Machine Laboratory Manual - II

8/10/2019 Machine Laboratory Manual - II

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Acknowledgement

The contributionrendered byfollowing persons in

preparing this manual is highlyappreciated.

1. Mr. Hari Shankar Singh Office Assistant (EEE Dept.)

2. Mr. Arbind Singh Sr. Technician, (EEE

Dept.)

3. Mr. Tagi !ishant Shradhanand "E #ina$ %ear (EEE) st&dent


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Content

Page1. Detai$s 'f Machine ab'rat'r . . i

2. *&ide $ines f'r +riting $ab '&rna$ . . ii

3. Magneti-ati'n characteristic 'f separate$ ecited D./. *enerat'r . 1

0. 'ad Test 'f a D./. sh&nt 't'r . . 3

. 'ad Test 'n a D./. sh&nt *enerat'r . .

. 'ad test 'n a D./. series *enerat'r . . 4

4. 'ad test 'n a D./. c'p'&nd *enerat'r. . . 5

6. Speed /'ntr'$ 'f D./. Sh&nt M't'r . . 12

5. 7ard e'nard eth'd 'f speed c'ntr'$ 'f D./. sh&nt 't'r. .3 1

18. S+inb&rne9s test . . 16

11. #ie$d9s test 'n t+' sii$ar d.c. series achines. 2 . .2 28

12. H'pkins'n9s test 1 . 1. 23

13. Open circ&it and sh'rt circ&it test 'n a sing$e phase transf'rer. . 2

10. 'ad test 'n a sing$e phase transf'rer . . 26

1. "ack:t':back test 'n t+' sing$e:phase transf'rer . . 38

1. Scott Connection . .0 33

14. Load test on 3-phase induction motor. . . 3

16. No- load and blocked-rotor test on 3-phase induction motor . . 36

15. Load test on 3 -phase induction motor (Electrical loading) . . 01

28. O./ and S./ test 'n a sing$e:phase ind&cti'n 't'r . . 03

21. Voltage regulation of a single-phase alternator b direct loading method .5 !"

##. Voltage regulation of an alternator b snchronous impedance method. .4 !$

#3. V % cur&es of a three % phase snchronous motor . .6 3

20. Slip 'est of a snchronous machine . .18


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Panel No. Types of Machine

1 D/ M't'r:generat'r Set

2. D/ M't'r:generat'r Set

3. D/ M't'r:generat'r Set0. D/ M't'r:generat'r Set

0A D/ Sh&nt 't'r +ith 3:phase generat'r

3:;hase ind&cti'n 't'r +ith D./. generat'r

D./. Sh&nt 't'r

A 3:phase ind&cti'n 't'r +ith ap$idne

4 3:phase transf'rer 088 2 n's.




11 3:phase ind&cti'n 't'r 13 D./. Series 't'r ? generat'r

13A 3:phase ind&cti'n 't'r

10 3:phase ind&cti'n 't'r +ith etadne

1 D./. 't'r +ith D./. series generat'r

1A 1:phase 't'r +ith D./. sh&nt generat'r

1 D./. 't'r +ith sing$e phase a$ternat'r

14 D./. 't'r +ith 3 phase a$ternat'r

16 D./. 't'r +ith 3 phase a$ternat'r

Details of Machine Laboratory

Symbols used on the panel of the lab:

A" @ Arat&re 7inding Terina$ 'f D/ Machine

/D @ Sh&nt #ie$d 7inding Terina$ 'f D/ Machine

E# @ Series 7inding Terina$ 'f D/ Machine

A# @ 3:;'int Starter9s Terina$

;!A# @ 0:;'int Starter9s Terina$

=7 @ Arat&re 7inding Terina$ 'f 3:;hase Snchr'n'&s Machine

BC @ #ie$d 7inding Terina$ 'f Snchr'n'&s Machine

@ Arat&re 7inding Terina$s 'f 1:;hase Snchr'n'&s Machine 123 @ 3:;hase S&pp$ Terina$s

; 1, 2 @ ;riar 7inding 'f 1:;hase Transf'rer

S 1, 2 @ Sec'ndar 7inding 'f 1:Transf'rer!, "!, %! @ 1:;hase A/ S&pp$ Terina$s

F @ D/ S&pp$

i


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Guide lines for writing labjournal ab rep'rt sh'&$d be s&bitted in b'&nded '&rna$ inf'$$'+ing f'rat Date@Eperient !'. @

!ae @Obect @

The'r @

Apparat&s &sed @

Machine specificati'n@

/irc&it diagra @

;r'ced&re (step +ise) @

Eperienta$ data @

Sap$e ca$c&$ati'n @

*raphs @

;reca&ti'n @

/'ents and c'nc$&si'n@

References @

1. The perf'rance and design 'f D/ achines b A.E. /$at'n

2. The'r 'f A/ achines b A.S. angsd'rf

3. ab'rat'r eperients 'n e$ectrica$ achines b /.C. /handa ? A. /hakrab'rt,

Dhanpat ai ? /'., De$hi 1554

0. ab'rat'r an&a$ f'r e$ectr'echanics b S.S. M&rt, ".;. Singh /.S.Bha and D.;.

C'thari, 7i$e Eastern td., De$hi, 1562.

ii


6/65

EXPERIMENT 1

Name: - Magnetization characteristic of separately excited !"! #enerator!

$im: % 'o plot magnetiation cur&e (E Vs f) for different &alues of speed.

Theory: %

*or +.C. ,enerator running at constant speed the epression for &oltage generated (E) in the

armature /inding can be /ritten as

E

B(1) /here 0 is the flu densit in air gap.

'he field intensit (1) is gi&en b

H If

()II

/here f is field current.

So relation bet/een E and f must be similar to that bet/een 0 and f and also must be similar to that

bet/een 0 and 1 for the magnetic circuit of the machine.

& p ecif i ca t io n o f th e m a c h in es

,enerator % #32V 34

Speed % !52r.p.m.

6otor % #32V $.#4

Speed % !52r.p.m.

$pparat's re('ired: %

. +.C. &oltmeter (2-#52V) % No.

#. +.C. ammeter (2-34) % No.

3. +ouble barrel rheostat (#227 % #.84) % No.

!. Single barrel rheostat (#$27 -.54) % #No.

5. 'achometer % No.

9. Connecting /ires.

"irc'it iagram

C:C;' +4,:46 *


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E@C'E+ +.C. ,ENE:4'


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Pro c ed' re: %

. 6ake the connection as per the circuit diagram.

#. Aeep the motor field rheostat at minimum resistance position and s/itch on +.C. suppl.

3. Start the +.C shunt motor using the starter and bring it to rated speed.

!. Set the potential di&ider to ero output position so that the generator field current f is ero.Note the terminal &oltage Vt of the generator.

5. ncrease the field current f in steps upto #5B of the rated &alue and note correspondingterminal &oltage Vt.

9. +ecrease the field current f in steps back to ero and note the corresponding terminal &oltageVt.

". 'ake another set of reading at a constant speed sa N less than the rated speed.

8. >lot magnetiation cur&e (Vt Vs f) for different &alues of speed.

