Induction motors can be started using a variety of techniques since they require more power to start. However, there is a danger that the motor could be damaged when the current flowing through the windings is excessive. Numerous beginning strategies are employed to solve this issue. DOL starters are a straightforward starting technique (Direct On-Line Starter). For the motor’s protection, the Direct Online starter has an MCCB, an overload relay, and a contactor. Under fault situations, the thermal overload relay can be used to unlock an electromagnetic contactor. Typically, distinct buttons like start and stop can be used to regulate a contactor. Because the contactor is electrically locked when an induction motor is operating, an auxiliary contact is used on the contactor across the start button.
What Is A DOL Starter?
A 3-phase induction motor can be started using a DOL starter, also called an immediate starter or an across-the-line starter. An induction motor is linked directly across its three-phase supply in a DOL starter, which then supplies the motor terminals with the full line voltage. The motor is not harmed despite this proximity. A DOL motor starter has safeguards and, occasionally, condition monitoring.
The DOL starter links the motor to the main supply line, which results in the motor drawing a far higher inrush current than it would under full load (up to 5-8 times higher). As the motor reaches its rated speed, the value of this enormous current falls. Only in situations where the high in-rush current of the motor does not yield an unacceptable voltage drop in the supply circuit can a direct starter be employed. A star delta starter should be used in its place if a significant voltage drop needs to be prevented. Small motors are frequently started using direct on-line starters, particularly 3-phase squirrel cage induction motors.
Working Mechanism of DOL Starter
Simply pressing the Start Push button initiates the DOL Starter, and pressing the Stop Push button ends it. The device may be easily controlled using this approach. Pushing the button activates the contactor, which then closes. Due to the latching mechanism, the contactor closes even after the push button release. The motor is currently operating faultlessly and smoothly. To protect the motor from a heavy rush of current, the normally closed auxiliary contact of the overload relay is linked to the motor. The overload trips each time the over-current is passed. The contactor coil is de-energized because of the auxiliary contact opening.
Constructing A DOL Starter
The DOL starter demonstrates two switches, green and red. The green switch starts the motor, while the red switch stops it. The DOL starter includes a circuit breaker, commonly called an MCCB. The motor’s two switches control the connections. The motor can be started when the contact is closed by pressing the green switch and the induction motor receives full line voltage. The contractors are typically 3-pole or 4-pole contractors. One holds on to contact, and three ordinarily open contacts make up a 4-pole type contactor, for instance. While the auxiliary contact is used to enhance the contactor coil when the start button is opened, the three NO contacts are utilized to connect the induction motor to the supply lines. In the event of a mistake, contactor holds are disabled. The induction motor is thus cut off from the main supply by the DOL starter.
Advantages of DOL Starter
Here are some of the advantages of a DOL Starter:
- It begins immediately and without interruption.
- Compared to other starters, it is less expensive.
- Simple implementation
- Compared to other starters, troubleshooting will be simple.
- High starting torque
- Small size
The Bottom Line
So that’s it; those are the key components of Direct Online Starters. Switching between devices is quite simple. These are most suited in situations where maximum currents can be used to operate tiny compressors, conveyor belts, water pumps, fans, etc., without risking harm.