Siemens 3RW4426-1BC44 Soft Starter – SIRIUS 3RW44

Siemens 3RW4426-1BC44 — Thyristor-Based Soft Starter for High-Inertia AC Motor Loads up to 90 kW

The Siemens 3RW4426-1BC44 is a three-phase AC semiconductor motor controller belonging to the SIRIUS 3RW44 product family. It is rated for a motor shaft output of 90 kW at 400 V and a continuous operational current of 200 A, with a supply voltage window of 200–480 V AC, 50/60 Hz. The device integrates a six-thyristor anti-parallel bridge topology with a factory-fitted bypass contactor, eliminating the need for an external bypass assembly in the motor control center (MCC) panel.

In a control loop context, the 3RW4426-1BC44 occupies the position between the main circuit breaker and the motor terminals. During the acceleration phase, the thyristor bridge modulates the RMS voltage applied to the stator windings via phase-angle firing, progressively increasing torque from a configurable starting torque level (typically 30–50% of rated torque) to full-voltage torque over a programmable ramp time of 1 to 20 seconds. Once the motor reaches synchronous speed, the internal bypass contactor closes, short-circuiting the thyristor stack and transferring the full load current through a low-resistance copper path — reducing steady-state power dissipation in the power semiconductors to near zero and extending thyristor service life significantly.

The control supply voltage range of 110–230 V AC accommodates both North American and European auxiliary power standards without transformer modification. The unit mounts on a standard DIN rail or via direct screw fixing to a back-plate, with IP00 ingress protection rating, making it suitable for enclosed panel installation in industrial environments.

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Technical Parameters

Hardware Logical Analysis

The 3RW4426-1BC44 employs a six-pulse thyristor bridge in anti-parallel configuration — two thyristors per phase, one conducting per half-cycle. The firing angle (α) is modulated by the internal DSP-based control board, which calculates the required conduction window per cycle to achieve the target RMS voltage at the motor terminals. This phase-angle control method produces a stepped voltage waveform; the harmonic content (predominantly 5th and 7th order) is within IEC 60947-4-2 limits for standard industrial installations and does not require additional line reactors for most applications below 200 A.

EMC Design: The power stage PCB incorporates RC snubber networks across each thyristor pair to suppress dV/dt transients during commutation, limiting voltage spikes to below 1,000 V/μs. The control board is galvanically isolated from the power stage via optocoupler barriers rated at 4 kV impulse withstand voltage, conforming to IEC 60664-1 reinforced insulation requirements. The device enclosure uses a conductive coating on internal surfaces to attenuate radiated emissions, supporting compliance with EN 61000-6-4 (industrial emission standard).

Bypass Contactor Logic: The bypass contactor is actuated by the internal control logic when the motor current waveform indicates that slip has reduced to near-synchronous speed — typically detected by monitoring the phase relationship between applied voltage and motor current. The contactor closes within one half-cycle of the detection event, ensuring a smooth transition with no perceptible torque disturbance. After bypass engagement, the thyristor gate pulses are suppressed, and the thyristors enter a blocking state, eliminating conduction losses entirely during steady-state operation.

Thermal Management: The thyristor stack is mounted on an extruded aluminum heat sink with a calculated thermal resistance of approximately 0.08 °C/W junction-to-ambient at rated current. The internal NTC thermistor on the heat sink feeds back to the control board; if the heat sink temperature exceeds 85 °C, the device triggers a thermal warning output before initiating a protective shutdown at 95 °C. This two-stage thermal protection prevents nuisance tripping while ensuring semiconductor junction temperatures remain within the 125 °C absolute maximum rating.

Motor Protection Integration: The PTC thermistor input (Type A, IEC 60947-8) accepts a direct connection from the motor winding temperature sensor. The control board monitors the thermistor resistance continuously; a resistance exceeding 3.4 kΩ triggers a motor overtemperature fault, isolating the motor before insulation damage occurs. This eliminates the need for a separate thermistor relay (e.g., Siemens 3RN1) in most standard applications, reducing BOM cost and panel wiring complexity.

System Integration Benefits

• Deterministic Acceleration Profile: The voltage ramp algorithm executes on a fixed 10 ms control cycle, ensuring repeatable acceleration curves across consecutive starts — critical for process lines where mechanical synchronization between multiple drives is required.
• Reduced Panel Footprint: The integrated bypass contactor eliminates one discrete component from the MCC panel, reducing panel width by approximately 45 mm and cutting field wiring terminations by 6 points per installation.
• TIA Portal Integration via PROFIBUS/PROFINET: With the optional 3RW4900-0KC00 (PROFIBUS) or 3RW4900-0KC01 (PROFINET) add-on module, the soft starter appears as a standard GSD/GSDML device in TIA Portal V16+, enabling parameter upload/download, real-time diagnostics, and remote fault acknowledgment from a SIMATIC S7-1200 or S7-1500 CPU without additional gateway hardware.
• Diagnostic Transparency: The device exposes 12 fault codes via the front-panel LED display and fieldbus interface, covering phase failure, overload, thermistor fault, bypass contactor failure, and internal hardware errors — enabling maintenance teams to identify root cause without removing the unit from the panel.
• Soft Stop Function: The programmable deceleration ramp (0–20 s) reduces mechanical stress on pump impellers and conveyor belts during shutdown, extending coupling and bearing service intervals in high-cycle applications.
• Wide Supply Voltage Tolerance: The 200–480 V AC main circuit range covers IEC 230 V, 400 V, and 480 V grid standards in a single catalog number, simplifying global procurement and reducing spare-parts inventory for multinational plant operators.
• CLASS 10 / CLASS 20 Overload Selectivity: Selectable trip class allows the protection characteristic to be matched to the motor’s thermal time constant — CLASS 10 for standard motors, CLASS 20 for high-inertia loads such as centrifuges and ball mills — without requiring an external overload relay.
• SIRIUS Ecosystem Compatibility: The 3RW4426-1BC44 is dimensionally and electrically coordinated with Siemens 3RT2 contactors, 3RV2 motor protection circuit breakers, and 3VA/3VL molded-case circuit breakers, enabling type-tested coordination (IEC 60947-4-2, Annex A) and simplifying panel certification for end-user acceptance.

Quality Assurance & Global Logistics

Every Siemens 3RW4426-1BC44 unit dispatched from our Xiamen, China facility is sourced exclusively through authorized Siemens distribution channels. Each unit carries a traceable Siemens factory serial number, which can be verified against Siemens AG manufacturer records. Before dispatch, our technical team performs a visual inspection of the housing, terminal blocks, label integrity, and firmware version against the current Siemens production standard.

Units are packaged in the original Siemens anti-static, moisture-barrier carton with shock-absorbing foam inserts. Export documentation — including commercial invoice, packing list, certificate of origin, and Siemens product datasheet — is prepared for each shipment to facilitate customs clearance in the destination country.

Shipping Options from Xiamen, China:

• DHL Express / FedEx International Priority: 3–5 business days to Europe, North America, Southeast Asia, and the Middle East
• UPS Worldwide Expedited: 5–7 business days, cost-optimized for mid-weight shipments
• Air Freight (Consolidated): 7–10 business days, suitable for bulk orders exceeding 50 kg
• Sea Freight (FCL/LCL): Available for large-volume orders; transit time varies by destination port

All shipments include full tracking, export customs clearance from China, and insurance coverage up to the declared commercial value. A 12-month warranty against manufacturing defects is provided on all units, with technical support available via email and WhatsApp for installation and commissioning queries.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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