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What is the starting method of 3 phase asynchronous motors?

Three-phase asynchronous motors are a type of motor commonly used in modern industrial production and commercial applications. Starting a three-phase asynchronous motor requires applying a starting torque to the motor shaft to bring the motor to a certain

Three-phase asynchronous motors, also known as induction motors, are a common type of motor used in industrial and commercial applications. They are widely used because of their high efficiency, reliability, and low cost. Starting a three-phase asynchronous motor requires a starting torque to be applied to the motor shaft to overcome the load torque and bring the motor up to a certain speed. There are several methods available for starting three-phase asynchronous motors, each with its advantages and disadvantages.

Start-up methods

  • A common method of starting a three-phase asynchronous motor is a direct on line (DOL) starter. The motor is connected directly to the three-phase power supply via a switch or contactor. This consumes high starting current and low power factor and is not suitable for larger motors or motors with high starting torque requirements, so it is often used for starting small motors.
  • Another method is star-delta starting. In this method, the motor is initially connected to the power supply in a star configuration, running in a triangle, and once the motor reaches a certain speed, the connection switches to a triangle configuration. Star-delta starters are suitable for motors with high starting torque requirements, but they require additional control circuitry and are more complex than DOL starters.
  • The third method is the variable frequency drive (VFD). In this method, a VFD is used to control the voltage and frequency of the power supply provided to the motor. The VFD can start the motor at low voltage and low frequency, gradually increasing the voltage and frequency as the motor accelerates. Variable frequency starters are suitable for motors with high starting torque requirements, but require more complex and expensive control systems.


There are several starting methods for three-phase asynchronous motors, and which starting method to use should depend on your motor type and application.

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