pehmeäkäynnistys

Pehmeäkäynnistys, also known as soft start, is a device or method used to gradually bring an electric motor up to its normal operating speed. This contrasts with a direct online start, where the motor is connected directly to the power supply and instantly reaches full voltage and speed. The primary purpose of a soft start is to reduce the excessive mechanical and electrical stresses that occur during a direct online start.

When a motor starts directly, it draws a very high inrush current, often several times its normal running current. This can lead to voltage drops in the power supply, potentially affecting other equipment. Additionally, the sudden surge of torque can cause mechanical shock and wear on the motor, gearbox, and driven machinery, leading to premature failure.

Soft starters achieve gradual acceleration by controlling the voltage supplied to the motor. Common methods include using silicon-controlled rectifiers (SCRs) or variable voltage transformers to limit the initial voltage and then progressively increase it over a set period. This controlled voltage ramp results in a smoother torque delivery, minimizing mechanical stress and reducing the inrush current.

The benefits of using a soft start include extended equipment life, reduced energy consumption (due to lower peak demand), and improved operational safety by preventing sudden jolts. They are particularly useful in applications involving conveyors, pumps, fans, and compressors, where smooth and controlled starting is essential for efficiency and longevity.