Hotwell Filling and Barring/Turning Gear Stoppage

Is the turning gear electric motor-driven? If so, what is the logic in the motor/clutch control circuit? I think that would give some good clues to follow up on.

Dear Mr. Madhusudhana,

Your posting shold contain some more detail. The Turbine Safe Guard, is when condensate pumps fail, the High Level of Hot well should trip - and barring gear should start. If it stops mean the Power Control loop is to be checked.

What is the need for filling the Hot Well.?

DHAYANANDHAN.S

If this is a topic not caused by logic of the trip or alarm system i assume that the weight of the condensate in the hotwell has an effect of the alignment of the turbine. Then rubbing will occure in the glands, the nesessary torque of the barring device-motor will increase. MCC will shut down the supply of the motor.

Check if the barring device is able to turn the rotor when you are lowering the condensat level in the hotwell.

Adding few more details:

500 MW unit was under shutdown condition to attend Boiler Tube leakage. Machine was on barring as it required a Warm start up. Oil Pressure is used to rotate Barring gear pelton wheel located on HP Turbine shaft. Barring speed was 85 rpm. While filling Condenser Hotwell, Barring stopped.

Normally one no of Auxiliary Oil Pump is sufficient to keep the machine on Barring. On that fateful day, we have kept both the pumps in service after the barring gear has stopped but our effort went in vain. We had to do Hand barring for 1.5 hours when the hand barring speed touched 5 rpm and Hydraulic barring has taken over.

There's a lot that doesn't make sense here, perhaps you can provide more detail:

1. Did the unit undergo a full load trip or was it slowly unloaded before it reached barring speed?

2. Why was the hotwell flooded?

3. How high did the hotwell level get?

4. Have you looked at the control logic for the lube oil pumps?

5. Were they inadvertently tripped or did they operate properly?

6. Was the barring gear ever properly engaged?

7. Was the unit returned to service without incident?

8. Were there any unusual noises coming from the turbine?

9. Was the unit inspected prior to restart?

10. Did anyone check the differential expansion charts?

11. Was the unit ever at zero speed during this event?

12. Did the manual barring feel different than usual?

13. What was the temperature of the hot well water?

14. Did anyone inspect the barring gear system for misoperation?

15. Are there any high-high-level autotrips in the hotwell logic?

16. Do you know if there was sufficient lube oil flow to the gear?

17. Had this unit operated for a long period without shutdown or maintenance?

18. Were the bearings inspected?

19. Were the bearing clearances within spec?

20. What did the manufacturer have to say about the incident?

The forum awaits your answers...