Electl Drives & Control 2 MARK

8/11/2019 Electl Drives & Control 2 MARK

1/19

Electrical Drives and Control ME36

MECHANICAL DEPARTMENT

THIRD SEMESTER(TW MAR!S"

#NIT I

$% De&ine Drive and Electric Drive%

Drive : A combination of prime mover, transmission equipment and mechanical working load is called a drive

Electric drive: An Electric Drive can be defined as an electromechanical device

for converting electrical energy to mechanical energy to impart motion to different

machines and mechanisms for various kinds of process control.

'% List ot so)e e*a)+les o& +ri)e )overs%

I. Engines, !team engine, "urbine or electric motors.

3% List ot so)e advanta,es o& electric drives%

i. Availability of electric drives over a wide range of power a few

watts to mega watts.

ii. Ability to provide a wide range of torques over wide range of speeds.

iii Electric motors are available in a variety of design in order to

make them compatible to any type of load.

-% .ive so)e e*a)+les o& Electric Drives%

i. Driving fans, ventilators, compressors and pumps.

ii. #ifting goods by hoists and cranes.

iii. Imparting motion to conveyors in factories, mines and warehouses

iv. $unning e%cavators & escalators, electric locomotives trains,

cars trolley buses, lifts & drum winders etc.

/% W0at are t0e t1+es o& electric drives2

'roup electric drives (!haft drive),

Individual Drives,

*ulti motor electric drives.

6% Classi&1 electric drives ased on t0e )eans o& control%

*anual, !emiautomatic, Automatic.

4% W0at is a .ro+ Electric Drive (S0a&t Drive"2

+ "his drive consists of single motor, which drives one or more

line shafts supported on bearings.

+ "he line shaft may be fitted with either pulleys & belts or gears,

by means of which a group of machines or mechanisms may beoperated.

5% W0at are t0e advanta,es and disadvanta,es o& .ro+ drive(S0a&t drive"2

Advantages:

+ A single large motor can be used instead of a number of small

motors.+ "he rating of the single motor may be appropriately reduced


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taking into account the diversity factor of loads.

Disadvantages:

+ "here is no fle%ibility, Addition of an e%tra machine to the main shaft is difficult.

+ "he efficiency of the drive is low, because of the losses occurring

in several transmitting mechanisms.+ "he complete drive system requires shutdown if the motor,

requires servicing or repair.

+ "he system is not very safe to operate+ "he noise level at the work spot is very high.

% W0at is an individal electric drive2 .ive so)e e*a)+les%

In this drive, each individual machine is driven by a separatemotor. "his motor also imparts motion to various other parts of the

machine.

!ingle spindle drilling machine, #athe machines etc.

$7% W0at is a )lti )otor electric drive2 .ive so)e e*a)+les%

In this drive, there are several drives, each of which serves toactivate on of the working parts of the driven mechanisms.

*etal cutting machine tools, paper making machines, rolling

mills, traction drive, "raveling cranes etc.,

$$% Write aot )anal control8 se)iato)atic control 9Ato)atic control2

*anual control: "he electric drives with manual control can be as

simple as a room fan, incorporating on switch and a resistance forsetting the required speed.

!emiautomatic control: "his control consists of a manual device

for giving a certain command (!tarting, braking, reversing, changeof speed etc.,) and an automatic device that in response to

command, operates the drive in accordance with a preset

sequence or order.Automatic control: "he electric drives with automatic control

have a control gear, without manual devices

$'% W0at is a load dia,ra)2 W0at are its t1+es2 W0at are re:ired to dra; a load

dia,ra)2

A load diagram is the diagram which shows graphically the variation of torque

acting on the electric drive. "he motor of the electric drive has to overcome the load

torque e%pressed as a function of time."ypes:

+ ne for the static or steady state process

+ ther for the dynamic process, when the dynamic componentsof torque are induced by the inertia of the motor & load.

(Instantaneous speed, acceleration, "orque & power) as a function

of time are required to draw

-..


3/19

$3% W0at are t0e t1+es Drive s1ste)s2

Electric Drives *echanical Drives Electromechanical Drives ydraulic drives.

$-% .ive an e*+ression &or t0e losses occrrin, in a )ac0ine%

"he losses occurring in a machine is given by/ 0 /c 1 %2 /v

/here /c 0 onstant losses

/v 0 3ariable losses at full load 4 0 load on the motor e%pressed as a function of rated load.

