnetic force (u) acting on the armature coil and the distance fromthe renter ofrotation that force is.The u is determined by the current owingthrough the armaturecoil and strength of the eld magnets.

49. E@3'ain the *&4in! 3inci3'e & thee 3hase in#cti&n m&t&.In three phase induction motor& the magnetic eld generated by the statorrotatesin the ac case. Three electrical phases are introduced through terminals&each phaseenergi,ing an indi#idual eld pole. %hen each phase reaches itsmaimum current& themagnetic eld at that pole reaches a maimum #alue. As the currentdecreases& so doesthe magnetic eld. ince each phase reaches its maimum at a di"erenttime within a

cycle of the current& that eld pole whose magnetic eld is largest isconstantly changingbetween the three poles& with the e"ect that the magnetic eld seen bythe rotor isrotating. The speed of rotation of the magnetic eld& 'nown as thesynchronous speed&depends on the fre2uency of the power supply and the number of polesproduced by thestator winding. >or a standard -B 5, supply& as used in the United tates&the maimum

synchronous speed is 6&-BB rpm.


10/25

In the three phase induction motor& the windings on the rotor are notconnected toa power supply& but are essentially short circuits. The most common typeof rotorwinding& the s2uirrel cage winding& bears a strong resemblance to the

running wheel usedin cages for pet gerbils. %hen the motor is initially switched on and therotor isstationary& the rotor conductors eperience a changing magnetic eldsweeping by at thesynchronous speed.>rom >aradayOs law& this situation results in the induction of currents roundtherotor windingsM the magnitude of this current depends on the impedanceof the rotorwindings. ince the conditions for motor action are now fullled& that is&current carryingconductors are found in a magnetic eld& the rotor eperiences a tor2ueand starts to turn.The rotor can ne#er rotate at the synchronous speed because there wouldbe no relati#emotion between the magnetic eld and the rotor windings and no currentcould beinduced. The induction motor has a high starting tor2ue.1$. E@3'ain the *&4in! 3inci3'e & sin!'e 3hase in#cti&n m&t&.ingle phase induction motor has only one stator winding (main winding)

andoperates with a single3phase power supply. In all single3phase inductionmotors& the rotoris the s2uirrel cage type. The single3phase induction motor is not self3starting. %hen themotor is connected to a single3phase power supply& the main windingcarries analternating current. This current produces a pulsating magnetic eld. Eueto induction&the rotor is energi,ed. As the main magnetic eld is pulsating& the tor2uenecessary for

the motor rotation is not generated. This will cause the rotor to #ibrate&but not to rotate.5ence& the single phase induction motor is re2uired to ha#e a startingmechanism that canpro#ide the starting 'ic' for the motor to rotate.The starting mechanism of the single3phase induction motor is mainly anadditional stator winding (start! auiliary winding) as shown in >igure. Thestart windingcan ha#e a series capacitor and!or a centrifugal switch. %hen the supply#oltage is

applied& current in the main winding lags the supply #oltage due to themain winding


11/25

impedance. At the same time& current in the start winding leads!lags thesupply #oltagedepending on the starting mechanism impedance. Interaction betweenmagnetic eldsgenerated by the main winding and the starting mechanism generates a

resultant magneticeld rotating in one direction. The motor starts rotating in the direction ofthe resultantmagnetic eld. 8nce the motor reaches about /FG of its rated speed& acentrifugal switchdisconnects the start winding. >rom this point on& the single3phase motorcan maintainsu@cient tor2ue to operate on its own.1(. E@3'ain the *&4in! 3inci3'e & sin!'e 3hase Ene!y Mete.An electric meter or energy meter is a de#ice that measures the amountofelectrical energy supplied to or produced by a residence& business ormachine.The most common type is a 'ilowatt hour meter. %hen used in electricityretailing& the utilities record the #alues measured by these meters togenerate an in#oicefor the electricity. They may also record other #ariables including the timewhen theelectricity was used.Dodern electricity meters operate by continuously measuring theinstantaneous

