3RW44 soft starters
12
Manual, 03/2017, NEB535219502000/RS-AB/008
Introduction
2
2.1
Basic physical principles of the three-phase asynchronous motor
and operating principle of the soft starter
2.1.1
Three-phase asynchronous motor
Application areas of the three-phase asynchronous motor
Three-phase asynchronous motors are used in a wide range of applications in commerce,
industry and trade owing to their simple, rugged design and their low-maintenance operation.
Problem
If a three-phase asynchronous motor is started directly, its typical current and torque
characteristics can cause disturbances in the supply system and the load machine.
Starting current
Three-phase asynchronous motors have a high direct starting current I
(startup)
. Depending on
the motor version it can amount to between three times and fifteen times the rated
operational current. Seven to eight times the rated motor current can be taken as a typical
value.