Conditions for using automatic control of drum water level:

1. Check whether the steam drum water level gauge of electric contact is consistent with the indication of steam drum of DCS system or not, if the deviation is less than 5 mm, it can be thought that the measurement of steam drum water level of DCS system is normal. If the deviation is big, at this moment the automatic control device cannot be put into use. 

2. The measurement of water supply flow rate and main steam flow is correct. 

3. Check whether the steam drum water level is within ± 10mm, if it is not within this scope, it can reach this range. The more it approaches 10 mm, the more it will be beneficial for using automatic control device. at this moment, the water flow shall be bigger than main steam flow by 1-3t/h. 

4. When the water supply pressure is insufficient, it is forbidden to switch into automatically control status. Conditions for using automatic control loop of steam drum water level According to the deviation of the main steam flow and water supply flow, set the set point for automatically control of water level to the appropriate value according to the fixed deviation value of steam and water, then switch the control loop of steam drum water level to the "automatically" on the desk of "boiler system" of the operating station. From automatic operation to manual operation: On desktop of boiler system in the operation station, switch the control circuit of steam drum water level to "manual".  

Handling of abnormal situation: 

1. During automatic operation process, if the transmitter (the measurement of drum water liquid level seriously deviates), it  shall be immediately switch back to "manual operated". 

2. If the boiler load change is too big, the water level automatic controlled  will vibrate, at this moment, it shall be immediately switched back to "manual operated" . 

3. If the phenomenon of the failure of water supply valve occurs, at this moment, the system shall be switched to "manually-operated". 

4. If the phenomenon of the failure of electric adjusting mechanism occurs, at this moment, the system shall be switched to "manually-operated". 

5. If the electric actuator is jammed, at this moment, the system shall be switched to "manually-operated". 

6. If the drum water level is too high or too low, at this time it shall be switched to "manually"operating. 

7. If the system is de-energized, at this moment, the system shall be switched to "manually-operated". 

8. When the pressure of feedwater suddenly drops, it shall be switched to "manually"operating.