What is soft start? How to implement soft start

Soft start is a motor starting method that controls the starting current of the motor to gradually accelerate the motor during the starting process, thereby reducing the current shock and mechanical shock during starting and extending the service life of the motor and equipment. Soft start technology has been widely used in industrial production, especially in the starting process of large motors and high-voltage motors.

1. The concept of soft start

Soft start is a motor starting method that controls the starting current of the motor to gradually accelerate the motor during the starting process, thereby reducing the current shock and mechanical shock during starting. Compared with the traditional direct starting method, soft start has the advantages of small starting current, short starting time, and smooth starting, which can effectively reduce the wear of the motor and equipment and extend the service life.

2. The principle of soft start

The basic principle of soft start is to control the starting current of the motor so that the motor can be gradually accelerated during the starting process. Specifically, when the motor starts, the soft starter adjusts the input voltage of the motor so that the starting current of the motor gradually increases until it reaches the rated current. In this process, the speed of the motor will also gradually increase until it reaches the rated speed.

The working principle of the soft starter can be divided into the following steps:

1. Starting preparation: Before the motor starts, the soft starter will perform a series of tests and preparations, including detecting the status of the motor, setting starting parameters, etc.

2. Voltage regulation: When the motor starts, the soft starter will gradually increase the input voltage of the motor according to the preset starting parameters. During this process, the starting current of the motor will also gradually increase.

3. Current control: During the motor starting process, the soft starter will monitor the motor current in real time to ensure that the current is within the preset range. If the current exceeds the preset value, the soft starter will reduce the input voltage to bring the current back to the preset range.

4. Acceleration control: During the motor starting process, the soft starter will adjust the input voltage in real time according to the motor speed and current, so that the motor gradually accelerates until it reaches the rated speed.

5. Startup completed: When the motor reaches the rated speed, the soft starter will adjust the input voltage to the rated value to complete the startup process.

3. Classification of soft start

According to different control methods and application scenarios, soft start can be divided into the following types:

1. Voltage controlled soft start: Soft start is achieved by adjusting the input voltage of the motor. This type of soft starter has a simple structure and low cost, and is suitable for small motors.

2. Current controlled soft start: Soft start is achieved by controlling the starting current of the motor. This type of soft starter has good starting performance and is suitable for medium-sized motors.

3. Torque control soft start: Soft start is achieved by controlling the starting torque of the motor. This type of soft starter has high starting performance and control accuracy and is suitable for large motors and high-voltage motors.

4. Frequency conversion control type soft start: soft start is achieved by adjusting the input frequency of the motor. This type of soft starter has high starting performance and control accuracy and is suitable for various types of motors.

4. Implementation of soft start

The implementation methods of soft start mainly include the following:

1. Thyristor soft starter: Soft start is achieved by adjusting the input voltage of the motor through thyristors. This soft starter has the advantages of simple structure and low cost, but it will generate large harmonics during the starting process.

2. Magnetic control soft starter: The input voltage of the motor is adjusted through the magnetic control element to achieve soft starting. This soft starter has the advantages of good starting performance and small harmonics, but the cost is relatively high.

3. Frequency conversion soft starter: The frequency converter is used to adjust the input frequency of the motor to achieve soft starting. This type of soft starter has the advantages of good starting performance and high control accuracy, but the cost is relatively high.

4. Electronically controlled soft starter: Soft start is achieved by adjusting the input voltage or current of the motor through electronic components and control algorithms. This type of soft starter has the advantages of good starting performance, high control accuracy and small harmonics, but the cost is relatively high.

5. Application Scenarios of Soft Start

Soft start technology has been widely used in industrial production, especially in the following scenarios:

1. Starting of large motors: During the starting process of large motors, soft starting can effectively reduce starting current and mechanical shock, and extend the service life of motors and equipment.

2. High-voltage motor starting: During the starting process of a high-voltage motor, soft starting can effectively reduce the starting current, reduce the impact on the power grid, and improve the stability of the power grid.

3. Frequently started motors: In motors that need to be started frequently, soft starting can effectively reduce wear during starting and extend the service life of the motor.

4. Motors with large load variations: In motors with large load variations, soft start can adjust the input voltage or current in real time to ensure stable operation of the motor.

5. Motors that require smooth starting: In motors that require smooth starting, soft starting can provide a smooth starting process and reduce the impact on the equipment.

6. Advantages and limitations of soft start

Soft start technology has the following advantages:

1. Small starting current: Soft start can effectively reduce the starting current of the motor and reduce the impact on the power grid.

2. Short starting time: Soft starting can shorten the starting time of the motor and improve production efficiency.