Technical specifications

Application examples for normal starting (CLASS 10)

¹⁾ The mass inertia of the fan is <10 times the mass inertia of the motor.

Application examples for heavy starting (CLASS 20)

Note:

These tables present sample set values and device dimensions. They are intended for information purposes only and are not binding. The set values depend on the application in question and must be optimized during commissioning.

For dimensioning soft starters under other boundary conditions, also for heavy starting up to CLASS 20, we recommend our Simulation Tool for Soft Starters (STS):
see https://support.industry.siemens.com/cs/ww/en/view/101494917
or contact our Technical Assistance:
Tel.: +49 (911) 895‑5900,
Email: technical-assistance@siemens.com.

Configuration

The 3RW solid-state soft starters are designed for easy starting conditions. In the event of deviating conditions or increased switching frequency, it may be necessary to choose a larger device.

Where long starting times are involved, the integrated solid-state overload relay for heavy starting should not be disconnected. PTC sensors are recommended. This also applies for the smooth ramp-down because during the ramp-down time an additional current loading applies in contrast to free ramp-down.

In the case of high switching frequencies in S4 mode, Siemens recommends the use of PTC sensors. For corresponding device versions with integrated thermistor motor protection or separate thermistor evaluation devices, see "Monitoring and Control Devices".

No capacitive elements are permitted in the motor feeder between the SIRIUS 3RW soft starter and the motor (e. g. no reactive-power compensation equipment). In addition, neither static systems for reactive-power compensation nor dynamic PFC (Power Factor Correction) must be operated in parallel during starting and ramp-down of the soft starter. This is important to prevent faults arising on the compensation equipment and/or the soft starter.

All elements of the main circuit (such as fuses and controls) should be dimensioned for direct starting, following the load short-circuit conditions. Fuses and switching devices must be ordered separately. Please observe the maximum switching frequencies specified in the technical specifications.

Note:

When three-phase motors are switched on, voltage drops occur as a rule on starters of all types (direct-on-line starters, wye-delta starters, soft starters). The infeed transformer must always be dimensioned such that the voltage dip when starting the motor remains within the permissible tolerance. If the infeed transformer is dimensioned with only a small margin, it is best for the control voltage to be supplied from a separate circuit (independently of the main voltage) in order to avoid the potential switching off of the soft starter.

Schematic circuit diagram of power electronics

A bypass contact system and solid-state overload relay are already integrated in the 3RW40 soft starter and therefore do not have to be ordered separately.

Status graphs

SIRIUS 3RW40 soft starters

Manual for SIRIUS 3RW30/40

In addition to relevant configuration, commissioning, and service information, the manual also contains example circuits and technical specifications for all devices. See https://support.industry.siemens.com/cs/ww/en/view/38752095.