Phenomenon: 

1. The AC lighting lamps in the central control room is out and the emergency lighting lamp lights. 

2. The indication of 380V voltmeter reaches to Zero.

3. The evaporation of boiler, steam pressure, steam temperature, and water level decline sharply. 

4. Thermal meter power is in outage and the indication is abnormal. 

5. DCS control system is in outgage, the automatic adjustment control is abnormal and cannot be operated, and the output of electric signal indicated in each position backs to zero. 

6. 380V motor in operating trips, the red light is out, the green light flashes, and the ammeter indication backs to zero and the emergency alarm buzzer calls. 

Causes: 

1. 10 kV auxiliary power is interrupted. 

2. 10 kV bus bar contact switch is in failure and trips. 

3. The auxiliary transformer is in failure.

4. 400V bus bar contact switch is in failure. 

5. The automatic switching device for standby powers source is in failure. 

6. The protection device is wrongly operated. 

7. The workers make  wrong operation. 

Treatment:

1. When the operating personnel found that 400V auxiliary power supply is interrupted, they shall reset the switches of the motors immediately. 

2. They shall immediately dispatch workers to locally operate the damper of the induced fan and the primary fan manually and report the issues to the chief-chief operator. 

3. If power supply can be recovered within short time, then the boiler shall be kept running at low load in order to ensure the normal water level normal and to stop discharging of the slag. After the power supply is recovered, the coal feeder shall be put into use and to recover normal operation. 

4. If the power supply cannot be recovered within short time, then the boiler shall be treated according to normal procedures of banking-up. Contact the operators for steam turbine to manually close the electric valve at outlet of superheated steam of boiler, close the stop valve for isolating the steam turbine and boiler, open the water draining valve of the header at the outlet of the superheated steam and water draining valve at the superheated steam pipe. 

5. The operation personnel should pay attention to monitor the rising of steam pressure rise, try to maintain normal main steam pressure, if it is higher than the working pressure  of steam drum pressure, the steam shall be exhausted to atmosphere. 

6. Special personnel shall be assigned to monitor the drum water level and to keep the water level of boiler steam drum water level slightly below the normal water level. The feed water adjustment shall be changed from automatic control to manual control, the remote electric adjustment shall be changed to local manual adjustment and close attention shall be paid to the change of water level. 

7. Other treatment is the same with that for 10 kV auxiliary power interruption.