Why do we use Direct Online Starter(DOL) || Dol starter

Summary

The DOL Starter, or Direct On Line Starter, is a straightforward method for starting a 3-phase induction motor by directly connecting it to the supply line. It features a simple control circuit with a green start button and a red stop button, along with a Motor Circuit Breaker (MCCB), contactor, and overload relay for protection. Despite the high inrush current, which can be 5-8 times the full load current, the DOL Starter is suitable for small motors, particularly 3-phase squirrel cage induction motors, where the inrush current does not cause significant voltage drop.

Takeaways

• 🔌 A DOL Starter, or Direct On Line Starter, is used for starting a 3-phase induction motor by connecting it directly to the power supply.
• ⚙️ The starter applies full line voltage to the motor terminals without causing harm, thanks to its protective devices.
• 🛠️ It includes a motor overload relay shown in the wiring diagram, which is essential for the starter's operation.
• 💡 The wiring diagram consists of a simple Hold ON contactor circuit with an overload relay for basic motor control.
• 🔘 The DOL starter has two buttons: a GREEN button to start the motor and a RED button to stop it.
• 🔐 It incorporates an MCCB (Motor Circuit Circuit Breaker) or circuit breaker, a contactor, and an overload relay for motor protection.
• ⚠️ The overload relay is crucial as it detects if the motor's current exceeds the rated amperage, preventing damage to the motor winding.
• 🔁 When the green push button is pressed, the motor starts, drawing a high inrush current, which decreases as it reaches rated speed.
• ⚡️ Direct on line starters are suitable for use when the high inrush current won't cause an excessive voltage drop in the supply circuit.
• ⭐ Direct on line starters are commonly used for small motors, particularly 3-phase squirrel cage induction motors.

Q & A

What is a DOL Starter?

A DOL Starter, also known as a direct on line starter, is a method used to start a three-phase induction motor by connecting it directly across its three-phase supply and applying the full line voltage to the motor terminals.

How does a DOL Starter protect the motor?

A DOL Starter protects the motor through the inclusion of protection devices such as motor overload relays, which are designed to detect and prevent potential damage from excessive current draw.

What is the purpose of the green and red buttons in a DOL Starter?

The green button is used to start the motor, while the red button is used to stop it. These buttons control the contacts within the starter circuit.

What components are typically included in a DOL Starter?

A DOL Starter typically includes an MCCB (Motor Circuit Circuit Breaker) or circuit breaker, a contactor, and an overload relay for protection.

Why is an overload relay important in a DOL Starter?

An overload relay is crucial in a DOL Starter because it monitors the motor's current. If the current exceeds the rated limit, the relay opens, causing the contactor to turn off and thereby preventing damage to the motor windings.

What is the significance of the high inrush current in a DOL Starter?

The high inrush current in a DOL Starter can be up to 5-8 times higher than the full load current. This current helps the motor to start but decreases as the motor reaches its rated speed.

In what circumstances should a DOL Starter not be used?

A DOL Starter should not be used when the high inrush current of the motor would cause an excessive voltage drop in the supply circuit, as this can affect the performance of other equipment on the same circuit.

What alternative starter is recommended to avoid high voltage drops?

To avoid high voltage drops, a star-delta starter is recommended instead of a DOL Starter, as it provides a more controlled starting sequence for the motor.

For what types of motors are direct on line starters commonly used?

Direct on line starters are commonly used for starting small motors, particularly three-phase squirrel cage induction motors.

How does the wiring diagram of a DOL Starter typically look?

The wiring diagram of a DOL Starter typically includes a simple hold-on contactor circuit with an overload relay, as shown in the script, which illustrates the connections for starting and stopping the motor.

What is the role of the thermal overload contact in a DOL Starter?

The thermal overload contact in a DOL Starter is a normally closed contact that opens when the motor current exceeds the overcurrent limit, thereby protecting the motor from potential damage due to overheating.

Outlines

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🔌 Understanding DOL Starters

A DOL Starter, also known as a direct on line starter, is a method used to start a 3-phase induction motor by connecting it directly to the 3-phase supply. Despite the full line voltage applied to the motor terminals, protection devices such as motor overload relays prevent harm to the motor. The starter includes a simple hold-on contactor circuit with an overload relay, and the wiring diagram is provided for clarity. The starter has two buttons: a green button for starting and a red one for stopping the motor. It also includes an MCCB or circuit breaker, a contactor, and an overload relay for protection. The overload relay is crucial as it detects if the motor's current exceeds the rated amperage, preventing damage to the motor winding by turning off the contactor if the current limit is exceeded. The video tutorial link for creating a hold-on circuit is mentioned in the description box. It's noted that the DOL starter causes a high inrush current when starting the motor, which can be up to 5-8 times higher than the full load current, but this value decreases as the motor reaches its rated speed. DOL starters are suitable for small motors, especially 3-phase squirrel cage induction motors, and are used when the high inrush current does not cause an excessive voltage drop in the supply circuit.

Keywords

💡DOL Starter

A DOL Starter, which stands for Direct On Line Starter, is a method used to start a three-phase induction motor by connecting it directly across its three-phase supply. This starter applies the full line voltage to the motor terminals, which can cause a high inrush current but is protected by devices like motor overload relays. In the context of the video, the DOL Starter is the central theme, explaining its function, components, and the circumstances under which it should be used.

💡Three-phase induction motor

A three-phase induction motor is a type of AC motor that uses a rotating magnetic field to induce current in the rotor, causing it to turn. It is a common type of motor used in industrial applications. In the video, the DOL Starter is specifically designed for starting this type of motor, emphasizing its importance in the operation of such motors.

