Static starts from a set of thyristor pairs (SCR, or combinations of thyristors / diodes), one at each power terminal of the electric motor. The firing angle of each pair of thyristors is controlled electronically for a variable voltage to the motor terminals during “acceleration”. This behavior is called the soft-starter.
At the end of the starting period which is adjustable according to the application, the voltage will reach its full value after a smooth acceleration or an upward ramp, so as not to be subjected to sudden increments or “jumps”, as with the autotransformer starting methods and star-triangle connection.
With this we can keep the starting current within a stipulated limit and with smooth variation, as desired. The current limit value allowed in the motor is a function of the application and the initial design of the motor. In addition to the advantage of voltage and current control during startup, the electronic key has the advantage of having no moving parts or generating an electric arc, such as in mechanical switches. This is one of the good points of the electronic keys, because their useful life is much longer and allows up to hundreds of millions of maneuvers.