E x pe'r,rt, en[- - L
STUDY
oF
3-Punse
IrVDuc'TroN
MOICR. SiA R
IAJ
T'R A NS\E NTS
OBJECTIVE:
a)
Studir of-3-phase Induction Motor Starting Transients *,ith the following Starling methods and
record cun'ent transients and compare the lbllowing:
i.
ii.
iii.
b)
DOL stafiing
Y-Astarting
Autotransfonner starting
Measure the parameters of tlie induction machine by conclucting no-load and blocked rotor
tests at rated voltagc and at raled curent.
c)
Sin-rulatc Squirrel Cage Induction l\,{otor in softwarc rvith the above starting methods.
APPARATUS REQUIRED:
Apparatu,v
T,pe
Runge
Ouantih;
Variac
Mr-iltimeter
Wattmeter
Arnmeter
TPDT sr,vitch
Tachor:reter
Star Delta Starter
THEORY:
Starting of Induction N{otors:
Valions methods can be used to reduce starting currents of induction motor
.
.
.
.
.
Stat-Drlru-Slarring
Auto-transformer-Starling
Stalting via chokes or resistors
Staning using elecu'onic soft starters
Starting using fi'equency converter
In this experiment, we will study a few of them
1.
Direct Online Starting:
l
Here, tlie rnotor is started by being subjected to the f'ull voltage of tire po\\,er supply.
Conscqucntly. high starting curl'ent florvs through the motor. This type of starting is suitable for
small inotors belorn, 5 HP (3.75 kW). It is not a prefen'ed method of starting.
2. Star-Delta starters
This is applicable for a delta connected motor. To reduce the star-ting current of the motor,
it is hor,vever, configured in a star connection during starling. The voltage applied to the individual
motor windings is theretbre reduced b,v a factor of l/r,-l 1:0.58) u,'hi1e the starting line current is
reduced to one third of the direct on iine starting cur:rcnt. During running condition, the motor is
sw'itched over to a delta connection thereby applying full voltage across the motor.
Due to the reduced starting torque, the star-delta-connection is suitabie for drives with a high
inertia mass with a load torque which is low or only increases r.vith increased specd. It is preferably
used for applications u'here the drive is subjected to a lou,cr load torque at starting i.e. fans,
centri llges, plrmps. venti lators, etc.
3. Autotranslbrmer-startin g
An autotransfomer starter enables the start of squirrci-cage nrotors using a reduced starting
cuffent, since the voltage is reduced during start. Contrary to a star-delta starteL, only three motor
connections are required.
TEST:
Following test are performed on the given motor:
1. No load test
2. Blocked rotor test
3. Retardation test
4. DOL Stading
5. Star Delta Staning
6. Auto transfonner starling.
NAME PLATE RATINGS:
CIRCTIIT DIAGRANIS:
iDr
Ql
IN
DUCTION''4AC i.'II!F
U
U2
lrt
\i)
!vl
W2
F1
UJ
5
rrr
c
N
O
tL
t0
nzET
u8
r4{>
tYl
{
F
$
U
At N near to Ns
jeuF
F
:l
83<E3
IIII
STATOR
LPF
ROTOR
NO LOAD TEST
Figl: For No Load
INDUCTION MACH]NI
HPF
B1nEL
UJ
Test
W1
U2
'rr
L
rrI
N
<o
of11
*.
o
t-
V2
!,J)
R) Z
I
t
N=0
!
f
!'/ 2
E]
\J2
HPF
STATOR
Fie2: Blocked Rotor Test
ROTOR
SQUIRREL CAGE
lNDUCTION MACHINE
lt')
UE
-Tflq;,
€.
ul
E
#
N
uI
Z
*.
F
l4
IL
\11
Li-
o
u1
m
$
'/r
v?
ti00,/
wl
F.
f
__1*
,/
@
w2
ROTOR
STATO&,
Fig3: For DOL and autotransformer start
INDUCTION I,lACHINE
DldLr
cl
tll
*t$-:-
{.
rl
,-
UJ
N
U
:t
o
U
ft
II
t
E
&
o
LL
t4
AlztZ
{d
F
o
F
UJ<E3
c
s
(,
{v}
l-j
l
Y
t*
!
i.il
n
d
!-
a
STATOR
ROTOR
Frg4: For star delta start
PROCEDURE:
No Load Test:
1.
2.
3.
Make the connections as per the circuit diagram in figl
Apply rated voltage to the rnduction motor through the tlree-phase VARIAC.
Note down the readings of porver, input voltage, input curent, speed.
.
Sr*)n
S*c
o
-t
a
j)et't
Blocked Rotor Test:
1. Make the connections as per the circuit
diagram in./ig2.
2. By adjusting the three-phase VARIAC allolv rated current thrcugh the stator rvhen rotor is
blocked.
3. Note down the readings of power, input voltage. input cun'ent.
Retardation Test:
L Make the connections as per the circuit diagram of no load test.figl.
2. Run the machine under no load condition by applying rated voltage through VARIAC,
and
note dorvn tire readings of no load speed of the machine.
Switch off the suppiy, notc down the time for the speed of the machine to drop to zero.
3.
STARTING I\{ETHODS:
DOL STARTIIT.IG:
l.
Connect the Induction motor as per the circuit diagram tnjfig3
Makc auto transtbnncr voltage to machine ratcd value.
Note down the values of starting current in ammeter.
2"
3.
STAR-DELTA STARTING:
1.
3.
Connect the Induction motor as per the circuit diagram in fi?4
Connect the star dclta starter kit in between supply and motor.
Make auto transformer voltagc to machine rated value and press the grccn button in the
4.
kit.
Note dorvn the values of-starting cur:rent in ammeter.
2.
AUTO TRA\ISFORMER STARTI}TIG :
1.
2.
3.
Connect the Induction motor as per the circuit diagram in.fig3
\{ake auto transfonner voltage to machine rated value.
Note down the values of starling cun'ent in arruneter'.
EXPERTMENTAL OBSERVATIONS
A*S
:
I{O LOAD TEST:
Ii,(A)
Vr,(V)
Fi"(W)
Speed
I
{oo
t
f,v
v
lvo
t.
t)
tt l.
ti
-*+
+s4c
BLOCKED ROTOR TEST:
Ii,(A)
Vi,(V)
Pm(W)
RETARDATION TEST:
Time taken by motor to drop to zero speed
from.
rpm is. . .. . ..seconds.
STARTI]\G METHODS:
Turns ratio
input Line starting Line current DOL
*uto transformer (A)
voltage (1)
i
starting Line current Y-A
(A)
40
57.7
60
70
80
90
100
PRTCAUTIONS:
l.
2.
Care must be taken while loading thc machine, i.e., current should not exceed the rated
value of either of the machines.
N{achine should be given voltage through a VARIAC slowly to avoid high starting current.
EXPERIMENTAL QUIZ:
1.
3.
Why Direct on Lrne stalting method is not preferred?
Which ratio of auto transformer u'ili give the starting pedbmrance same as in star delta
method and rvhy'?
What is the relation betrveen starting currents of DOL, star delta starlel- and auto
4.
transicrrmer starl?
What is the reiation between starting Torques of DOL, star delta stafier and auto
2.
translonner start?
REFERENCES:
l.
Fundamentals of Electric Drives by Gopal K. Dubey,l'trarosapubliccttiott,2"d edition
,2001.
,t'