ec-i lab mannual

7/25/2019 Ec-i Lab Mannual

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EXPERIMENT NO: 1

Aim of the experiment:

Speed variation of DC motor by eld / ux control method.

Apparatus required:

Sl.n

o.

Name of the Item Type Range Quantity

1. D.. Shunt motor D.. !!"#$1%A$1&""R'

($&)'

1

!. * 'oint starter D.. !!"#$1%A$&)' 1*. Ammeter (.. "+!A D 1,. #oltmeter (.. *""# 1&. Rheostat or

armature

resistan-e

ire+

/ound

!""0$!A 1

. Ta-hometer digital !"""R'( 12. onne-ting /ires S..3. 4 S..3. As per

req.4. 5ine tester + &""# 1

T)67R8:

Field ux control method is based on the fact that by varying the ux

the motor speed can be changed and hence the name flux control

method. ! variable resistance "no#n as shunt eld rheostat is

connected in series #ith the shunt eld #inding to vary the eld

resistance and hence the shunt eld current. $he bac" emf of a D.C.

motor is given by


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Eb %PZN

60A

%&' %60EbA

PZ

%&' % ()Eb

#here ( %60A

PZ is constant.

%&' *Eb

%&' *

Eb

If +, * If

- hereIf

is eld current

%&' *VIaRa

If

ence this e0uation clearly states that speed of the D.C. motor

can be controlled above the rated speed by decreasing the current in

the eld circuit by including an external resistance in the form of a

rheostat as variable resistance.

ir-uit diagram:


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'ro-edure:+i- Connect the D.C. 1otor as per the circuit diagram.+ii- 2nsure that the external resistance connected in the eld

circuit is minimum.+iii- !fter ensuring step 3 +ii- s#itch on the D.C. supply.+iv- (eep the applied voltage to the armature constant at its rated

value. 4ary the eld current of the motor by varying the

rheostat resistance R1 in the eld circuit and record the eld

current and the corresponding speeds of the motor.+v- 5epeat step3 +iv- for various values of eld current till the

speed of the motor is about 6.7 times the rated speed of the

motor.+vi- 8ring the rheostat resistance 56to its minimum position again.+vii- S#itch o9 the motor supply to stop the motor.


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+viii- :lot the graph of the eld current + If - 4/s change in speed of

motor +'-.

Ta9ulation:

Sl.no

.

ield

-urrent;If IaRa - +"eeping eld current constant-

%&' * 4 > Ia + Ra ?5-

ir-uit diagram:


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Procedure:

+i- Connect the D.C. motor as per circuit diagram.+ii- 2nsure that the external resistance in the armature circuit is

maximum.+iii- !fter ensuring step3 +ii- s#itch on the D.C. Supply as a result

motor #ill start running at normal speed.+iv- (eeping the eld current to the shunt eld current constant

vary the voltage across armature by the external resistance in

the armature circuit.+v- 5ecord the applied voltage and the corresponding speed.+vi- 5epeat step3 +iv- for various values of applied voltage across

armature and record the corresponding speed.+vii- 8ring the external resistance to its maximum position again.+viii- S#itch o9 the main supply to stop the motor.

+ix- :lot the graph of the armature voltage +4a- 4/s speed of themotor +'-.


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Ta9ulation:

Sl.no

.

Armature

=oltage;=< in #75T

Speed of

motor;N


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EXPERIMENT NO: 3


Determination of open circuit characteristics +


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%& Eg * +"eeping ' constant-

ence at constant given speed no load emf Eg is directly

proportional to the flux per pole #hich in turn depends upon the

eld current +If-. $he characteristic curve sho#ing the relationshipbet#een the eld current + If - and generated emf Eg at no load and

at a constant speed is "no#n as magnetiAation characteristic or open

circuit characteristic.

IR?IT DI3RA(:

'ro-edure:6- Connect the D.C. motor and the D.C. generator as per circuit

diagram.B- !dust the rheostat in the eld circuit of the motor so that the

additionalresistance in this circuit is Aero.


