30-12-2010, 12:26 PM
VIVEK DESHMUKH
FAZAL METAKAR
AVDHUT PAWAR
SHRIRAM AMILKANTHWAR
SHIRISH KEDAR
FAZAL METAKAR
AVDHUT PAWAR
SHRIRAM AMILKANTHWAR
SHIRISH KEDAR
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3-Phase Induction Motors Introduction
• 3-phase induction motors
are simple, low cost,
and easy to maintain.
• They run at essentially
constant speed from
zero-to-full load.
• Therefore, they are the
motors most frequently
encountered in industry.
Induction Motor Components
A 3-phase induction motor has two main parts:
• A stator – consisting of a steel frame that supports a hollow,
cylindrical core of stacked laminations. Slots on the internal.
• A rotor – also composed of punched laminations, with rotor slots for
the rotor winding.
Induction Motor Components
Squirrel cage rotor consists
of copper bars, slightly
longer than the rotor,
which are pushed into the
slots.
The ends are welded to
copper end rings, so that
all the bars are short
circuited.
In small motors, the bars
and end-rings are diecast
in aluminium to form
an integral block.
Induction Motor Components
A wound rotor has a 3-phase winding, similar to the stator winding.
The rotor winding terminals are connected to three slip rings which turn with the rotor. The slip rings/brushes allow external resistors to be connected in series with the winding.
The external resistors are mainly used during start-up –
under normal running conditions the windings shortcircuited
externally.
Induction Motor: Operating principle
The following sequence of events takes place:
1. A voltage E = BLv is induced in each conductor while it is being cut by the Flux (Faraday’s Law)
2. The induced voltage produces currents which circulate in a loop around the conductors (through the bars).
3. Since the current-carrying conductors
lie in a magnetic field, they experience a mechanical force (Lorentz force).
4. The force always acts in a direction to
drag the conductor along with the
magnetic field.
Induction Motor – Rotating Field: Direction of rotation
The phase current waveforms
follow each other in the
sequence A-B-C.
This produces a clockwise rotating
magnetic field.
If we interchange any two of the
lines connected to the stator,
the new phase sequence will
be A-C-B.
This will produce a counter clockwise rotating field,
reversing the motor direction.
• 3-phase induction motors
are simple, low cost,
and easy to maintain.
• They run at essentially
constant speed from
zero-to-full load.
• Therefore, they are the
motors most frequently
encountered in industry.
Induction Motor Components
A 3-phase induction motor has two main parts:
• A stator – consisting of a steel frame that supports a hollow,
cylindrical core of stacked laminations. Slots on the internal.
• A rotor – also composed of punched laminations, with rotor slots for
the rotor winding.
Induction Motor Components
Squirrel cage rotor consists
of copper bars, slightly
longer than the rotor,
which are pushed into the
slots.
The ends are welded to
copper end rings, so that
all the bars are short
circuited.
In small motors, the bars
and end-rings are diecast
in aluminium to form
an integral block.
Induction Motor Components
A wound rotor has a 3-phase winding, similar to the stator winding.
The rotor winding terminals are connected to three slip rings which turn with the rotor. The slip rings/brushes allow external resistors to be connected in series with the winding.
The external resistors are mainly used during start-up –
under normal running conditions the windings shortcircuited
externally.
Induction Motor: Operating principle
The following sequence of events takes place:
1. A voltage E = BLv is induced in each conductor while it is being cut by the Flux (Faraday’s Law)
2. The induced voltage produces currents which circulate in a loop around the conductors (through the bars).
3. Since the current-carrying conductors
lie in a magnetic field, they experience a mechanical force (Lorentz force).
4. The force always acts in a direction to
drag the conductor along with the
magnetic field.
Induction Motor – Rotating Field: Direction of rotation
The phase current waveforms
follow each other in the
sequence A-B-C.
This produces a clockwise rotating
magnetic field.
If we interchange any two of the
lines connected to the stator,
the new phase sequence will
be A-C-B.
This will produce a counter clockwise rotating field,
reversing the motor direction.
