When both the power grid and the load are allowed, it is better to start the motor directly, because the control is convenient and economical.
Auto-decompression startup is often used to start large capacity squirrel cage induction motors. Although auto-decompression startup is an old-fashioned startup equipment, it can not only meet the needs of multiple load startup, but also obtain larger starting torque by using multi-tap decompression of auto-transformer. In addition, it has perfect overload and Voltage-loss protection due to the installation of thermal relay and low-voltage tripper. It has been widely used.
Star triangle startup mode has good current characteristics and poor torque characteristics, so it is only suitable for no-load or light-load startup situations, but this mode has the simplest structure and the cheapest price, which can save power consumption in light-load operation.
These start-up modes belong to step-by-step decompression start-up, which has obvious shortcomings, that is, secondary impulse current occurs in the start-up process.
Comparison of advantages and disadvantages of decompression startup, soft startup and frequency conversion startup
Decompression startup, usually star-triangle startup, has the disadvantage of small startup moment, which is only suitable for no-load or light-load startup. The advantage is that the price is cheap.
Soft start can set start time and start initial moment to realize soft start and soft stop, and can limit start current, the price is moderate.
Frequency conversion startup, can start smoothly according to the set time, and let the equipment run at the set frequency, the price is higher.