What are the starting methods for three-phase asynchronous motors?

Three-phase asynchronous motors are commonly used in industrial production. There are many different starting methods, and different starting methods are suitable for different working conditions and load requirements. This article will introduce the starting methods of three-phase asynchronous motors in detail, including direct starting, star-delta starting, autotransformer starting, soft starter starting, inverter starting, etc., and analyze the advantages and disadvantages of various starting methods.

1. Direct start

1. definition

Direct starting refers to the method of starting a three-phase asynchronous motor by directly connecting it to a three-phase power supply with rated voltage.

1. Features

(1) Simple structure, easy operation and low cost.

(2) The starting current is large, about 5-7 times the rated current, which has a greater impact on the power grid.

(3) The starting torque is large, about 1.5-2.5 times the rated torque.

(4) The starting time is short, which is suitable for starting with light load or no load.

1. Applicable occasions

Suitable for motors with lower power and lighter load, such as small fans and pumps.

2. Star-Delta Starting

1. definition

Star-delta starting means that when the motor is started, the motor winding is first connected in star shape, and then switched to delta after the motor starts.

1. Features

(1) The starting current is small, about 1/√3 times of direct starting, and has less impact on the power grid.

(2) The starting torque is small, about 1/√3 times that of direct starting.

(3) The starting time is longer and it is suitable for motors with heavier loads.

(4) The structure is more complicated and requires a star-delta switching device.

1. Applicable occasions

Suitable for motors with high power and heavy load, such as large fans and pumps.

3. Autotransformer starting

1. definition

Autotransformer starting refers to a starting method in which the starting voltage of the motor is reduced by an autotransformer when the motor is started, thereby reducing the starting current and starting torque.

1. Features

(1) The starting current is small, and the starting voltage can be adjusted as needed to achieve multi-stage starting.

(2) The starting torque is small, and the starting voltage can be adjusted as needed to achieve multi-stage starting.

(3) The starting time is longer and it is suitable for motors with heavier loads.

(4) The structure is more complex and requires an autotransformer and switching device.

1. Applicable occasions

Suitable for motors with high power and heavy load, such as large fans and pumps.

4. Soft starter starting

1. definition

Soft starter starting refers to the use of a soft starter to control the starting process of the motor to achieve a smooth starting method.

1. Features

(1) The starting current is small and can be adjusted as needed to achieve multi-stage starting.

(2) The starting torque is smooth, which can achieve impact-free starting.

(3) The starting time is adjustable and can be adjusted as needed.

(4) The structure is more complex and requires a soft starter and control device.

1. Applicable occasions

It is suitable for electric motors with special requirements for the starting process, such as smooth starting, impact-free starting, etc.

5. Inverter starting

1. definition

Inverter starting refers to the use of inverter to control the starting process of the motor to achieve variable frequency speed regulation starting method.

1. Features

(1) The starting current is small and can be adjusted as needed to achieve multi-stage starting.

(2) The starting torque is adjustable, which can achieve stepless speed regulation.

(3) The starting time is adjustable and can be adjusted as needed.

(4) The structure is relatively complex and requires a frequency converter and control device.

1. Applicable occasions

Suitable for electric motors that require speed control, such as stepless speed regulation, energy saving, etc.

VI. Conclusion

There are many starting methods for three-phase asynchronous motors, and different starting methods are suitable for different working conditions and load requirements. When choosing a starting method, it is necessary to comprehensively consider factors such as the motor's power, load, and starting requirements. Direct starting is suitable for light load or no-load starting, star-delta starting and autotransformer starting are suitable for motors with heavier loads, and soft starter starting and inverter starting are suitable for motors with special requirements for the starting process.