Woodward 9907-147

The 9907-147 is a ProTech203 series 24VDC power-off tripping three-redundancy overspeed protection device. It relies on three independent magnetic probes to collect rotational speeds and realizes overspeed shutdown protection for steam turbines and gas turbines through hardware three-to-two voting. The power-off tripping architecture is safer than the power-on type. It can trigger the shutdown in case of power failure or probe failure. It is compatible with industrial 24V DC auxiliary power systems and has explosion-proof certification, online single-channel testing, and module replacement without shutdown. Installation requires proper shielding, grounding and static protection. The three parameters must be unified. It is widely used in power generation, chemical industry explosion-proof rotating machinery and is a core overspeed security device that meets high-level safety standards

Product Function

1. Speed collection: Three independent magnetic probes collect gear pulse signals and send them to the A/B/C three independent processing units. Each channel has its own power supply, CPU, and collection circuit, which do not interfere with each other.

2. Rotational speed calculation: The CPU converts the real-time rotational speed based on the number of gear teeth and pulse frequency, and continuously compares it with the overspeed set value and the MPU fault threshold.

3. Three-to-two voting logic: Each unit drives two internal voting relays, and the six relays form a series and parallel voting circuit. Under normal circumstances, the intermediate relay is energized. If ≥2 channels are determined to be speeding, the voting circuit will be disconnected, the intermediate relay will lose power, and the external shutdown actuator will be triggered.

4. Power-off tripping characteristics: The 9907-147 is of the power-off tripping type. Power failure of the equipment, single-channel failure, and overspeed will all cause the intermediate relay to lose power and shut down.

5. Faults and Startup Logic: During the startup stage, timing is carried out. If the timeout speed does not reach the threshold, the MPU fault is determined. If the probe signal drops sharply during operation, it indicates that the probe is damaged. You can choose to alarm only or trip directly.

6. Online testing principle: Switch the key to PROGRAM mode, long press OVSP TEST to switch the built-in oscillator to simulate the speed, adjust the potentiometer to modify the test frequency, verify the protection logic of a single channel separately, and maintain the protection of the entire machine for the other two channels.

The reasons for choosing model 9907-147

1. Highest safety priority: Woodward officially recommends the power-off trip type. Compared with the power-on trip model (9907-146), when the system loses power, it can forcibly shut down, eliminating the major safety hazard of overspeed and loss of control after power loss, and meeting the mandatory safety standards for explosion-proof units in power plants and chemical plants.

2. Compatible with 24VDC industrial standard power supply: The vast majority of auxiliary control DC systems for steam turbines and gas turbines are 24VDC, with a wide voltage range of 18-32VDC compatibility, eliminating the need for additional power conversion.

3. Three-redundancy high reliability: Three completely independent power supplies, data acquisition and computing channels, single-channel modules can be replaced online, and the unit can be maintained without shutdown, reducing downtime losses.

4. Explosion-proof compliance: Meets UL Class I Div2 and ATEX Zone2 explosion-proof certifications, suitable for hazardous working conditions in oil and gas and chemical industries;

5. Independent circuit isolation: Power supply, MPU signal, alarm, and trip contacts are completely isolated, resistant to EMI interference, and suitable for strong electromagnetic factory environments.