)*ser+ation Ta*le: %

. 4t Speed N

&!No! If ,$-

,Increasing-

.t (=) If ,$-

,ecreasing-

.t ,.-

#. 4t Speed N#

&!No! If ,$-,Increasing-

.t (=) If ,$-,ecreasing-

.t ,.-

P reca' tion s :

. E&er time before starting the motor make sure that the motor field rheostat is set at

minimum resistance position.

#. 'ake care (i) not to let the field current f fall back in &alue during the increasing process

and (ii) not to let f rise in &alue during the decreasing process.

3. 4 +.C. motor should not be stopped b forcing the starter handle to the off position.


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6

EXPERIMENT /

Name: % 0oad Test of a !"! sh'nt motor

$im: % >lot the follo/ing characteristics

. Speed Vs 0.1.> and 'orue Vs 0.1.>

#. Current and efficienc Vs 0.1.>

3. Speed Vs 'orue

Theory: %

'he load test is conducted to determine the efficienc of a +.C. shunt motor b actual loading. 1ere

brake load arrangement is used /hich consists of brake drum coupled to shaft of motor and belt

connected to t/o tension spring. 'he load is applied b tightening the belt.

M achin e sp ecif icat io n

Voltage rating % #32V

Current rating % 9.84

Speed % !52r.p.m

B.H.P =WN

888D FSpring balance reading (lb) NFr.p.m

$p p a rat's re(' ir ed

. :heostat % (#227 #.84) % No.

#. +.C. ammeter - (2-#24) % No.

3. +.C. ammeter % (2-.54) % No.

!. +.C. &oltmeter % (2-#52V) % No.

5. 'achometer % No.

9. Connecting /ires

"irc'it iagram


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Proced're: %


#. Aeep the motor field rheostat at minimum resistance position and s/itch on +.C. suppl.

3. Start the motor using the starter and bring it to the rated speed b adGusting the rheostat in

the field circuit.!. 4t no load note do/n the speed and the readings of all the meters.

5. ncrease the load on the motor in steps upto rated load of the motor and at each step note

do/n speed and readings of all the meters.

9. Set the motor field rheostat to minimum resistance position unload the motor and s/itch off

the +.C. suppl.

". 6easure armature resistance b ammeter-&oltmeter method.

8. 6ake the reuired calculations and plot the reuired characteristics.

)*ser+ation Ta*le

&l! No! ield "'rrent ,$- $rmat're "'rrent ,$- .$2 ,.-&peed N

,RPM-

3

Preca'tions

. E&er time before starting the motor make sure that the motor field rheostat is set at

minimum resistance position.

#. hile starting the motor the handle of the starter must be mo&ed slo/l.

3. 'o a&oid too much heating of the drum be fast in performing the eperiment.

!. 4 +.C. motor should not be stopped b forcing the starter handle to the off position.


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EXPERIMENT 3

Name: % 0oad Test on a !"! sh'nt #enerator


. 'erminal &oltage Vs load current#. *ield current Vs load current

3. nternal or total characteristic

Theory: %

'he load test is performed on a +.C. shunt generator to kno/ mainl ho/ its terminal &oltage

&aries /ith load current at constant rated speed and constant field circuit resistance corresponding to

the rated terminal &oltage at no load. f a +.C. shunt generator after building up to its rated no load

&oltage be loaded its terminal &oltage drops. 'he relation bet/een the terminal &oltage and load

current is called eternal characteristic. +uring the test the speed of the generator is maintained

constant.

'he reasons of &oltage drop in +.C. shunt generator /ith load areH

(i) due to armature resistance drop.

(ii) decrease of field current due to reduction in armature &oltage.

(iii) due to armature reaction.

*urther b this test the efficienc and &oltage regulation at different load can also be determined.

M ac h in e s p ecif ica t io n

Motor #enerator

#32 V $.#4 #32V 34

5A 3AV4

:.>.6 % !52 :.>.6 % !52

$ p p a r a t' s r e (' ir ed

. +.C. &oltmeter (2-#32V) % No.

#. +.C. ammeter - (2-#24) % No.

3. :heostat (#$27 .54) % # Nos.

!. Lamp load (#52V #22) % #Nos.

5. 'achometer % No.

9. Connecting /ires


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"irc'it iagram

3:p'int starter

Proced're: %


#. Aeep motor field rheostat at minimum resistance position. S/itch on +.C. suppl.

3. Start +.C. Shunt motor /ith the help of starter and adGust the speed b adGusting motor field

rheostat to rated speed of the generator.

!. 4dGust the field rheostat of the +.C. Shunt ,enerator to obtain rated terminal &oltage /ith no

load. n case the &oltage does not build up re&erse the direction of field current.

5. Note do/n the readings of all meters on no load.9. 4ppl the load on generator in steps and note do/n readings of all meters. ,o upto rated

load. 6aintain the speed constant (rated speed) at each load.

". :emo&e the load in steps and s/itch off the suppl.

8. 6easure armature resistance b ammeter-&oltmeter method.

$. >lot the reuired characteristics.

)*ser+ation Ta*le

Constant speed N F

Sl. No. *ield current (4) Load Current (4) 'erminal &oltage (V)

3

Preca'tions: %

. E&er time before starting the motor see that the field rheostat is set at minimum

resistance position.

#. 4 +.C. motor should not be stopped b forcing the starter handle to the off position.


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EXPERIMENT 4

Name: % 0oad test on a !"! series #enerator

$im: % 1! 'o stud ho/ the terminal &oltage of a +.C. series ,enerator &aries /ith load

current at constant rated speed

#. 'o dra/ the eternal characteristics (terminal &oltage &s load current)

Theory: %

n a d.c. series generator the armature /inding series field /inding and load resistance are

connected in series. 'herefore the field current is eual to the armature and load current. hen the

load current increases under constant speed the terminal &oltage increases.


#enerator Motor

#32 V $.34 #32V #34

51.> 91.>

:.>.6 % !52 :.>.6 % !52


. +.C. &oltmeter (2-#32V) % No.

#. +.C. ammeter - (2-#24) % No.

3. :heostat (#$27 .54) % No.!. Lamp load (#52V #22) % #Nos.

5. 'achometer % No.

9. Connecting /ires

"irc'it iagram 3:p'int starter

C:C;' +4 , : 4 6 *< : L < 4 + ' ES ' < N +.C. S E : E S , E N E : 4 ' < :


14/65

Proced're: %

. 6easure the armature and field /inding resistances of the d.c. series generator b the

ammeter and &oltmeter method.

#. 6ake the connections as per the circuit diagram.

3. Set the motor field rheostat at minimum resistance &alue and s/itch on d.c. suppl.!. Start the d.c. shunt motor using the three point starter and bring it to rated speed of the d.c.

series generator b &aring motor field rheostat.

5. 4ppl load on the generator in steps and note do/n readings of all meters. ,o upto rated

load. 6aintain constant speed (rated speed) at each load.

9. Set the motor field rheostat at minimum resistance &alue remo&e the load in steps and

s/itch off d.c. suppl.

