For Operation in the Control Cabinet © Siemens AG 2009 3RW Soft Starters 3RW30 for standard applications Overview Function The SIRIUS 3RW30 soft starters reduce the motor voltage through variable phase control and increase it in ramp-like mode from a selectable starting voltage up to mains voltage. During starting, these devices limit the torque as well as the current and prevent the shocks which arise during direct starts or wye-delta starts. In this way, mechanical loads and mains voltage dips can be reliably reduced.
The space required by the compact SIRIUS 3RW30 soft starter is often only about one third of that required by a contactor as- sembly for wye-delta starting of comparable rating. This not only saves space in the control cabinet and on the standard mount- ing rail but also does away completely with the wiring work needed for wye-delta starters. This is notable in particular for higher motor ratings which are only rarely available as fully wired solutions. Soft starting reduces the stress on the connected equipment and results in lower wear and therefore longer periods of trouble- free production.
The selectable start value means that the soft starters can be adjusted individually to the requirements of the application in question and unlike wye-delta starters are not restricted to two-stage starting with fixed voltage ratios. At the same time the number of cables from the starter to the motor is reduced from six to three. Compact dimensions, short start-up times, easy wiring and fast commissioning make them- selves felt as clear-cut cost advantages. The SIRIUS 3RW30 soft starters are characterized above all by their small space requirements.
Integrated bypass contacts mean that no power loss has to be taken into the bargain at the power semiconductors (thyristors) after the motor has started up. This cuts down on heat losses, enabling a more compact design and making external bypass circuits superfluous. The bypass contacts of these soft starters are protected during operation by an integrated solid-state arc quenching system. This prevents damage to the bypass contacts in the event of a fault, e. g. brief disconnection of the control voltage, mechanical shocks or life-related component defects on the coil operating mechanism or main contact spring. Various versions of the SIRIUS 3RW30 soft starters are available:
Standard version for fixed-speed three-phase motors, sizes S00, S0, S2 and S3, with integrated bypass contact system Version for fixed-speed three-phase motors in a 22.5 mm enclosure without bypass The new series of devices comes with the "polarity balancing" control method, which is designed to prevent direct current com- ponents in two-phase controlled soft starters. On two-phase controlled soft starters the current resulting from superimposition of the two controlled phases flows in the uncontrolled phase. This results for physical reasons in an asymmetric distribution of the three phase currents during the motor ramp-up.
This phe- nomenon cannot be influenced, but in most applications it is non-critical. Soft starters rated up to 55 kW (at 400 V) for standard applica- tions in three-phase networks are available. Extremely small sizes, low power losses and simple commissioning are just three of the many advantages of this soft starter. Controlling the power semiconductors results not only in this un- balance, however, but also in the previously mentioned direct current components which can cause severe noise generation on the motor at starting voltages of less than 50 %.
The control method used for these soft starters eliminates these direct cur- rent components during the ramp-up phase and prevents the braking torque which they can cause. It creates a motor ramp-up that is uniform in speed, torque and current rise, thus permitting a particularly gentle, two-phase starting of the motors. At the same time the acoustic quality of the starting operation comes close to the quality of a three- phase controlled soft starter. This is made possible by the on-go- ing dynamic harmonizing and balancing of current half-waves of different polarity during the motor ramp-up. Hence the name "po- larity balancing".
Soft starting with voltage ramp; the starting voltage setting range U s is 40 % to 100 % and the ramp time t R can be set from 0 s to 20 s Integrated bypass contact system to minimize power loss Setting with two potentiometers Simple mounting and commissioning Mains voltages at 50/60 Hz, 200 to 480 V Two control voltage versions 24 V AC/DC and 110 to 230 V AC/DC Wide temperature range from -25 °C to +60 °C The built-in auxiliary contact ensures user-friendly control and possible further processing within the system (for status graphs see 6/16) 6 6/5 Siemens LV 1 T · 2009