#oltage (#olts) and current (amperes) and nding the product of these togi#einstantaneous electrical power (watts) which is then integrated againsttime to gi#eenergy used (oules& 'ilowatt3hours etc). The meters fall into two basiccategories&electromechanical and electronic.The energy meter operates by counting the re#olutions of an aluminiumdiscwhich is made to rotate at a speed proportional to the power. The numberof re#olutions

is thus proportional to the energy usage. It consumes a small amount ofpower& typicallyaround 9 watts.The metallic disc is acted upon by two coils. 8ne coil is connected in sucha waythat it produces a magnetic u in proportion to the #oltage and the otherproduces amagnetic u in proportion to the current. The eld of the #oltage coil isdelayed by Bdegrees using a lag coil. This produces eddy currents in the disc and the

e"ect is such that


12/25

a force is eerted on the disc in proportion to the product of theinstantaneous current and#oltage. A permanent magnet eerts an opposing force proportional to thespeed ofrotation of the disc 3 this act as a bra'e which causes the disc to stop

spinning whenpower stops being drawn rather than allowing it to spin faster and faster.This causes thedisc to rotate at a speed proportional to the power being used.The type of meter described abo#e is used on a single3phase AC supply.Ei"erentphase congurations use additional #oltage and current coils.The aluminium disc is supported by a spindle which has a worm gearwhichdri#es the register. The register is a series of dials which record theamount of energyused. The dials may be of the cyclometer type& an odometer3li'e displaythat is easy toread where for each dial a single digit is shown through a window in theface of themeter& or of the pointer type where a pointer indicates each digit. Itshould be noted thatwith the dial pointer type& adacent pointers generally rotate in oppositedirections due tothe gearing mechanism.

1 MARKS1. DETERMINE T=E EI%ALENT RESISTANCE BETWEENTERMINALS A 7 B8+UTI80FB 49.F A7?


13/25

incorrect. In actuality& I9 is owing in a counter3cloc'wise direction at a#alue of(positi#e) 4 amp1$. E@3'ain the *&4in! & a m&-in! i&n ty3e inst#ments.These instruments are widely used in laboratories and switch board at

commercial fre2uencies because these are cheaper in cost& robust inconstruction andcan be manufactured with re2uired accuracy.These are generally of two types134. The attraction type.9. The repulsion type.The attraction type instrument operate on the principle of attraction of asingle piece ofsoft iron into a magnetic eld and repulsion type instrument operate onthe principle ofrepulsion of two adacent iron pieces magnied by the same magneticeld. 7epulsiontype instrument are more sensiti#e than attraction type instrument as inrepulsion typeinstrument large separating tor2ue is de#eloped by ha#ing two ironelement positionalclass together inside the eld coil where the magneti,ing e"ect ismaimum.In both type of these instruments& the current under measurement ispassed through a coilof wire. This current carrying coil set up the necessary eld depending on

the magnitudeof the current to be measured. The coil may be of a few turns of #eryhea#y conductor orof many turns of ne wire. The instrument to be used as an ammeter ispro#ided with acoil of few turns of thic' wire in order to ha#e low resistance and carrylarge current andthat to be used as a #oltameter is pro#ided with a coil of large number ofturns of wire inorder to ha#e high resistance and draw as small current as possible.(. Dei-e the e@3essi&n & t&9#e 3ce in m&-in! i&n

inst#ment.+et + be the self inductance corresponding to a total angular deection of2 radians and change in inductance be d+ correponding to small change indeection angel d2 due to small change in current.The change in energy of magnetic eld&dw = Td dince change in energy d? = wor'done& dwTd d = S I9d+Td = S I9d+!dwhere I is in amperes& + is in 5enry and is in 7adians.

Thus toru2e is proportional to the s2uare of the instrument current and tothe rate


14/25

of change of inductance with deection.+. An ene!y mete e-&'-es 1 e-&'#ti&ns & isc & #nit &ene!y.