". >lot the terminal &oltage &s load current characteristics.

)*ser+ation Ta*le:

Constant speed N rpm

&l! No! 0oad c'rrent ,$- Terminal .oltage ,.-

3

Preca'tions: %

. 'he d.c. shunt motor should al/as be started /ith minimum eternal resistance in the field

circuit.#. 'he starter handle must be mo&ed slo/l /hile starting the motor.

3. +.C. motor should not be stopped b forcing the starter handle to the off position.


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EXPERIMENT 5

Name: % 0oad test on a !"! compo'nd #enerator.

$im: % +ra/ the eternal characteristic (terminal &oltage &s. load current) for the

follo/ing. Shunt ,enerator

#. +ifferentiall Compounded ,enerator

3. Cumulati&el Compounded ,enerator

Theory: %

'he load test is performed on d.c. compound generator to kno/ mainl ho/ its terminal &oltage &aries

/ith load current at constant rated speed and constant shunt field circuit resistance corresponding to

the rated terminal &oltage at no load.

n a +.C. compound machine both the series and shunt field coils are present /hile shunt field is the

main field series field either help it or opposes. 'he first tpe /hen the t/o fields help each other is

kno/n as cumulati&e compounding /hile the other is differentiall compounding.

+.C. s hunt g e ne r a t or H f a d.c. shunt generator after building up its &oltage to the rated no load

&oltage at the rated speed is loaded its terminal &oltage drops. 'he reasons of &oltage drop in d.c.

shunt generator /ith load are (i) due to armature resistance drop. (ii) due to armature reaction. (iii)

decrease of field current due to reduction in armature &oltage.

'he terminal &oltage drop of the d.c. shunt generator /ith load makes this tpe of d.c. generator

unsuitable for constant &oltage application. 4 fairl good constanc in terminal &oltage can be

achie&ed b cumulati&e compounding.

Cu m u lati & e l c o m pou n ded +.C. , e ne r ator H

'he &oltage drop in armature resistance and the drop due to armature reaction take place in this case

also but the are compensated b the increase in flu due to the m.m.f established b series /inding

carring the load current depending on the degree of compensation.

+ iffe r entia ll c o m pound e d +.C. g ene r a t or@

'he reasons for the terminal &oltage drop due to load in this case are (i) armature resistance drop (ii)

armature reaction effect (iii) reduction in flu per pole due to the series filed /inding m.m.f. opposing

the shunt filed /inding m.m.f.

'he series field /inding m.m.f opposing the shunt filed /inding m.m.f is mainl responsible in this

case for rapid fall of the terminal &oltage compared /ith the shunt generator or cumulati&e compound

generator characteristics.


Motor #enerator

#32 V $.#4 #32V 34

:.>.6 % !52 :.>.6 % !52


16/65


. +.C. &oltmeter (2-#32V) % No.

#. +.C. ammeter - (2-#24) % No.

3. :heostat (#227 #.84) % # Nos.

!. Lamp load (#52V #22) % Nos.

"irc'it diagram

3: p'int starter

C:C;' +4,:46 *lot the terminal &oltage Vs load current cur&es for shunt differentiall compounded and

cumulati&el compounded d.c. generators on the same graph. No load terminal &oltage

should be same in all three cases.


17/65

)*ser+ation ta*les:

Constant speedH N r.p.m.

Ta*le

,a- or &h'nt #enerator &l! No! Terminal +oltage ,.- 0oad c'rrent ,$-

3

,*- or differentially compo'nded #enerator

&l! No! Terminal +oltage ,.- 0oad c'rrent ,$-

,c- or c'm'lati+ely compo'nded #enerator

&l! No! Terminal +oltage ,.- 0oad c'rrent ,$-

Preca'tions: %

. 4s gi&en in Eperiment % !.


18/65

EXPERIMENT 7

Name: % &peed "ontrol of !"! &h'nt Motor


. Speed Vs armature &oltage (*ield current being constant)

#. Speed Vs field current (4rmature &oltage being constant )

Theory: %

'he speed of the d.c shunt motor is gi&en b the relation

! == G

a

a

C(r.p.)

here VF applied &oltage

GaF 4rmature current :aF 4rmature resistance F *ield flu per pole in /ebers.

CF constant F Z P

38 A

here IF No. of armature conductors

;F No. of poles

AF No. of parallel path in armature /indings.

*or the epression for speed it is seen that the speed of d.c. shunt motor can be &aried b &aring

. 'he &oltage applied to armature

/! 'he armature circuit resistance :a

3! 'he field flu


#enerator Motor

#32 V 34 ##2 V #2 4

:.>.6 % 522 >o/er % 3 A 522 r.p.m


. :heostat (#227 #.8 4) % No.

#. :heostat (227 5 4) % No.

3. +.C. &oltmeter (2-#52 V) % No.

!. +.C. ammeter (2-.54) % No.

5. 'achometer % No.

9. Connecting /ires.


19/65

"irc'it diagram

3:p'int starter

Proced're: %

$ r ma t' r e + o lta g e c ont r o l

. 6ake the connections as per the circuit diagram.

#. Set the field rheostat to minimum and armature rheostat to maimum resistance &alue.

3. S/itch on the d.c. suppl and start the d.c. shunt motor /ith the help of 3-point starter.

!. 4dGust the field current to rated &alue.

5. Note do/n the speed the &oltage across armature and the field current.

9. Change the speed b &aring the rheostat in armature circuit. Note do/n the speed and

armature &oltage the field current remaining constant.

". :epeat the procedure for different field current.

8. >lot speed Vs armature &oltage characteristics for different &alues of field current.

l' x c ont r o l o r ield c ont r o l

. Aeep the rheostat in the armature circuit to ero &alue. Note do/n the &oltage across

armature the field current and speed.

#. Var the field current and note do/n corresponding speed keeping armature &oltage same.

3. Change the &oltage across the armature to some &alue b adGusting the rheostat in armature

circuit and repeat the procedure (#).

!. >lot speed Vs field current cur&es for different &alues of armature &oltage.


20/65

)*ser+ation Ta*le

a- $rmat're +oltage control

&l! No! ield c'rrent ,$- $rmat're +oltage ,.- &peed N ,r!p!m!-

3

*- l'x control

&l! No! ield c'rrent ,$- $rmat're +oltage ,.- &peed N ,r!p!m!-

Preca'tions:

4s gi&en in Eperiment % !.


21/65

EXPERIMENT 6

Name: % 8ard 0eonard method of speed control of !"! sh'nt motor

$im: % 'o control the speed of a +.C. shunt motor b ard % Leonard method.

Theory: %

'he speed can be controlled o&er a /ide range in either direction b ard Leonard method. 'he

ard Leonard sstem consists of a motor - generator set and the main motor /hose speed is to be

controlled. 'he ecitation current for both motor and generator is obtained from the eciter mounted

on the same shaft as the generator. 'he ard Leonard set is started b starting the dri&ing motor.

