3 Phase Direct On Line Starter/ Explain with Circuit Diagram, DOL Direct online starter 

Different starting methods are used to start 3 phase induction motor like star delta starter, autotransformer starter, variable frequency drive,soft starter,dol starter(direct online starter) because the Induction motor draws a large current at starting.
Direct On-Line is the simplest and cheapest method used for starting three-phase motor. Dol is used for up to 5 HP motor. dol starter is more popular due to the low price.
DOL starter connects the motor directly to supply without a reduction in supply voltage and applies full line voltage to 3 phase motor. this is the main disadvantage of dol starter.
A small HP motor can be started simply by plugging into the power supply. But large HP motor required a special unit called a motor starter.
Direct online starter for 3-phase induction motor contain parts like miniature circuit breaker (MCB) for motor protection purpose, overload relay, power contactor, fuse unit, start button, stop button.
Small size dol starter is operated manually but for larger HP motor, dol motor starter are operated using electromechanical contactor (relay) to switch motor ON and OFF.
DOL Motor Starter can be used, if a high starting current cannot cause an excessive voltage drop in the motor circuit.
The demerits of dol starter is that gives the highest possible current to motor. Which is 6 to 7 time of rated current of the motor.
Besides the DOL starter draws the starting current there also exists a current peak that can rise up to 14 times the rated current since the motor is not energized from the first moment when starting.
DOL starter control circuit diagram consist components like Main power contactor, start button, stop push button and overload relay is connected in series this circuit is called control circuit of dol motor starter. All controlling of starter are controlled by this circuit.
DOL starter power circuit diagram :
Direct Online starter power diagram has fuse unit, Main power contactor (K1), overload relay. Also, we can connect MCB for protection purpose in a direct On-Line motor starter.