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- Set the potential divider feeding to the eld circuit of the

generator for Aerooutput voltage.

7- S#itch on the D.C. supply to the D.C. motor and start it using the

starter. 1ove the starter arm slo#ly till the motor builds up thespeed and nally cut out all the resistance steps of the starter.

Starter arm #ill then be hold by the holding magnet of the starter.E- 5ecord the generator emf due to residual magnetism.- !dust the speed of the D.C. motor to rated value by varying the

resistance in the eld circuit/armature circuit.G- S#itch on the D.C. supply across the eld circuit of the generator.H- 4ary the eld current of the generator in steps and record its

value and the corresponding generated emf of the generator.


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6'6RI(6NT N7: ",


:lotting of external characteristic of D.C. shunt generator.

Apparatus required:

Sl.no.

Name of the item Type Range Quantity

6.D.C. shunt motor +as

prime mover-D.C. > 6

B. >:oint starter D.C. > 6. D.C. Shunt generator D.C. > 67. !mmeter 1.C. K>6K! +D.C.- 6E. 4oltmeter 1.C. K>KK4 +D.C.- 6. 5heostat > .E!EKL 6

G.$achometer

>K>EKKKK

rpm6

H. Mamp ban" load resistive > 6J. Connecting #ire S..N. > !s per re0.

Theory:

$he external characteristics of D.C. generator present the graphical

relationship bet#een the terminal voltage and the load current the

generator being operated at constant rated speed and #ith the same


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excitation as under no load condition. $he nature of the characteristics

depends upon.

6> 4oltage drop in the armature #inding.B> 4oltage drop at brush contact.> 4oltage external characteristic indicate the fall in the terminal

voltage as the load on the generator increases.

'ro-edure:

6> Connect the circuit of motor and generator as per the circuit

diagram.B> Set the rheostat +56- so that there is no external resistant in

the eld circuit of the motor.

> Set the rheostat +5- so that there is minimum externalresistant in the eld circuit of the resistant.

7> S#itch on the supply to the DC motor and start it #ith the help

on a three point starter. $he starter arm should be moved

slo#ly till the motor builds up its speed.E> !dust the speed of the motor to rated value by varying the

resistant in the eld circuit of the motor.> !dust the eld current of the generator by rheostat +5B- so as

the obtained rated voltage at no load.G> S#itch on the tamp bac" load and adust a certain value of load

current say approximately 6KI of full load current. 5ecord the

load current and terminal voltage.H> 5epeat step +7- for various the values of load current. $ill load

current of the generator.J> S#itch o9 the load on the generator.6K> $o stop the DC motor s#itch o9 the DC supply.

66> :lot he graph of load current IL VS terminal voltage +4-.

Ta9ulation:

Si.N

o.

Terminal

#oltage ;#EKKKK

rpm6

?S6 RATIN3:Fuse rating % 7K I of rated current% 7K/6KK ) 6G % .H !Q 6K !

Theory:


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;n this method the losses are measured separately and from their"no#ledge eOciency at any desired load can be predetermined. encethe only running test needed is the no load test. $his test is applicableto the machine in #hich ux is practically constant i.e shunt #ound

and compound #ound machines. $he machine is to run as a motor atits rated voltage. $he speed is adusted to rated speed #ith help ofshunt eld regulator. $he no load current and eld current aremeasured using ammeters. $his test is convenient and economicalbecause po#er re0uired to test a large machine is small i.e. only inputpo#er is re0uired. $he eOciency can be predetermined at any loadbecause constant losses are "no#n. ;n this test #e are not ta"ing intoaccount the change in iron loss from no load to full load. ;n this test itis impossible to "no# that #hether commutation #ould be satisfactoryat full load and #hether temperature rise #ould be #ithin specied

limits.

'R6A?TI7NS3

6. $he eld rheostat must be "ept in minimum resistance position.B. $he starter handle must be "ept in


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7R(?5A:

Constant Mosses C% 4;


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on-lusion:

EXPERIMENT NO: &'

Ai o! t"e e(perient:

Determination of eOciency and voltage regulation by open circuit test on single phase

transformers.

