7 single phase Electrical and Electronics Engineering

EEE related topics

1. Single Phase
Induction Motor
Dr. Sanjay Jain
Department Of EE/EX

2. Application :-The single-phase induction machine is
the most frequently used motor for refrigerators,
washing machines, clocks, drills, compressors,
pumps, and etc.
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3. The single-phase motor stator has a laminated iron
core with two windings arranged perpendicularly.
1. One is the main and
2. The other is the auxiliary winding or starting
winding

5. The single-phase induction motor operation
can be described by two methods:
–Double revolving field theory; and
–Cross-field theory.
• Double revolving theory is perhaps the
easier of the two explanations to understand
• Learn the double revolving theory only

6. Doublerevolvingfieldtheory
•Asingle-phaseaccurrentsuppliesthemain
windingthatproducesapulsatingmagnetic
field.
•Mathematically,thepulsatingfieldcouldbe
dividedintotwofields,whicharerotatingin
oppositedirections.
•Theinteractionbetweenthefieldsandthe
currentinducedintherotorbarsgenerates
opposingtorque

8. Double revolving field theory
• Each of the rotating fields induces a voltage in the
rotor, which drives current and produces torque.
• An equivalent circuit, similar to the equivalent
circuit of a three phase motor, can represent each
field
• The parameters of the two circuits are the same
with the exception of the slip.

9. Double revolving field theory
• The two equivalent circuits are connected in series.
• Fig. shows the equivalent circuit of a singlephase
motor in running condition.
• The current, power and torque can be calculated
from the combined equivalent circuit using the Ohm
Law
• The calculations are demonstrated on a numerical
example

12. AC Motor:::
•AnAC motoris anelectric motordriven by analternating current(AC).

13. Types of AC Motor::: [depending on the type of rotor used]
1. The first type is theinduction motoror asynchronous motor:
This type relies on a small difference in speed between the rotating
magnetic field and the rotor toinducerotor current.
2.The second type is thesynchronous motor:
This type does not rely on induction and as a result can rotate exactly
at the supply frequency or a sub-multiple of the supply frequency.

16. Types of Single Phase Motors Are:::
[construction & method of starting]
These motors are designed to operate from single phase supply, are
manufactured in large no. of types for the use in home, offices,
factories etc. small motors come in Kilo Watt power ratings.
•Induction Motors
•Repulsion Motors
•A.C. Series Motors
•Un-exited Synchronous Motors

17. Double Revolving Field Theory:::
1.If the rotor is given an initial rotation in either direction, the torque
due to the rotating field acting in the direction of initial rotation coil
will be more than that due to the other rotating field and the motor
will develop a net positive torque in the same direction as the initial
rotation.
2. Thus the motor will keep running in the direction of initial rotation.
3. According to this theory, any alternating quantity can be resolved into
two rotating components which rotate in opposite directions and each
having magnitude as half of the maximum magnitude of the alternating
quantity.

18. 3.In case of single phase induction motors, the stator winding
produces an alternating magnetic field having maximum magnitude
of Φ
1m.
4.According to double revolving field theory, consider the two
components of the stator flux, each having magnitude half of
maximum magnitude of stator flux i.e. (Φ
1m/2).
5. Both these components are rotating in opposite directions at the
synchronous speed N
swhich is dependent on frequency and stator
poles.

19. •Let Φ
fis forward component rotating in anticlockwise direction
•while Φ
bis the backward component rotating in clockwise direction.
•The resultant of these two components at any instant gives the
instantaneous value of the stator flux at the instant.
•So resultant of these two is the original stator flux.

20. fig shows the stator flux and its two components Φ
fand Φ
b.
At start both the components are shown opposite to each other in the
Fig.1(a).
Thus the resultant Φ
R= 0.
This is nothing but the instantaneous value of the stator flux at start.
After 90
o
, as shown in the Fig. 1(b), the two components are rotated in
such a way that both are pointing in the same direction.
Hence the resultant Φ
Ris the algebraic sum of the magnitudes of the
two components. So Φ
R= (Φ
1m/2) + (Φ
1m/2) =Φ
1m. This is nothing but
the instantaneous value of the stator flux atθ= 90
o
as shown in the Fig
1(c).
Thus continuous rotation of the two components gives the original
alternating stator flux.