$/% W0at are t0e ass)+tions )ade ;0ile +er&or)in, 0eatin, 9

coolin, calclation o& an electric )otor2

i. "he machine is considered to be a homogeneous body having a uniform

temperature gradient. All the points at which heat generated have the same

temperature. All the points at which heat is dissipated are also at same

temperature.ii. eat dissipation taking place is proportional to the difference

of temperature of the body and surrounding medium. 5o heat is radiated.iii. "he rate of dissipation of heat is constant at all temperatures.

$6% W0at are t0e &actors t0at in&lence t0e c0oice o& electrical drives2

6. !haft power & speed 66. !peed range

2. 7ower range 62. Efficiency

8. !tarting torque 68. Influence on the supply network

9. *aintenance 69. !pecial competence. "otal purchase cost 6. ost of energy losses

;. Influence on power supply 6;. Environment


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$% W0at are t0e classes o& dties2

6. ontinuous duty

2. !hort time duty operation of motor *ain classes of duties8. Intermittent periodic duty

9. Intermittent periodic duty with starting

. Intermittent periodic duty with starting & braking;. ontinuous duty with intermittent periodic loading


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8. *ethod of equivalent current

9. *ethod of equivalent "orque

'6% De&ine 0eatin, ti)e constant 9 Coolin, ti)e constant2

"he time required to heat the machine parts to ;8.8 of its final

temperature rise is called as heating time constant."he time required to cool the machine parts to 8;.; of its final

temperature fall is called as cooling time constant.

'4% W0at are t0e varios &nction +er&or)ed 1 an electric drive2

6. Driving fans, ventilators, compressors & pumps etc.,

2. #ifting goods by hoists & cranes

8. Imparting motion to conveyors in factories, mines & warehouses and9% $unning e%cavators & escalators, electric locomotives, trains,cars, trolley buses

and lifts etc.

'5% Write do;n t0e 0eat alance e:ation%eat balance equation is given by

'hd? 1 !? .dt 0 p.dt

#NIT II

$% W01 a sin,le +0ase indction )otor does not sel& start2

/hen a single phase supply is fed to the single phase induction motor. Its stator

winding produces a flu% which only alternates along one space a%is. It is not asynchronously revolving field, as in the case of a 2 or 8phase stator winding, fed from 2

or 8 phase supply.

'% W0at is )eant 1 +l,,in,2

"he plugging operation can be achieved by changing the polarity of the motor

there by reversing the direction of rotation of the motor. "his can be achieved in ac

motors by changing the phase sequence and in dc motors by changing the polarity.

3. .ive so)e a++lications o& DC )otor.

S0nt ? driving constant speed, lathes, centrifugal pumps, machine tools, blowersAnd fans, reciprocating pumps

Series ? electric locomotives, rapid transit systems, trolley cars, cranes and hoists,

conveyors

Co)+ond ? elevators, air compressors, rolling mills, heavy planners.

-% W0at are t0e di&&erent t1+es o& electric ra@in,2

Dynamic or $heostatic braking, ounter current or plugging and $egenerativebraking


6/19

/% W0at is t0e e&&ect o& variation o& ar)atre volta,e on NT crve and 0o; it can

e ac0ieved2

"he 5" curve moves towards the right when the voltage is increased. "his can beachieved by means of additional resistance in the armature circuit or by using thyristor

power converter.

6% Co)+are electrical and )ec0anical ra@in,%

Mec0anical Electrical

Frakes require frequent maintenance very little maintenance5ot smooth smooth an be applied to hold the system at any position cannot produce

holding torque.

4% W0en does an indction )otor e0ave to rn o&& as a ,enerator2

/hen the rotor of an induction motor runs faster than the stator field, the slip

becomes negative. $egenerative braking occurs and the G.E. of the rotating parts is return

back to the supply as electrical energy and thus the machine generates power.

5% De&ine sli+%

! 0 5s H 5r/here, 5s 0 synchronous speed in rpm.

5r 0 rotor speed in rpm

! 0 !lip

% De&ine s1nc0ronos s+eed%

It is given by 5s 0 62?f p rpm.

