What are the methods to reduce the motor starting current?
Common starting methods to reduce the starting current of the motor are direct start, series resistance start, self-turning transformer start, star delta decompression start and inverter start method to reduce the impact on the grid.
Direct start
The direct start is to directly connect the stator winding of the motor to the power supply and start at the rated voltage. It has the characteristics of large starting torque and short starting time, and is the simplest, most economical and most reliable starting method. The current is large when starting at full pressure, and the starting torque is not large, the operation is convenient, and the starting is rapid, but this starting mode has relatively large requirements on the grid capacity and load, and is mainly suitable for starting the motor below 1W.
String resistor start
The motor string resistor is activated, which is a method of step-down startup. In the starting process, the series resistance is connected in the stator winding circuit. When the starting current passes, a voltage drop is generated on the resistor, and the voltage applied to the stator winding is reduced, so that the purpose of reducing the starting current can be achieved.
Automatic transformer start
The multi-tap decompression of the autotransformer can not only meet the needs of different load starting, but also obtain a larger starting torque. It is a decompression starting method that is often used to start a large capacity motor. Its biggest advantage is that the starting torque is large. When its winding tap is at 80%, the starting torque can reach 64% of the direct starting, and the starting torque can be adjusted by the tap.
Star triangle decompression start
For a squirrel-cage asynchronous motor in which the normal running stator winding is a delta connection, if the stator winding is connected to a star at the start, and then connected to the triangle after the start, the starting current can be reduced and the grid can be reduced. The impact. Such a starting method is called a star-delta decompression starting, or simply a star-delta starting (y-& starting). When starting with the star-delta, the starting current is only 1/3 of the original starting directly by the delta connection. When starting at the star triangle, the starting current is only 2-2.3 times. This means that when starting with the star-delta, the starting torque is also reduced to 1/3 of the original direct start by the delta connection. Suitable for applications with no load or light load start. And compared to any other decompression starter, the structure is the simplest and the cheapest. In addition, the star-delta starting method has the advantage that when the load is light, the motor can be operated in star connection. At this time, the rated torque can be matched with the load, which can improve the efficiency of the motor and save power consumption.
Inverter start
The frequency converter is the motor control device with the highest technical 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 power grid. Because it involves power electronics technology and microcomputer technology, it is costly and has high requirements for maintenance technicians. Therefore, it is mainly used in areas where speed regulation is required and speed control is required.