15/25

system without controlling system the irrespecti#e magnitude of currentandmoreo#er& once deected it would not return to its ,ero position onremo#ingthe current.

In attraction type instrument it is produced by spring control and in lemingOs left hand rule.It is the current in amperes owing through the coil of turns 0 and length lmeters ; is u density in test as in air gap13

Then& deecting force > = ;il0 newtons.If r is the distance in meters in between the centers of the coil and force >.Then deecting tor2ue Td = > r = ;il0r 0m>rom the abo#e epression it is ob#ious that if u density ; in the air gapisconstant& thendeecting tor2ue Td = i & Tc= Tdo& = iAnd since 2 is directly proportional to current& the scale of the basic dc


16/25

*ith the he'3 & ia!am"Ans*e.This type of instrument is similar in design and principle to thedynanometertype ammeter and #oltameter.

%87*I0 A0E C80T7UCTI8013 %hen the instrument of this type isused as wattmeter& the ed coil which is di#ided into two e2ual portionsinorder to pro#ide them uniform eld & is employed as current coil andmo#ingcoil is used as pressure coil. The ed coil which is di#ided into two e2ualportion in order to pro#ide them uniform eld& is employed as current coilandthe mo#ing coil is used as pressure coil& i.e the ed coil carries thecurrentproportional to the #oltage across the circuit. A high non inducti#eresistanceis connected in series with the mo#ing coil in order to limit current. Themagnetic eld of the ed and mo#ing coil react on one another causingthemo#ing coil to turn about itOs ais. The mo#ement is controlled by hairspringswhich also leads the current into and out of the mo#ing element. Eampingispro#ided by light aluminium mo#ing in an air dash pot. The pointer is edto

the mo#ing coil spindle and mo#es o#er a suitable caliberated scale.T5?87V13 +et us be the supply #oltage& i the load current and 7 the loadresistance of the mo#ing coil circuit.Current through ed coil& if = iCurrent through mo#ing coil& im = $!7deecting tor2ue& Td W if im W $!7>or a EC circuit the deecting tor2ue is thus proportional to the power andforany circuit with uctuating tor2ue. The instantaneous to theinstantaneouspower.

0. C&m3ae meits an emeits & m&-in! i&n ty3e inst#mentsanynam&mete ty3e inst#ments. Which &ne is s#3ei& *hy"Ans*e.4. T87U? 5?I5T 7ATI813 Eynamometer type instruments ha#e e2ualsmalltor2ue height ratio.9. >7ICTI80 ?778713 Eynamometer type instruments ha#e considerablefriction error.6. >7ICTI80 +813 8wing to hea#y mo#ing system& dynamometer type

instruments ha#e more friction losses.L. C8T A0E ?0ITI$ITV T8 8$?7+8AE13 As a result of measures to


17/25

reduce the frictional error& the dynamometer type instruments are moresensiti#eto o#erloads and mechanical impactsis in comparison to mo#ing iron typeinstruments.F. ?0TI$ITV13 The sensti#ity of dynamometer instrument is typically #ery

poor due to poor deecting tor2ue.-. ?CT 8> T7AV DA0?TIC >I?+E13 There is no e"ect of straymagnetic eld on mo#ing iron type while dynamometer type are mostsensiti#etowards it.P. 5VT?7II A0E ?EEV CU77?0T ?778713 Eynamometer typeinstruments are free from these erors while mo#ing iron ha#e these errors.. ?>>?CT 8> %A$? >87D13 Eynamometer type instruments are #eryusefulfor accurate measurement of runs #oltage while fre2uency change seriouse rrorsin AC measurement in mo#ing iron type instruments.4B. CA+I;7ATI8013 Eynamometer type instruments ha#e same calibrationforAC and EC measurements while mo#ing iron type ha#e a di"erencebetween ACand EC calibration.1. Why sh#nt is #s#a''y #se -&'tmete an ammete" A m&-in!c&i'

inst#ment has a esistance & + _ an !i-es #'' eecti&n &1m-.Sh&* h&* the inst#ment may be #se t& meas#e;1. -&'ta!e #3t& +%2. c#ent #3t& 1AAns*e.hunt is usually used in #oltmeter and ammeter to etend the range of#oltmeter and ammeters.7m = F_$m = 4BBm#Im = $m!7m = 4BBm#!F_ = 9BmA

1.


