9905-870

About the 9905-870

There are three separate speed-sensing units in the 9905-870 overspeed protection device, all kept within the same, key-locked IP65-certified enclosure. These three identical units are configured in a way that the individual magnetic pickup (MPU) interfaced with each and the separate speed calculations performed by each unit, work together in a two-out-of-three hardware vote to determine whether an overspeed condition has occurred.

 In the event of an overspeed condition, a trip relay is activated. After a unit is tripped, it requires either a reset or a power cycle to return to normal operations. Aside from the detection of an overspeed condition, things such as a loss of MPU signal, an interlock fault, or lack of a reset before the turbine is re-started could all cause a trip. Woodward ProTech 203 Overspeed Protection System Manual 85191 (B) has complete information on troubleshooting trip relays.

The three speed-sensing units in the 9905-870 model are identical. Each unit comes with its own 120 Vac/dc power supply, and they each have a separate operator interface with an LCD, touchpad, and functional status LEDs. On the LCD, operators can view the actual speed of the individual unit, and the LEDs offer a quick first-step identification of problems within a unit, such as a failed MPU or an improperly functioning CPU. Both an LED and an alarm output are used to alert operators of a tripped unit.