15-10-2016, 10:44 AM
SOFT START OF 3 PHASE INDUCTION MOTOR BY USING 2 NUMBERS BACK TO BACK SCRS IN EACH PHASE
1459146254-File1389864521.pptx (Size: 1.55 MB / Downloads: 7)
Project overview
These Solid State Switches are phase controlled in a similar manner to a light dimmer, in that they are turned on for a part of each cycle.
The average voltage is controlled by varying the conduction angle of the switches.
Increasing the conduction angle will increase the average output voltage.
Controlling the average output voltage by means of solid state switches has a number of advantages.
One of the major advantages being the vast improvement in efficiency relative to the primary resistance starter, due to its low on state voltage of the solid state switches.
Typically, the power dissipation in the starter, during start, will be less than 1% of the power dissipated in a primary resistance starter during start.
Another major advantage of the solid state starter is that the average voltage can be easily altered to suit the required starting conditions.
By variation of the conduction angle, the output voltage can be increased or reduced, and this can be achieved automatically by the control electronics.
Three Phase Induction Motor
It consists of the fixed stator or frame, a three-phase winding supplied from the three-phase mains and a turning rotor
There is no electrical connection between the stator and the rotor
Stator and rotor are made of highly magnetizable core sheet providing low eddy current and hysteresis losses
Working of project
To start the motor with low current, two SCR’S are connected back to base in each phase.
They are triggered slowly initially and gradually the triggering pulse is increased, so that motor gets high current after a time delay when windings are in the position of withstanding the high current.
To trigger the gates of SCRS the op-amps are used.
Op-amp is configured to get a level voltage that will initially be high and gradually fall to zero.