1. Direct start
Direct starting is the method where the stator winding of the motor is directly connected to the power supply and started at the rated voltage. This procedure is characterized by high starting torque and short starting time.
It's the simplest, most economical and most reliable way to get started. Full voltage starting draws a large current without a significant increase in starting torque. It is convenient and quick to start, but requires greater network capacity and load. This method is mainly suitable for starting motors below 1W.
2. Start of series resistance
Series resistance starting is a method of reducing voltage during the starting process. A resistance is connected in series in the stator winding circuit during startup. As the starting current passes, a voltage drop occurs across the resistance, reducing the voltage applied to the stator winding, thus achieving the objective of reducing the starting current.
3. Autotransformer Initialization
Using multiple taps of an autotransformer for voltage reduction can accommodate the startup needs of different loads and achieve greater startup torque. It is a commonly used method for starting larger capacity engines.
Its biggest advantage is the substantial starting torque. When the winding shunt is at 80%, the starting torque can reach 64% of that during direct starting, and the starting torque can be adjusted through the shunt.
4. Star-Delta Reduced Voltage Startup
For a squirrel cage asynchronous motor with delta-connected stator winding under normal operation, if the stator winding is star-connected during starting and switched back to delta after starting, the starting current may be reduced, mitigating its impact on the electrical grid. This method is known as reduced voltage star-delta starting or simply star-delta starting.
With star-delta starting, the starting current is only one third of that during direct starting with delta connection. During star-delta starting, the starting current is only 2-2.3 times that of the original. This means that in star-delta starting the starting torque also drops to one third of that during direct starting with delta connection.
It is suitable for no-load or light-load startup situations. Compared to any other voltage reduction starter, it has the simplest structure and is the most economical.
Furthermore, the star-delta starting method has another advantage: when the load is light, the motor can operate in star connection. At this time, the rated torque can match the load, which can increase the efficiency of the motor and save energy consumption.
5. Variable frequency drive startup (soft start)
The frequency inverter is the most technologically advanced, comprehensive and effective motor control device in the field of modern motor control. Adjusts the speed and torque of the motor by changing the frequency of the electrical network.
Due to its dependence on power electronics and microcomputer technology, it is expensive and requires a high level of skill from maintenance technicians.
Therefore, it is mainly used in areas that require speed control and high speed control standards.
