ABB PSTX142-600-70 Soft Starter – PSTX Series

ABB PSTX142-600-70 — Thyristor-Based Soft Starter for Three-Phase Induction Motor Control

The PSTX142-600-70 is a three-phase electronic soft starter manufactured by ABB under the PSTX platform, rated at 142 A continuous operational current, 600 V AC maximum supply voltage, and 70 kW motor power at 400 V. It is designed for applications where direct-on-line starting is mechanically or electrically unacceptable — including centrifugal pumps, axial fans, belt conveyors, compressors, and agitators operating in continuous industrial duty cycles.

Unlike earlier voltage-ramp-only starters, the PSTX series implements closed-loop torque control via a six-thyristor (SCR) bridge topology. The firing angle of each SCR pair is modulated in real time by the internal DSP, which compares measured motor current against a user-defined torque reference curve. This approach decouples the acceleration profile from supply voltage fluctuations — a critical advantage in weak-grid industrial environments where bus voltage can sag 10–15% during heavy motor starts.

The unit ships with an internal bypass relay that closes once the motor reaches full synchronous speed. This relay shorts the SCR stack, eliminating thyristor conduction losses during steady-state run mode and extending the thermal life of the power semiconductors. Panel designers benefit from a simplified BOM: no external bypass contactor, no separate overload relay, and no additional thermistor module are required for standard installations.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

The PSTX142-600-70 power stage is built around a fully controlled six-pulse SCR bridge — two anti-parallel thyristors per phase — giving the DSP-based firing controller 360° of phase-angle authority over each half-cycle. At 50 Hz, this translates to a firing resolution of approximately 0.28° per DSP interrupt cycle, enabling smooth torque increments of less than 0.5% rated torque per control loop iteration.

EMC Architecture: The unit’s PCB layout separates the high-dV/dt SCR gate drive circuitry from the low-level signal processing board using a double-sided ground plane with stitching vias at 5 mm pitch. Optocoupler isolation (minimum 2.5 kV creepage) is used on all gate drive outputs, preventing common-mode noise from the thyristor switching transients from coupling into the measurement and control circuits. Snubber networks (RC type, 100 Ω / 100 nF per SCR) suppress voltage spikes at commutation, keeping dV/dt below 200 V/μs — within IEC 61000-4-4 Level 4 burst immunity margins.

Thermal Management: The SCR stack is mounted on an extruded aluminium heatsink with a calculated thermal resistance of approximately 0.18 °C/W junction-to-ambient at rated current. At 142 A continuous with the bypass relay closed, SCR conduction losses drop to near zero, allowing the heatsink to operate well below its thermal limit. During the start phase (typically 5–30 seconds), the DSP monitors an NTC thermistor embedded in the heatsink and will issue a thermal warning at 80 °C and a trip at 95 °C, protecting the SCRs from thermal runaway during repeated starts.

Torque Control Loop: The closed-loop torque controller samples motor current at 10 kHz via Hall-effect current transformers on all three phases. The DSP computes the RMS current vector and compares it against the torque reference ramp. A PI controller adjusts the SCR firing angle to maintain the torque error within ±2% of setpoint. This architecture is fundamentally different from open-loop voltage ramp starters, which cannot compensate for load inertia variations or supply voltage sags during the start transient.

Redundancy and Fault Arbitration: The PSTX142-600-70 implements a watchdog timer on the DSP core with a 10 ms timeout. If the main control loop fails to reset the watchdog — due to firmware exception or hardware fault — the unit immediately opens the main contactor output relay and logs a fault code to non-volatile EEPROM. This fail-safe behavior ensures the motor is de-energized within one half-cycle of a control system failure, a requirement in SIL 1 and SIL 2 safety-instrumented systems when combined with appropriate safety relays.

System Integration Benefits

• Deterministic Start Torque Repeatability: Closed-loop torque control delivers start torque within ±2% of setpoint across supply voltage variations of ±15%, ensuring consistent conveyor belt tension and pump head pressure on every start cycle.
• Inrush Current Reduction: Current limit function caps motor inrush to a user-defined value (typically 3–4× FLA), reducing peak demand charges and preventing nuisance tripping of upstream MCCBs and fuses.
• Diagnostic Transparency via Fieldbus: When equipped with a PROFIBUS DP or PROFINET module, the PSTX exposes 32 process data words including motor current, thermal load index, start counter, last fault code, and heatsink temperature — all readable by a Siemens S7-300/400/1500 PLC without additional instrumentation.
• Elimination of External Protection Relays: Built-in overload, phase loss, phase imbalance, thermistor, stall, and locked-rotor protection removes the need for a separate motor protection relay (e.g., Siemens 3RU, ABB TF series), reducing panel footprint by up to 40 mm DIN rail width per motor circuit.
• Pump Stop Function: Programmable deceleration ramp (0–120 seconds) controls motor coast-down speed, suppressing water hammer pressure transients in pipeline systems without requiring a separate soft-stop valve or hydraulic accumulator.
• Parameter Copy via HMI Keypad: The integrated keypad supports parameter upload/download between units using the keypad memory function, reducing commissioning time for multi-motor installations from hours to minutes.
• Wide Supply Voltage Tolerance: Operational from 208 V to 600 V AC without hardware modification, covering North American 480 V 60 Hz, European 400 V 50 Hz, and 525 V mining supply systems from a single stock unit.
• Reduced Mechanical Stress on Driven Equipment: Controlled torque ramp eliminates the 6–8× rated torque shock of DOL starting, extending coupling, gearbox, and impeller service intervals — a measurable reduction in maintenance cost over a 10-year asset lifecycle.
• Energy Optimization Mode: At partial load, the PSTX can reduce applied voltage to minimize magnetizing current losses in lightly loaded motors, delivering measurable kWh savings in variable-load applications such as mixers and agitators.
• IEC 60947-4-2 Compliance: Full compliance with the international standard for AC semiconductor motor controllers ensures interoperability with third-party switchgear and acceptance by third-party inspection bodies (TÜV, Bureau Veritas, Lloyd’s Register).

Quality Assurance & Global Logistics

Every PSTX142-600-70 unit offered through siemensplc.com is sourced from verified ABB authorized distribution channels or traceable OEM surplus stock. Incoming inspection includes label authentication, serial number cross-reference against ABB’s product traceability database, and a functional power-on verification test. Units are stored in ESD-controlled, climate-regulated warehousing in Xiamen, China, maintaining ambient conditions of 20–25 °C and 40–60% RH to preserve component integrity.

Export documentation — commercial invoice, packing list, certificate of origin, and ABB factory test certificate (available on request) — is prepared to comply with customs requirements in the EU, USA, Southeast Asia, and the Middle East. Standard export packaging uses anti-static foam inserts and double-wall corrugated cartons rated for 30 kg drop test per ISTA 2A protocol.

Shipping is executed via DHL Express, FedEx International Priority, or UPS Worldwide Expedited, with typical transit times of 3–5 business days to Europe and North America, and 2–4 business days to Southeast Asia. For bulk orders exceeding 50 kg, sea freight via Xiamen Port (CNXMN) is available with full FCL/LCL consolidation services. All shipments are covered by cargo insurance at declared value. A 12-month warranty against manufacturing defects is provided, with DOA (Dead on Arrival) replacement dispatched within 7 business days of confirmed fault report.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
© 2026 siemensplc.com. All rights reserved.