/here 5s 0 synchronous speed, p 0 no. of stator poles, f 0 supply frequency in B

$7% W01 a sin,le +0ase indction )otor does not sel& start2

/hen a single phase supply is fed to the single phase induction motor. Its stator

winding produces a flu% which only alternates along one space a%is. It is not asynchronously revolving field, as in the case of a 2 or 8phase stator winding, fed from 2

or 8 phase supply.

$$% W0at is )eant 1 re,enerative ra@in,2

In the regenerative braking operation, the motor operates as a generator, while it

is still connected to the supply here, the motor speed is grater that the synchronous speed.

*echanical energy is converter into electrical energy, part of which is returned to thesupply and rest as heat in the winding and bearing.

$'% .ive so)e a++lications o& DC )otor%

!hunt : driving constant speed, lathes, centrifugal pumps, machine tools, blowers

and fans, reciprocating pumps

!eries : electric locomotives, rapid transit systems, trolley cars, cranes and hoists, conveyors

ompound : elevators, air compressors, rolling mills, heavy planners.


7/19

$3% Co)+are electrical and )ec0anical ra@in,%

Mec0anical Electrical

Frakes require frequent maintenance very little maintenance5ot smooth smooth

an be applied to hold the system at any position cannot produce holding

torque.

$-% Di&&erentiate c)lative and di&&erential co)+ond )otors%

C)lative

"he orientation of the series flu% aids the shunt flu%

di&&erential

series flu% opposes shunt flu%

$/% W0at is )eant 1 )ec0anical c0aracteristics2

A curve drawn between the parameters speed and torque.

$6% W0at is )eant 1 electrical c0aracteristics2A curve drawn between the armature current and armature torque.

$4. W0at is )eant 1 +er&or)ance c0aracteristics2"he graph drawn between the output power 3s speed , efficiency, current and

torque.

$5% W0at do 1o )ean 1 R0eostatic ra@in,2

In this braking armature is removed and connected across a variable rheostat.

$% Is Indction )otor rns ;it0 s1nc0ronos s+eed or not%

Induction motor never runs with synchronous speed. It will stop if it tries to

achieve synchronous speed.

'7% W01 t0e ar)atre core in d%c )ac0ines is constrcted ;it0 la)inated steel

s0eets instead o& solid steel s0eets2

#amination highly reduces the eddy current loss and steel sheets

provide low reluctance path to magnetic field.

'$% W01 co))tator is e)+lo1ed in d%c%)ac0ines2

onduct electricity between rotating armature and fi%ed brushes, convert

alternating emf into unidirectional emf (mechanical rectifier).

''% Distin,is0 et;een s0nt and series &ield coil constrction2

!hunt field coils are wound with wires of small section and have more

5o of turns. !eries field coils are wound with wires of larger cross section and have lessno of turns.

'3% Ho; does d%c% )otor di&&er &ro) d%c% ,enerator in constrction2

'enerators are normally placed in closed room and accessed by skilled


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operators only. "herefore on ventilation point of view they may be constructed with large

opening in the frame. *otors have to be installed right in the place of use which may

have dust, dampness, inflammable gases, chemicals-.etc. to protect the motors againstthese elements, the motor frames are made either partially closed or totally closed or

flame proof.

'-%Ho; ;ill 1o c0an,e t0e direction o& rotation o& d%c%)otor2

Either the field direction or direction of current through armature

conductor is reversed.

'/% W0at is ac@ e)& in d%c% )otor2

As the motor armature rotates, the system of conductor come across alternate

north and south pole magnetic fields causing an emf induced in the conductors. "hedirection of the emf induced in the conductor is in opposite to current. As this emf always

opposes the flow of current in motor operation it is called as back emf.

#NIT III$% Mention t0e Starters sed to start a DC )otor%

"wo point !tarter

"hree point !tarter

@our point !tarter

'% Mention t0e Starters sed to start an Indction )otor%

D..# !tarter (Direct nline !tarter)!tarDelta !tarter

Auto "ransformer !tarter

$eactance or $esistance starter!tator $otor !tarter ($otor $esistance !tarter)

3% W0at are t0e +rotective devices in a DCBAC )otor Starter2

ver load $elease (.#.$) or 5o volt coilold on oil

"hermal $elays

@uses(!tarting $unning)ver load relay

-% Is it +ossile to incldeB E*clde e*ternal resistance in t0e rotor o& a

S:irrel ca,e indction )otor2% sti&15o it is not possible to include E%clude e%ternal resistance in the rotor of a

!quirrel cage induction motor because, the rotors bars are permanently short

circuited by means of circuiting rings (end rings) at both the ends. i.e. no sliprings to do so.

