Product description 3.3 Functional principle of the SIRIUS 3RW30 and 3RW40 soft starters / 8 // ˳ ˞ ˞ ˞ * Figure 3-5 Phase angle control and schematic diagram of a two-phase controlled soft starter with integral bypass contacts 3.3.1 Method of operation of a two-phase controlled soft starter A special method of operation is used for the SIRIUS 3RW30 and 3RW40 two-phase controlled soft starters based on SIEMENS' patented "polarity balancing" control principle. Two-phase control The SIRIUS 3RW30 and 3RW40 soft starters are two-phase controlled soft starters, in other words they are designed with two antiparallel thyristors in each of phases L1 and L3.
Phase 2 is an uncontrolled phase, which is merely guided through the starter by a copper connection. In a two-phase controlled soft starter, the current that results from the superimposition of the two controlled phases flows in the uncontrolled phase. The main advantages of two-phase control include the more compact size compared to a three-phase version and the lower hardware costs. The occurrence of DC components, caused by the phase angle and the overlapping phase currents, is a negative physical effect of two-phase control during the startup process that can mean a louder noise is produced by the motor.
The "polarity balancing" control principle was developed and patented by SIEMENS to prevent these DC components during starting. , $ , $ , $ Figure 3-6 Current characteristic and occurrence of DC components in the three phases without "polarity balancing" W V W V W V SIRIUS 3RW30 / 3RW40 20 Manual, 01/2010, 535 1995-02 DS01 8 / / 0 a