Apparatus required:

Sl.

No.

Name of the

items

Type Range Quantity

6. $ransformer 6>R 6 "va 6B. !mmeter 1.;. K>B! 6. attmeter dyn E! 6EKK4 67. 4oltmeter 1.;. K>KK4 6E. Single phase varic 6>R K>BGK4E! 6


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T"eor#:

;n the test lo# voltage #inding +primary- is connected to a supply of a normal voltage

and fre0uency +as per the rating of transformer- and the high voltage #inding is left open.$he primary #inding dra#s very lo# current hardly to E percent of full load current unde

this condition. !s such copper losses in the primary #inding #ill be negligible. $he mainly

iron losses occurs in the transformer under no load or open circuit condition #hich are

indicated by the #attmeter connected in the circuit. ence total iron losses % w

0

+#attmeter reading-. From observations of this test the parametersR

0 andXm of the

parallel branch of the e0uivalent circuit can also be calculated follo#ing the steps given

belo#.

:o#er dra#w

0 % V

0 ) I

0 cos,

$hus no load po#er factor cos,% W

0 / V

0 ) I

0

Core loss component of no load currentIm %

I0 cos

0

!nd magnetiAing component of no load currentIm %

I0 sin

0

20uivalent resistance representing the core loss R0 %4 Iw

1agnetiAing reactance representing the magnetiAing currentXm %4/

Im

Procedure:

i- Connect the circuit as per circuit diagram.ii- 2nsure that the setting of the variac is at lo# output voltage.


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iii- S#itch on the supply and adust rated voltage across the transformer circuit.iv- 5ecord no load current voltage applied and no load po#er corresponding to the

rated voltage of the transformer #inding.v- S#itch o9 the !.C. supply.

Ta)ulation:

Sl.n

o.

#oltmeter

reading ; V0

< in =olt

Ammeter reading

; I0 < In amp

attmeter

reading ;

W0 < in

/att1.

*alculation:

*onclusion:

;t is observed that since normal fre0uency is applied to the lo# voltage side normal

ux #ill be set up in the core. ence normal iron loss #ill occurs so in the !.C. test a #attmeter reading gives only the measurement of iron loss i.e. #att.

'o load currentI

0 %amp and no load po#er factor cos,%.


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6'6RI(6NT N7: "

Ai o! t"e e(perient: Determination of eOciency and voltage regulation by short circuit test on single phase

transformers.

Apparatus required:

Sl.n

o.

Name of the

items

Type Range Quantity

6. !mmeter 1.;. K>B! 6B. 4oltmeter 1.;. K>KK4 6. attmeter dyn > 67. $ransformer 6>R 6 "va 6

E. Single phase varic 6>R K>BGK4E! 6

. Connecting #ire insulated > !s per re0.G. Combination plier insulated > 6

T"eor#: ;n this theory test lo# voltage #inding is short circuit and lo# voltage hardly E to H

percent of the rated voltage of the high #inding is applied to this #inding. this test is

performed at rated current follo#ing in both #inding. ;ron losses occurring in the

transformer under this condition is negligible because of very lo# applied voltage. ence

the total loss occurring under short circuit are mainly the copper losses of both the

#inding #hich are indicated by the #attmeter connected in the circuit. $hus the total full

load copper loss%

Wse+reading of #attmeter-. $he e0uivalent resistance 5e0 and

reactance Te0 referred to a particular #inding can also be calculated from the observation

of this best follo#ing the step given belo#. 20uivalent reactance referred to .4. #inding.

5 e0 % Wse / I

2

also e0uivalent impedance to .4. #inding @e0% Vse /

Ise


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$hus e0uivalent reactance referred to .4. #inding T e0% Zeq2 ? Req2

Procedure:i- Connected the circuit as per the circuit diagram.

ii- !dust the setting of variac so that output voltage is Aero.iii- S#itch on the !.C. supply to the circuit.iv- ;ncreases the voltage applied slo#ly till the current in the #inding and of the

transformer is full load of rated value.v- 5ecord short circuit current corresponding applied voltage and po#er #ith full load

current follo#ing under short c"t test condition.vi- S#itch o9 the !.C. supply.

