13
2024
-
12
交流 asynchronous motor soft-start and optimization technology
Direct starting is a relatively simple method of starting.
1. The Dangers of Direct Startup
Direct-on-line starting is a relatively simple method, where the motor is directly connected to the power grid via a knife switch or contactor during startup. While this method offers the advantages of straightforward starting equipment and rapid acceleration, it also poses significant risks:
(1) Grid Impact: Excessively high starting currents—ranging from 4 to 7 times the rated current during no-load starts, and even 8 to 10 times or more under loaded conditions—can cause a drop in grid voltage, disrupting the normal operation of other electrical equipment. This may also trigger undervoltage protection mechanisms, leading to unwanted tripping of equipment. Meanwhile, these excessive starting currents generate significant heat in the motor windings, accelerating insulation aging and ultimately shortening the motor's lifespan.
(2) Mechanical Impact: Excessive impact torque often leads to the breakage of rotor cage bars and end rings in electric motors, as well as insulation wear on the stator end windings, resulting in breakdowns, motor burnout, shaft distortion, damage to couplings and transmission gears, and even belt tearing.
(3) Impact on production machinery: Sudden pressure changes during the startup process often lead to damage in pump system pipelines and valves, reducing their service life; they can also compromise transmission accuracy and even disrupt normal process control.
All of these pose threats to the safe and reliable operation of the equipment, while also leading to excessive energy losses during startup—especially when start-and-stop operations occur frequently. Therefore, there are the following limitations for direct motor starting:
(1) Whether the production machinery allows the electric motor to be directly started by dragging is a prerequisite;
(2) The motor's capacity should not exceed 10% to 15% of the supplying transformer's capacity;
(3) The voltage drop △U during the starting process should not exceed 15% of the rated voltage. For medium- and high-power motors, direct starting is generally not permitted; instead, specific starting equipment must be used to ensure a smooth and reliable startup operation.
Previous page
Previous page
Relevant information
Douyin