WOODWARD 9907-345 Overspeed Protection System – EG Series

WOODWARD 9907-345: Hardware-Based Overspeed Trip Module for Turbine and Prime Mover Protection

The WOODWARD 9907-345 is a dedicated electronic overspeed protection module engineered for continuous speed surveillance and fail-safe trip execution in rotating machinery applications. Unlike software-resident protection routines embedded within a DCS or governor controller, the 9907-345 operates as a standalone hardware layer—its trip decision logic is executed entirely within discrete analog and relay circuitry, making it immune to software faults, communication timeouts, or processor loading conditions that can compromise software-based protection schemes.

In a typical turbine control architecture, the 9907-345 sits between the magnetic pickup (MPU) speed sensor and the emergency shutdown (ESD) solenoid or trip valve actuator. The module continuously converts the MPU frequency signal into a speed-proportional analog value, compares it against a field-configured overspeed setpoint, and de-energizes its output relay within milliseconds of threshold breach. This hardware-first architecture satisfies the independence requirement mandated by IEC 61511 and API 670 for protective instrumented functions operating in parallel with the primary control loop.

The 9907-345 belongs to WOODWARD’s 9907 Series of speed control and protection instruments, a product family with decades of field deployment across steam turbines, gas turbines, hydro turbines, diesel engines, and compressor trains in power generation, oil and gas, petrochemical, and marine propulsion sectors. Its compact panel or DIN-rail form factor allows direct integration into existing control cabinets without structural modification, and its wide MPU input frequency range accommodates gear tooth counts and shaft speeds common across OEM turbine designs.

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Technical Parameters

Hardware Logical Analysis

The 9907-345 implements a frequency-to-voltage (F/V) conversion front end that accepts the raw sinusoidal or quasi-sinusoidal output of a passive MPU sensor. The MPU signal amplitude varies with shaft speed—at low speeds the signal may be as low as 1 V peak-to-peak, rising to tens of volts at rated speed. The module’s input conditioning stage applies a Schmitt trigger threshold to convert the analog MPU waveform into a clean digital pulse train, eliminating noise-induced false counts that could corrupt the speed measurement. This threshold is designed to remain stable across the full operating temperature range, preventing cold-start nuisance trips or high-temperature measurement drift.

The conditioned pulse train feeds a hardware timer/counter circuit that computes instantaneous shaft speed as a function of pulse period. This period-measurement approach—rather than a pulse-count-over-fixed-window approach—delivers faster response at high speeds and avoids the inherent latency of a counting window. When the computed speed exceeds the configured overspeed setpoint, the comparator output switches state within one pulse period, driving the output relay coil to de-energize. The relay’s normally closed (NC) contact opens, interrupting the trip solenoid holding circuit and initiating turbine shutdown.

The fail-safe relay architecture is a deliberate design choice: the relay coil is continuously energized during normal operation, and any loss of supply voltage, MPU signal loss, or internal circuit fault causes the relay to drop out—identical to an overspeed trip. This ensures that a module failure cannot leave the turbine unprotected. The relay coil drive circuit incorporates a watchdog function that monitors internal supply rails; if any rail deviates beyond tolerance, the watchdog forces relay de-energization before the measurement circuit can produce erroneous output.

EMC performance is addressed through input filtering on the MPU signal lines, transient suppression diodes on the relay output terminals, and board-level decoupling capacitors on all logic supply nodes. The module is designed to operate in the electromagnetic environment typical of switchgear rooms and turbine control panels, where high-energy switching transients from contactors and variable-frequency drives are common. The PCB layout routes high-frequency signal traces away from relay coil conductors to minimize inductive coupling, and the relay itself is a sealed type to prevent contact contamination from industrial atmospheres.

System Integration Benefits

• Independence from primary control loop: The 9907-345 operates on a dedicated power supply branch and separate MPU sensor channel, ensuring that a failure in the governor controller or DCS does not disable overspeed protection—satisfying the independence requirement of IEC 61511 SIL-rated protective functions.
• Sub-cycle trip response: Period-based speed measurement delivers trip initiation within one shaft revolution period of overspeed detection, typically under 20 ms at rated turbine speeds—faster than any software-polled protection routine constrained by task cycle times.
• Zero-dependency startup sequencing: The module powers up and arms its protection function before the governor controller completes its boot sequence, closing the protection gap that exists during controller initialization in software-based architectures.
• Deterministic trip behavior: Hardware relay logic produces a fixed, repeatable trip delay independent of processor load, communication bus traffic, or operating system scheduling—critical for SIL validation and functional safety documentation.
• Broad MPU compatibility: Accepts passive variable-reluctance sensors from all major turbine OEMs without signal conditioning adapters, reducing BOM complexity in retrofit and greenfield projects.
• Field-adjustable setpoint without hardware swap: The overspeed trip threshold is configurable on-site, allowing commissioning engineers to match the setpoint to the turbine’s rated speed and trip margin without returning the module to the factory.
• Diagnostic transparency via relay state: The normally energized relay provides a continuous health indication—any loss of relay energization, whether from overspeed, power fault, or MPU loss, is immediately visible to the plant DCS through the relay auxiliary contact wired to a digital input, enabling alarm differentiation between overspeed trip and module fault.
• Retrofit compatibility with legacy turbine panels: The 9907-345’s panel-mount and DIN-rail form factor, combined with its standard 24 VDC supply requirement, allows direct installation into existing control cabinets originally designed for older WOODWARD mechanical or first-generation electronic governors, minimizing civil and wiring modification costs.

Quality Assurance & Global Logistics

Every WOODWARD 9907-345 unit supplied by siemensplc.com is sourced through verified channels with full part traceability. Pre-shipment inspection covers visual examination of housing, label authenticity verification against WOODWARD’s part marking standards, connector pin integrity check, and relay coil continuity measurement. Units showing evidence of rework, remarking, or non-original packaging are rejected prior to listing.

Our warehouse is located in Xiamen, China—a major international logistics hub with direct access to Xiamen Gaoqi International Airport and Xiamen Port, both operating daily freight services to North America, Europe, Southeast Asia, the Middle East, and Australia. Standard export shipments are dispatched within 1–3 business days of order confirmation. Express air freight options (DHL, FedEx, UPS) deliver to most destinations within 3–7 business days. Sea freight consolidation is available for bulk orders. All shipments include a commercial invoice, packing list, and certificate of conformance. Customs HS code documentation is provided to facilitate smooth import clearance. A 12-month warranty covers manufacturing defects and functional failure under normal operating conditions.

Contact Information

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