M achin e sp ecif icat io n

Ind'ction motor !"! #enerator !"! motor Exciter

3->hase 521 #32V $4 #32 V $4 #32V #4

". A !22 V !4 !.! A 3A 2.!9 A

:.>.6 - !#2 :.>.6 - !#2 :.>.6 % 222 :.>.6 - !#2


. +.C. &oltmeter (2-#52V) % No.

#. +.C. ammeter (2-.54) % No.

3. :heostat double barrel (#22 7 #.8 4) % No.

!. 'achometer % No.


22/65

"irc'it diagram

4

V (2-#52 V)

0

A (2-.5 4)

C:C;' +4,:46 *


23/65

Proced're: %


#. S/itch on 3-phase 4.C. suppl. Start 3-phase nduction motor b using the Star-+elta starter.

3. n field control keeping the armature &oltage constant at 22B of rated &alue &ar the field

current. Note do/n field currents and corresponding speeds.!. :epeat steps 3 for armature &oltage constant at "5B of the rated &alue.

5. n armature &oltage control keeping the field current constant at the rated &alue &ar the

armature &oltage. Note do/n armature &oltages and corresponding speeds.

9. :epeat step 5 for the field current constant at "5B of its rated &alue.

". +ra/ (i) speed Vs. armature &oltage graphs /ith field current constant and (ii) speed Vs. field

current graphs /ith armature &oltage constant.

)*ser+ation Ta*les:

$rmat're +oltage constant

&l! No! $rmat're +oltage ,.- ield c'rrent ,$- &peed , rpm -

3

ield c'rrent constant

&l! No! ield c'rrent ,$- $rmat're +oltage ,.- &peed , rpm -

3

Preca'tions:

. 6otor speed should not go much abo&e its rated &alue.


24/65

EXPERIMENT 9

Name: % &in*'rne;s test

$im: % 'o conduct S/inburneIs test on +.C. Shunt machine and determine its efficienc /hile

operating as (i) 6otor and (ii) ,enerator

Theory: %

t is a simple indirect method of determining the efficienc of +.C. Shunt machine. n this method field

resistance and armature resistance are measured separatel. So losses can be easil calculated on

&arious loads since on no load mechanical output of the machine is ero so the /hole of the input on

the no-load is used to suppl in turn all the losses in the machine i.e shunt field copper loss and

armature copper loss and rotational loss. 'he rotational loss includes iron friction and /indage lossD

iron loss consist of hsteresis and edd current loss.

M ac h in e & p ecif ic a t io n

+.C. shunt machine

! A #32 V 9.8 4

!52 rpm


. +.C. &oltmeter (2-322V) % No.

#. +.C. ammeter (2-24) % No.

3. +.C. ammeter (2-#4) % No.

!. :heostat (#22 7 #.84) % No.

5. :heostat (22 7 54) % No.

9. 'achometer % No.

"irc'it iagram 0:;'int Starter

V ,


25/65

Proced're: %


#. Set the field rheostat in minimum resistance position and rheostat in armature circuit at ero

&alue. S/itch on the d.c. suppl and start the motor /ith the help of starter.

3. 4dGust speed of motor to rated &alue /ith the help of field rheostat and armature rheostat.!. Note do/n meters reading and no load speed.

5. Calculate rotational losses and constant losses.

9. +etermine efficienc for different loads

". >lot efficienc Vs output characteristics

)*ser+ation Ta*les:

$-

&l! No! &'pply +oltage ,.- No load armat're c'rrent ,$- ield c'rrent ,$- &peed , rpm -

3

2- $rmat're resistance meas'rement

&l! No! $rmat're +oltage .a ,.- $rmat're "'rrent Ia ,$- Ra = .a> Ia ,ohm-

3

"- ield resistance meas'rement&l! No! .oltage across sh'nt

field inding .f ,.-

ield c'rrent If ,$- Rf = .f> If ,ohm-

3

Preca'tions:

4s gi&en in Eperiment % !.


26/65


27/65


28/65


29/65

EXPERIMENT 1 38 A)


33/65

Proced're:

a) o/er input () Secondar s.c.

current (4)

3.

Preca'tion: %

. 'he open circuit test must be performed at rated &oltage

#. 'he short circuit test must be performed at rated current.

3. Lo/ po/er factor /attmeter should be used.


34/65

EXPERIMENT 1/

Name: % 0oad test on a single phase transformer

$im: %

. 'o perform load test at unit po/er factor.

#. 'o calculate &oltage regulation and efficienc

Theory: %

'he &oltage appearing across the secondar terminal of a transformer depends upon the load

connected. deall the secondar &oltage must be independent of the load. 'he figure of merit /hich

determines the &oltage drop characteristics of a transformer is the &oltage regulation. t is defined as

Voltage regulation =Secondar! Voltage at no load Secondar! voltage at load

188K

Secondar! Voltage at no load0esidesD the coils and the core of the transformer cause copper loss and core loss reducing the

efficienc of the transformer. t is defined as

Efficienc! ="utput

188KInput

&pecification of transformer

>hase % Single

>o/er F 3AV4

>rimar Voltage F #32V

Secondar Voltage F 5V

*reuenc F 521

>rimar current F 3.#4

Secondar current F #9.4


. 4utotransformer (Single phase #32V 54 521)

#. 4.C. ammeter (2-54) %No.

3. 4.C. ammeter (2-324) % No.

!. attmeter (#24 322V) % No.

5. 4.C. &oltmeter (2-#52V) % No.

9. 4.C. &oltmeter (2-52V) %No.

". Load (#22 2V) % No.


35/65


36/65

EXPERIMENT 13

Name: % 2acA%to%*acA test on to single%phase transformer

$im: %

. 'o determine the iron loss full load copper loss and eui&alent circuit parameters.

#. +ra/

a) B efficienc VsB load cur&e for 2.8 pf lagging 2.8 pf. Leading and unit po/er factor

load.

b) B regulation VsB load cur&e.

Theory: %

'his test pro&ides data to calculate regulation efficienc and heating and is done /hen t/o similar

transformers are a&ailable. 0efore performing this test polarit test is carried out on both

transformers. rimar #32 V 3.# 4mps

Secondar 5 V #9. 4mps


. '/o Single-phase transformer

#. 4.C. ammeter (2-5 4) %No.

3. 4.C. ammeter (2-32 4) % No.

!. 4.C. &oltmeter (2-#52 V) % No.

5. 4.C. &oltmeter (2-#5 V) % No.

9. attmeter (5 4 #52 V) % No.

". attmeter (32 4 52 V) % No.


37/65

"irc'it iagram

Proced're: %

. 6ake connections as per the circuit diagram.

#. Set the autotransformers to ero output &oltage position.

3. Connect the secondaries in phase opposition the procedure for /hich is as follo/sH

Connect the terminals S and S together keeping s/itch A open. ith the primar suppl

on note the &oltage across S# and S#. 'he &oltmeter /ill read either ero or t/ice the

secondar &oltage. f it is ero the secondaries are in phase oppositionD other/ise connect

S of transformer and S# of transformer # (the &oltage no/ across S# of transformer and

S of transformer # should be ero).

!. 4fter checking /hether the secondaries are in phase opposition connect them to a lo/

&oltage suppl as sho/n in the circuit diagram.

