Starting current and running current respond quite differently to changes in supply voltage. A drop in line voltage results in a lower starting current and a higher running current. A 5% increase in line voltage improves starting current while significantly decreasing operating current. If the line voltage climbs by more than 5%, the starting and running currents will rise as well.
In comparison to the running condition, the induction motor draws a large beginning current. The starting current of an induction motor is approximately six times that of the motor's full load current.
When a three-phase supply is applied to the induction motor's stator, the motor uses magnetising current to create a rotational magnetic flux in the air gap. The flux passes through the air gap, and the magnetic flux is cut off by the short-circuited rotor conductor. When the rotor conductor cuts the magnetic flow, a voltage is induced. The current begins to flow through the rotor conductor. The torque is created by the interaction of the rotor current and the main flux.
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