Many methods are utilized to start an induction motor, as this motor needs more power to start. If there is a high current flow through the windings, the motor can suffer some damage. To tackle this issue, multiple types of starter modes are utilized. A simple starter technique is a direct-on-line (DOL) starter. This starter has a contactor, overload relay, and MCCB or circuit breaker to protect the motor.
An electromagnetic contactor can be unlocked via the thermal overload relay below fault conditions. Typically, buttons such as start, and stop are used to control a contactor. The contactor utilizes an auxiliary contact along with the start button as it is electrically connected while the induction motor works.
What is a DOL Starter?
A DOL starter offers an easy, economical, and fundamental way to operate a three-phase induction motor. This starter links three-phase motors across the phases supply. The best part is a DOL starter can be connected directly to the motor, and it has no impact on the induction motor. Such starter shave primary contacts and a protective device.
DOL Starter Construction
A DOL starter has a green switch to start the motor and a red switch to stop it. As mentioned earlier, this starter has a contactor, overload relay, and MCCB or circuit breaker to protect the motor. The motor’s two switches control the contacts. You can start the motor by pressing down the green switch to shut the contact, and a full-line voltage goes to the induction motor.
Contactors are generally 3-pole or 4-pole types. For example, a 4-pole contactor has three open contacts, and a holds on or auxiliary contact. You can use the three NO contacts to link the induction motor to the supply line and the auxiliary contact to enhance the contactor coil after the start button is switched. If there is an error, the holds on the contactor become deactivated. In this way, the DOL starter delinks the induction motor from the supply mains.
Additional Resource: What Are Magnetometers Used For?
Wiring of DOL Starter
A DOL starter’s connections or wiring have multiple parts, including thermal overload relay, relay coil connections, normally closed contacts, normally open contacts, and main contact.
How does it work?
ADOL starter connects the three-phase main wiring with the induction motor’s L1, l2, and L3 after the start button is pressed. In general, a DOL starter works in two stages, which are the control circuit and power circuit. The control circuit is linked to any two phases and is activates only from these two phases. When you press the start button, power will flow through the contactor wind and control circuit. The current boosts the contactor coil and closes the contacts, enabling the induction motor to access the three-phase supply.
When you press the stop switch, the current flow will be stopped through the contact, and the induction motor cannot access the power supply. The same result occurs while the overload relay functions. With the breaking of the motor supply, the device will shift to relax. Further, the contactor coil obtains power supply even if the start switch is opened as it gets current from the main contacts.
Advantages of DOL Starter
• It’s easy to understand and troubleshoot issues
• The starter can be operated and controlled in an effortless manner
• In the initial stages, it provides almost full starting torque
• It is inexpensive
Drawbacks of DOL Starter
• Needlessly high starting torque
• It can reduce the machine’s lifespan
• Only appropriate for small motors as it causes a vital voltage dip
• Beginning current is high
DOL Starter Applications
• DOL starters are ideal for motors in which the three-phase induction motor has a low rating and low input (5v) as it can function at low rating and speed.
• This starter is utilized where maximum power does not create any damage, for example, to operate small fans, water pumps, conveyor belts, compressors, etc.
We urge you to consult licensed professionals to get advice on the electrical systems you need for your business and pick a suitable DOL Starter!