Len!s Law
Flemings Let "and rule
Interaction o two magnetic felds
 
Induction  #hen the magnetic
$ux through a circuit is changing an induced EMF is setu% in that circuit and its magnitude is %ro%ortional to the rate o change o $ux&
  Simulation
Len!s Law ' (he direction o
an induced EMF is such that its e)ect tends to o%%ose the change %roducing it&
Simulation
Flemings Right "and rule*sed to measure
 
Flemings Let "and rule
 
 
 
Production o (hree Phase Rotating Magnetic Field
RMF may +e set u% in two-%hase or three- %hase machines,
 (he num+er o %ole %airs must +e the same as the num+er o %hases in the a%%lied .oltage,
 
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S%eed o RMF
 (he magnetic feld esta+lished rotates at a s%eed gi.en +y
 
 
 
Sli%
 Induction Motor- Intro,  (he induction motor is the most commonly
used ty%e o ac motor, It is sim%le6 low cost and rugged in construction,
 
 
 
measured in RPM 
expressed as a percentage 
The greater the slip speed, the greater is the force on
 each conductor and the torque exerted y the !hole"  
 
Starting Current  (he starting current is .ery high which may
damage the stator winding,
 (o reduce this hea.y starting current6 star- delta starting switch is used,
 
 
  is small and inductance high,
 (hus on starting rotor current and the rotor em are nearly :3 degrees out o %hase,
 
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As the rotor current come into %hase with the rotor em with increased rotor s%eed ;decreased sli% and inducti.e reactance< the rotor and the stator $ux comes more into %hase and the tor/ue increases,
Torque- Running
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Methods = Im%ro.ing Starting  (or/ue In creasing the resistance o the rotor
conductors
 
 
 (he single %hase induction motor %roduces a %ulsating feld,
 
S%lit Phase Induction Motor 
 (wo %hases are %roduced +y s%litting a single %hase, A ca%acitor is inserted in
one o the windings and is called a %ermanent-s%lit ca%acitor motor,  (he direction o the motor is
 
0o need or sli% rings and thereore less maintenance,
"as a high starting current reduced +y star- delta switch,
"as a %oor starting tor/ue,
 
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?irection o rotation can +e re.ersed +y interchanging any two stator %hases, Is o two ty%es de%ending on motor
construction@ S/uirrel Cage or Sli% Ring
 
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*ses in Aircrat 7, Constant s%eed with .arying loads and
 
Synchronous Machine Construction
synchronous s%eed i,e, the s%eed o the RMF,
Stator is similar in construction to that o an induction motor6 so same %rinci%le is a%%lied to the synchronous motor rotor,
 
Synchronous Motor- Princi%le
 
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An increase in the load !ill cause the rotor to lag the stator field ut still maintain
synchronous speed" Increase in load has increased the torque component, ut the
field strength has decreased due to the increase in length of the air gap et!een the
rotor and the stator"
If the synchronous motor is o#erloaded it pulls out of synchronism and comes to
rest" The minimum amount of torque !hich causes this is called the $ pull out
torque%"
&ightly
loaded
motor 
Starting (or/ue It cannot +e started rom a standstill +y
 
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Im%ro.ement o starting tor/ue It is started +y using a s/uirrel cage within a
rotor construction and thereore starts as an induction motor,
 
7, re/uires to +e started +y an external %rime mo.er,
, Runs only at synchronous s%eed6 this is an ad.antage where continuous s%eed is re/uired +ut a disad.antage where a .aria+le s%eed is re/uired,
 
Maintenance Practices-A,C, Motors
Clean6 +ut dont orget to ins%ect +eore and ater cleaning
ChecD electrical connections or security6 the insulation to +e in satisactory condition,
Examine or signs o o.er heating
ChecD that the motor is secure
?o an audi+le checD
Ensure that the motor is not o.er heating when o%erating6 a rule o thum+ is that i it is too hot or the hand6 it is too high,
#hen re%lacing a motor always ensure that the load6 .al.e has not sei!ed,
Also ensure that the motor o%erates in the correct direction 
End o Motors