9905-751

About the 9905-751

Manufactured by Woodward in the company’s ProTech 203 series of overspeed protection devices, 9905-751 is a de-energize-to-trip model. This device uses three speed-sensing units, each interfaced with a separate magnetic pickup (MPU), to monitor prime mover speed. These nearly identical units are configured for a hardware two-out-of-three vote. Prime mover speed is sampled every 5 ms, with a max system response time of 40 ms. Units A and B have 24Vdc input, while Unit C has 120 Vac/dc input.

The three speed-sensing units are in one, NEMA 4X certified enclosure, which is key locked. Programming of model 9905-751 is only accessible with key lock access. Tunable parameters and other programming specifications and instructions are in ProTech 203 Overspeed Protection System Manual 85196.

Each unit has its own front panel that includes:

• Touchpad
• Two-line by 16-character LCD display
• Separate LED functional status indicator for a failed MPU/wiring, CPU operating outside of normal parameters, and a tripped unit

There are many conditions that might prompt one of the 9905-751 units to trip, such as the speed exceeding the trip setpoint, an MPU fail timeout, or no reset before re-starting the turbine. Troubleshooting details for these and other conditions can be found in the product manual.