/% .ive t0e +ri)e +r+ose o& a starter &or )otors%

when induction motor is switched on to the supply, it takes about to = times full


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load current at starting. "his starting current may be of such a magnitude as to

cause obJectionable voltage drop in the lines. !o !tarters are necessary

6% W01 )otor ta@e 0eav1 crrent at startin,2

/hen 8 phase supply is given to the stator of an induction motor, magnetic field

rotating in space at synchronous speed is produced. "his magnetic field is cut bythe rotor conductors, which are short circuited. "his gives to induced current in

them. !ince rotor of an induction motor behaves as a short circuited secondary of a

transformer whose primary is stator winding, heavy rotor current will requirecorresponding heavy stator balancing currents. Thus motor draws heavy

current at starting

4% W0at are t0e )et0ods to redce t0e )a,nitde o& rotor crrent (rotor

indced crrent" at startin,2%

Fy increasing the resistance in the rotor circuit

Fy reducing the magnitude of rotating magnetic field i.e by reducing the applied

voltage to the stator windings.

5% W0at is t0e oective o& rotor resistance starter (stator rotor starter"2

"o include resistance in the rotor circuit there by reducing the induced rotor

current at starting. "his can be implemented only on a slip ring induction motor.

% W01 s:irrel ca,e indction )otors are not sed &or loads re:irin,

0i,0 startin, tor:e2

!quirrel cage motors are started only by reduced voltage starting methods

which leads to the development of low starting torque at starting. "his is thereason /hy squirrel cage induction motors are not used for loads requiring high

starting torque.

$7% Ho; redced volta,e startin, o& Indction )otor is ac0ived2.

D..# !tarter (Direct nline !tarter)

!tarDelta !tarterAuto "ransformer !tarter

$eactance or $esistance starter

$$% .ive t0e relation et;een line volta,e and +0ase volta,e in a

(i) Delta connected network (ii) !tar connected network

Delta connected net;or@?

3phase 0 3line

Star connected net;or@?

3phase 0 3line K8

$'% .ive so)e advanta,es and disadvanta,es o& D%%L starter%

Advanta,es?

ighest starting torque

#ow cost

'reatest simplicity


10/19

Disadvanta,es?

"he inrush current of large motors may cause e%cessive voltage drop in the weak

power system "he torque may be limited to protect certain types of loads.

$3% E*+lain dole sta,e redction o& line crrent in an Ato trans&or)er

starter%@irst stage reduction is due to reduced applied voltage

!econd stage reduction is due to reduced number of turns

$-% W0at is t0e &nction o& novolta,e release coil in d%c% )otor starter2

As long as the supply voltage is on healthy condition the current

through the 53$ coil produce enough magnetic force of attraction and retain the starter

handle in 5 position against spring force. /hen the supply voltage fails or becomeslower than a prescribed value then electromagnet may not have enough force to retain so

handle will come back to @@ position due to spring force automatically.

$/% En)erate t0e &actors on ;0ic0 s+eed o& a d%c%)otor de+ends250 (3Ia$a)L so speed depends on air gap flu%, resistance of armature,

voltage applied to armature.

$6% #nder W0at circ)stances does a dc s0nt ,enerator &ails to ,enerate2

Absence of residual flu%, initial flu% setup by field may be opposite indirection to residual flu%, shunt field circuit resistance may be higher than its critical field

resistance, load circuit resistance may be less than its critical load resistance.

$4% De&ine critical &ield resistance o& dc s0nt ,enerator2

ritical field resistance is defined as the resistance of the field circuit

which will cause the shunt generator Just to build up its emf at a specified field.

$5% W01 is t0e e)& not >ero ;0en t0e &ield crrent is redced to >ero in dc

,enerator2

Even after the field current is reduced to Bero, the machine is left outwith some flu% as residue so emf is available due to residual flu%.

$% n ;0at occasion dc ,enerator )a1 not 0ave residal &l*2

"he generator may be put for its operation after its construction, inprevious operation, the generator would have been fully demagnetiBed.

'7% W0at are t0e conditions to e &l&illed 1 &or a dc s0nt ,enerator to ild ac@

e)&2

"he generator should have residual flu%, the field winding should be connected in

such a manner that the flu% setup by field in same direction as residual flu%, the fieldresistance should be less than critical field resistance, load circuit resistance should be

above critical resistance.


