Startup of Heavy-Duty Motors
The voltage of heavy-duty motor at startup may have a considerable impact on the system. If direct starting is adopted, the current may be up to 5-7 times the rated current. The sharp voltage drop at startup may also lead to severe power-grid fluctuation, and the resultant overlong starting time may reduce motor insulation and increase the mechanical shock abrasion, so that the lifespan of the motor may be directly affected.
In addition, the surge current occurring at direct motor starting may generate electromagnetic wave that may hinder the normal operation of secondary control instruments. A lot of harmonic waves may be generated inside the transformer. These waves may affect the safety and service life of the whole electrical system.
In physical production process, many types of electrical devices may be used to limit the starting current of motor and their functional characteristics are given below.
|Name||Converter||Fluid resistance soft starter||Thyristor soft starter||Ordinary reactance soft starter||Magnetic control soft starter|
|Safety and reliability||High||Low||Low||High||High|
|System principle||Power-unit series-connection multi-level technology, capable of altering frequency and controlling current||Control the current by changing the distances of pole plates immersed in the conducting liquid||Control conduction angle to control current by connecting thyristors in series||Utilize core saturation principle to limit current uncontrollable||Utilize core saturation principle to limit current, use direct current to control alternate current|
|High-voltage loop element||Many||Many||Many||A few||A few|
|Volume||Large (4-side cubicles)||Large (3-side cubicles)||Small (1-side cubicle)||Medium (1-side cubicle)||Medium (1-side cubicle)|
|Maintenance task||Many||Many||Many||A few||A few|
|Environmental impact||No impact||Medium||Minor||No impact||No impact|
The result of comparison with other starting modes shows that the magnetic control soft-start technology is characterized by intellectualization, high reliability, simple structure, easy installation, less maintenance, high continuous starting capacity, wide working range, and high performance/price ratio. It is the optimum option among so many soft-start modes.