10 kV auxiliary power interruption of boiler: 10KV motors for the boiler are: Induced draft fan (900 kw), primary fan (1250 kw), the secondary fan (800 kw) : 

1. The motors of induced draft fan and primary fan motor all stop operating, MFT acts to interlocking trip off other motors , DCS displays that the ammeter indication backs to zero and DCS displays the indication of voltage backs to zero.

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

3. Thermal meter power is in outage and indication is abnormal. 

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

5. Motor trips, a red light is gone, the green light flashes and the emergency alarm calls. 

6. The feedwater pressure decreases (during running one or more feed water pump trip) or the feedwater pressure decreases to zero ( during running, all the feed water pumps trip). 

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

Causes: 

1. The power system is in failure, so that the busbar of  SectionⅠ, Ⅱ,  Ⅲ of 10kV de-energizes in the same time.

2. Two generators are in failure. 

3. The two steam turbines are in failure. 

4. The contact opening/closing of 10 kV busbar is in failure and trips. 

5. The protection devices false trip. 

6. The operators make wrong operation. 

Treatment: 

1. When the operator finds that 10 kV auxiliary plant power  is interrupted, the switches of motors shall be immediately reset, and the vice stoker shall quickly close the dampers at the induced draft fan, primary fan and secondary fan. The stoker or the boiler monitor shall report it to the shift chief –operator.

 2. Before the power supply is not recovered, the boiler is treated according to procedures of normal banking-up, and contact the operator for the steam turbine to manually close the electric valve at the outlet of the boiler superheated steam, to close the isolated stop valve of the steam turbine boiler, to open the water draining valve at the header at the outlet of the  superheated steam and the water draining valve on the  superheated steam pipe. 

3. The operation personnel shall pay attention to monitoring of steam pressure rising, the steam drum pressure cannot exceed the working pressure of the steam drum. If it is higher than that of steam drum pressure, the normal pressure of main stream shall be maintained as possible. 

4. Stop the operation of water draining, blowdown and dewatering in order to maintain the water level of boiler. 

5. Special person shall be assigned to monitor the water level of boiler steam drum, to change the adjustment of feed water  from automatic adjustment to  manual adjustment, and to pay close attention to the change of water level. 

6.  MFT is reset. 

After auxiliary power supply is recovered, the operation of the boiler operation is as follows: 

1. If 10 kV auxiliary power is interrupted within short time, the water level still can be seen in the drum water level gauge, at this time, water shall be immediately fed to the boiler, so that the steam drum water level is slightly lower than the normal water level, and then make preparations for starting. After contacting with the shift chief-operator and getting the command from the shift chief-operator, start the boiler in sequences. 

2. If the interruption time  of 10 kV auxiliary power is longer, and after the power source of auxiliary power is recovered, and the water level of boiler drum cannot be seen. If the water is in shortage, it is forbidden to feed water to the boiler. It is required to close the water inlet valve and the boiler shall be treated according to the procedures of emergency shutdown of the boiler. 

3. In the early stage of emergency shut down the boiler, it is forbidden to start the coal feeding system, air and fume system. 

4. After the boiler has been shut down for 4 hours, part of the boiler slag can be discharge and the thickness of materials of layer of boiler shall be kept at the thickness of starting the boiler. 

5. When the boiler bed temperature falls  below 200 ℃, slowly feed water  to the boiler  to normal water level, and then make preparations before starting the boiler. After contacting with the shift chief-operator and getting the command from the shift chief-operator, restart the boiler. 

6. During starting the boiler, it is required to contact with electric person to start the boiler one by one and it is forbidden to start the 10 kV auxiliary engine at the same time.