The number of stator poles produced in the rotating magnetic field of an 3phase induction motor having 3 slots per pole per phase is ________.
a) 12 b) 2 c)6 d) 8
Solution: P = 2n
= 2(3)
= 6
Sunday, February 28, 2010
= equivalent reactance due to the power develop by the rotor
S= slip
Rs-1= rotor resistance referred to the stator
X2-1= stator reactance referred to the stator
Induction motor = rotating inductor transformer
IT= stator current/ph
¬IR = rotor current/ph
I2= component of I1 that will supply ¬IR
IN=no load current
I= magnetizing current
r2= rotor resistance/ph
r1= stator resistance/ph
X1= stator leakage reactance/ ph
X2= stator leakage reactance/ ph
Xn= magnetizing reactance
S= slip
Rs-1= rotor resistance referred to the stator
X2-1= stator reactance referred to the stator
Induction motor = rotating inductor transformer
IT= stator current/ph
¬IR = rotor current/ph
I2= component of I1 that will supply ¬IR
IN=no load current
I= magnetizing current
r2= rotor resistance/ph
r1= stator resistance/ph
X1= stator leakage reactance/ ph
X2= stator leakage reactance/ ph
Xn= magnetizing reactance
AC MOTORS
Induction motors (1 & 3)
Is one in which the motor field is induced by currents flowing through the stator. The rotor circuit has no connection whatsoever to supply the circuit. The power factor of this motor is lagging and operate with a lagging pf.
General types of 3 and 1 INDUCED MOTOR
a) Squirrel cage rotor type = its rotor is self contained and resembles a bird cage. The rotor conductors are permanently short circuited by end rings.
Speed characteristic: nearly constant or adjustable speed
Torque characteristic: in general it has medium starting torque
Uses: blower, compressor, pump, prime mover of generators
b) Wound rotor = its rotor has insulated coil of wire and resembles a DC armature. The rotor conductors are connected to slip rings and shorted through branches.
Speed characteristic: variable speed
Torque characteristic: high starting torque
Uses: hoist, crane, escalator, conveyor, elevator, etc.
CIRCUIT DIAGRAM
Is one in which the motor field is induced by currents flowing through the stator. The rotor circuit has no connection whatsoever to supply the circuit. The power factor of this motor is lagging and operate with a lagging pf.
General types of 3 and 1 INDUCED MOTOR
a) Squirrel cage rotor type = its rotor is self contained and resembles a bird cage. The rotor conductors are permanently short circuited by end rings.
Speed characteristic: nearly constant or adjustable speed
Torque characteristic: in general it has medium starting torque
Uses: blower, compressor, pump, prime mover of generators
b) Wound rotor = its rotor has insulated coil of wire and resembles a DC armature. The rotor conductors are connected to slip rings and shorted through branches.
Speed characteristic: variable speed
Torque characteristic: high starting torque
Uses: hoist, crane, escalator, conveyor, elevator, etc.
CIRCUIT DIAGRAM
Advantages of Rotating Field with Stationary Armature
1. Rotating field is comparatively light and can run with high speed.
2. High voltage can be generate due to high speed and there is very little difficulty in providing high voltage on a stationary part than a moving part.
3. It is easier to insulate armature coils for high pressure usually generated (6.6 to 11 kV). Since the stator is outside the rotor, so more space is available for greater insulation required for armature winding.
4. Very little difficulty is experience in supplying the field magnet current as it is very low in comparison with the armature current.
Relationship among f. P. and N
2. High voltage can be generate due to high speed and there is very little difficulty in providing high voltage on a stationary part than a moving part.
3. It is easier to insulate armature coils for high pressure usually generated (6.6 to 11 kV). Since the stator is outside the rotor, so more space is available for greater insulation required for armature winding.
4. Very little difficulty is experience in supplying the field magnet current as it is very low in comparison with the armature current.
Relationship among f. P. and N
Two Types of Rotor
1. Salient Pole or Projecting Pole Rotor
- it has large number of poles. It is made of cast iron or steel of good magnetic quality. These type of rotors are use in low speed and medium speed machines. These machines have short axial length and large diameter. Hydropower alternators and diesel engine alternators are of this type.
- it has large number of poles. It is made of cast iron or steel of good magnetic quality. These type of rotors are use in low speed and medium speed machines. These machines have short axial length and large diameter. Hydropower alternators and diesel engine alternators are of this type.
Construction of Alternator
1. STATOR –It is build up with stamping which are insulated with proper varnish. The stator is house in a frame which is fabricated from electricity welded steel plates.
2. ROTOR – Has the rotating magnetic field poles as in DC generator which is separately exited from source known as exciter.
2. ROTOR – Has the rotating magnetic field poles as in DC generator which is separately exited from source known as exciter.
General Types of Alternator
A. SYNCHRONOUS GENERATOR
A generator called synchronous because it is driven at constant speed (synchromous speed) and it is used in almost all type of application.
B. INDUCTION GENERATOR
It is an induction motor which run as generator with speed above synchronous speed. Its pf is usually leading and connected in parallel with a synchronous generator in order to supply power.
C. INDUCTION ALTERNATOR
It generates voltage at higher frequency (500 hertz to 10,000 hertz) it is used to supply power to induction furnace in order to hit and melt the metal.
A generator called synchronous because it is driven at constant speed (synchromous speed) and it is used in almost all type of application.
B. INDUCTION GENERATOR
It is an induction motor which run as generator with speed above synchronous speed. Its pf is usually leading and connected in parallel with a synchronous generator in order to supply power.
C. INDUCTION ALTERNATOR
It generates voltage at higher frequency (500 hertz to 10,000 hertz) it is used to supply power to induction furnace in order to hit and melt the metal.
ALTERNATOR (AC GENERATOR)
Is an electric machine that converts machine energy to electric energy in the form of alternating current?
An alternator is exactly the same as that dc generator. In fact all the generators alternators is which alternating voltages are set-up and it is the commutator which converts this ac into dc.
In the dc generator, it is essential for the armature to rotate in the magnetic field produced by the stationary magnetic field to give the unidirectional voltage. However in alternator it is not essential for the armature to rotate and either the armature or field can be made to rotate while the other is kept constant. But nowadays, armature is kept stationary and the field rotates under it.
An alternator is exactly the same as that dc generator. In fact all the generators alternators is which alternating voltages are set-up and it is the commutator which converts this ac into dc.
In the dc generator, it is essential for the armature to rotate in the magnetic field produced by the stationary magnetic field to give the unidirectional voltage. However in alternator it is not essential for the armature to rotate and either the armature or field can be made to rotate while the other is kept constant. But nowadays, armature is kept stationary and the field rotates under it.
Note: that the value arrived from equilateral triangle:
h = 2
= 0.866 X 100
= 86.6%
VAB = 240/_00
VBC = 240/_-1200
VCA = 240/_-2400
Solve for
VAO = 0.866(240)
Prove that VAO = 207.84V
= 207.84V
Equation:
VAB = VAO+VOB
VAO = VAB+VBO
= VAB+VBO
=240/_00+ VBC = 240/_00+ (240/_-1200)
VAO = 207.84/_-300
Prove that VCO = (0.50)(240)
VCO = 1200
VCO = -VOC
VOC = VOC
= 240/_-1200
= - (120/_-120)
= 120/_-1200+1800
VCO = 120/_600V
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