The two methods for decreasing the starting voltage are to provide current at the normal voltage, temporarily forcing the electric motor, to be connected to the grid, with the winding for a higher voltage, thus using the star-delta starting system and generating current below the normal voltage, by means of resistors, inductors or autotransformer.
All starting systems with reduced voltage present some drawbacks as the starter torque reduces in the ratio of the square of the voltage reduction supplied to the motor.
In order for the link between motors and a public power grid to be made, it is necessary to follow some important guidelines for this purpose, established by specific standards.
Most often, it is necessary to remove an electric motor at full voltage in order to make the most of the starting torque. If the startup at full voltage of an electric motor generates a voltage drop higher than the maximum permissible, use a starter with low voltage, taking care, however, to analyze if the torque is sufficient to drive the load.