10-01-2012, 12:55 PM
LINEAR INDUCTION MOTOR
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INTRODUCTION
In a sector motor when the sector is laid out flat and a flat
squirrel-cage winding is brought near to it ,we get a Linear
Induction Motor.In practice,instead of a flat squirrel-cage
winding ,an aluminium or copper or iron plate is used as a
‘Rotor’.The flat stator produces a flux that moves in a straight
line from its one end to the other at a linear synchronous speed
given by:
Vs = 2Wf
As the flux moves linearly,it drags to rotor plate along with it in
the same direction . However, in many practical applications,the
‘Rotor’is stationary,while the stator moves .
For eg: In high speed trains,which utilize magnetic leviations
the rotor is composed of thick aluminium plate that is fixed to the
Ground and extends over the full length of the track .
VARIABLE VOLTAGE & VARIABLE FREQUENCY LIM SYSTEM
Early developments in LIM have been done at EPFL.In the newer LIM applications, the existing motor is reused with variable voltage and variable frequency & this achieved with a modern IGBT PWM-Inverter fed through a diode rectifier from the AC Network.
The output of the PWM-Inverter can be controlled measuring only the DC voltage, which needs only one voltage sensor.
MOTOR(STATOR)
The used LIM is a three-phase Linear Induction Motor with double inductor. In this utilisation, the neutral point isn’t connected, but a connector exists so it can be done if desired in the future.
Its main characteristics are:
· Sn= 36[kVA] : nominal apparent power
· In=41[A] : nominal current
· Un=165[V] : nominal phase voltage
· p=1 : number of pole pairs
· tp=129[mm] : pole length
· vs=12 [m/s] : synchronous speed
· Ns=58[turns/inductor]
· Zn=12: number of slots
· Star coupling, free neutral point
· d=2[mm] : air gap
RAIL(ROTOR)
The motor rail is a simple V-shaped aluminium I-profile carrying and guiding the moving stator by rolls.Steep and reduced power climbing segments simulate conditions similar to a roller coaster, allowing high accelerations and fast movements but also stand-still under load conditions, as test-conditions for the control performances.
