if ac power from the grid and the black start is lost on a frame 9 using a cranking ac motor how do you bring the system to rest safely and put it in turning gear?

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You have given us no idea of how the turning gear system would operate in the absence of AC power. There are Frame 9Es and Frame 9Fs, and there are lots of differences between the two, and in the cooldown mechanisms employed as "turning gears."

The turbine will be tripped and it will coast down to zero speed and hopefully the 125 VDC battery will supply power to the Emergency Lube Oil Pump motor and pump to lubricate the bearings during the coastdown and possibly for a short period after reaching zero speed to provide cooling Lube Oil flow to the bearings to prevent them from being damaged by the heat of the shaft. The Emer. L.O. Pump might even by cycled periodically for the same reason until AC power can be re-established and the Aux. L.O. Pump can be re-started.

Again, you have provided very little information for us to be able to provide any more in the way of assistance.

The topic of loss of AC power and what to do with the turbine if you can't get it on turning gear or cranking within about 20-30 minutes of reaching zero speed after a trip from load has been covered several times on control.com. Please use the 'Search' feature at the top right corner of the menu bar to find past threads and information.

 

If you lose all AC power then you will come to zero speed and stay there only on your DC oil pump. You will then need to decide when to return the unit to cooldown and what tests need to be done.

Why do you want to start the cranking motor if AC power is lost from the grid ?

This may be a moot point and not required. At our frame 9E site if the grid is dead we have no where to send the power so are offline. What we do have is an essential low voltage bus powered by standby diesel generators. If the grid is dead the essential bus supplies power to run down the unit on the auxiliary lube oil motor and keep the turbines on cooldown. Motors on the essential bus include include 88QA, 88TG, 88BQ, 88QV, 88TM. When the grids returns we can then energize the auxiliary transformer and restart the units immediately.

Our frame 6B site is a true black start site cranked by a diesel engine. We are paid extra to have this black capability and have to demonstrate it periodically. In 7 years we have never had to use this in anger.