Asynchronous motor starters

When an electric motor is put into operation, the required mains current is increased and can, especially if the section of the power conductor is insufficient, cause a voltage drop that may affect the operation of the loads. Sometimes this voltage drop is such high way that it is noticeable in lighting appliances. To avoid these drawbacks, some dealers’ facility regulations prohibit the use of engines with direct starting above a given power. Others simply impose, as a function of engine power, the relationship between the starting current and the rated current.

The short-circuit rotor motor is the only one that can be directly connected to the network, through simple devices, since the characteristics of the rotor are determined. Since the rotor characteristics are determined by the manufacturer, the various starting processes generally consist of varying the voltage at the stator terminals. In this type of motor, with constant frequency, the reduction of the peak of current is automatically accompanied by a strong reduction of the conjugate. Only the ends of the stator windings will be available on the terminal board.