11/19

'$% De&ine ar)atre reaction in dc )ac0ines2

"he interaction between the main flu% and armature flu% cause disturbance

called as armature reaction.

''% W0at are t;o n;anted e&&ects o& ar)atre reactions2

ross magnetiBing effect & demagnetiBing effect.

'3% W0at is t0e &nction o& caron rs0 sed in dc ,enerators2

"he function of the carbon brush is to collect current fromcommutator and supply to e%ternal load circuit and to

'-% Na)e an1 t;o starters ;0ic0 can e sed ;it0 onl1 sli+rin, indction )otor

$otor resistance starter!olid state rotor resistance starter

#NIT I$% .ive t0e e*+ression &or s+eed &or a DC )otor%

!peed 5 0 k (3Ia$a)Jwhere 3 0 "erminal 3oltage in volts

Ia 0 Armature current in Amps

$a 0 Armature resistance in ohmsJ0 flu% per pole.

'% W0at are t0e ;a1s o& s+eed control in dc )otors2

@ield control by varying the flu% per pole. for above rated speed

Armature control by varying the terminal voltage for below rated speed

3% .ive t0e Li)itation o& &ield control

a. !peed lower than the rated speed cannot be obtained.

b. It can cope with constant k/ drives only.

c. "his control is not suitable to application needing speed reversal.

-% W0at are t0e 3 ;a1s o& &ield control in DC series )otor2

M @ield diverter controlM Armature diverter control

M *otor diverter control

M @ield coil taps control

M !eriesparallel control

/% W0at are t0e )ain a++lications o& WardLeonard s1ste)2

M It is used for colliery winders.M Electric e%cavators

M In elevators

M *ain drives in steel mills and blooming and paper mills.


12/19

6% W0at are t0e )erits and de)erits o& r0eostatic control )et0od2

M Impossible to keep the speed constant on rapidly changing loads.

M A large amount of power is wasted in the controller resistance.M #oss of power is directly proportional to the reduction in speed. ence

efficiency is decreased.

M *a%imum power developed is diminished in the same ratio as speed.M It needs e%pensive arrangements for dissipation of heat produced in the

controller resistance.

M It gives speed below normal, not above.

4% W0at are t0e advanta,es o& &ield control )et0od2

M *ore economical, more efficient and convenient.

M It can give speeds above normal speed.

5% Co)+are t0e vales o& s+eed and tor:e in case o& )otors ;0en in

+arallel and in series%

M "he speed is one fourth the speed of the motor when in parallel.M "he torque is four times that produced by the motor when in parallel.

% Mention t0e s+eed control )et0od e)+lo1ed in electric traction%

!eriesparallel speed control.

$7% W0at is t0e e&&ect o& insertin, resistance in t0e &ield circit o& a dc

s0nt )otor on its s+eed and tor:e2

@or a constant supply voltage, flu% will decrease, speed will increase and

torque will increase.

$$% W0ile controllin, t0e s+eed o& a dc s0nt )otor ;0at s0old e done

to ac0ieve a constant tor:e drive2

Applied voltage should be maintained constant so as to maintain field strength

$'%State t0e advanta,es o& dc c0o++er drive%

Dc chopper drive s has the advantages of

igh efficiency

@le%ibility in control

#ight weight!mall siBe

Nuick response

$3%W01 c0o++er ased DC drives ,ive etter +er&or)ance t0an recti&ier controlled

drives%

#ess harmonic#ow ripple content

igh efficiency


13/19

$-%Na)e t0e solid state controllers sed &or t0e s+eed control o& DC s0nt )otor

and series )otor8

7hase controlled rectifier fed D driveshopper fed D drives

$/%.ive a++lication o& WardLeonard s1ste) o& s+eed controlIt is used for elevators,hoist control and for main drive in steel mills where motor

of ratings


14/19

@ield flu%

Armature voltage

'-%State control strate,ies o& c0o++ers

"ime ratio control

urren limit control

#NIT $% W0at is a controlled recti&ier2

A controlled rectifier is a device which is used for converting controlled dc powerfrom a control voltage ac supply.

'% W0at is &irin, an,le2

"he control of dc voltage is achieved by firing the thyristor at an adJustable angle

with respect to the applied voltage. "his angle is known as firing angle.