18/25

&btaine"Ans*e.The earliest and simplest form of attraction mo#ing ironinstrumentsuses a solenoid and mo#ing o#al shaped soft iron pinoted eccentrically. Tothis iron a pointer is attached so that it may deect along with the mo#ing

irono#er a graduate scale. The iron is made of sheet metal specially shaped togi#ea scale as nearby uniform as possible. The mo#ing iron is drawn into eldofsolenoid when current ows through it. The mo#ement of the iron alwaysfrom wea'er magnetic eld outside the coil into the stronger eld insidethecoil regardless the direction of ow of current. %hen the current to bemeasured is passed through the solenoid& a magnetic eld is set up insidethesolenoid& which in turn magnetises the iron. Thus the iron is attached intothecoil causing the spindle and the pointer to rotate.o much instruments normally ha#e spring control and pneumaticdampingforces.12. $ ( 3&'e in#cti&n m&t& is s#33'ie &m $ +=> ac s#33'y.


19/25

types of temperature controlM open loop and closed loop control. 8penloop is themost basic form and applies continuous heating!cooling with no regard fortheactual temperature output. It is analogous to the internal heating system

in a car.8n a cold day& you may need to turn the heat on to full to warm the car to/FY.5owe#er& during warmer weather& the same setting would lea#e the insideof thecar much warmer than the desired /FY.Open loop control block diagramClosed loop control is far more sophisticated than open loop. In a closedloop application& the output temperature is constantly measured andadusted tomaintain a constant output at the desired temperature. Closed loopcontrol isalways conscious of the output signal and will feed this bac' into thecontrolprocess. Closed loop control is analogous to a car with internal climatecontrol. Ifyou set the car temperature to /FY& the climate control will automaticallyadustthe heating (during cold days) or cooling (during warm days) as re2uiredtomaintain the target temperature of /FY.

A temperature controller is a de#ice used to hold a desired temperature ataspecied #alue. The simplest eample of a temperature controller is acommonthermostat found in homes. >or instance& a hot water heater uses athermostat to controlthe temperature of the water and maintain it at a certain commandedtemperature.Temperature controllers are also used in o#ens. %hen a temperature is setfor an o#en& acontroller monitors the actual temperature inside of the o#en. If it falls

below the settemperature& it sends a signal to acti#ate the heater to raise thetemperature bac' to the setpoint. Thermostats are also used in refrigerators. o if the temperaturegets too high& acontroller initiates an action to bring the temperature down.1(. E@3'ain abt &3en '&&3 an c'&se '&&3 c&nt&' system.>igure 4 shows an open loop system. A computed force is applied to thesystemwhich is epected to respond based on the specications. If the system

fails to respond


20/25

correctly (because your estimates were o") or an unanticipateddisturbance acted on it&then there is no way to correct the course. 8n the other hand& gure 9shows a feed3bac'system. The response C(s) is measured using the sensor 5(s) and the

resultant iscompared with the input 7(s). The resultant di"erence (error) is actedupon by thecontroller which wor's on the actuator. The actuator then applies there2uired force onthe system.The closed loop thus contains the sensor dynamics& the controllerdynamics& theactuator dynamics in addition to the system we are interested in. It shouldbe noted thatall measurements ha#e to be done or con#erted if necessary into one unitso thatcomparison with the target signal is possible. Usually& measurementsresult in currentsand #oltages. 5ence& this con#ersion from a mechanical input to anelectrical output isalso included in the sensor& controller and actuator dynamics.In designing the full control system the dynamics of all the componentsneed to beaccounted for. If the controller is #ery slow compared to the system& it willnot send the