5. ith the help of autotransformer in primar circuit adGust the primar &oltage to the rated &ale

V. ith the help of autotransformer in the secondar circuit (s/itch A closed) adGust the


38/65

secondar inGected &oltage to the reuired &alue so that the circulating current # is eual to

the rated secondar current.

9. Note do/n the &oltage current and po/er of both the primar and secondar sides.

)*ser+ation Ta*le: %&l! No! .1 ,.- I1 ,$- 81 ,8- ./ ,.- I/ ,$- 8/ ,8-

1!

Preca'tion: %

. 'he transformers used should be similar.

#. 'he secondar &oltage should be increased carefull so that circulating current does not

eceed the rated secondar current.

3. 'he multipling factor of the /attmeter should be noted.


39/65

EXPERIMENT 14

Name: % &cott "onnection

$im: %

. 'o connect t/o single phase transformers to obtain balanced t/o-phase suppl from

balanced three-phase suppl.

#. 'o determine the 3-phase current for different &alues of #-phase

a. 0alanced load

b. ;nbalanced load.

and dra/ the corresponding phasor diagram.

Theory: %

'/o-phase electric euipments such as electric furnaces or t/o-phase control motors ma

need a t/o-phase suppl /hereas onl three-phase suppl ma be a&ailable. 'his problem can be

sol&ed /ith the help of Scott connected transformer /hich makes the three-phase to t/o-phase

transformation.

0 means of a Scott connected transformer a three-phase sstem can be con&erted to a t/o-

phase one and &ice-&ersa. *or Scott connection t/o similar single-phase transformers ha&ing N

number of turns in the primar and N# number of turns in the secondar are reuired.


40/65


41/65

b) *or balanced load

Sl. No. >rimar line&oltage (V)

>rimar linecurrent (4)

Secondar Voltages (V) Secondar Current (4)

Vab Vbc a c

3.

c) *or unbalanced load

Sl. No. >rimar line &oltage (V) >rimar currents (4) Secondar&oltages (V)

Secondarcurrents (4)

V40 V0C VC4 4 0 C Vab Vbc a c

3.

Preca'tions: %

. 'he 3-phase line &oltage applied to the primar of the Scott connected transformer should not

be more than the rated primar &oltage of the main transformer.


42/65

EXPERIMENT 15

Name: % 0oad test on 3%phase ind'ction motor!

$im: % 'o obtain load characteristics of a 3-phase induction motor:

>ercent speed 01> Efficienc 'orue >o/er factor and Slip &ersus >ercent normal full-load

current cur&es.

Theory: %

e kno/ that as the induction motor is loaded the speed drops do/n current increases and

the po/er factor impro&es. 'he purpose of the load test is to stud the beha&iour of an induction

motor under load.

Suppose the motor is running on no load. 'he slip is small and a small no load current flo/s.

4s the mechanical load on the motor is increased the speed drops due to its retarding effect the

current and the rotor po/er output all increase. 'hus the motor adGust itself to the ne/ load

conditions of increased output. Corresponding to /hich the input current also increases and the

speed drops a

little.

4t the light load the p.f. is lagging and poor and under rated load it is lagging but impro&es.

WN'he 01> is gi&en b the relation BHP = .

888

/here is the spring balance reading (lb) and N is the speed (r.p.m.)

Machine &pecification:

3->hase nduction 6otor

!22 M !!2 V !."5 4 3 1>

52 1 $52 r.p.m.


. 4.C. &oltmeter (2-522 V) % No.

#. 4.C. 4mmeter (2-2 4) % No.

3. attmeter (2 4 522 V) % #Nos.

!. 'achometer


43/65

A

"irc'it iagram

! ( ) *

!+

" ' ,tarter

Proced're: %


#. Aeep the belt on brake drum in loose position s/itch on 3-phase 4.C. suppl.

3. Start the motor using ?MO starter

!. 'ighten the belt around the brake drum so that the ammeter reading becomes about .#5

the rated current.

5. Note do/n the readings of &oltmeter spring balance ammeter /attmeter and speed and

enter them as the first set of readings in tabulation

9. +ecrease the tension in the belt o&er brake drum so that the ammeter sho/s a reading

less than the pre&ious &alue.

". Note do/n the readings of &oltmeter spring balance ammeter /attmeter and speed and

enter them in tabulation as net set of readings

8. :epeat steps 9 " till the belt tension is completel released i.e. motor run on no-load

)*ser+ation Ta*le:

&l! No! Inp't line+oltage ,.-

Inp't linec'rrent ,$- Inp't Poer ,8-

&pring *alancereading ,l*- &peed

,rpm-81 8/ 81 B 8/

3

Preca'tions: %

. 'he 3-phase induction motor should be started on no-load (0elt on brake drum in looseposition) using Star-+elta starter.


44/65

EXPERIMENT 17

Name: % No% load and *locAed%rotor test on 3%phase ind'ction motor

$im: %

. 'o determine eui&alent circuit parameters

#. 'o dra/ circle diagram and calculate po/er factor efficienc and slip at full load

3. 'o dra/ performance characteristicsH

>ercent ' 01> p.f. and s &ersus percent normal full-load current cur&es.

Theory: %

,a- 2locAed Rotor Test

'his is similar to the short-circuit test on the transformer because the stand still condition

(obtained b holding or blocking the rotor and thus not allo/ing it to rotate /ith reduced &oltageapplied) is like the short circuit on transformer. 1ence the blocked-rotor test is also termed as short-

circuit test.

,*- No 0oad Test

n the no-load test the motor is run at no load /ith the rated &oltage applied the slip is then

uite small and hence the total rotor resistance becomes uite large. +ue to this /e can ignore the

rotor current and sa that the rotor (secondar side of the machine) is open circuited. 1ence the no-

load test is also termed as open-circuit test.

Machine &pecification:

3-phase nduction motor

&tator Rotor

!22M!!2 V !.$5 4 322 V 5.# 4

!22 rpm 52 1 /indingH ?

01> F 3


. 3-phase auto transformer % No.

#. 4.C. ammeter (2-24) % No.

3. 4.C. &oltmeter (2-522V) % No.

!. 4.C. &oltmeter (2-322V) % No.

5. attmeter (24 522V) % #Nos.


45/65

-

"irc'it iagram

&'autotransformer

Proced're: %

a- or *locAed rotor test


#. Set the autotransformer to ero output and s/itch on the 3-phase 4.C. suppl.

3. 4ppl a lo/ &oltage (holding the rotor shaft so as to disallo/ rotation) so that the stator

current does not eceed the rated &alue.

!. 4t the rated stator current note do/n the ammeter &oltmeter and /attmeter readings.

*- or no load test


#. Set the autotransformer to ero output and s/itch on the 3-phase 4.C. suppl.

3. Start the motor b appling the &oltage graduall (for slip ring motors cut off eternal

resistances)

!. 4ppl a &oltage eual to the rated &alue and note do/n the reading of /attmeters &oltmeter

and ammeter.

c- &tator and Rotor inding resistance meas'rement

. 6easure d.c. resistance of stator and rotor (in case of /ound rotor) b using ammeter-

&oltmeter method.