3% .ive so)e a++lications o& +0ase control converters%

7hase control converters are used in the speed control of fractional k/ dc motorsas well as in large motors employed in variable speed reversing drives for rolling mills.

/ith motors ratings as large as several */Os.

-% W0at is t0e )ain +r+ose o& &ree ;0eelin, diode2

@ree wheeling diode is connected across the motor terminal to allow for thedissipation of energy stored in motor inductance and to provide for continuity of motor

current when the thyristors are blocked.

/% W0at is a &ll converter2

A full converter is a tow quadrant converter in which the voltage polarity of the

output can reverse, but the current remains unidirectional because of unidirectionalthyristors.

6% W0at is natral or line co))tation2

"he commutation which occurs without any action of e%ternal force is callednatural or line commutation.

4% W0at is &orced co))tation2

"he commutation process which takes place by the action of an e%ternal force is

called forced commutation.

5% W0at is a c0o++er2A chopper is essentially an electronic switch that turns on the fi%edvoltage dc

source for a short time intervals and applies the source potential to motor terminals in

series of pulses.


15/19

% W0at are t0e t;o )ain di&&iclties o& variale &re:enc1 s1ste)2

ontrol of 3a requires variation of chopper frequency over a wide range. @ilter

design for variable frequency operation is difficult.At low voltage, a large value of toffmakes the motor current discontinuous.

$7% Classi&1 co))tation%M 3oltage commutation

M urrent commutation.

$$% W0at is volta,e co))tation2

A charged capacitor momentarily reversebias the conducting thyristor to turn it

off. "his is known as voltage commutation.

$'% W0at is crrent co))tation2

A current pulse is forced in the reverse direction through the conducting thyristor.

As the net current becomes Bero, the thyristor is turned @@. "his is known as current

commutation.

$3% W0at is load co))tation2

"he load current flowing through the thyristor either becomes Bero (as in natural

or line commutation employed in converters) or is transferred to another device from the

conducting thyristor. "his is known as load commutation.

$-% W0at are t0e di&&erent )eans o& controllin, indction )otor2

M !tator voltage control.

M @requency controlM 7ole changing control.

M !lip power recovery control.

$/% W0at are t0e t;o ;a1s o& controllin, t0e RMS vale o& stator volta,e2

M 7hase control

M Integral cycle control

$6% Mention t0e t;o sli++o;er recover1 sc0e)es%

M !tatic scherbius scheme

M !tatic Gramer drive scheme.

$4% .ive t0e asic di&&erence et;een t0e t;o sli++o;er recover1 sc0e)es%

"he slip is returned to the supply network in scherbius scheme and in Gramerscheme, it is used to drive an au%iliary motor which is mechanically coupled to the

induction motor shaft.

$5% Write s0ort notes on inverter recti&ier%

"he dc source could be converted to ac form by an inverter, transformed to a

suitable voltage and then rectified to dc form. Fecause of two stage of conversion, the

setup is bulky, costly and less efficient.


16/19

$% .ive t0e s+ecial &eatres o& static sc0eris sc0e)e%

M "he scheme has applications in large power fan and pump drives which requires speed control in anrrow range only.

M If ma%. slip is denoted by !ma%, then power rating of diode, inverter and

transformer can be Just !ma% times motor power rating resulting in a low cost drive.

M "his drive provides a constant torque control.

'7% W0at are t0e advanta,es o& static !ra)er s1ste)88 over static sc0eris s1ste)2

M !ince a static Gramer system possesses no line commutated inverter, it causes

less reactive power and smaller harmonic contents of current than a static

scherbius.M /hat is electrical power supply systemP

M "he generation, transmission and distribution system of electrical power is

called electrical power supply system.

'$% W0at are t0e - )ain +arts o& distrition s1ste)2

M @eeders,M Distributors and

M !ervice mains.

''% W0at are &eeders2

@eeders are conductors which connect the stations (in some cases generating

stations) to the areas to be fed by those stations.

'3% W0at are t0e advanta,es o& 0i,0 volta,e dc s1ste) over 0i,0 volta,e ac s1ste)2

M It requires only tow conductors for transmission and it is also possible to

"ransmit the power through only one conductor by using earth as returningconductor, hence much copper is saved.

M 5o inductance, capacitance, phase displacement and surge problem.

M "here is no skin effect in dc, cross section of line conductor is fully utiliBed.

