For Operation in the Control Cabinet © Siemens AG 2009 3RW Soft Starters 3RW40 for standard applications Overview The starting current of particularly powerful operating mecha- nisms can place an unjustifiable load on the local supply system. Soft starters reduce this starting current by means of their volt- age ramp. Thanks to the adjustable current limiting, the SIRIUS 3RW40 soft starter takes even more pressure off the sup- ply system. It leaves the set start ramp during the ramp-up – the ramp gradient is fixed by the starting voltage and the ramp time – as soon as the selected current limit is reached.
From this mo- ment the voltage of the soft starter is controlled so that the cur- rent supplied to the motor remains constant. This process is ended either by completion of the motor ramp-up or by tripping by the intrinsic device protection or the motor overload protec- tion. As the result of this function the actual motor ramp-up can well take longer than the ramp time selected on the soft starter. SIRIUS 3RW40 soft starters have all the same advantages as the 3RW30 soft starters. The SIRIUS 3RW40 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 de- sign and making external bypass circuits superfluous. At the same time this soft starter comes with additional inte- grated functions such as adjustable current limiting, motor over- load and intrinsic device protection, and optional thermistor mo- tor protection. The higher the motor rating, the more important these functions because they make it unnecessary to purchase and install protection equipment such as overload relays.
Internal intrinsic device protection prevents the thermal over- loading of the thyristors and the power section defects this can cause. As an option the thyristors can also be protected by semi- conductor fuses from short-circuiting. Thanks to integrated status monitoring and fault monitoring, this compact soft starter offers many different diagnostics options. Up to four LEDs and relay outputs permit differentiated monitor- ing and diagnostics of the operating mechanism by indicating the operating state as well as for example mains or phase failure, missing load, non-permissible tripping time/class setting, ther- mal overloading or device faults.
Soft starters rated up to 250 kW (at 400 V) for standard applica- tions in three-phase networks are available. Extremely small sizes, low power losses and simple start-up are just three of the many advantages of the SIRIUS 3RW40 soft starters. Thanks to the integrated motor overload protection according to IEC 60947-4-2 there is no need of an additional overload relay on the new soft starters. The rated motor current, the setting of the overload tripping time (Class times) and the re- set of the motor overload protection function can be adjusted easily and quickly. Using a 4-step rotary potentiometer it is pos- sible to set different overload tripping times on the soft starter.
In addition to Class 10, 15 and 20 it is also possible to switch off the motor overload protection if a different motor management con- trol device is to be used for this function, e. g. with connection to PROFIBUS. Device versions with thermistor motor protection evaluation are available up to a rating of 55 kW (at 400 V). A "Thermoclick" mea- suring probe can be connected directly, as can a PTC of type A. Thermal overloading of the motor, open circuits and short-cir- cuits in the sensor circuit all result in the direct disconnection of the soft starter.
And if ever the soft starter trips, various reset op- tions are available the same as with intrinsic device protection and motor load protection: manually with the reset button, auto- matically or remotely through brief disconnection of the control voltage. "Increased safety" type of protection EEx e according to ATEXdirective 94/9/EC The 3RW40 soft starter sizes S0 to S12 are suitable for the start- ing of explosion-proof motors with "increased safety" type of pro- tection EEx e. See "Appendix" –> "Standards and approvals" –> "Type over- view of approved devices for potentially explosive areas (ATEX explosion protection)" .
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.
6 Function The space required by the compact SIRIUS 3RW40 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.
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 current components during the ramp-up phase and pre- vents the braking torque which they can cause. It creates a mo- tor 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 op- eration comes close to the quality of a three-phase controlled soft starter.
This is made possible by the on-going dynamic har- monizing and balancing of current half-waves of different polar- ity during the motor ramp-up. Hence the name "polarity balancing". At the same time the number of cables from the starter to the mo- tor 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 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. 6/17 Siemens LV 1 T · 2009