Ta)ulation:

Sl.n

o.

#oltmeter reading ;Vse

< in =olts

Ammeter

reading ; Ise

< in amp

attmeter

reading ;Wse < in /att

1.

*alculation:

*onclusion: From the above calculation it is observed that the parameter of the transformer

e0uivalent impedance +@e0-e0uivalent resistance +5e0-e0uivalent reactance +Te0- #here

found to to . respectively.

;t is observed that since the applied voltage is very lo# the resistance from losses are also

small and may be negligleble so in the short circuit test the #attmeter reading UseV

gives only measurement of copper loss.


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EXPERIMENT NO: &+

Ai o! t"e e(perient: :olarity test and parallel operation of t#o single phase transformers.

Apparatus required:

Sl.n

o.

Name of the

items

Type Range Quantity

6. $ransformer > > BB. !mmeter 1.;. > . 4oltmeter 1.;. > 6

. attmeter Dyn > 7. Moad > > 6E. Combination plier insulated > 6. Scre# driver > > 6G. Connecting #ire > > !s per re0.

T"eor#:

:arallel operation to transformer is fre0uently necessary in the po#er system net#or"

#hich consist of a number of transformers installed at generating stations substations etc

#hen operating t#o or more transformers in parallel connection +on the primary as #ell as

secondary side- their satisfactory performance re0uire the follo#ing condition must be

satised for single phase transformer.

a-. the same polarity.

b-. the same voltage ratio.


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Polarit#:

:olarity of the t#o transformers connected in parallel can be either right or #rong.

$he #rong polarity of the transformer connected in parallel #ould result in a dead short

circuit on the transformer.

,olta$e ratio:

!n e0ual voltage ratio of t#o transformers operating in parallel is necessary to avoid

no load circulating current. ;n case of une0ual voltage ratio circulating current #ill o# in

the close circuit formed by the primary and secondary sides even at no load #hich result

in additional I2

5 loss. $he no load circulating current should not be permitted to exceed

6KI of its normal rated value for satisfactory parallel operation.

Procedure:

i- $a"e t#o transformers having same voltage ratio and percentage impedance.ii- Find the polarity M.$. and M.. side of both transformer.iii- Connect the circuit as per the circuit diagram. 2nsure that the t#o secondary

have been connected properly as per the polarity determined.iv- Close the s#itch Us6V to energiAe both the primary. 2nsure that the s#itch UsBV is

"ept open in case the voltage ratio of the t#o transformer are une0ual. $here #il

be a circulating current #hich may be recorded.v- Close the s#itch UsBV adust a particular load on the secondary and record the

reading of all the instrument connected in circuit.vi- 5epeat step+v- for various value of load current up to the rated capacity of the

t#o transformer operating in parallel.vii- S#itch o9 the load slo#ly open the s#itchVsBV an then s#itch o9 supply to

primary of the transformer.

Procedure !or t"e polarit# c"ec- o! t"e trans!orer

)e!ore operatin$ in parallel:

i- Connected the circuit as per the diagram.ii- S#itch on the supply to the primary circuit #here the primaries of the

transformers are connected in parallel.

iii- $he voltmeter connected in the secondary circuit of the transformers #ill redeither Aero or t#ice of the secondary terminal voltage of each transformer.

iv- ;f the voltmeter reads Aero. Connected a6 to a6 and aB to aB for the secondary

to be in parallel.v- ;n case the voltmeter reads t#ice the secondary terminal voltage then

connected a6 to aB and aB to a6 for parallel operation of the t#o transformer.

Precautions:


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i- Connection should be connect and tight.ii- 4oltage ratio of both the transformer should be same.iii- Same polarity must be connected together.iv- Nive the rated voltage to the primary side.

Ta)ulation:Sl.n

o.

VL ;in

=olt

ec-i lab mannual

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