"ircle diagram

'he circle diagram of an induction motor enables us to calculate its performance under different load

conditions.


46/65

)*ser+ation Ta*les:

a) 0locked-rotor test

&l! No! Inp't line +oltage

,.-

Inp't line c'rrent

,$-

Inp't Poer ,8-

81 8/ 81 B 8/

1!

b) No-load test

&l! No! Inp't line +oltage

,.-

Inp't line c'rrent

,$-

Inp't Poer ,8- &peed

,r!p!m!-81 8/ 81 B 8/

1!

Preca'tions: %

. 0efore s/itching on the mains set the &ariac to ero output

#. n case of slip ring motor short-circuit the slip-rings before starting.

3. 0locked rotor test should be performed at rated current

!. No %load test should be performed at rated &oltage


47/65

EXPERIMENT 16

Name: % 0oad test on 3 %phase ind'ction motor ,Electrical loading-

$im: %

. 'o stud the beha&iour of an induction motor under load

#. 'o plot the speed Vs output efficienc Vs output and torue Vs load graphs

Theory: %

4s for a load test on an motor the suppl &oltage remains the constant uantit the load put on the

motor (using a coupled d.c. ,enerator and loading it) is increased and the corresponding reading for

the current po/er and the speed are noted

&pecification of Machines:

3 %Phase Ind'ction Motor !"! &h'nt #enerator

!!2V 8.3 4 1> F 5.552 1 !52 r.p.m.

3 A#32 V 3 4

!32 r.p.m.


. 4.C. &oltmeter (2-522V) % No.

#. 4.C. ammeter (2-24) % No.

3. +.C. &oltmeter (2-322V) % No.

!. +.C. ammeter (2-#24) % No.

5. +.C. ammeter (2 % 4) % No.

9. :heostat (#22 #.8 4) % No.

". Lamp load (#22 #52 V) - No.

8. attmeter (2 4 522 V) % #Nos

$. 'achometer % No.

"irc'it iagram

3 phaseautotransformer


48/65

Proced're: %


#. >ut all the load s/itches off. Set the ,enerator field rheostat to its maimum. Set the &ariac to

ero output. S/itch on 3-phase 4.C. suppl.

3. Start the motor (at no-load) b appling &oltage through the &ariac graduall increasing to therated &oltage and run to its normal speed.

!. Ecite the +.C. shunt ,enerator to its rated &oltage. Note the po/er input to the motor and

speed at no-load.

5. >ut some load on the ,enerator and bring the +.C. ,enerator &oltage to its rated &alue. Note

do/n the +.C. ,enerator &oltage and current induction motor input &oltage input current

input po/er and speed.

9. 'ake more readings increasing the load graduall till the full load is reached maintaining the

d.c. generator &oltage constant to its rated &alue and note do/n meters readings.

)*ser+ation Ta*le

&l! No!

Motor side !"! #enerator side

Inp't line

.oltage ,.-

Inp't line

c'rrent ,$-

Inp't Poer ,8- &peed .oltage ,.- "'rrent ,$-

# P #

3

Preca'tions: %1! n case of /ound-rotor induction motor short-circuit the slip-rings before starting

/! Start the induction motor using a starter.


49/65

EXPERIE!"# $%

!ame: & '() and S() test on a single&phase

indu*tion motor

Aim:&

+A, ,tudythat

1. The 1'phase induction motor does not de/elop starting tor0ue withoutauiliary windings

#. The starting tor0ue in a 1'phase induction motor is de/eloped by

connecting capacitor either in main or auiliary winding. ote the direction

of rotation in each case2

+-, Determine the losses and the e0ui/alentcircuit parameters

+), Draw the e0ui/alent circuit and mention the /aluesof parameters.

+., Determine the performance characteristics of the test machine using

the e0ui/alent circuit parameters.

"heory: &

,ingle'phase induction motors ha/e many applications such as dri/ing

fans3 blowers3 compressors etc. Most of the fractional horse power motors

are single'phase induction motors.

The beha/iour of a single'phase induction machine can be studied by (a+

double re/ol/ing field theory or (b+ cross field theory. As the double

re/ol/ing field theory is simpler and gi/es a clearer physical concept3 it is

preferred for the analysis of single phase machines.

4n double re/ol/ing field theory3 a pulsating mmf produced by the stator

(main+ winding of a pure single'phase machine can be resol/ed into two

oppositely rotating mmf 5f and 5b of

constant and e0ual magnitude which can bemathematically epressed by

# =NI

Lc's ()ct's

()M +2

6 5f 7 5b


50/65

t +

where 6 effecti/e number of turns formain winding

4 6 main winding current

8owe/er flues f and b produced by the mmf9s 5f and 5b

respecti/ely are of e0ual magnitude only at standstill. -nder running

condition (at all speeds+ f : b. ;ach component of flu produces

electromagnetic tor0ue i.e. forward tor0ue Tf is produced by forward flu f

and bac


51/65

Thus once the motor is started using the starting winding mmf3 it

continues the rotation. The tor0ue'slip characteristic of a single'phase

induction motor has been shown in the

figure below.

ig: 'orue diagram of a single-phase induction motor

&pecification of Machine

Single-phase nduction motor

#32V 5.! 4mps

:.>.6. % !#2

01> .5


. 4.C. &oltmeter (2-#52V) % No.#. 4.C. &oltmeter (2-52V) % No.3. 4.C. ammeter (2-54) % No.!. 4.C. ammeter (2-24) % No.5. attmeter (54 322V) % No.9. attmeter (24 52V) % No.". Single-phase autotransformer (2 4 322 V) % No.

8. Capacitor (2 *) % No.


52/65

"irc'it iagram

Proced're: %

or )!"! Test


#. Close s/itch S. Set the &ariac to ero output and s/itch on the single-phase 4.C. suppl.

3. Start the motor b appling the &oltage through the &ariac graduall upto the rated &oltage.

!.


53/65

o r s t a to r ind in g r es i s t a n ce m e as ' r eme n t

6easure the +.C. resistance of the main and auiliar /indings b using 4mmeter-&oltmeter method

and find the effecti&e 4.C. &alue

)*ser+ation Ta*les:,a-


54/65

EXPERIMENT 1?

Name: % .oltage reg'lation of a single%phase alternator *y direct loading method

$im: % 'o plot percent &oltage regulation &ersus load current cur&e b direct

loading

Theory: %

n direct loading method the alternator is dri&en at snchronous speed and the terminal &oltage is

adGusted to its rated &alue V. 'he load is &aried until the &oltmeter and ammeter indicated the rated

&alues. 'hen the entire load is remo&ed /hile the speed and field ecitation are kept constant.

f open circuit &oltage in read as E2 then

B regulation =E

8V

188KV

&pecification of Machine

!"! &h'nt Motor &ingle Phase $lternator

1> F 5

#32 V #2 4

522 r.p.m.

3 AV4 52 1

#32 V 3 4 cos F 2.8

522 r.p.m.

