Question

Sketch the lay out of a solid state soft starter motor for a bow thruster unit powered from a dedicated diesel alternator.

Outline the advantages of the system sketched in relation to systems deriving power from the main switch board and from dedicated diesel alternator without soft starter motor.

"Soft" Starting

This method of supplying a gradually increasing a.c. voltage during start-up generally refers to an efficient electronic switching technique.

A basic method shown in Fig, is to use back-to-back connected thyristors or triacs in the supply lines which are "gated" to delay "turn-on" within each a.c. half-cycle. This delayed switching applies a reduced average a.c. voltage to the motor.

The applied motor voltage is gradually ramped up by the starter software program until the full voltage level is reached. To achieve maximum efficiency, the electronic switching circuit can now be bypassed for normal running

In this system starting voltage is applied gradually

The thyristers are used back to back in the system.

The thyristers are gated to provide delay in each A.C. half cycle.

Eliminates arcing burning and mechanical movement.

They are capable of dealing with up to 1000A and 1000V

Reduced voltage to the motor not frequency