Let’s take closer look at a typical sensor for a large wind turbine. The sensor mounts to the main frame; its gear is driven by the yaw ring.
This sensor employs an incremental encoder that tracks nacelle position, along with a group of limit switches dedicated to cable twist control
Here we can see the terminal connections for Channel A and Channel B of the encoder. The outputs of the four limit switches are labeled Cam 1, 2, 3, and 4.
The cams are shown here. The drive gear rotates the cams, which activate switches that send signals to the controller.
As the drive gear turns, the cams work the switch-es. For this demonstration the gear is turning much faster than normal.
Here we can see the switches that are activated or deactivated
Each cam serves a different purpose.
- Cam 4 presses on its switch when the nacelle has rotated between 2.3 and 5.1 turns counter-clockwise.
- Cam 3 indicates clockwise rotation of 2.3 to 5.1 turns.
- Cam 2 counts each revolution.
- The switch for Cam 1 is activated at all times until the nacelle has rotated 4.7 turns in either di-rection.
The output of the four switches is combined and sent to the controller. The table shows the switch-es that are assigned to each bit, the standard values and their meanings. Notice that the output from Switch 105 may be either a zero or a one in any of the described states. Values that are not listed on the table will trigger a yaw sensor error alarm
The cam timing can be adjusted by loosening the release screw and rotating the cams
Proper adjustment is shown on a calibration diagram. Cams must be calibrated during commission-ing, but may also need to be adjusted if an error alarm occurs
Nacelle’s position is also tracked by an incremental encoder. This encoder generates two thousand seventy-four pulses for each revolution of the nacelle. Clockwise rotation from the initial position of zero adds to the position signal, counter clock-wise rotation subtracts from it
The controller calculates position in degrees based on this information. A proximity switch is used to reset the degree position to zero each turn. The target for this switch is installed with the nacelle facing North, allowing the PLC to calcu-late azimuth from true North on each revolution.
Highland Community College as part of WindTechTV.org