right input at the right time. In this class& we will assume perfect sensorand actuatordynamics& i.e.& what goes into the sensor (it is commonly denoted by 5(s))and theactuator comes out unmodied instantaneously. o we replace them withunity transferfunctions.1+. E@3'ain the e'ati&n bet*een -&'ta!e c#ent an esistanceAn electric circuit is formed when a conducti#e path is created to allowfreeelectrons to continuously mo#e. This continuous mo#ement of free

electrons throughthe conductors of a circuit is called a current& and it is often referred to interms ofNow&N ust li'e the ow of a li2uid through a hollow pipe.The force moti#ating electrons to NowN in a circuit is called voltage.$oltageis a specic measure of potential energy that is always relati#e betweentwo points.%hen we spea' of a certain amount of #oltage being present in a circuit&we are

referring to the measurement of how muchpotential energy eists tomo#e electrons


21/25

from one particular point in that circuit to another particular point.%ithout referenceto two particular points& the term N#oltageN has no meaning.>ree electrons tend to mo#e through conductors with some degree offriction& or opposition to motion. This opposition to motion is more

properlycalled resistance. The amount of current in a circuit depends on theamount of#oltage a#ailable to moti#ate the electrons& and also the amount ofresistance inthe circuit to oppose electron ow. Zust li'e #oltage& resistance is a2uantityrelati#e between two points. >or this reason& the 2uantities of #oltage andresistance are often stated as being NbetweenN or NacrossN two points in acircuit.To be able to ma'e meaningful statements about these 2uantities incircuits& we need to be able to describe their 2uantities in the same waythat wemight 2uantify mass& temperature& #olume& length& or any other 'ind ofphysical2uantity. >or mass we might use the units of N'ilogramN or Ngram.N >ortemperature we might use degrees >ahrenheit or degrees Celsius. 5ereare thestandard units of measurement for electrical current& #oltage& andresistance116. E@3'ain the c&nst#cti&n & DC machine *ith neat ia!am.

A E.C. machine consists mainly of two part the stationary part calledstator andthe rotating part called stator.The stator consists of main poles used to produce magnetic u&commutatingpoles or interpoles in between the main poles to a#oid spar'ing at thecommutator but inthe case of small machines sometimes the interpoles are a#oided andnally the frame oryo'e which forms the supporting structure of the machine.The rotor consist of an armature a cylindrical metallic body or core with

slots in itto place armature windings or bars& a commutator and brush gearsThe magnetic u path in a motor or generator is show below and it iscalled themagnetic structure of generator or motor.C&ss secti&na' -ie* & a DC Machinerame is the stationary part of a machine on which the main poles andcommutator poles are bolted and it forms the supporting structure byconnecting the

frame to the bed plate. The ring shaped body portion of the frame whichma'es the


22/25

magnetic path for the magnetic ues from the main poles and interpolesis called&4e.

&4eIn early days Vo'e was made up of cast iron but now it is replaced by caststeel.

This is because cast iron is saturated by a u density of B.P %b!s2.mwhere as saturationwith cast iron steel is about 4.F %b!s2.m.o for the same magnetic udensity the crosssection area needed for cast steel is less than cast iron hence the weightof the machinetoo. If we use cast iron there may be chances of blow holes in it whilecasting. so nowrolled steels are de#eloped and these ha#e consistent magnetic andmechanical properties.

