1. Over speed Trip Issue in unit 3

2. When the over speed trip valve actuates, two trip signals are activated simultaneously.
1st signal
2nd signal

3. One signal is sent to the air intake butterfly valve, it fails closed through the actuated linkage.
This linkage trips the air intake butterfly valve closed.
The trip linkage fails in the direction of the arrow (plant North).

4. The other signal bleeds the air from the fuel rack manifold causing the fuel rack to close.
When the over speed condition occurs the vale trips bleed off the fuel rack air header which in turn closes the fuel supply.

5. When the over speed test on unit 3 Alpha diesel was performed the fuel rack side did not actuate.

6. The reason is thought to be from a sticky valve that relieves the air from the fuel rack manifold.

7. The valve was replaced and the new valve was set-up using the work order instructions.