Why does a Motor draw High Current during Starting?
When an induction motor starts, it initially has very low back EMF because the rotor is not yet rotating. As a result, the motor draws a high current from the supply to produce the starting torque.
The starting current can typically be several times higher than the motor’s full-load current. As the motor accelerates, back EMF increases, slip decreases, and the current gradually falls toward its normal operating value.
Common methods used to reduce starting current include:
• Star-Delta Starter
• Auto-Transformer Starter
• Soft Starter
• Variable Frequency Drive (VFD)
• Reduced-voltage starting methods
Understanding motor starting current is important for proper cable sizing, protective-device selection, voltage-drop calculations, and power-system design.