Käivituvoolu

Käivituvoolu, also known as inrush current or starting current, is the maximum instantaneous current drawn by an electric device, particularly motors and transformers, when it is first connected to the power supply. This surge of current is significantly higher than the device's normal operating current.

The primary reason for käivituvoolu is the initial state of the device. For example, in an AC motor, the rotor is stationary at the moment of startup. This creates a very low impedance, allowing a large current to flow until the rotor gains speed and generates a back electromotive force (EMF) that opposes the applied voltage, thereby reducing the current to its normal operating level. Similarly, in transformers, the magnetic core is initially unmagnetized, leading to a high initial current flow as it builds up the magnetic field.

The magnitude of käivituvoolu can be several times the normal operating current, often ranging from 3 to 8 times, and in some cases, even higher. This high current can cause several issues. It can trigger circuit breakers or blow fuses, leading to an interruption of power. It can also cause voltage dips in the power supply network, affecting other connected equipment. Furthermore, repeated or prolonged exposure to high käivituvoolu can lead to premature wear and overheating of the device's components, reducing its lifespan.

To manage käivituvoolu, various starting methods are employed, such as soft starters, variable frequency drives (VFDs), or star-delta starting for motors. These methods gradually increase the voltage or control the motor speed, thereby limiting the initial current surge. Proper sizing of electrical components, including wiring and protective devices, is also crucial to accommodate the käivituvoolu without causing malfunctions or damage.