The usual method to reduce the motor starting current

Update:12 Aug 2020

Generally, the starting methods to reduce the starting current of motor include direct starting, series resistance starting, auto coupling transformer starting, star delta voltage reducing starting and frequency converter starting to reduce the impact on the power grid.

Direct start
Direct starting is to connect the stator winding of the motor directly to the power supply and start under the rated voltage. It has the characteristics of large starting torque and short starting time. It is also the simplest, most economical and reliable starting method. It is easy to operate and fast to start. However, this starting mode requires a large amount of power grid capacity and load, and is mainly suitable for motor starting under 1W.

Series resistance starting
Motor series resistance start, that is, a method of step-down starting. In the start-up process, the resistance is connected in series in the stator winding circuit. When the starting current passes through, the voltage drop on the resistance is generated, which reduces the voltage added on the stator winding, so as to reduce the starting current.
Start up of autotransformer
The multi tap decompression of autotransformer can not only meet the needs of starting with different loads, but also get larger starting torque. It is a kind of reduced pressure starting method which is often used to start large capacity motor. When the winding tap is at 80%, the starting torque can reach 64% of that of direct starting, and the starting torque can be adjusted by tapping.

Star delta decompression start
For the squirrel cage asynchronous motor with triangle stator winding, if the stator winding is connected into a star during starting and then connected into a triangle after starting, the starting current can be reduced and its impact on the power grid can be reduced. Such starting mode is called star delta decompression starting, or star delta starting (Y - & starting). When star delta starting is adopted, the starting current is only 1 / 3 of that of direct starting according to triangle connection. In star delta starting, the starting current is only 2-2.3 times.
That is to say, when star delta starting is adopted, the starting torque is reduced to 1 / 3 of that of direct starting by triangle connection. It is suitable for no load or light load starting. Compared with any other vacuum starter, its structure is the simplest and the price is the cheapest.
In addition, star delta starting mode has an advantage, that is, when the load is light, the motor can run in star connection. At this time, the rated torque and load can be matched, which can improve the efficiency of the motor and save power consumption.

Inverter start
Frequency converter is the motor control device with the highest technology content, the most complete control function and the best control effect in the field of modern motor control. It adjusts the speed and torque of the motor by changing the frequency of the grid. Because it involves power electronic technology, microcomputer technology, so the cost is high, and the requirements for maintenance technicians are also high, so it is mainly used in the field of speed control and speed control.

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