9905-979

About the 9905-979

Part 9905-979 is an overspeed protection device with an accuracy rating of 0.05% of point + 2 Hz over the operating temperature range. This is a de-energize-to-trip system that continually monitors prime mover speed using three magnetic pickups (MPUs). Whether or not the system activates a trip relay is based on three separate calculations which are put to a hardware two-out-of-three vote. These calculations are performed by three identical speed-sensing units.

This part was manufactured by Woodward as part of the company’s ProTech 203 Overspeed Protection System series. Devices in this series are available in several power source options. 9905-979 is a 120 Vac/dc model; all three units have their own 120 Vac/dc power supply.

The design of this system, including the individual power supplies, permits the prime mover to remain online in situations such as:

• The testing of individual speed-sensing units
• Replacement of an individual unit
• One unit is offline due to a trip relay

Even though the units are in a modular manner, they are all kept in the same enclosure. This enclosure meets IP 65 / NEMA 4 standards. It is locked to prevent unauthorized access to PROGRAM mode and unit testing functions. More information on programming is in ProTech 203 manual 85195.