22. •Both the components are rotating and hence get cut by the motor
conductors.
•Due to cutting of flux, e.m.f. gets induced in rotor which circulates
rotor current.
•The rotor current produces rotor flux.
•This flux interacts with forward component Φ
fto produce a torque in
one particular direction say anticlockwise direction.
•While rotor flux interacts with backward component Φ
bto produce a
torque in the clockwise direction.
•So if anticlockwise torque is positive then clockwise torque is
negative.

23. At start these two torque are equal in magnitude but
opposite in direction.
Each torque tries to rotate the rotor in its own
direction.
Thus net torque experienced by the rotor is zero at
start. And hence the single phase induction motors
are not self starting.

24. Torque speed characteristics:::
•The two oppositely directed torques and the resultant torque can be shown effectively
with the help oftorque-speed characteristics.

26. Starting methods:::
osingle-phase capacitor-start motors
ocapacitor-run motors
osplit-phase motors
oshaded-polemotors
osmall poly phase induction motors.

27. Single Phase Induction Motor
• The single-phase motor starting torque is zero
because of the pulsating single-phase magnetic flux.
• The starting of the motor requires the generation of a
rotating magnetic flux similar to the rotating flux in
a three-phase motor.
• Two perpendicular coils that have currents 90°outof-
phase can generate the necessary rotating
magnetic fields which start the motor.
• Therefore, single-phase motors are built with two
perpendicular windings.

28. The phase shift is achieved by
connecting
–a resistance,
–an inductance, or
–a capacitance
in series with the starting winding.
• Most frequently used is a capacitor to
generate the starting torque.

35. Capacitor start induction motor:::

36. Capacitor run motors:::

37. Split phase motor:::

40. Shaded pole motors:::

41. Blocked Rotor test for Induction Motor:::
•Blocked rotor testis conducted on aninduction motor. It is also known asshort circuit testor
locked rotor test or stalled torque test.
•From this testshort circuit currentatnormal voltage,power factoron short circuit, totalleakage
reactance,starting torqueof the motor can be found.
•The test is conducted at low voltage because if the applied voltage was normal voltage then the
current flowing through the stator windings were high enough to over heat the winding and
damage them.
•Theblocked rotor torque testis not performed on a wound rotor motors because the starting
torque can be varied as desired. However,blocked rotor current testis conducted on squirrel cage
rotor motors.
{some one can hold this
shaft to block the rotation}
0-10A
0-300V

42. Method:::
•In the blocked rotor test, therotoris locked
•A low voltage is applied on the stator terminals so thatfull load currentflows in the
stator winding.
•The current, voltage and power input are measured at this point.
•When the rotor is stationary theslip ,S=1.
•The test is conducted at 1/4
th
the rated frequency as recommended by IEEE.
•This is because the rotor's effective resistance at low frequency may differ at high
frequency.
•The test can be repeated for different values of voltage to ensure the values obtained are
consistent.
•As the current flowing through the stator may exceed the rated current, the test should
be conducted quickly.
•By using the parameters found by this test, the motor circle diagram can be constructed.

43. No Load Test of Induction Motor:::
•By the name no load test it means that there is no load-that is load is zero. But it is exact
opposite. No load means infinite load test. It is because in no load there is NO load , and no load
means it is open circuit . Open circuit means infinite resistance.
•But that was the case in transformers, where you can open circuit the low voltage of transformer
and obtain readings. But how will you do that in Induction motor? How can you make infinite
resistance at loadside?
•If slip=0, then Rl' will be infinite. And you can make slip zero by making synchronous
speed Nsequal to actual speed N.
•So slip will be zero. Load resistance will be infinite.
No load at output of motor
0-300V
0-10A

44. Method:::
•Connect the circuit.
•Supply the rated voltage to induction motor, keep it running.
•The current drawn by motor is quit low
•Take care of the voltmeter should be of voltage ratings of induction
motor & the ratings of ammeter should be low because the current
drawn by motor is very small.
•Take the readings of voltmeter, ammeter and wattmeter.