DOL – 3 Phase Motor Starter

In this tutorial, I am going to show you how to change the rotation of a 3 phase motor.

Here I will show you the simulation carried out in the Cade-Simu.

This tutorial can be a good kickstart for future development skills in the area of electromechanical, you can see this simple starter system in industrial manufacturing.

A DOL Starter is a Direct-On-line motor starter that is used as a simple motor starter for large electric induction motors providing full-line voltage to the motor terminals.

DOL Starters essentially operate as a basic stop/start switch for an electric motor and are often fitted with overload protection devices to prevent short circuits and overheating.

The method of DOL is the most popular and cheapest way to start a motor, but its use limited to smaller HP motor (MAX 5 HP [1 HP = 1,0139 CV]), to start higher rating 3 phase motors, a star-delta (Y-Δ) starter is used. Delta-wye (Y-Δ) starter is useful where all six terminals of the motor are accessible (not in this case)

Parts Required

  • Software Cade-Simu 4.0 (for electrical simulation).

DOL Working

To start the engine, start button S1 (13-14) is activated.

This excites the coil (KM1) of the contactor so that it closes all its open contacts due to the magnetic force and the voltage reaches the motor (see the power circuit) so that it starts at that moment.

Even if S1 is released, the motor continues to rotate due to the auxiliary contact (KM1 13-14) of the contactor (see control circuit), which is closed because its coil is energized, that is, the auxiliary contact (KM1) serves to make a feedback to the contact (S1).

To stop the motor, press S2 (11-12) which interrupts the coil and opens the contactor.

If the engine is running and an overload occurs, the Motor-circuit breaker (Q1) opens its power contacts, and interrupts the motor, in turn, the same occurs in the control circuit which interrupts all power from the auxiliary contact (Q1 13-14).

Power Circuit Diagram

The power circuit supply is a three-phase 400 VAC (can be another electrical voltage value depending on the country of operation), then it is supplied with a motor-circuit breaker (Q1), which is the most used in the industry today. In series, it is connected with a contactor (KM1) that will supply the motor (M1).

Control Circuit Diagram

The control circuit is powered by 24VDC for this we use a power supply (PS1) that is powered by 230v, a phase and neutral protected by a Gg fuse (F1), and its output is 24VDC protected by a fuse as well Gg (F2).


Contactor KM1 – The contactor is an electromechanical device (as well as a relay) that allows the activation of loads from the polarization of a coil,

Motor Circuit-Breaker Q1 – is a device that combines protection and control for electric motors. It was developed especially for the activation and protection of electric motors. The great advantage of this circuit breaker is that it is able to combine fuse, thermal relay, and contactor functions in a single device.

Push buttons S1, S2 – the pushbutton s1, is a start button that contains an NO 13-14 contact which, when activated, will close.

The pushbutton s2 is a stop button that contains an NC 11-12 contact which, when activated, will close.

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