$ p p a r a t' s r e (' i r ed. 4.C. &oltmeter (2 % #52 V) % No.

#. 4.C. ammeter (2 % 5 4) % No.

3. +.C. ammeter (2 % 4) % No.

!. Single barrel rheostat (#$2 7 .5 4) % #No.

5. +ouble barrel rheostat (#22 7 #.8 4) % No.

9. Lamp load (#22 #52 V)

". 'achometer % No.


55/65

"irc'it iagram

"IR"CIT I$#R$M )R .)0T$#E RE#C0$TI)N ) 1%P@ $0TERN$T)R 2D IRE"T 0)$IN# MET@)

Proced're: %

. 6ake the connection as per the circuit diagram#. Aeeping +.C. motor field rheostat in minimum resistance position start the +.C. motor /ith the

help of starter and adGust the motor speed to snchronous speed /ith the help of motor fieldrheostat.

3. Load the alternator to its rated current maintaining rated &oltage and snchronous speed.!. Note do/n the alternator load current field current speed and terminal &oltage.5. 'hro/ off the entire load. Note do/n the no-load &oltage after adGusting the speed and field

ecitation to its rated &alue.9. :epeat this for "5B 52B and #5B loading.

)*ser+ation: %

$t load $t no load

Sl.No.

'erminal &oltage(V)

LoadCurrent (4)

*ieldcurrent (4)

Speed(rpm)

'erminal&oltage (V)

*ieldcurrent (4)

Speed(rpm)

3

Preca'tions: %. 0efore starting +.C. shunt motor set the field rheostat to its minimum resistance &alue

position.#. +.C. motor must be started using a starter.

3. 6aintain snchronous speed through out the eperiment.


56/65

EXPERIMENT /lot on the same grapha. lot percent &oltage regulation Vs. percent load current.3. +ra/ phasor diagram at rated armature current for 2.8 pf lagging.

Theory:

'he terminal &oltage of an alternator changes /ith load. 1o/e&er the userIs &oltage shouldbe maintained /ithin pre-specified limits /hich demands proper &oltage regulation. 'he &oltageregulation is an important characteristics of an alternator and its predetermination is necessar for itsnormal operation (as /ell as for designing suitable ecitation control schemes)

'he &oltage regulation of an alternator is the per unit &oltage rise at its terminals /hen a gi&en

load at a gi&en po/er factor is thro/n off the speed and ecitation current remaining constant.:egulation is go&erned b the armature resistance leakage reactance and armature reaction.

'he snchronous impedance method is one of the eperimental methods of determining &oltageregulation. 'his method is based on the simple eui&alent circuit and the phasor diagram gi&en in thefigure. 'he per phase impedance =s F :a P G@s is called the snchronous impedance /here :arepresents the armature resistance and @s F @l P @ar (combination of leakage reactance and armaturereaction reactance) is the snchronous reactance. +etermination of =s reuires the kno/ledge of


57/65

&pecification of machines:

!"! &h'nt Motor 3%Phase $lternator

5 1.>. #32V $.3 4522 r.p.m.

M % #32 M !22 V".5 M !.35 4

cosF 2.8 3 AV4522 r.p.m.


. +ouble barrel rheostat (#227 #.84) % No.

#. +.C. ammeter (2-4) % No.

3. 4.C. &oltmeter (2-322V) % No.

!. 4.C. ammeter (2-24) % No.

5. 'achometer % No.

9. :heostat (3227 .54) % No.

"irc'it iagram

3:p'int starter

"IR"CIT I$#R$M )R )PEN "IR"CIT TE&T )N 3% $0TERN$T)R


58/65


59/65

or &!"! Test


#. Set the d.c. motor field rheostat in minimum resistance position and the potential di&ider

across the alternator field to gi&e ero output.

3. S/itch on d.c. suppl. Start the d.c motor /ith the help of 3-point starter.!. 4dGust the speed of the motor to snchronous speed.

5. Aeeping speed constant graduall increase the alternator field current from its initial &alue of

ero until full load armature current is achie&ed.

9. Note the corresponding &alues of armature current and alternator field current.

". S/itch off d.c. suppl .

or meas'rement of armat're resistance ,per phase-

. 6easure the armature resistance :dc b using the 4mmeter-Voltmeter method.

#. 'ake effecti&e resistance as :a F .5 :dc

)*ser+ation Ta*les:

a-

)pen "irc'it Test &hort "irc'it Test

Sl. No. *ield current (4) 'erminal &oltage (V) *ield current (4) Short circuit current (4)

3

*- $rmat're resistance meas'rement

Sl. No. Voltage (V) Current (4) :dc F Voltage M current () :a F .5 :dc ()

3

Preca'tions:

. Snchronous speed should be maintained throughout the eperiment.

#. n case of s.c. test lo/ &oltage should be generated so that s.c. current does not eceed

rated current.

3. 0efore starting d.c. shunt motor its field rheostat must be set to minimum resistance position.


60/65

a

EXPERIMENT /1

Name: % . c'r+es of a three phase synchrono's motor

$im: % ,a- +ra/ the armature current &ersus field current cur&es for

(i) No load

(ii) 1alf load and

(iii) *ull load

,*- +ra/ the unit p.f. l ine on the abo&e cur&es

Theory: %

n a po/er sstem maGorit of loads /ork at lagging po/er factors /hile for economicoperation it is essential that the sstem po/er factor be made as close to unit as possible. 'hesnchronous motor has the propert that its po/er factor &aries /ith the &ariation of ecitation andthis propert can be used in impro&ing the po/er factor of a sstem. 'herefore the stud of &ariation

of armature current and po/er factor of a snchronous motor /ith its ecitation is important.*or a snchronous motor the armature current phasor is gi&en b

/here

I =V EZ

$

V is the applied &oltage phasor and is constantE is induced emf phasor and its magnitude depends on the d.c. ecitation and=s is snchronous impedance

*rom the abo&e relation it is seen that the magnitude and angle of the phasor a depend on

the &alue of d.c. ecitation. 'he phasor diagrams (gi&en belo/) sho/ that a snchronous motor dra/slagging current /hen it is under-ecited and leading current /hen o&er-ecited. 'he ecitation at unitp.f. is kno/n as the normal ecitation. f the ecitation is increased abo&e the normal ecitation thearmature current increases and the p.f. is leading. Similarl if the ecitation is reduced belo/ thenormal ecitation the armature current increases again but p.f. /ill be lagging p.f. 4t normal ecitationthe armature current /ill be minimum. 'herefore the cur&e sho/ing the relationship bet/een thearmature current and the ecitation is of V-shape hence called V-cur&e.

'he obGecti&e of this eperiment is to determine and plot the V-cur&es of a snchronous motorunder constant po/er output.


61/65

&pecification of machines:

!"! &h'nt Motor 3%Phase $lternator

5 1.>

#32V $.3 4

522 rpm

M - #32M!22 V

".5 M !.35 4

3 AV4 cosF 2.8

Ect. % #32 V


. 4.C. ammeter (2-".5 4) % No.

#. +.C. ammeter (2- 4) % No.

