käynnistysvirrat

Käynnistysvirrat, a Finnish term, translates to "starting currents" in English. It refers to the high electrical current that flows through a motor when it is first energized and begins to rotate. This surge of current is significantly greater than the motor's normal operating current, often ranging from five to eight times the full load current, and in some cases even higher. The magnitude of the starting current is influenced by several factors, including motor design, voltage, and the initial state of the motor (e.g., whether it is at rest or already partially rotating).

The primary reason for this high starting current is the inductive nature of the motor's windings. When a motor is stationary, there is no back electromotive force (back EMF) generated. Back EMF opposes the applied voltage and typically reduces the current drawn by the motor once it reaches its operating speed. Without this opposing force, the motor's impedance is at its lowest, leading to a large influx of current to establish the magnetic field necessary for rotation.

Understanding and managing starting currents is crucial in electrical engineering. Excessive starting currents can lead to several issues, including voltage dips in the power supply, which can affect other connected equipment. They can also cause premature wear on motor components, such as brushes and commutators in DC motors, or reduce the lifespan of windings due to thermal stress. Therefore, various methods are employed to limit starting currents, such as soft starters, variable frequency drives (VFDs), or reduced voltage starting techniques like star-delta starters. These methods gradually increase the voltage or frequency supplied to the motor, thereby controlling the magnitude of the starting current and protecting both the motor and the electrical system.