Question: How does a DOL motor starter work?

The DOL starter comprises an 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. To start the motor, we close the contact by pushing the Green Button, and the full line voltage appears to the motor.

What is a DOL motor starter?

The DOL starter is a type of motor starter that connects the electric motor directly to the line voltage. It is the simplest and cheapest method to start an induction motor. In the DOL start, the terminals of the motor are connected to the power supply through a contactor and overload protection device.

What are the working principles of the direct online DOL starter?

Principle of DOL Starter:

The Direct Online starter works on full voltage or across-the-line technique where the motor is directly connected to the full voltage supply. Since there is no voltage reduction, the starting current is very high that leads to high starting torque.

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How does DOL starter reduce starting current?

Direct-on-Line (DOL) Starter

This heavy current reduces as the motor accelerates to its rated speed. If induction motor is connected directly to the supply, the starting current will not damage the motor unless it is started and stopped repeatedly over a short span of time.

Can we use DOL starter for 10 hp motor?

These motor control units particularly suitable to command surface and submersible electric pumps. The range includes DOL from 5.5 HP to 70 HP and ASD from 10 HP to 150 HP control panels for one motor start.

Is DOL Star or Delta?

As you will see, the DOL starting method features a very high locked-rotor current which eventually flattens and becomes constant. The star-delta starting method features a lower locked-rotor current, but peaks during the starting process as the changeover from star to delta is made.

What is difference between VFD and DOL starter?

As a basic starting method, a DOL starter applies full voltage, current, and torque immediately to the motor after the start command. … A VFD converts the AC line voltage to DC voltage, and then inverts it back to a simulated AC voltage for the motor.

Why DOL starter is used up to 5 HP?

Dol is used for up to 5 HP motor. … DOL starter connects the motor directly to supply without a reduction in supply voltage and apply full line voltage to 3 phase motor. this is the main disadvantage of dol starter. Small HP motor can be started simply plugging into the power supply.

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What are disadvantages of DOL starting method?

Disadvantages of DOL Starter

  • It does not reduce the starting current of the motor.
  • High Starting Current: Very High Starting Current (Typically 6 to 8 times the FLC of the motor).
  • Mechanically Harsh: Thermal Stress on the motor, thereby reducing its life.

What is the range of DOL starter?

D.O.L Starters: Range: 0.5 to 7.5Hp:

Contactor protects the motor against under voltage where as the relay protects the same against overloads.

How do you calculate DOL starter?

As per above chart:

  1. Type of Contactor = AC7b.
  2. Size of Main Contactor = 100%X Full Load Current (Line).
  3. Size of Main Contactor = 100%x6 = 6 Amp.
  4. Making/Breaking Capacity of Contactor = Value above Chart x Full Load Current (Line).
  5. Making/Breaking Capacity of Contactor = 8×6 = 52 Amp.

How many connectors are used in DOL starter?

The DOL starter consists of two switches namely Green and Red where the green switch is used to start and red switch is used to stop the motor. The DOL starter comprises a circuit breaker (or) MCCB, overload relay & contactor for protecting the motor. The two switches of the motor control the contacts.

What is the difference between Star Delta and DOL starter?

During a DOL start, the starting torque is very high and is usually higher than required for most applications. The starting torque of a star delta starter is reduced to about 30% of the torque available at a DOL start. Star delta method only works when the application is lightly loaded during the start.

For which motors DOL starter can be used?

2. For which motors DOL starter can be used? Explanation: DOL starters are limited to the small rating motors where distribution system (mains supply) can withstand high starting currents without excessive voltage dips.

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Why starters are required in a DC motor?

Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.