3. 4.C. &oltmeter (2-522 V) % No.

!. Single barrel rheostat (#227 .5 4) % No.

5. +ouble barrel rheostat (#227 #.8 4) % No.

9. >hase seuence meter % No.

". *reuenc meter % No.

8. 'achometer % No.

"irc'it iagram

Snchr'ni-ingS+itch

L13:;h

008 =L2 8 H-

s&pp$

L3

"IR"CIT I$#R$M )R ETERMIN$TI)N ) . "CR.E ) $ 3% &DN"@R)N)C& M)T)R


62/65

Proced're: %


#. Set the eternal resistance in the field circuit of the d.c. machine to the minimum &alue.

S/itch on d.c. suppl.

3. Start the d.c. machine as motor using 3-point starter and bring it to the snchronous speed.!. Snchronise the alternator to the mains. 0efore t/o three-phase sstems can be

snchronised the follo/ing conditions should be metH

a) *reuenc of both the sstems should be same.

b) 'erminal &oltages must be eual.

c) >hase seuence of both the sstems should be same.

5. 4fter fulfilling the snchronising conditions snchronie the alternator to the 3-phase suppl

b using null-&oltmeter method.

9. +isconnect the d.c. machine armature b taking out the fuse connected in the armature

circuit.

". No/ the snchronous machine is /orking as a snchronous motor and d.c. machine as

separatel ecited generator.

8. ith no load on the d.c. generator adGust the snchronous motor field current to the minimum

such that the armature current is of rated &alue.

$. No/ &ar the snchronous motor field current in the increasing direction in steps up to a &alue

corresponding to rated armature current. Note the simultaneous readings of field current and

armature current at each step. (/ith increase in field current the armature current /ill

decrease up to a minimum &alue and then increase gi&ing V-shape cur&e)

2. 'hese readings /ill gi&e V-cur&e under no load condition.

. No/ load the snchronous motor b connecting load to the d.c. generator and repeat steps 8

and $ for constant output of #5B 52B and 22B of full load.

)*ser+ation Ta*le:

&l!No! ield c'rrent ,$- $rmat're c'rrent ,$-

3.

Preca'tions:

. Snchroniing s/itch should ne&er be closed unless (a) all the snchroniing conditions are

satisfied and (b) the needle of &oltmeter (used as null &oltmeter) connected bet/een the

main and alternator suppl terminals comes to ero.


63/65

EXPERIMENT //

Name: % &lip Test of a synchrono's machine

$im: % 'o determine @d and @ of a snchronous machine and dra/ the phasor diagram for 2.8 p.f

lagging.

Theory:

Se&eral reactances ha&e been defined depending upon the tpe of snchronous machine and

time of the transient in /hich one is interested. *or salient pole machine there are t/o classes of

reactances pertaining to polar and interpolar ais (d-and -ais) respecti&el. +etermination of the

reactances of snchronous machines help in predicting short circuit currents from the point of &ie/ of

design of circuit breakers.

'he direct and uadrature ais snchronous reactances @d and @ can be determined b a

slip test. ith the field open circuited the salient pole alternator is dri&en b a prime mo&er at a speed

slightl less than the snchronous speed. 'he armature is connected to a reduced balanced three-

phase &oltage (to limit armature current) /hich sets up mmf /a&e rotating in the same direction as

the rotor. 'he rotating armature mmf ais graduall changes on account of the slipI bet/een

coincidence /ith the d-ais and -ais successi&el. hen the d-ais and the armature mmf ais

coincide the &oltage applied to the armature is eual to the &oltage drop caused b @d. Similarl /hen

the armature mmf ais is in uadrature /ith the d-ais the applied &oltage is eual to the &oltage drop

caused b @. 'he reluctance of the magnetic circuit &aries cclicall bet/een an upper and a lo/er

limit and the armature current conseuentl changes in the re&erse sense. 'herefore the armature

current and &oltage undergo &ariation at slip freuenc. f the slip is small the maimum andminimum &alues of &oltage and current can be read from an indicating &oltmeter and ammeter. 'he

&alues of @d and @ are gi&en bH

d =%axi&u& value of ar&ature voltage < p'a$e

%ini&u& value of ar&ature current

#32 V $ 4

522 r.p.m.

M % #32 M !22 V

".5 M !.35 4

3 AV4 cos F 2.8

522 r.p.m.

Ect. % #32 V


64/65


. 4.C. ammeter (2-".5 4) % No.

#. 4.C. &oltmeter (2-522 V) % No.

3. 4.C. Voltmeter (2-322 V) % No.

!. +ouble barrel rheostat (#22 7 #.8 4) % No.5. 'achometer - No.

9. >hase seuence meter % No.

". 'hree phase &ariac % No.

"irc'it iagram

/ 0S

122

3

142V

&'point starter

+2&522 V,

V1(%A

.)Supply

# #.= A ('& !+

&'hase /ariac

"IR"CIT I$#R$M )R &0IP TE&T ) &DN"@R)N)C& M$"@INE

Proced're: %


#. Set the 3-phase &ariac output to ero. S/itch on d.c. suppl. Close s/itch S after setting

potential di&ider output to ero.

3. ith minimum resistance in the field circuit start the d.c. motor /ith the help of 3-point starter.

4dGust field rheostat for snchronous speed.

!. ncrease alternator field current to generate about rated &oltage.

5. S/itch on 3-phase 4.C. suppl. 4dGust the 3-phase &ariac output &oltage nearl eual to

alternator generated &oltage.

9. Check the phase seuence of alternator &oltage and the &ariac output &oltage using phase-

seuence meter. f the are not same interchange an t/o of the &ariac output terminals and

check phase seuence again.

". S/itch off +.C. suppl. S/itch off 3-phase 4.C. suppl. Set the three-phase &ariac output to

ero and the +.C. motor field rheostat for minimum resistance &alue.

8. 4fter ensuring the phase seuence remo&e the alternator field ecitation (open s/itch S) and

connect the ;V terminals of the alternator to the corresponding :?0 output terminals of the

&ariac.


65/65

$. *ollo/ing proper procedure start d.c. motor and bring it near to snchronous speed. S/itch

on the 4.C. suppl and appl a small &oltage. 'he &oltmeter reading connected across the

field /inding terminals Q A should fluctuate and remain /ithin rated &alue if the slip is small

and direction of rotation is correct. 'he armature current reading should also fluctuate.

2. ncrease the 4.C. &oltage applied to the armature from the &ariac such that maimum currentis nearl eual to the rated full load current of the armature.

. Note the maimum and minimum &alues of armature applied &oltage and current. Calculate

the applied &oltage per phase (Vp F VL M 3).

#. :ecord the readings for different applied &oltages.

)*ser+ation Ta*le:

&l! No! &peed ,r!p!m!- $rmat're .oltage per phase ,.- $rmat're c'rrent per phase ,$-

Maxim'm Minim'm Maxim'm Minim'm

3

Preca'tions: %

. Ensure that the direction of rotation of the rotor is in the direction of rotating magnetic field.

#. Aeep alternator field /inding open.

Machine Laboratory Manual - II

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