---------------------- Forwarded by Jeff Duff/EWC/Enron on 04/23/2002 10:01 
AM ---------------------------


Garth Ripton
04/23/2002 09:11 AM
To: Jeff Duff/EWC/Enron@ENRON
cc:  

Subject: Re: Nacelle Position Configuration  

Hi Jeff,

The nacelle position is relative to the zero position so any rotation counter 
clockwise is negative ("yaw left") and any rotation clockwise ("yaw right")  
is positive. The point at which unwinding occurs is controlled by two 
parameters- 11.5 and 11.6. If the turbine is not in load operation and number 
of nacelle rotations reaches P11.5 (usually set to 1.8) the cable untwist 
will start. If the turbine is in load operation and the number of nacelle 
rotations reaches P11.6 (usually set to 2) the turbine will untwist. The 
number of rotations that start the untwisting operation is an absolute value 
(the number of either positive or negative revolutions).

This is from the internal software description document published by the 
controls group in Rheine:
1.7.2 Cable Unwinding
From the azimuth rotating head signals (DI11.1, DI11.2), the cable winding is 
measured, i.e. how often the nacelle has rotated around the tower axis 
relative to the 0o nacelle position (cable not twisted). If the number of 
rotations is reached at a standstill or while spinning P11.5 or otherwise 
P11.6, the automatic wind tracking is blocked, the turbine is braked to the 
spinning state and then the cable unwinding to the left (rotations > 0) or to 
the right (rotations < 0) is carried out for a whole number of rotations. The 
brake and motors are controlled as in 1.7.1. Thereafter, automatic wind 
tracking is reactivated.

Hopefully this answers your question.