'-% W0at do 1o )ean 1 t0e ter) eart0in,2

"he term earthingC means connecting the noncurrent carrying parts of electrical

equipment to the neutral point of the supply system to the general mass of earth in such amanner that at all time an immediate discharge of electrical energy takes place without

danger.

'/% W0at are t0e di&&erent )et0ods o& +rovidin, netral eart0in,2

M !olid earthing

M $esistance earthing

M $eactance earthing

M Arc suppression coil or 7eterson coil earthing.


17/19

Electrical Drives and Control ME36

MECHANICAL DEPARTMENT

THIRD SEMESTER

($6 MAR!S"

#NIT I

INTRD#CTIN

6. E%plain the factors governing the selection of motors. (6;)

2. Discuss in detail the determination of power rating of motors. (6;)8. (i) E%plain the different types of loading of drives. (=)

(ii) E%plain the choice of selection of the motor for different loads. (=)

9. (i) Describe the simplifications based on which the heating and coolingcalculations of an electric motor are made. (8)

(ii) Establish the heating time constant and the heating curves.

(68). (i) ompare the D. and A. drives. (;)

(ii) /rite a brief note on classes of duty for an electric motor. (6?);. Draw the typical temperature risetime curve and derive the equation for

temperature rise in an electric drive. (6;)


18/19

(ii) E%plain the method of regenerative braking employed in D *otors.

(=)

62. E%plain about the speedtorque characteristics of a D ompound*otor with suitable graph and equations. (6;)

#NIT IIISTARTIN. METHDS

6. Draw a neat schematic diagram of a three point starter and e%plain its

working. (6;)2. Draw a neat schematic diagram of a four point starter and e%plain its

working. (6;)

8. E%plain with neat circuit diagram, the stardelta starter method of starting

squirrel cage induction motor. (6;)9. E%plain the typical control circuits for D !eries and !hunt motors (6;)

. E%plain the different starting methods of three phase squirrel cage

induction motors with neat sketches. (6;)

;. E%plain different methods of starting of D *otors. (6;). Draw and e%plain the manual autotransformer starter for three phaseinduction motor. (6;)

#NIT I

CNENTINAL AND SLID STATE SPEED CNTRL F

D%C DRIES

6. E%plain with neat sketch the chopper control method of speed control of

D *otors. (6;).2. E%plain with neat sketches about the D !hunt *otor speed control by

using single phase fully controlled bridge converter. (6;)

8. Discuss the /ard#eonard speed control system with a neat circuitdiagram. Also mention its advantages and disadvantages. (6;)

9. E%plain how the speed of a D !hunt *otor can be varied both above

and below the speed at which it runs with full field current. (6;)

. (i) E%plain with neat sketch the operation of chopper fed D !eries*otor drive. Also, derive the e%pression for average motor current. (6?)

(ii) E%plain "ime ratio control and urrent limit control. (;)

;. E%plain the speed control schemes of D !eries *otor. (6;). E%plain the single phase half wave converter drive speed control for D

drive with waveforms. (6;)

6?. E%plain in detail the single phase semiconverter speed control for D

drive for separately e%cited motor. (6;)


19/19

#NIT CNENTINAL AND SLID STATE SPEED CNTRL F

A%C DRIES

6. Draw the power circuit arrangement of three phase variable frequencyinverter for the speed control of three phase induction motor and e%plain its

working. (6;)

2. E%plain the 3f control method of A drive with neat sketches. (6;)

8. Discuss the speed control of A motors by using three phase A3oltage regulators. (6;)

9. E%plain the speed control schemes of phase wound induction motors.

(6;)

. E%plain the concatenation operation of three phase induction motors.ence derive the speed e%perienced for the cascaded set. (6;)

;. E%plain in detail about !lip power recovery scheme. (6;). E%plain in detail rotor resistance method of speed control of a slip ring

induction motor. (6;)

6?. (i) E%plain the operation of 7ole changing method of speed control. (=)(ii) E%plain the pole amplitude modulation method. (=)

66. E%plain the static Gramer method and static scherbius method of speed

control of three phase induction motor. (6;)62. E%plain in detail about the various methods of solid state speed control

techniques by using inverters. (6;)

68. E%plain the solid state stator voltage control technique for the speedcontrol of three phase induction motor. (6;)

69. E%plain the various methods of speed control of a three phase induction

motor when fed through semiconductor devices. (6;)

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Electl Drives & Control 2 MARK