💡Overload relay

An overload relay is a protective device used in electrical systems to prevent damage to the motor due to excessive current. It is part of the DOL Starter's circuitry and is designed to trip if the motor's current exceeds the rated limit, thus protecting the motor from overheating or damage. The video script mentions that the overload relay is a crucial component of the DOL Starter, ensuring the safe operation of the motor.

💡Inrush current

Inrush current refers to the initial surge of current that flows through an electrical device when it is first powered on. In the case of a DOL Starter, the motor draws a very high inrush current, which can be up to 5-8 times higher than the full load current. This concept is important in the video as it explains why certain precautions are necessary when using a DOL Starter, particularly in terms of the potential for voltage drop in the supply circuit.

💡Voltage drop

Voltage drop is a reduction in voltage that occurs as electrical current flows through a conductor. In the context of the video, a high inrush current from a DOL Starter can cause an excessive voltage drop in the supply circuit, which may affect the performance of other devices on the same circuit. The video discusses this as a consideration when deciding whether to use a DOL Starter or an alternative like a star delta starter.

💡Star delta starter

A star delta starter is an alternative to the DOL Starter, used to start three-phase induction motors. It reduces the inrush current by initially starting the motor in star (Y) configuration and then switching to delta (Δ) configuration once the motor is up to speed. The video mentions star delta starters as an option to avoid high inrush current and voltage drop issues associated with DOL Starters.

💡Squirrel cage induction motor

A squirrel cage induction motor is a type of three-phase induction motor with a rotor that resembles a squirrel cage due to its bars and end rings. It is widely used in industrial applications due to its simplicity and robustness. The video script specifies that DOL Starters are commonly used for starting small motors, particularly squirrel cage induction motors, highlighting their suitability for this type of motor.

💡MCCB or Circuit Breaker

MCCB stands for Molded Case Circuit Breaker, which is a type of circuit breaker used for protection against overcurrent conditions in electrical systems. In the video, the MCCB is mentioned as a component of the DOL Starter, serving to protect the motor and the electrical system from potential damage due to excessive current.

💡Contactor

A contactor is an electrically controlled switch used for making and breaking connections in an electrical circuit. In the DOL Starter, the contactor is responsible for connecting the motor to the supply when the start button is pressed and disconnecting it when the stop button is pressed. The video script illustrates the role of the contactor in the operation of the DOL Starter.

💡Thermal Overload

Thermal Overload is a protective mechanism that responds to excessive heat, typically caused by an overload current in a motor. The video explains that the thermal overload contact, which is normally closed, will open if the motor's current exceeds the safe limit, causing the contactor to turn off and thus protecting the motor from damage.

💡Hold ON circuit

A Hold ON circuit is a type of control circuit that maintains the connection between the motor and the supply even after the start button is released. The video script mentions a simple Hold ON contactor circuit with an overload relay, which is part of the DOL Starter's design to ensure that the motor continues to run once it has been started.

Highlights

DOL Starter is a method of starting a 3-phase induction motor.

An induction motor in a DOL Starter is connected directly across its 3-phase supply.

DOL Starter applies full line voltage to the motor terminals without harming the motor.

Protection devices like motor overload relays are included in a DOL motor starter.

The wiring diagram of a DOL starter features a simple Hold ON contactor circuit with an overload relay.

A direct online starter includes two buttons: GREEN for starting and RED for stopping the motor.

The DOL starter consists of an MCCB or circuit breaker, contactor, and an overload relay for protection.

Green and Red buttons control the contacts in the DOL starter.

The overload relay detects if the motor operates within its rated amperes.

If the motor current exceeds the over current limit, the thermal overload contact opens, turning off the contactor.

The thermal overload contact prevents motor winding damage or burning.

A video tutorial on making a HOLD ON circuit is linked in the description box.

The motor is started by pressing the green push button in a DOL starter.

DOL starters can draw a very high inrush current, up to 5-8 times higher than the full load current.

The large inrush current decreases as the motor reaches its rated speed.

Direct on line starters are used when high inrush current does not cause excessive voltage drop.

Star delta starters should be used to avoid high voltage drops.

Direct on line starters are commonly used for small motors, especially 3-phase squirrel cage induction motors.

Transcripts

What is DOL Starter?

A DOL starter (also known as a direct on line starter or across the line starter) is a method

of starting a 3 phase induction motor.

In a DOL Starter, an induction motor is connected directly across

its 3-phase supply, and the DOL starter applies the full line

voltage to the motor terminals.

Despite this direct connection, no harm is done to the motor.

A DOL motor starter contains protection devices such as motor overload relays.

shown in wiring diagram of a DOL starter.

this is a simple Hold ON contactor circuit with Overload relay.

The wiring diagram for a DOL stater is shown below.

A direct online starter consists of two buttons, a GREEN button for starting and

a RED for stopping purpose of the motor.

The DOL starter consists of MCCB or circuit breaker, contactor and an overload relay for

protection.

These two buttons, i.e. Green and Red or start and stop buttons control the contacts.

Overload relay is used here to detect if motor is operating as per rated ampares, if motor

current exceeds the Over current limit , the Thermal Overload

contact , Which is a normal close contact opens up and contactor turns OFF, thus it

prevents the motor winding being damaged or burnt.

How do we can make a HOLD ON circuit , video tutorial link is in description box with complete

explantion of control circuit wiring.

lets start the motor by pressing the green push button.

Since the DOL starter connects the motor directly to the main supply line, the motor draws a

very high inrush current compared to the full load current of the

motor (up to 5-8 times higher).

The value of this large current decreases as the motor reaches its rated speed.

A direct on line starter can only be used in circumstances when the high inrush current

of the motor does not cause an excessive voltage drop in the supply circuit.

If a high voltage drop needs to be avoided, a star delta starter should be used instead.

Direct on line starters are commonly used to start small motors, especially

3 phase squirrel cage induction motors.