Five common starting methods of electric motors

# Direct Starting - **Principle**: Connect the stator winding of the electric motor directly to the power supply and start it at the rated voltage, enabling

the motor to reach the rated speed in the shortest possible time. - **Characteristics**: The starting method is simple and reliable, and the cost of starting equipment is low. However, the starting current is

large, generally 4 to 7 times the rated current, which will cause a large impact on the power grid, may cause voltage fluctuations in the

power grid, and affect the normal operation of other electrical equipment. - **Application Scope**: It is usually suitable for small-capacity motors, generally with a power of less than 10kW, and has high requirements

for the capacity of the power grid. It can be used when the power grid capacity is large enough to withstand the impact current during the

direct starting of the motor.Youtube：https://youtube.com/shorts/74Z53uprQw4

### Star-Delta Starting - **Principle**: During starting, connect the stator winding of the motor in a star shape. At this time, the voltage applied to each phase winding

is 1/√3 of the rated voltage, and the starting current is reduced to 1/3 of that during direct starting. When the motor speed approaches

the rated speed, switch the stator winding to a delta shape, allowing the motor to operate normally at the rated voltage. - **Characteristics**: The starting current is relatively small, and the impact on the power grid is smaller compared to direct starting. The starting

equipment is relatively simple, and the cost is low. However, the starting torque is also small, only 1/3 of that during direct starting, and it is only

suitable for light-load or no-load starting situations. - **Application Scope**: It is suitable for motors whose stator windings are connected in a delta shape during normal operation, and is widely

used in various industrial fields for asynchronous motors with a power of 4kW and above. ### Autotransformer Starting - **Principle**: Use an autotransformer to reduce the voltage applied to the stator winding of the motor to limit the starting current. During

starting, the motor is connected to the power supply through the autotransformer. The taps of the autotransformer can provide different

step-down ratios, generally with taps such as 65% and 80% available for selection. After the motor speed rises to a certain extent, cut off

the autotransformer and make the motor directly connected to the power supply for operation. - **Characteristics**: Different taps can be selected according to needs to adjust the starting voltage and starting current, and the starting

torque is larger than that of star-delta starting. However, the autotransformer is large in size, heavy in weight, and relatively expensive in price.

Moreover, a switching operation is required during starting, which may generate a certain amount of arc and impact. - **Application Scope**: It is suitable for motors with a large capacity and situations where a large starting torque is required, such as large fans,

water pumps, etc. ### Soft Starter Starting - **Principle**: By controlling the conduction angle of the thyristor, change the voltage on the stator winding of the motor to achieve smooth

starting of the motor. During the starting process, the soft starter can automatically adjust the output voltage according to the set parameters,

such as starting time and starting current, so that the starting current and starting torque of the motor are within a reasonable range. - **Characteristics**: The starting current is small, and the starting parameters can be flexibly adjusted according to the load situation to achieve

smooth starting, with little impact on the power grid and equipment. It has a variety of protection functions, such as overcurrent protection and

overheating protection, which can effectively protect the motor and other equipment. However, the price is relatively high, and certain maintenance

and debugging are required. - **Application Scope**: It is suitable for motors of various powers, especially for situations with high requirements for starting smoothness

and large load changes, such as elevators, cranes, etc. ### Variable Frequency Starting - **Principle**: Use a frequency converter to change the frequency of the power supply, thereby changing the speed of the motor. During starting,

the output frequency of the frequency converter gradually increases from 0, causing the speed of the motor to gradually rise, achieving smooth

starting. - **Characteristics**: The starting performance is superior, stepless speed regulation can be achieved, the speed and torque of the motor can be

accurately adjusted according to the load demand, and the energy-saving effect is remarkable. The harmonic pollution to the power grid is small,

and it can effectively protect the motor and other equipment. However, the frequency converter is expensive and has high requirements for the

operating environment and maintenance. - **Application Scope**: It is widely used in situations with high requirements for speed regulation performance, such as industrial automation

production lines, central air-conditioning systems, etc., and is also suitable for motors that need to be started and stopped frequently.