A detailed explanation of the five common starting methods for electric motors
The motor should be the most familiar electrical equipment for electrician maintenance technicians. The motor can be started at various times, including direct start, star-delta step-down start, auto-coupling decompression start, soft starter start, inverter start-up. Waiting for the way. The following is a detailed explanation of the five main starting methods of the motor.
1, full pressure direct start
If both full-voltage direct start is allowed in both grid capacity and load, you can consider the full-voltage direct start. The direct start of full pressure has the advantages of convenient operation control, simple maintenance, and economical. It is mainly used for starting low-power motors. From the perspective of saving energy, this method is not recommended for motors larger than 11 kW.
2, star triangle step-down 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 converted to a triangle after the start, you can reduce the starting current, and the grid can be reduced. The impact. Such a startup mode is called a star-delta decompression start or simply a star-delta start.
When starting with the star triangle, the starting current is only one-third of the original, starting directly with the delta connection. When starting with the star triangle, the starting torque is also reduced to one-third of the original direct start when the triangle is connected. Therefore, Star Delta Buck Start is suitable for applications with no load or light load start. And compared with any other decompression starter, its structure is the simplest, the lowest price, and the equipment circuit maintenance cost is also the lowest. In addition, the star triangle startup method has the advantage that when the load is light, you can operate the motor in a star connection. At this time, you can match the rated torque with the load, improving the efficiency of the motor and saving power consumption.
3, auto-decompression start
The multi-tap decompression of the autotransformer can meet the needs of different load starting and obtain a larger starting torque. It is a decompression starting method that is often used to start a large capacity motor. The biggest advantage of an auto-coupling start-up is that the starting torque is large. For example, when the winding tap is at 80%, the starting torque can reach 64% when it is directly started. And you can adjust the starting torque by tapping. Thus, it is still widely used today.
4, soft starter
This is the use of the thyristor's phase shift voltage regulation principle to achieve the voltage regulation start of the motor, mainly used for the start control of the motor, the starting effect is good, but the cost is high. Furthermore, due to thyristor components, the thyristor has a large harmonic interference during operation and has a certain impact on the power grid. In addition, fluctuations in the grid can also affect the conduction of the thyristor components, especially when there are multiple thyristors in the same grid. Therefore, the failure rate of the thyristor component is high, and because of the power electronics technology, the requirements for professional electricians and technicians are also high.
5, the inverter starts
The frequency converter is the motor control device with the highest technical content, the complete control function, and the best control effect in 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 to start the motor with the inverter, and it has high requirements for electrician maintenance technicians. Therefore, it is mainly used in areas where speed regulation is required, and speed control is required, as we often see. The elevator that arrives, now the starting mode of the traction motor in the elevator machine room is completed by the inverter start.
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