DOL Starter

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Working of DOL Starter

 The wiring connection of DOL starter with start and stop buttons is shown in figure below. The DOL starter main terminals are connected between the mains supply terminals and motor terminals while the control circuit is energized with two terminals of three phase supply as illustrated in figure




When the start button is pressed, current will flow through one phase to the control circuit and the contactor coil to the other phase. This current energizes the contactor coil which makes to close the contacts thereby three phase supply is connected to the motor. Since the start button is of pushbutton, when it is released the control circuit still maintains the supply through hold-on contact.

If the stop button is pressed or overload relay coil operate, the current path through contactor coil will break and hence the contactor contacts drops out, thus breaking the supply to the motor. Once the power supply is interrupted, again the supply to the motor is established by pressing the start button.

The thermal overload protection relay operates depending on the heating effect of the load current. When the load current heats the thermal coils, bimetallic strip inside of it expands such that it trips out the spring-loaded contact in the control circuit. The speed at which relay operates decided by the current adjustment. Typically it will be four to five times the rated motor current.

DOL starter can be operated remotely for remote control switching of motor from any number of desired places. For remote control switching one should remember that, all the remote ON push buttons must be connected in parallel to ON pushbutton of the starter whereas all remote OFF push buttons must be connected in series with OFF pushbutton of the starter. Connect the remote ON and OFF switches as shown in dotted line in the figure for remote control operation.

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