Manual 35018V1
505XT Digital Control System for Steam Turbines
Woodward
51
Direction of Rotation Detection
Figure 3-2. Speed Probe mounting for Detection Test
To enable the 505XT to calculate the direction of rotation – two speed signals must be used and should
be mounted in an orientation as shown above, with approximately 90 degrees between them. This will
work with both passive and active types of probes, however both channels must be configured as the
same type of probe. If MPU’s (passive) are used the direction will only be detected once the speed is
above the failed speed level threshold. If slow speed detection of rotation is required then active probes
should be used.
The direction of rotation can be determined by viewing the Phase Difference value on either of the speed
input channels. For both channels the phase difference output will always indicate the number of degrees
from speed signal #1 to speed signal #2. Both channels must be healthy for the Phase Difference value to
be meaningful. If probes are setup as the above diagram, a reading of approximately 270 degrees
indicates that the turbine is spinning clockwise and a reading of 90 degrees indicates it is spinning
counter clockwise.
Figure 3-2. Speed Input Channel – Phase Difference
There is an alarm that can be enabled related to the unit running in reverse rotation. It is found under the
Service menus. This feature has two other selections required. A confirmation of which direction is the
correct direction (clockwise or counter clockwise), and a minimum speed to enable this detection – this
value should be a speed that can be detected by the probes being used. This value can be lower than the
Failed speed level setting and is valid even when the speed signal override is active. However, the
voltage signal on the probes must be one Vrms or greater – that means if this needs to be detected at
very slow speed then active probes should be used.