Causes of sudden vacuum drop during vacuum pump switching

 First, cause analysis

   1. The pneumatic valve and check valve of vacuum pump are jammed;
   2. Improper operation, stop the vacuum pump without confirming that the pneumatic inlet valve has been closed.
Second, the main phenomena are as follows
   1. The vacuum of the exhaust device drops rapidly, and the low vacuum gives an alarm;
   2. The liquid level of air-water separator of vacuum pump decreased.
III. treatment measures
   1. When the vacuum pump stops and the vacuum drops, start other vacuum pumps immediately.
   2. Immediately order the local personnel to open the manual valve beside the make-up water solenoid valve of the gas water separator to make up water to the high water level of the steam water separator.
   3. If the vacuum still drops and there is no tendency to turn back, the local personnel shall immediately close the pneumatic valve in front of the pneumatic valve of ᦇ 1 vacuum pump and the manual valve in front of the pneumatic valve, and start ᦇ 3 vacuum pump.
   4. When the vacuum drops too fast, manually reduce the load to below 400MW to prevent the unit from triggering RB. If RB acts, it shall be treated as RB normally.
   5. If the treatment is not timely and the vacuum is too low, which leads to turbine trip, it shall be treated as emergency shutdown.
IV. preventive measures
   1. The monitoring system is implemented for major operations;
   2. Switch according to the correct switching method, and make all possible assumptions;
   3. When the vacuum pump is stopped, the inlet valve can be closed first, and the pump can be stopped after confirming the closure.

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