Types of Motor Starters: DOL, Star-Delta, Soft Start, and More!

standard circuit of a motor to start

If you are not familiar with engines, you can read about their basic concepts and startup methods in this article. Learn about the DOL (Direct Overload) motor starting process, star delta starting, motor soft starting, and variable speed motor starts. Hopefully you will feel more confident starting your own engines. And don't worry if you don't understand some of the terminology.

I am going to take you on a journey through the different types of motor starters, explaining their differences, advantages, disadvantages, and their uses in various applications. My goal is to help you better understand these technologies so that you can apply them to your own engineering projects. So, let's get started!

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Direct start of a motor

Direct starting is the simplest and most direct method of starting a motor. In a direct start, the motor is directly connected to the mains through a switch.

Main Features

CharacteristicDescription
Easy to useIt is the simplest and most direct method of starting an engine.
EconomyIt requires fewer components and is therefore cheaper.
SpeedStart the engine immediately.
high initial chargeIt can produce a very high current spike at startup.

Operation Steps

  1. The switch closes, connecting the motor directly to the mains.
  2. Current flows through the motor, producing an electromagnetic field.
  3. This field generates a force that turns the rotor of the motor.

Practical example

A typical example of direct starting is found in household appliances such as blenders or vacuum cleaners.

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Star-Delta Start

Star-delta starting is a motor starting method that reduces initial current by connecting the motor in a star configuration during starting, and then switches to a delta configuration for normal operation.

Main Features

CharacteristicDescription
Initial current reductionReduces starting current to about one third of direct starting current.
Less stress on the engineIt causes less mechanical stress on the engine during starting.
Increased complexityIt is more complex than direct boot and requires a special driver.

Operation Steps

  1. When starting, the motor is connected in a star configuration.
  2. The starting current is reduced due to the high resistance in the wye configuration.
  3. Once the engine has started and picked up speed, it is switched to a delta configuration for normal operation.

Practical example

Star-delta starting is often used in high-powered industrial motors, such as those found in water pumps or air conditioning systems.

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Soft start

Soft starting is a method that controls the voltage applied to the motor to provide gradual starting and stopping. An electronic device called a soft starter is used to reduce the voltage applied to the motor in the starting phase.

Main Features

CharacteristicDescription
soft start and stopMinimizes current spikes and mechanical stress on the motor and mechanical load.
tension controlIt provides voltage control during the start and stop phase.
Less equipment wearMaintains power supply quality and reduces wear and tear on equipment.

Operation Steps

  1. When starting the crank, the voltage applied to the motor is reduced.
  2. The voltage is gradually increased until the motor reaches full operating speed.
  3. During stopping, the voltage is reduced in a controlled manner to ensure a smooth stop.

Practical example

Soft starts are commonly used in industrial applications where it is important to avoid current spikes and mechanical stress, such as in conveyor systems or process pumps.

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Starting with Autotransformer

Autotransformer starting is a starting method that uses an autotransformer to reduce the voltage applied to the motor during the starting phase.

Main Features

CharacteristicDescription
Starting current reductionSignificantly reduces starting current.
engine protectionProvides excellent protection for the engine during the starting phase.
Greater cost and sizeAutotransformers are larger and more expensive than other starting methods.

Operation Steps

  1. When starting the start, a reduced voltage is applied to the motor through the autotransformer.
  2. Once the motor has started and reached a certain speed, full voltage is applied.

Practical example

Autotransformer starting is common in industries that use high horsepower motors, such as mineral processing industries and paper mills.

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Start by Stator Resistance

Stator resistance starting is a starting method used in wound rotor induction motors. In this method, resistors are added to the rotor circuit during startup to limit the current.

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CharacteristicDescription
Starting current limitationThe use of resistors reduces the starting current.
Starting torque improvementProvides good starting torque despite current limitation.
complexity and costThis method is more complex and expensive than other boot methods.

Operation Steps

  1. At the start of the start, resistors are inserted into the rotor circuit.
  2. These resistors limit the starting current and allow for improved starting torque.
  3. Once the motor has reached its running speed, the resistors are removed from the circuit.

Practical example

This type of starting is common in industrial applications that require high starting torque, such as cranes and elevators.

Variable Frequency Start

Variable frequency starting, also known as variable frequency drive, is a starting method that controls motor speed by adjusting the frequency of the power supply.

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Characteristics:

CharacteristicDescription
Speed ​​controlAllows precise control of motor speed.
Energy efficiencyIt is efficient in terms of energy, especially for applications that require speed variations.
Increased cost and complexityVariable frequency drives are more expensive and require more maintenance.

Operation Steps

  1. The VFD adjusts the frequency of the power supply to the motor.
  2. This allows precise control of the engine speed.
  3. The motor can operate at any speed within its range, not just its rated speed.

Practical example

Variable frequency starting is used in a wide range of industrial applications, such as conveyors, fans and pumps, where precise speed control is required.

Start by Wound Rotor

The wound rotor starter, also known as a slip ring motor, is a type of induction motor that has a wound rotor instead of a squirrel cage rotor. Starting is done by inserting external resistors into the rotor circuit.

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Main Features

CharacteristicDescription
starting torque controlAllows precise control of starting torque.
greater flexibilityAllows a wide range of speeds and torques.
Higher cost and maintenanceIt is more expensive and requires more maintenance than a squirrel cage motor.

Operation Steps

  1. At start start, external resistors are inserted into the rotor circuit.
  2. These resistors control the current and allow the starting torque to be adjusted.
  3. As the motor accelerates, the resistors are gradually removed until the motor is operating at its rated speed.

Practical example

Wound rotor motors are used in applications that require a wide range of speeds and torques, such as mills, cranes, or presses.

Start by Rotor in Short Circuit

Description

The short-circuited rotor start, also known as a squirrel cage motor, is the most commonly used type of induction motor. This type of motor has a squirrel cage rotor instead of a wound rotor.

Main Features

CharacteristicDescription
Easy to useIt is the simplest and easiest type of motor to use.
Low costIt is cheaper and requires less maintenance than a wound rotor motor.
speed control limitationIt does not allow for as precise speed control as a wound rotor motor.

Operation Steps

  1. At start start, voltage is applied to the stator coils.
  2. The rotating magnetic field induced by the stator coils causes a current to flow in the rotor.
  3. This current in the rotor generates its own magnetic field, which interacts with the stator field to produce torque and start the motor.

Practical example

Squirrel cage motors are used in a wide variety of applications, from small household appliances to large industrial machines.

 

These are just a few of the engine starting methods available, each with their own advantages, disadvantages, and suitable applications. I hope this guide has given you a solid foundation in understanding these methods and choosing the right one for your needs. I encourage you to continue learning and researching more about these and other engine starting methods. Engineering is a continuous field of study and there is always more to learn!

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