Principle Of Operation Of The 3Rw44 Electronic Soft Starter - Siemens 3RW44 Manual

Introduction
2.1 Basic physical principles of the three-phase asynchronous motor and operating principle of the soft starter
Disadvantages
This results in the following disadvantages
● A higher load is placed on the machine's mechanical components
● Higher costs for replacing worn parts and maintaining the application
Figure 2-2
Solution
The SIRIUS 3RW44 electronic soft starter allows the current and torque characteristics
during startup to be optimally adapted to the requirements of each application.
2.1.2

Principle of operation of the 3RW44 electronic soft starter

The 3RW44 soft starter features two antiparallel thyristors in each of the phases. There is
one thyristor for the positive and one thyristor for the negative half-wave.
The rms value of the motor voltage is increased (from an adjustable starting voltage or
starting torque) to the rated motor voltage within a definable starting time by means of the
leading-edge phase. This is achieved using various control methods.
The motor current changes in proportion to the voltage applied to the motor. The starting
current is thus reduced by the factor of the voltage applied to the motor.
The torque changes in squared proportion to the voltage applied to the motor. The starting
torque is thus reduced in squared proportion to the voltage applied to the motor.
14
Typical starting torque characteristic of a three-phase asynchronous motor
Manual, 03/2017, NEB535219502000/RS-AB/008
3RW44 soft starters