En Shie's & Beain!sIf the armature diameter does not eceed 6F to LF cm then in addition topoles endshields or frame head with bearing are attached to the frame. If thearmature diameter isgreater than 4m 3eesta' ty3e beain!s are mounted on the machinebed plate outsidethe frame. These bearings could be ball or roller type but generally plainpedestralbearings are employed. If the diameter of the armature is large a b#shh&'e y&4e is

generally ed to the frame.18. E@3'ain the W&4in! & ynam&mete ty3e*attmeteThe principle of operation of the electrodynamometer3type wattmeter isthe sameas that for dynamo3electric machines. The deection tor2ue is producedby theinteraction of two magnetic ues. 8ne of the ues is produced by aed coil whichcarries a current proportional to the load current and therefore called the

current coil. Theother u is created by a mo#able coil which carries a current proportionalto the load#oltage and thus called the #oltage or potential coil. A high non3inducti#eresistance isconnected to the potential coil so that its current is almost in phase withthe load #oltage.The control tor2ue is pro#ided by a control spring.In a dynamometer type wattmeter the ed coil (current coil) is connectedinseries with the load.This coil is di#ided in to two parts and they are 'ept

parallel to each


23/25

other. The coil is thic' in cross section and has less number of turns.Themo#ing coil(pressure coil) is connected across the load. It is thin in cross 3 section andhas hundredsof turns. It has a non 3 inducti#e high resistance in series with it

The wattmeter is an electrodynamic instrument for measuring the electricpoweror the supply rate of electrical energy of any gi#en circuit. The de#iceconsists of a pair ofed coils& 'nown as current coils& and a mo#able coil 'nown as thepotential coil.The current coils are connected in series with the circuit& while thepotential coil isconnected in parallel. Also& on analog wattmeters& the potential coilcarries a needle thatmo#es o#er a scale to indicate the measurement. A current owingthrough the currentcoil generates an electromagnetic eld around the coil. The strength ofthis eld isproportional to the line current and in phase with it. The potential coil has&as a generalrule& a high3#alue resistor connected in series with it to reduce the currentthat owsthrough it. The result of this arrangement is that on a dc circuit& thedeection of theneedle is proportional to both the current and the #oltage& thus

conforming to the e2uation%=$A or


24/25

Therefore& a wattmeter is rated not only in watts& but also in #olts andamperes.1/. E@3'ain the c&nst#cti&n & tans&me *ith neat ia!am.A transformer is an electrical de#ice used to con#ert AC power at a certain#oltage le#el to AC power at a di"erent #oltage& but at the same

fre2uency.The construction of a transformer includes a ferromagnetic core aroundwhichmultiple coils& or windings& of wire are wrapped. The input line connects tothe OprimaryOcoil& while the output lines connect to OsecondaryO coils. The alternatingcurrent in theprimary coil induces an alternating magnetic u that OowsO around theferromagneticcore& changing direction during each electrical cycle. The alternating uin the core inturn induces an alternating current in each of the secondary coils. The#oltage at each ofthe secondary coils is directly related to the primary #oltage by the turnsratio& or thenumber of turns in the primary coil di#ided by the number turns in thesecondary coil.>or instance& if the primary coil consists of 4BB turns and carries LPB #oltsand asecondary coil consists of 9F turns& the secondary #oltage is then1secondary #oltage = (LPB #olts) K (9F!4BB) = 49B #olts

Two coils of wire (called windings) are wound on some type of corematerial. Insome cases the coils of wire are wound on a cylindrical or rectangularcardboard form. Ine"ect& the core material is air and the transformer is called an AI73C87?T7A0>87D?7. Transformers used at low fre2uencies& such as FB hert,and LBB hert,&re2uire a core of low3reluctance magnetic material& usually iron. This typeof transformeris called an I7803C87? T7A0>87D?7. Dost power transformers are ofthe ironcore

type. The principle parts of a transformer and their functions are1The C87?& which pro#ides a path for the magnetic lines of u.The


25/25

sheets of steel dissipates heat readilyM thus it pro#ides for the e@cienttransfer of power.The maority of transformers you will encounter in 0a#y e2uipmentcontain laminatedsteelcores. These steel laminations are insulated with a non conducting

material& such as#arnish& and then formed into a core. It ta'es about FB such laminations toma'e a core aninch thic'. The purpose of the laminations is to reduce certain losses.

beee 2 marks

Documents