28-08-2012, 01:46 PM
SPEED CONTROL OF INDUCTION MACHINE
SPEED CONTROL.PPT (Size: 637.5 KB / Downloads: 51)
Variable voltage, constant frequency
To control the speed of the motor.
To control the starting and braking behavior of the motor.
To maintain optimum efficiency in the motor .
Fig a, b & c shows the semiconductor voltage
controller circuit for controlling the voltage.
By varying the firing angle ‘α’ of the thyristor or
triac, speed control of the machine can be obtained.
Single-phase and three phase voltage controllers
allows a stepless control of voltage from its initial
value.
These are also used for soft starting of motors.
Applications
It is applicable where torque demand reduces with speed i.e suitable in fan and pump drives.